# AC 65-9A: Airframe & Powerplant Mechanics General Handbook - Type: Advisory circular (guidance, not mandatory unless a rule or AD requires it) - Status: Historical - Approved: January 1, 1976 - Last reviewed: October 22, 2024 - This change: Canceled by FAA Handbook, FAA-H-8083-9. FAA-H-8083-30A (Aviation Maintenance Technician Handbook-General) has replaced AC 65-9A. - Family: AC 65-9 - 14 CFR parts: 1 - Pages: 521 - PDF: https://openairdocs.org/files/sha256/f9/ea/f9eaae5ef3d38f23fe1dbd885e17e97704411c9938cecfa8a1cab574a38da38b - FAA DRS: https://drs.faa.gov/browse/excelExternalWindow/A563729E3DAAC121862569F1005F80F1.0001 - DRS record last changed: November 21, 2025 - Page: https://openairdocs.org/ac/65-9 ## Versions - [AC 65-9A](https://openairdocs.org/ac/65-9) (Historical), approved Jan 1, 1976, 521 pages. Canceled by FAA Handbook, FAA-H-8083-9. FAA-H-8083-30A (Aviation Maintenance Technician Handbook-General) has replaced AC 65-9A. ## ADs that cite it (1) - [AD 80-07-03](https://openairdocs.org/ad/80-07-03): Oil Pressure · Cessna R172K. Effective Mar 31, 1980 ## Text Each page's text from the PDF; open the PDF at a page with #page=N. ### Page 1 AC65-9A Airframe 4 Powerplant **MECHANICS** **GENERAL HANDBOOK** **CONSOLIDATED** REPRINT (includes CHG 1, dated 3/31/99) U.S. DEPARTMENT OF TRANSPORTATION ### Page 2 . " :.,,-~-=~-'" -~-----"===---'--.'\,i/ **AIRFRAME AND POWERPLANT** **MECHANICS** **GENERAL HANDBOOK U.S. DEPARTMENT OF TRANSPORTATION** FEDERAL AVIATION ADMINISTRATION Flight Standards Service First Edition 1970 First Revision 1976 For sale by the U.S. Government Printing Office Superintendent of Documents, Mail Stop: SSOP, Washington, DC 20402-9328 . :~\ ### Page 3 PREFACE This handbook was developed and first printed in 1970 as one of a series of three handbooks for persons preparing for mechanic certification with airframe or powerplant ratings, or both. It is intended that this handbook will provide basic information on principles, fundam€ntals, and technical procedures in the subject matter areas common to both the airframe and powerplant ratings. Emphasis in this volume is on theory and methods of application. The handbook is designed to aid Students enrolled in a formal course_of instruc­ tion as well as the individual who is studying on his own. Since the knowledge requirements for the airframe and powerplant ratings closely parallel each other in some subject areas, the chapters which discuss fire protection systems and electrical systems contain some material which is also duplicated in the Airframe and Power­ plant Mechanics Powerplant Handbook, AC 65-12A, and the Airframe and Power­ plant Mechanics Airframe Handbook, AC 65-ISA. This volume contains information on aircraft ·drawings, weight and balance, air­ craft materials and processesi physics, electricity, inspection, ground support, and tools. Knowledge gained from the study of this handbook is essential before pro­ ceeding in a course of study in either the airframe or powerplant handbooks. Because there are so many diffrrent types of airframes and powerplants in use today, it is reasonable to expect that differences exist in the components and systems of each. To avoid undue repetition, the practice of using representative systems and units is carried out throughout the handbook. Subject matter treatment is from a generalize-cl point of view~ and should be supplemented by reference to manufacturers' manuals or other textbooks if more detail is desired. This handbook is not intended to repiace, substitute for, or supersede official regulations or the manufacturers' instructions. Grateful acknowledgement is extended to the manufacturers of airframe and airframe components for their cooperation in making material available for inclusion. Copyright material is used by special permission of the following organizations and may not be extracted or reproduced without permission of the copyright owner. Monsanto Chemical Skvdrol ® Fluids Townsend Corporation Ch.erry Rivets J. 0. King, Inc. Gravines. Inc. Walter Kidde DuPont DeNemours National Fire Protection Association National Association of Fire Extinguisher Distributors Flight Safety Foundation American Petroleum Institute Exxon Parker Hannifin Acres Sleeves Acres Sleeves Fire Extinguishers Fire Extinguishers Fire Extinguishants Fire Extinguisher and Extinguishant Specifications Fire Extinguishers Refueling Data Aviation Fuels A\'iation Fuels Aircraft Fittings The advancements in aeronautical technology dictate that an instructional hand­ book must be under continuous review and brought up to date periodicaliy to be valid. Flight Standards requested comments. from the cntificatE'l rule ,vhich is accurate only to·,/.- of an inch. 7 To use this measurement, we can use the process of Hrounding. ' 1 A decimal expression is Hrounded off" by retaining the lligits for a certain number of places and discarding the rest. The retained number is an approximation of the computed or exact number. The degree of accuracy desired determines the number of digits to Le retained. When the sircd denominator. The result will be the numerator of the desired fraction. EXA\!PLE When accurate hol1•s of 1miform diameter are required, they are first drilleri -/i inch undcrsize and reamed to the df'"sir,~d rl.iameter. -W'hat size drill would he used before n.·arning a h0lc to .763? FIRST: !\lultiply tht: d('('irnal ln· the desired denomin:itnr ,,r /i l. :'liEXT: TIIEl\: X<•.1. :)0.):2 . --.. J.,) I {) l{ound the prodtwl lo a whok numlwr ;:i,nd ('Xpre~,, it a,.; t!w numt•ralnr of1hc desireil dcnominatnr. .j<) 48.832 ~- - (>.l To d<'tnminc tlw drill Rize. suhtrart "l\\ inch from the finish('d hok i:.ize. JO 6 l l (d ., :' .inch drill. 1 8 Converting Common Fractions to Decimals To convert a common fraction, whether proper or improper, to a decimal, divide the numerator by the denominator. Add zeros to the right to permit carrying the quotient to the desired accu­ racy. EXAMPLE Find the distance the center of the hole (figure 1-2) is from the plate edges when the center of the hole is in the center of the plate. Express the length and width of the plate in decimal forms, and then divide each by 2. Express the final result to the nearest 32nd. FIRST: NEXT: THEN: Change the mjxed numbers to im­ proper fractions. 7 87 5-- = -· 16 16' .5 29 3- = -8 8 Convert the improper fractions to decimal expressions. 87 5 3 0 - = .. 4 7o: 16 . , 29 = 3.625 8 Divide the decimal expressions by 2 to find the center of the plate. .5.4375 - -~·-- = 2. 7188; 2 3 .625 = 1.813 2 FINALLY: Express the final results to the nearest 32nd. 2.7188 PERCENTAGE 26 1-32 Then· :ire- many problems that arise every day in\-olving tlw !Wrt't'tlt expression. The greatest 1111mlwr of perc,~ntage problems involve some kind of ('n111parison of a part to the whole. Such com~ pari~ 90° Acute D. - all ,._ < 90° OBTUSE b ACUTE FIGURE 1-7. Types of triangles. while in an acute triangle all the angles are less than 90°. The various types of triangles are shown in figure 1-7. The altitude of a triangle is the perpendicular 17 line drawn from the vertex to the base. In some triangles, as in figure 1-8, it may be necessary to extend the base so that the altitude will meet it. The base of a triangle is the side upon which ### Page 28 ; . 2'6" ALTITUDE I I I I _I_ - - - -"-------....::::,~ f+--3'2" BASE -I FIGURE 1-8. Triangle. the triangle is supposed to stand. Any side may he taken as the base. The area of any triangle may be calculated by using the formula: I A= -ab 2 where A is equal to Area; ! is a given constant; a is the altitude of the triangle; and b is the base. EXAMPLE Find the area of the triangle shown in figure 1-8. FIRST: Substitute the known values in the area formula. NEXT: I A= -ab= A 2 1 X 2 16" X 31 211 2 Solve the formula for the unknown value. I A = - X 30 X 38 2 A = 570 sq. in. 1140 2 Circumference and Area of a Circle To find the circumference (distance around) or the area of a circle it is necessary to use a number called pi (11"). This number represents the ratio of the circumference to the diameter of any circle. Pi cannot be found exactly because it is a never­ ending decimal, but expressed to four decimal places it is 3.1416, which is accurate enough for most computations. (See figure 1-9.) Circumference The circumference of a circle may be found by using the formula: C = 1rd where C is the circumference; 1r is the given con­ stant, 3.1416; and dis the diameter of the circle. 18 Diameter d \ 1\ <:;- \ ~ \ " \ ' ' ' FIGURE 1-9. A circle. EXAMPLE The diameter of a certain piston is 5 inches. What is the circumference of the piston? FIRST: Substitute the known values in the formula, C = 1rd. C = 3.1416 X 5 NEXT: Solve the formula for the unknown value. C = 15. 7080 inches. Area The area of a circle, as in a rectangle or triangle, must be expressed in square units. The distance that is one-half the diameter of a circle is known as the radius. The area of any circle is found by squaring the radius and multiplying by 1r. The formula is expressed thus: A = 1rr2 where A is the area of a circle; 1r is the given constant; and r is the radius of the circle. EXAMPLE The bore (inside diameter) of a certain aircraft engine cylinder is 5 inches. Find the cross sectional area of this bore. FIRST: Substitute the known values in the formula, A = 1rr2• A = 3.1416 X 2.52 NEXT: Solve the formula for the unknown value. A = 3.1416 X 6.25 A = 19.635 sq. in. ### Page 29 b, FIGURE 1-10. A trapezoid. The Trapezoid A trapezoid (figure 1-10) is a quadrilateral having one pair of parallel sides. The area of a trapezoid is determined by using the formula: 1 A = 2(b, + b,)h where A is the area; ·} is the given constant; b1 and b2 are the lengths of the two paraHe] sides; and h is the height. EXAMPLE What is the area of a trapezoid whose hases are 14 inches and IO inches, and whose altitude is 6 inches? (Sec fig. 1-11.) FIRST: Substitute the known values in the formula. 1 A = 2(b, + b2 )h 1 A = 2(10 + 11)6. NEXT: Solve the formula for t hP, unknown value. Wing Area A= 1 A = - X lH 2 A = 72 sq. in. To dC'scribc lhc planform of a '"'·ing (figure ]-12), several terms arc requlred. To calculate wing area, it will be necessary to consider the meaning of the terms-span and chord. The wing span is the length of the wing from wing tip to wing tip. The chord is the width of the wing from leading 19 FIGURE 1-11. Computing the area of a trapezoid. edge to trailing edge. If the wing is a tapered wing, the average width or chord, known as the mean chord, must be known in finding the area. The formula for caJculating wing area is: A= SC where A is the area expressed in square feet, S is the wing span, and C is the average chord. The process used in caJculating wing area will depend upon the shape of the wing. In some instances it will be necessary to use the formula for finding wing area in conjunction with one of the formulas for the area of a quadrilateral or a circle. **EXAMPLES** 1. Find the area of the wing illustrated in figure 1-13. To determine the area, it is necessary to decide what formula to use. It can be seen that the wing tips would form a 7-foot-diameter circle; the re­ mainder of the wing planform is then in the shape of a rectangle. By combining the formulas for wing area and area of a circle, the area of a wing having circular tips can be calculated. FIRST: Substitute the known value in the formula. A A SC+ 1rR2 (25 - 7) (7) + (3.1416) (3.52). The value for Sis represented by the original wing span less the diameter of the circular tips. NEXT: Solve the formula for the unknown value. A (18 X 7) + (3.1416 X 12.25) A 126 + 38.5 A = 164.5 sq. ft. .; " ### Page 30 r. s ' C A= Wing Area, ft.s C = Average chord, ft. S = Span, ft. FIGURE 1~ 12. Wing planform. 2. Find the area of a tapered wing (figure 1-14) whose structural span is 50 feet and whose mean chord is 6'8". FIRST: Substitute the known values in the formula. A SC A 50' X 6'8". NEXT: Solve the formula for the unknown value. A = 50' X 6.67' A = 333.5 sq. ft. 3. Find the area of a trapezoidal wing (shown in figure 1-15) whose leading edge span measures 30 feet, whose trailing edge span measures 34 feet, and whose chord is 5 feet. FIRST: Substitute the known values in the formula. 1 A = 2(b1 + b2 )h A = ~(30 + 34)5. NEXT: Solve the formula for the unknown value. 1 -A = ·-(64)o 2 1 A = 2(320) A = 160 sq. ft. FIGURE 1-13. Wing with circular tips. COMPUTING THE VOLUME OF SOLIDS Solids are objects with three dimensions­ length, breadth, and thickness. They are of many shapes, the most common of which are prisms, cyHnders, pyramids, cones, and spheres. Occa­ sionaBy, it is necessary to determine the volume of a rectangle, a cube, a cylinder, or a sphere. Since all volm 1es are not measured in the same units, it is necessary to know all the common units of volume and how they are related to each other. For example, the mechanic may know the volume of a tank in cubic feet or cubic inches, but when the tank is full of gasoline, he will be interested in how many gallons it contains. The foHowing table shows the relationship between some of the common units of volume. UNITS OF SPACE MEASURE 1,728 cu. in. 1 cu. ft. 27 cu. ft. 1 cu. yd. 231 cu. in. 1 gal. 7.5 gals. 1 cu. ft. 2 pts. 1 qt. 4 qts. 1 gal. Volume of a Rectangular Solid A rectangular solid is a solid bounded by rec­ tangles. In other words, it is a square-cornered FIGURE 1-14. Tapered wing with sweepback. ### Page 31 30 feet ;1 feet \ 34 feet FIGURE 1-15. Trapezoid wing. volume such as a box (figure 1-16). If the solid has equal dimensions, it is called a cube. The formula for determining the volume of a rectangular solid may he expressed thus: V = lwh where: V = Volume. l = length. w = width. h = height. EXAMPLE A rectangular-shaped baggage compartment measures 5 feet 6 inches in length, 3 feet 4 inches in width, and 2 feet 3 inches in height. How many cubic feet of baggage will it hold? FIRST: Substitute the known values into the formula. V = lwh V = 5'6" X 3 1 4" X 2'3". NEXT: Solve the formula for the unknown value. T h 1 1 1 V = 5-X 3- X 2-2 3 4 11 10 9 V=-X-X-2 3 4 165 V = 4 = 41.25 cu. ft. 1'-----1 FIGURE 1-16. A rectangular solid. 21 , ... ___ , -•• !IA'/ • ::,..J FIGURE 1-17. A cube. If 1he rectangular solid is in the shape of a cube (figure 1-17), the formula can be expressed as the cube of the sides: V = 5' where Vis the volume and S is the side measure­ ment of the cube. Area and Volume of a Cylinder A solid having the shape of a can, length of pipe, or other such object is called a cylinder. The ends of a cylinder are identical circles as shown in figure 1-18. Surface Area The surface area of a cylinder is found by multiplying the circumference of the base by the altitude. The formula may be expressed as: A = 1rdh where A is the area, 1r is the given constant, d is the diameter, and h is the height of the cylinder. h FIGURE 1-18. A cylinder. ;' -·,r. ### Page 32 -----d -- -----d----- T 0 Piston II 0 / ' / -----/ ' / " I \ I -- \ ,,...-., \ -I I I \ t \ \ , I ' I -- \ \ I \. / "- / "- / -- / PISTON AT TOP CENTER PISTON AT BOTTOM CENTER FIGURE 1-19. Cylinder displacement. EXAMPLE How many square feet of aluminum sheet would be needed to fabricate a cylinder 12 feet long and 3 feet 6 inches in diameter? 22 FIRST: Substitute the known values in the formula. A = 1rdh A = 3.1416 X 3'6" X 12'. ### Page 33 NEXT: Solve the formula for the unknown value. A 3.1416 X 3.5' X 12' A = 132.95, or 133 sq. ft. Volume The volume of a cylinder may he found by nmltiplying the cross-sectional area by the height of the cylinder. The formula may be expressed as: V = 1rr2h where V is the volume; 1r is the given constant; r2 is the square of the radius of the cylinder; and his the height of the cylinder (figure 1-19). EXAMPLE The cylinder of an aircraft engine has a bore (inside diameter) of 5.5 inches, and the engine has a stroke of 5.5 inches. What is the piston displacement of one cylinder? The stroke repre­ sents the height of the cylinder to he measured, .:.;.,ecause the volume displaced by the piston de­ pends on the length of the stroke. FIRST: Substitute the known values in the formula. V = 1rr2h V = (3.1416) (2.75 2) (5.S). NEXT: Solve the formula for the unknown value. V = 17.28 X 7.56 V = 130.64 cu. in. GRAPHS AND CHARTS Graphs and charts are pictorial presentations of data, equations, and formulas. Through their use the relationship between two or more quan­ tities may be more clearly understood. Also, a person can see certain conditions or relationships at a glance, while it would require considerable time to obtain the same information from a written description. Graphs may be used in a number of ways, such as representing a single equation or formula, or they may be used to solve two equa­ tions for a common value. Graphs and charts take many forms. A few of the more common forms are called bar graphs, pictographs, broken-line graphs, continuous­ curved-line graphs, and circle graphs. An example of each is shown in figure 1-20. The most useful 23 of these graphs in technical work is the continuous­ curved-line graph. Interpreting or Reading Graphs and Charts It is more important, from the mechanic's view­ point, to be able to read a graph properly than it is to draw one. The relationship between the horsepower of a certain engine at sea level and at any altitude up to 10,000 feet can be determined by use of the chart in figure 1-21. To use this type of chart, simply find the point on the hori­ zontal axis that represents the desired altitude; move upward along this line to the point where jt intersects the curved line; then move to the left, reading the percent of sea level horsepower avail­ able on the vertical axis. EXA.WPLE "\Vhat percent of the sea level horsepower is available at an altitude of 5,000 feet? FIRST: Locate the point on the horizontal axis that represents 5,000 feet. Move upward to the point where the line intersects the curved line. ',EXT: Move to the left, reading the percent of sea level horsepower available at 5,000 feet. The available horsepower is 80%. Nomograms It is often necessary to make calculations using the same formula, but using different sets of values for the variables. It is possible to obtain a solution by use of a slide rule or by preparing a table giving the solution of the formula resulting from successive changes of each variable. However, in the case of formulas involving several mathe­ matical operations, the labor entailed would usu­ ally be very great. It is possible to avoid aJI this labor by using a diagram representing the formula, in which each variable is represented by one or more graduated lines. l<'rom this diagram, the solution of the formula for any given variable may be read by means of an index line. A diagram of this type is known as a nomogram. Much of the information needed to solve aero­ nautical problems will be presented in nomogram form. Instruction manuals for the various aircraft contain numerous nomograms, many of which . , r -, ·~· ### Page 34 (a) Bar graph ( c) Broken line graph 1955 ++ 1960 +++ 1965 +++++ ( b) Pictograph ( d) Continuous curved-line graph ( e) Circle graph FIGURE 1-20. Types of graphs. ### Page 35 100 90 ~ r--,..._ I 80 - 70 ] 60 ., ~ " 50 1 40 & 30 20 10 0 SL 1 -,.... ...... r--.... ' "- 2345678 Altitude X 1000 h ' 9 10 FIGURE 1-21. Horsepower vs. altitude chart. appear quite complex. Many of the presentations will possess several curves on the same coordinate axis, each curve drawn for different constants in the equation. In the latter case, it is essential to select the proper curve for the desired conditions. Again, as with the simpler graphs, it is more important for the mechanic to be able to read nomograms than it is to draw them. The following example is taken from the main­ tenance manual for the Allison 501-DI3 turboprop 25 engine. A nomogram (figure 1-22) is used to de­ termine the power requirements when the engine is operating at minimum torque. The OAT (out­ side air temperature), station barometric pressure, and engine r.p.m. are three factors that must be known to use this particular nomogram. EXAMPLE Determine the calculated horsepower of a cer­ tain engine, using the nomogram in figure l-22. Assume that the OAT is 10° C., the barometric pressure is 28.5 in. Hg, and the engine is operating at 10,000 r.p.m. FIRST: Locate the reference points on the OAT scale and on the barometric pressure scale that correspond to the given temperature and pressure read­ ings. These are identified as (0 and ®, respectively, on the chart. With the aid of a straightedge, connect these two points and establish point ® on the pivot line. NEXT: Locate the engine speed, identified as @, on the engine speed r.p.m. scale. Using a straightedge, connect points ® and © and establish point ® on the calculated horsepower scale. The calculated horsepower is read at point ®· The calculated horsepower is 98%. ### Page 36 l ., •., MODEL 501-Dl3 ENGINE AND MODEL 606 PROPELLER **CALCULATED TORQUEMETER** OUTSIDE AIR (READING) HORSEPOWER TEMP ENGINE SPEED PIVOT BAROMETRIC RPM ·c •F PRESSURE - IN. HG LINE 140 10500 -10 32.0 -20 130 31.0 10400 0 -15 NOTE: VALID FOR WINDS 120 30.0 BELOW 11 M. P. H. 10300 10 ® -10 29.0 110 20 10200 -5 28,0 0 30 -- 27.0 10100 "° --- __... ........ °' ........ 40 26.0 .. 5 -- - 10000 I _,__... © 10 50 25.0 9900 15 60 80 24.0 20 9800 70 23.0 25 70 80 22.0 9700 30 90 EXAMPLE 35 21.0 9600 100 60 40 110 55 20.0 9500 FIGURE 1-22. Power requirements at minimum torque. ### Page 37 MEASUREMENT SYSTEMS Our customary system of measurement ( figure 1-23) is part of our cultural heritage from the days when the thirteen colonies were under British rule. It started as a hodge·podge of Anglo-Saxon, Roman, and Norman-French weights and measures. Since medieval times, commissions appointed by various English monarchs had reduced the chaos of meas­ urement by setting specific standards for some of the most important units. Early records, for in­ stance, indicate that an inch was defined as the length. of "three barleycorns, round and dry" when laid together; a pennyweight, or one-twentieth of a Tower ounce, was equal to 32 wheatcorns from the "midst of the ear." The U.S. gallon is the British wine gallon, stand­ ardized at the beginning of the 18th century (and about 20 percent smaller than the Imperial gallon that the British adopted in 1824 and have since used to measure most liquids). In short, as some of the founders of this country realized, the customary system was a makeshift based largely on folkways. LENGTH MASS VOLUME METRIC Meter Kilogram Liter CUSTOMARY inch ounce fluid ounce foot pound teaspoon year ton tablespoon fathom grain cup rod dram pint mile quart gallon barrell peck bushel Metric System The metric system is the dominant language of measurement in use today. Most of the world countries used the metric system prior to World War II. Since the war, more countries have con­ verted or are in the process of converting to the metric system. Only the United States and 13 smaller countries have not made the conversion. Congress has the power to define the standa~d of weights and measures. Repeated~y the metnc system has been proposed and each time the ques­ tion has been voted down. The metric system was developed by a French statesman, Talleyrand, Bishop of Autum, using a "meter" as a standard; the meter being a specific portion of the circumference of the earth at the equator. From this base measurement the meter was developed and accepted as the standard. Di­ visions and multiples of the meter are based on the decimal system. **ELECTRIC** TEMPJ,RATURE CURRENT TIME Celsius (Centigrade) Ampere Second Fahrenheit ampere second FIGURE l-23. Some common units. - '. 1 ### Page 38 '·' . The Logic of Metric No other system of measurement that has heen actually used can match the inherent simplicity of International Metric. It was designed ·deliberately to fill all the needs of scientists and engineers. Laymen need only know and use a few simple parts of it. It is logically streamlined, whereas other system:c. developed more or less haphazardly. At this time there are only six base units in the lntC'rnational ~·fetric System. The unit of length is the meter. The unit of mass is the kilogram. The unit of time is the second. The unit of electric current is the ampere. The unit of temperature is the kelvin ( which in common use is translated into the dPgree Celsius, formerly called degree centi­ grade). The unit of luminous intensity is the candela. All the other units of measurement in the Inter­ national Metric System are derived from these six ba:-.e units. Area is measured in square meters; speed in meters per second; density jn kilograms per cubic meter. The newton, the unit of force, i,- a simple relationship involving meters, kilograms, an4.7ff.l been converted to decimal divisions of inches and to millimeters. lnchc, Inch .. , \1).1 MM Fra~tinm D<·c•mals Fractim1s J),.dmals - "2.165 55 3-11/16 3.6875 93.663 :'.-3/16 2. 187,5 55.,563 - 3.7008 '" - 2.2047 56 "l-23/32 3.7Hl 84.456 :'.-7/32 2.219 5(;.356 - ,1.7401 95 - 2.244 S7 l-.1/4 3.7.50 85.2.50 2-1/4 2.2,;o 57.150 - 3.779.5 96. 2-1)/32 2.:'.81 .57.944 3-25/32 3.781 96.()44 - :'..281.5 58. -1-1-'3/16 .'3.812,5 96.838 2-5/16 2.112 58.7,18 - l.8188 97. - 2.:)228 59. 3-27/32 .1.844 87.6,11 2-l 1/,12 2.344 59.531 - 1.858.1 98. - 2.3622 BO. J-7/8 .1.875 98.42,5 2-.318 2,37,) 60.325 - 3.8976 99. - 2.4016 OJ l-2\J/J2 3.8062 99.21\J 2-l:3/32 2.406 61.1 JH - .'3.IJ.170 WO 2·7/!f; 2.4.'38 61.91,1 .}.J.5/lfl 3.().'375 l!10.0J3 - 2.HO\J 62. .'3-11/32 ,3.%:J 100.f'l()fi 2-l.5/1/i 2.468 62.70fl - J.8764 101. - 2.4803 63. 4 4.000 !OJ.HOO 2.(/2 2.500 63 .. 500 4-1/16 4.0fl2 103.188 - 2:.5197 64. 4-1/8 4.125 104.775 2-17/:32: 2.5.'J.l 64.2()4 - 4.1338 105 - 2 .. 559 65. ~--1/16 4.1875 106.363 2·9/l(i 2.562 65.088 4-l/4 4.250 107.!150 2-1\)/.'32 2.594 Wl.881 ·1--5/16 4 .. 112 100 . .538 - 2.S%4 66 - 4.3307 I JO. 2-.5/8 2:.625 M.fi75 4"3/8 4.375 111.125 - :.f),'l8 e7 l-7/16 4.4.18 112.713 :."-21 /.J2 2.fl5(S 67.4E\'l 1-1/2 4_;)00 l 14 .. 100 - 2:.677:?: 6S 4.5275 l l.5. 2-11/16 2.fl875 i>8.2Wl ~-9/16 ·1..562 115.888 - 2.71(15 60 4-5/H 4.625 J 17.475 :?.-2.'J/32 2.718 69.0,5(; 4-1 J /lfl 4.6875 !19.0fi3 2-,1/4 2.7.5() 6fl.f'l50 - ,1 7:':44 l20 - :?..755,J 70 4-:3/4 4.750 120.650 :?.-2'>/12 2.781 70.fl43'1 4-J:J/1(; 4.8125 122 238 - 2.7!153 71 4-7/8 4.875 12,3.825 2.131](; 2.SW) 71.437/i - 4.9212 125. - 2 8346 72 4-1')/lfl 4.9.175 125.413 2-27/32 2 844 72.2314 5 5.000 127 000 - 2.8740 73 . - 5.1181 130. 2-7/8 2x:-s 73.02S .5-1/4 .5.250 1.13.350 2-2\)/32 2.9002 73.819 .5-1/2 5.500 13H.700 - 2.!1114 74. - 5.518 140 2-15/16 :?. 0375 74.611 .5-1/4 5 750 146.050 - 2.U,527 75 - 5.9()55 150 2-31132 2.869 75 406 (; 6.()00 152.400 - 2.9\J:?.J 76 6-1/4 {l.2.50 1,58.750 3 3.000 76.200 - 6.2!1()2 160. '3-1/12 2.0.112 76.9!.J.~ fl-1/2 R.500 165.100 - l.0,)15 77. - 6.6929 170. 'J-1/16 .1.062 77.7S8 {l-3/4 6.750 171.450 - 3.0"iM 78 7 7.000 177.800 3-3/32 3.094 78.581 - 7.0866 UlO. - 3.1 Hl2 78 - 7.4fl03 ]90 J-1/8 3.12.5 70.375 7-1/2 7.500 !fJ0.,500 - . 3.1486 80 - 7.8740 200 . 3-5/32 'l.J.56 80.169 8 8.000 20.3.2(){) 3-.1/Tfi 3.lll75 80.00~J - 8.2677 210, - .1.1880 81. 8-1/2 8.5DO 215.900 "l-7 /12 .1.ZHJ 81.7.58 - 8.(,614 220. - .}.228.3 SC ,, n.r100 228.600 l-1/4 .1.25() s2.s5n - 'l.0551 230 - 1.2n77 8.1. - ').4488 240. l-\j/32 3.28! 83.344 !J-1/2 0.500 241.300 3 .')Oil 84. - 9.842,5 250. 3-5/16 3.312 84.1.177 '" I0.000 254.001 .3-11/,12 3.341 84.8314 10.2162 260. - .1.3464 85. .. JO 6299 :?:70. ->-V8 .1.375 83.72~ " 11.000 279.4111 - .'3.3858 "' - 11.0236 280. .).\.3/,12 3.406 86 .. 5!\J - 11.4173 290, - 3.42,52 87. - 11.8110 100. 3-7/16 3.438 ~7.313 12 12.000 :J04.8{JJ - 3.4646 88. ,1 13.000 .130.2n1 3-15/.32 J.4fl0 8f!.l06 - 13.7795 350. .3-1/2 ., 500 88 'll"lO '4 1.1.000 3.'>.5.601 - 3 .. )0,')9 fl9. \.5 15.000 381.001 .'3-17/32 .1.5.11 fl'l.694 - 15.7-180 400. .1.5433 80 rn 16.000 l06.40] l-'J/16 .'l.562 00 4877 '7 17.000 43U;GJ - 1.5fl27 91 - 17.7165 450 3-19/.)2 .1.594 91.281 rn 18.000 457.201 - 3.622 92 HJ rn.ooo 482 601 3-.'5/8 3.625 92.075 - 18.63,50 500 ,1-21/.'32 3 656 02.869 20 20.000 .508.001 - .1.1m14 91. FIGl~RE 1-26. Fractions, decimals, and millim('ters. ### Page 41 FUNCTIONS OF NUMBERS The Functions of Numbers chart (figure 1-27) is included in this chapter for convenience in mak- No. Square Cube Square Root 1 1 1 1.0000 2 4 8 1.4142 3 9 27 1.7321 4 16 64 2.0000 5 25 125 2.2361 6 36 216 2.4495 7 49 343 2.6458 8 64 512 2.8284 9 81 729 3.0000 10 100 1,000 3.1623 11 121 1,331 3.3166 12 144 1,728 3.4641 13 169 2,197 3.6056 14 196 2,744 3.7417 15 225 3,375 3.8730 16 256 4,096 4.0000 17 289 4,913 4.1231 18 324 5,832 4.2426 19 361 6,859 4.3589 20 400 8,000 4.4721 21 441 9,261 4.5826 22 484 10,648 4.6904 23 529 12,167 1.7958 24 576 13,824 4.8990 25 625 15,625 5.0000 26 676 17,576 5.0990 27 729 19,683 5.1962 28 784 21,952 5.2915 29 841 24,389 5.3852 30 000 27,000 5.4772 31 1,961 29,791 5.5678 32 1,024 32,768 5.6569 33 1,089 35,937 5.7446 34 1,156 39,304 5.8310 35 1,225 42,875 5.9161 36 1,296 46,656 6.0000 37 1,369 50,653 6.0828 38 1,444 54,872 6.1644 39 1,521 59,319 6.2450 40 1,600 64,000 6.3246 41 1,681 68,921 6.4031 42 1,764 74,088 6.4807 43 1,849 79,507 6.5574 44 1,936 85,184 6.6332 45 2,025 91,125 6.7082 46 2,116 97,336 6.7823 47 2,209 103,823 6.8557 48 2,304 110,592 (i.9282 49 2,401 117,649 7.0000 50 2,500 125,000 7.0711 ing computations. Familiarization with the various parts of this chart will illustrate the advantages of using "ready-made" computations. Cube Circum- Root ference Area 1.0000 3.1416 0.7854 1.2599 6.2832 3.1416 1.4422 9.4248 7.0686 1.5874 12.5664 12.5664 1.7100 ]5.7080 !9.635 1.8171 18.850 28.274 1.9129 21.991 38.485 2.0000 25.133 50.266 2.0801 28.274 63.617 2.1544 31.416 78.540 2.2240 34.558 95.033 2.2894 37.699 113.10 2.3513 40.841 132.73 2.4101 43.982 153.94 2.4662 47.124 176.71 2.5198 50.265 201.06 2.5713 53.407 226.98 2.6207 56.549 254.47 2.6684 59.690 283.53 2.7144 62.832 314.16 2.7589 65.973 346.36 2.8020 69.115 380.13 2.8439 72.257 415'.48 2.8845 75.398 452.39 2.9240 78.540 490.87 2.9625 81.681 530.93 3.0000 84.823 572.56 3.0366 87.965 615.75 3.0723 9!.106 660.52 3.1072 94.248 706.86 3.1414 97.389 754.77 3.1748 100.53 804.25 3.2075 103.67 855.30 3.2396 106.81 907.92 3.2717 109.96 962.11 3.3019 IJ.3.10 1,017.88 3.3322 116.24 1,075.21 3.3620 119.38 1,134.11 3.3912 122.52 1,194.59 3.4200 125.66 1,256.64 3.4482 128.81 1,320.25 3.4760 131.95 1,385.44 3.5034 135.09 1,452.20 3.5303 138.23 1,520.53 3.5569 141.37 1,590.43 3.5830 144.51 1,661.90 3.6088 147.65 1,734.94 3.6342 J.50.80 1,809.56 3.6593 153.94 1,885.74 3.6840 157.08 1,963.50 FIGERE 1-27. Functions of numbers. 31 ' . ' .'.;~ ### Page 42 Numbers The number column contains the numbers 1 Square No. Square Cube Root 51 2,601 132,651 7.1414 52 2,704 140,608 7.2111 53 2,809 148,877 7.2801 54 2,916 157,464 7.3485 55 3,025 166,375 7.4162 56 3,136 175,616 7.4833 57 3,249 185,193 7.5498 58 3,364 195,112 7.6158 59 3,481 205,379 7.6811 60 3,600 216,000 7.7460 61 3,721 226,981 7.8102 62 3,844 238,328 7.8740 63 3,969 250,047 7.9373 64 4,096 262,144 8.0000 65 4,225 274,625 8.0623 66 4,356 287,496 8.1240 67 4,489 300,763 8.1854 68 4,624 314,432 8.2462 69 4,761 328,509 8.3066 70 4,900 343,000 8.3666 71 5,041 357,911 8.4261 72 5,184 373,248 8.4853 73 5,329 389,017 8.5440 74 5,476 405,224 8.6023 75 5,625 421,875 8.6603 76 5,776 438,976 8.7178 77 5,929 456,533 8.7750 78 6,084 474-,552 8.8"318 79 6,214 493,039 8.8882 80 6,400 512,000 8.9443 81 6,561 531,441 9.0000 82 6,724 551,368 9.0554 83 6,889 571,787 9.1104 84 7,056 592,704 9.1652 85 7,225 614,125 9.2195 86 7,396 636,056 9.2376 87 7,569 638,503 9.3274 88 7,744 681,472 9.3808 89 7,921 704,969 9.4340 90 8,100 729,000 9.4868 91 8,281 753,571 9.5394 92 8,464 778,688 9.5917 93 8,649 804,357 9.6437 94 8,836 830,584 9.6954 95 9,025 857,375 9.7468 96 9,216 884,736 9.7980 97 9,409 912,673 9.8489 98 9,604 941,192 9.8995 99 9,801 970,299 9.9499 100 10,000 1,000,000 10.0000 through 100. The other columns contain compu­ tations for each number. Cube Circum- Root ference Area 3.7084 160.22 2,042.82 3.7325 163.36 2,123.72 3.7563 166.50 2,206.18 3.7798 169.65 2,290.22 3.8030 172.79 2,375.83 3.8259 175.93 2,463.01 3.8485 179.07 2,551.76 3.8709 182.21 2,642.08 3.8930 185.35 2,733.97 3.9149 188.50 2,827.43 3.9365 191.64 2,922.47 3.9579 194.78 3,019.07 3.9791 197.92 3,117.25 4.0000 201.06 3,126.99 4.0207 204.20 3,381.31 4.0412 207.34 3,421.19 4.0615 210.49 3,525.65 4.0817 213.63 3,631.68 4.1016 216.77 3,739.28 4.1213 219.91 3,848.45 4.1408 233.05 3,959.19 4.1602 226.19 4,071.50 4.1793 229.34 4,185.39 4.1983 232.48 4,300.84 4.2172 235.62 4,417.86 4.2358 238.76 4,536.46 4.2543 241.90 4,656.63 4.2727 245.05 4,778.36 4.2908 248.19 4,901.67 4.3089 251.33 5,026.55 4.3267 254.47 5,153.00 4.3445 257.61 5,281.02 4.3621 260.75 5,410.61 4.3795 263.89 5,541.77 4.3968 267.04 5,674.50 4.4140 270.18 5,808.80 4.4310 273.32 5,944.68 4.4480 276.46 6,082.12 4.4647 279.60 6,221.14 4.4814 282.74 6,361.73 4.4979 285.88 6,503.88 4.5144 289.03 6,647.61 4.5307 292.17 6,792.91 4.5468 295.31 6,939.78 4.5629 298.45 7,088.22 4.5789 301.59 7,283.23 4.5947 304.73 7,389.81 4.6104 307.88 7,542.96 4.6261 311.02 7,697.69 4.6416 314.16 7,853.98 FIGURE 1-27. Functions of numbers (continued). ### Page 43 Square Square is the prO'duct obtained by multiplying a number by itself: lXl=l, 2X2=4, 17Xl7=289, Squaring may be considered a special form of area computation: Area= Length multiplied by Width, A=LXW, Cube Cube is the product obtained by multiplying a number by itself, then multiplying that product by the number again: lXlXl=l, 2X2X2=8, 13 X 13 X 13 =2,197, Cubing may be considered a specialized form of volumn computation: Volume= Length multiplied by Width by Heigh th, V=LXWXH. Square Root Square root is the opposite of a "squared" num­ ber. The square root of a number is, that number which when multiplied by itself (squared) will produce the original or desired number: For ex­ ample, the square root of 1 is 1, 1 X 1 = l. The square root of 4 is 2. The square root of 24 is 4.8990. If an area of 24 square inches must be a perfect square, the length of each side would be 4.8990 inches. Cube Root A cube root is the opposite of a "cubed" number. The cube root of a number is that number which 33 when multiplied by itself (cubed) will produce the original or desired number. The cube root oJ 1 is 1, 1 X 1 X l = 1. The cube root of 27 is 3, 3X3X3=27. If a container of 100 cubic inches and cubic in shape is desired, then the length of each side would be 4.6416. Circumference of A Circle Circumference is the linear measurement of the distance around a circle. The circumference is calculated by multiplying the diameter of the circle by the constant 3.1416 (.,,). This constant was calculated by dividing the circumference of circles by their ·diameter. For example, diameter=!, circumference=3.1416, 1X3.1416=3.1416. Di­ ameter=lO, 10X3.1416=31.4160, diameter=l2, 12X3.1416=37.699. Area of A Circle Area of a circle is the number of square units of measurement contained in the area circumscribed by a circle of the diameter of the listed number. This is calculated by the formula ( ,,-) X r' = a, ( ,r) multiplied by the radius squared equals area. The radius is equal to one half the diameter. For example, diameter=2, radius= 1. 3.1416X 1 = 3.1416 square units in a circle which has a diam­ eter of 2. Another example, diameter =4, radius= 2. 3.1416X2'=3.1416X4,=12.5664 square units. lion micrograms. ### Page 44 PRINTS The exchange of ideas is essential to everyone, regardless of his vocation or position. Usually, this exchange is carried on by the oral or written word; but under some conditions the use of these alone is impractical. Industry discovered that it could not depend entirely upon written or spoken words for the exchange of ideas because mis­ understanding and misinterpretation arose fre­ quently. A written description of an object can be changed in meaning just by misplacing a comma; the meaning of an oral description can be completely changed by the use of a wrong word. To avoid these possible errors, indus­ try uses drawings to describe objects. For ·this reason, drawing is called the Draftsman's Lan­ guage. Drawing, as we use it, is a method of conveying ideas concerning the construction or assembly of objects. This is done with the help of lines, notes, abbreviations, and symbols. It is very important that the aviation mechanic who is to make or assemble the object understand the meaning of the different lines, notes, abbreviations, and sym~ bols that are used in a drawing. (See especialJy ~rThe Meaning of Lines" section of this chapter.) Prints are the link between the engineers who design an aircraft and the men who build, main~ tain, and repair it. A print may be a copy of a working drawing for an aircraft part or group of parts, or for a design of a system or group of systems. They are made by placing a tracing of the drawing over a sheet of chemically treated paper and exposing it to a strong light for a short period of time. When the exposed paper is developed, it turns blue where the light has penetrated the transparent tracing. The inked lines of the tracing, having blocked out the light, show as white lines on a blue background. Other types of sensitized paper have been developed; prints may have a white background with colored lines or a colored background with white lines. **35 CHAPTER 2** AIRCRAFT DRAWINGS A print shows the various steps required in building anything from a simple component to a complete aircraft. WORKING DRAWINGS Working drawings must give such information as size of the object and all of its parts, its shape and that of all of its parts, specifications as to the material to be used, how the material is to be finished, how the parts are to be assembled, and any other information essential to making and assembling the particular object. Working drawings may be divided into three classes: (1) Detail drawings, (2) assembly draw­ ings, and (3) installation drawings. Detail Drawing A detail drawing is a description of a single part, given in such a manner as to describe by Jines, notes, and symbols the specifications as to size, shape, material, and methods of manufacture that are to be used in making the part. Detail drawings are usually rather simple; and, when single parts are sma1l, several detail drawings may be shown on the same sheet or print. (See detail drawing at the top of figure 2-1.) Assembly Drawing An assembly drawing is a description of an object made up of two or more parts. Examine the assembly drawing in the center of figure 2-l. It describes the object by giving, in a genera] way, the size and shape. Its primary purpose is to show the relationship of the various parts. An assembly drawing is usua11y more complex than a detail drawing, and is often accompanied by detail drawings of various parts. ### Page 45 NOTE: -ALL BEND RADII 3/16 -RADIUS OF CUT OUT - IS 1/4 -L.H. IS SHOWN -R.H.-! OPPOSITE 4 3/8 1 DETAILS i-= 2-3/18 :Ct **MATERIAL -024 24ST ALCLAD 4 1/8 ASSEMBLY 3 J/2 , , 5/16 SYM.** **81219AD4 RIVETS 12 REQ, 2 PLATE .064 24ST ALCLAD I REQ.** **36-31290 SIDE I REQ 36-31290 SIDE I REQ.** **4---- FORWARD I I I I I I I** I INSTALLATION I I I I I I I STA 167 FIGVRE 2-l. Working drawings. 36 Installation Drawing An installation drawing is one which includes all necessary information for a part or an assembly of parts in the final position in the aircraft. It shows the dimensions necessary for the location of specific parts with relation to tP,e other parts and reference dimensions that are helpful in later work in the shop. (See installation drawing at the bottom of figure 2-1.) CARE AND USE OF DRAWINGS Drawings are both expensive and valuable; consequently, they should be handled carefully. Open drawings slowly and carefully to prevent tearing the paper. When the drawing is open, smooth out the fold lines instead of bending them backward. To protect drawings from damage, never spread them on the floor or lay them on a surface covered with tools or other objects that may make holes in the paper. Hands should be free of oil, grease, or other unc1ean matter than can soil or smudge the print. Never make note-s or marks on a print, as they may confuse other persons and lead to incorrect work. Only authorized persons are permitted to make notes or changes on prints, and they must sign and date any changes they make. W'hen finished with a drawing, fold and return it to its proper place. Prints are folded originally in a proper size for filing, and care should be taken so that the original folds are always used. TITLE BLOCKS Every print must have some means of identifi­ cation. This is provided by a title block (see figure 2-2). The title block consists of a drawing number and certain other data concerning the drawing and the object it represents. This infor­ mation is grouped in a prominent place on the print, usually in the lower right-hand corner. Sometimes the title block is in the form of a strip extending almost the entire distance across the bottom of the sheet. Although title blocks do not follow a standard form, insofar as layout is concerned, all of them will present essentially the following information: l. A drawing number to identify the print for filing purposes and to prevent confusing it with any other print. ### Page 46 **FEDERAL AVIATION ADMIN.** **AERONAUTICAL CENTER OKLAHOMA CITY, OKLA.** N~ I ADF" "T" ANTE N lsJA LOCATION ~ DETAILS SCALE, FULL s IZ:E APPROVED: SUBMITTED: ,TO$El"H OOE 8.8.l!LACK DR.BY: IISF I DATE DR. AC-A-735 CK.BY, TDY J 4-8-68' FIGURE 2-2. Title block. 2. The name of the part or assembly. 3. The scale to which it is drawn. 4. The date. 5. The name of the firm. 6. The name of the draftsmen, the checker, and the person approving the drawing. Drawing or Print Numbers All prints are identified by a number, which appears in a number block in the lower right-hand corner of the title block. It may also be shown in other places-such as near the top border line, in the upper right-hand corner, or on the reverse side of the print at both ends-so that the number will show when the print is folded or rolled. The purpose of the number is for quick identification of a print. If a print has more than one sheet and each sheet has the same number, this information is included in the number block, indicating the sheet number and the number of sheets in the series. Reference and Dash Numbers Reference numbers that appear in the title block refer a person to the numbers of other prints. When more than one detail is shown on a drawing, dash numbers are used. Both parts would have the same drawing number plus an individual number, such as 40267-1 and 40267-2. In addition to appearing in the title block, dash numbers may appear on the face of the drawing near the parts they identify. Dash numbers are also used to identify right-hand and left-hand parts. In aircraft, many parts on the left side are like the corresponding parts on the right side but in reverse. The left-hand part is always shown in the drawing. The right-hand part is called for in 37 the title block. Above the title hlock will be found a notation such as: 470204-lLH shown; 470204- 2RH opposite. Both parts carry the same number, but the part called for is distinguished hy a dash number. Some prints have odd numbers for left­ hand parts and even numbers for right-hand parts. Universal Numbering System The universal numbering system provides a means of identifying standard drawing sizes. In the universal numbering system, each drawing number consists of six or seven digits. The first digit is always 1, 2, 4, or 5 (figure 2-3), and indicates the size of the drawing. The remaining digits identify the · drawing. Many firms have modified this basic svstem to conform to their particular needs. Lett~rs may be used instead of numbers. The letter or number depicting the standard drawing size may be prefixed to the num­ ber, separated from it by a dash. Other number­ ing systems provide a separate box preceding the drawing number for the drawing size identifier. In other modification of this system the part num­ ber of the depicted assembly is assigned as the drawing number. SIZE I 2 4 5 LENGTH I t" 17 11 22" INDEFINITE (ROLL) WIDTH 8-1/2" 11" 17 11 17, 22,25.50,34, and 36 inches FIGURE 2-3. Standard blueprint paper sizes. BILL OF MATERIAL A list of the materials and parts necessary for the fabrication or assembly of a component or system is often included on the drawing. The list usually will be in ruled columns in which are listed the part number, name of the part, material from which the part is to be constructed, the quantity required, and the source of the part or material. A typical bill of material is shown in figure 2-4. On drawings that do not have a hill of material, the data may be indicated directly on the drawing. On assembly drawings, each item is identified by a number in a circle or square. An arrow con­ necting the number with the item assists in lo­ cating it in the bill of material. .· ,-: ### Page 47 BILL OF MATERIAL ITEM PART NO. REQUIRED SOURCE CONNECTOR UG-210/U 2 STOCK FIGURE 2-4. A typical bill of material. OTHER DATA Revision Block Revisions to a drawing arc necessitated by changes in dimensions, design, or materials. The changes are usually listed in ruled columns either adjacent to the title block or at one corner of the drawing. All changes to approved drawings must be carefully noted on all existing prints of the drawing. 'When drawings contain such correction:-., atten­ tion is directed to the changes by lettering or numbering them and listing those changes against the symbol in a revision block (figure 2~5). The revision block contains the identification symbol, the date, the nature of the revision, the authority for the change, and the name of the draftsman who made the change. To ·distinguish the correctPd dra,ving from its previous version, many firms are including, as part of the title block, a space for entering the appro­ priate sjrmhol to designate that the drav,.ring has been changed or revised. **2 CHANGED PART NO. 5 E.0.1 2/3/7( 8.K.** **I REVISED DIMENSIONS J.L.M. 7/1/69 E.K.P.** **NO. REVISION AUTH. DATE SIGN.** FIGCRE 2-.S. Revision block. Notes Notes are added to dra,vings for various rea­ sons. Some of these notes refer to methods of attachment or construction. Others give alter­ natives, so that the drawing can be used for different styles of the same object. Still others list modifications that are available. Notes may be found alongside the item to which they refer. If the notes are lengthy, they may be placed elsewhere on the drawing and identified by letters or numbers. Notes are used 38 only when the information cannot be conveyed in the conventional manner or when it is desirable to avoid crowding the drawing. Figure 2-1 illus­ trates one method of depicting notes. When the note refers to a specific part, a light line with an arrowhead leads from the note to the part. If it applies to more than one part, the note is so worded that no mistake can be made as to the parts to which it pertains. When there are several notes, they are generally grouped together and numbered consecutively. Zone Numbers Zone numbers on dra,v·ings are similar to the numbers and letters printed on the borders of a map. They arc there to help locate a particular point. To find a point, mentally draw horizontal and vertical lines from the letters and numerals specified; the point where these lines would inter­ sect is the area sought. Cse the same method to locate parts, sections, and views on large drawings, particularly as­ sembly drawings. Parts numbered in the title block can be located on the drawing by finding the numbers in squares along thP. lower border. Zone numbers read from right to left. Station Numbers A numbering system is used on large assemblies for aircraft to Jocate stations such as fuselage frames. Fuselage Frame-Sta 18.S indicates that the frame is lK) inches from the datum of the aircraft. The measurement is usuaily taken from the nose or zero station, but in some instances it may be taken from the fire wall or some other point chosen by the manufacturer. The same station numbering system is used for wing and stabilizer frames. The measurement is taken from the center line or zero station of the aircraft. Finish Marks Finish marks are used to indicate the surface that must be machine finished. Such finished surfaces have a better appearance and allow a doser fit with adjoining parts. During the finishing process the required limits and tolerances must be observed. Do not confuse machined finishes with those of paint, enamel, chromium plating, and similar coating. ### Page 48 F1GlJRE 2-6. Pictorial drawing. Tolerances When a given dimension on a print shows an allowable variation, the plus ( +) figure indicates the maximum, and the minus ( - ) figure the minimum, allowable variation. The sum of the plus and minus allowance figures is called toler­ ance. For example, using .225 + .0025 - .0005, the plus and minus figures indicate the part will he acceptable if it is not more than .0025 larger than the .225 given dimension, or not more than . 0005 smaller than the .225 dimension. Tolerance in this example is .0030 (.0025 max. plus .005 min.). If the plus and minus aHowances are the same, you will find them presented as .224 ± .0025. The tolerance would then be .0050. Allowance can be indicated in either fractional or decimal form. When very accurate dimensions are necessary, decimal allowances are used. :Fractional allow­ ances are sufficient when close dimensions are not required. Standard tolerances of -.010 or -%2 may be given in the title block of many drawings, to apply throughout the drawing. METHODS OF ILLUSTRATING OBJECTS A number of methods are used to illustrate objects graphically. The most common are pic­ torial drawings, orthographic projections, and diagrams. Pictorial Drawings A pictorial drawing, figure 2-6, is similar to a photograph. It shows an object as it appears to the eye, but it is not satisfactory for showing complex forms and shapes .. Pictorial drawings are useful in showing the general appearance of an object and are used extensively with orthographic projection drawings. Pictorial drawings are used in maintenance, overhaul, and part numbers. 39 Orthographic Projection Drawings fn order to show the exact size and shape of all the parts of complex objects, a number of views are necessary. This is the system used in ortho­ graphic projection. In orthographic projection there are six possible views of an object, because all objects have six sides~front, top, bottom, rear, right side, and left side. Figure 2-7(a) shows an object placed in a transparent box, hinged at the edges. The projections on the sides of the box are the views as seen looking straight at the object through each side. If the outlines of the object are drawn on each surface and -ihe box opened as shown in (b), then laid flat as shown in (c), the .result is a six­ view orthographic projection. It is se]dom necessary to show all six views to portray an object clearly; therefore, only those views necessary to iHustrate the required char­ acteristics of the object are drawn. One-view, two. view, and three~view drawings are the most com­ mon. Regardless of the number of views used, the arrangement is generaHy as shown in figure 2-7, with the front .view being the principal one . If the right-side view is shown, ii will be to the right of the front view. If the left-side view is shown, it will be to the left of the front view. The top and bottom views, if included, will be shown in their respective positions relative to the front view. One-view drawings are commonly used for ob­ jects of uniform thickness, such as gaskets, shims, and plates. A dimensional note gives the thickness as shown in figure 2-8. One-view drawings are also commonly used for cylindrical, spherical, or square parts if all the necessary dimensions can be properly shown in one view. When space is limited and two views must be shown, symmetrical objects are often represented by ha1f views, as illustrated in figure 2-9. Aircraft drawings seldom show more than two principal, or complete, views of an object. In­ stead, generally there will he one complete view and one or more detail views or sectional views. Detail View A detail view shows only a part of the object but in greater detail and to a larger scale than the prindpal view. The part that is shown in detail elsewhere on the drawing is usually encircled by a heavy line on the principal view. Figure 2-10 is an example of the use · of detail views. The ### Page 49 r---- ~ /OJ--7) //; I I ,- ,~I / -- ~,,-/ : I --..... / W '\.,...,.. I I -,- - _ _ _ / _ ---1 I I tJ I ---L-- J I I \ I / I -.. I cs I g : ,,,..- ,,,,-- __ _ // l - /1 ,, I ,, I I":--~' //,,- I I -- I 1 I I I ,,-l I I I ,,,...- - I 1/ - -1 I _ _,, I I I I ,,- __ I I / I -- -) I / I _,, le,, / - I .,,/'' - -- -.1/ (a) OhJect ,---------, I I CD TOP I I I I ,-- - I -----+--- \ I I Q\ \ I I I \ I I L. ______ j (b) Hotated I I r------------ --l------- -------, 1 I I I 1 I I I I I ID I : -- I I I : LEFT SIDE FRONT I RIGHT SIDE I REAR J L------------I I I I I I --f------------J I DJ : BOTTOM I L _ - - - - __ J (c) FIGURE 2-7. Orthographic projection. principal view shows the complete control wheel, while the detail view is an enlarged drawing of a portion of the control wheel. Sectional Views A section or sectional view is obtained by cutting away part of an object to show the shape and construction at the cutting plane. The part or parts cut away ~re shown by the use of section (cross-hatching) lines. Sectional views are used when the interior con­ struction or hidden features of an object cannot 40 he shown clearly by exterior views. For example, figure 2-11, a sectional view of a coaxial cable connector, shows the internal construction of the connector. This is known as a full section. Other types of sections are described in the following paragraphs. Half Sections In a half section, the cutting plane extends only halfway across the object, leaving the other half of the object as an exterior view. Half sections are ### Page 50 I -4-- --4- 1 , 032 I THICK - -- - - +- - - "--.:: I I I I I -$-- I --~-- - FIGURE - . 2 8 One-view drawing. 3 . I oh3"ect with exterior F E 2 9 Symmetnca IGI;R - • • half view. :FIGURE 2-10. Detail view. 41 ',:---' ### Page 51 FIGURE 2-11. Sectional view of a cable connector. used to advantage with symmetrical objects to show both the interior and exterior. Figure 2-12 is a half-sectional view of a quick disconnect used in aircraft fluid systems. Revolved Sections A revolved section drawn directly on the ex­ terior view shows the shape of the cross section of a part, such as the spoke of a wheel. An example of a revolved section is shown in figure 2-13. Removed Sections Removed sections illustrate particular parts of an object. They are drawn like revolved sections, except that they are placed at one side and, to QUICK DISCONNECT COUPLING -- bring out pertinent details, are often drawn to a larger scale than the view on which they are indicated. Figure 2-14 is an illustration of removed sec­ tions. Section A-A shows the cross-sectional shape of the object at cutting plane line A-A. Section B-B shows the cross-sectional shape at cutting plane line B-B. These sectional views are drawn to the same scale as the principal view; however, as already mentioned, they are often drawn to a 1arger scale to bring out pertinent details. THE MEANING OF LINES Every drawing is composed of lines. Lines mark the boundaries, edges, and intersection of surfaces. Lines are used to show dimensions and hidden surfaces, and to indicate centers. Obviously, if the same kind of line is used to show all of these things, a drawing becomes a meaningless collection of lines. For this reason, various kinds of standard­ ized lines are used on aircraft drawings. These are illustrated in figure 2-15, and their correct uses are shown in figure 2-16. Most drawings use three widths, or intensities, of lines: thin, medium, or thick. These lines may vary somewhat on different drawings, but there will always be a noticeable difference between a thin and a thick line, with the width of the medium line somewhere between the two. FIGURE 2-12. Half section. ### Page 52 FIGURE 2-13. Revolved sections. Center Lines Center lines are made up of alternate long and short dashes. They indicate the center of an object or part of an object. Where center lines cross, the short dashes intersect symmetrically. In the case of very smaJI circles, the center lines may be shown unbroken. Dimension Lines A dimension line is a light solid line, broken at the midpoint for insertion of measurement indi· cations, and having opposite pointing arrowheads at each end to show origin and termination of a measurement. They are generally parallel to the line for which the dimension is given, and are usually placed outside the outline of the object and between views if more than one view is shown. All dimensions and lettering are placed so that they will read from left to right. The dimension of an angle is indicated by placing the degree of the angle in its arc. The dimensions of circular parts are always given in terms of the diameter of the circle and are usually marked with the letter D or the abbreviation DIA following the dimension. The dimension of an arc is given in terms of its radius and is marked with the Jetter R following the dimension. ParalJel dimensions are placed so that the longest dimension is farthest from the outline and the shortest dimension is closest to 43 4 • B-B FIGURE 2-14. Removed sections. the outline of the object. On a drawing showing several views, the dimensions will be placed upon each view to show its details to the best advantage. In dimensioning distances between holes in an object, dimensions are usually given from center to center rather than from outside to outside of the holes. When a number of holes of various sizes are shown, the desired diameters are given on a leader followed by notes indicating the ma­ chining operations for each hole. If a part is to have three holes of equal size, equally spaced, this information is given. For precision work, sizes are given in decimals. Diameters and depths are given for counterbored holes. For countersunk holes the angle of countersinking and the diam­ eters are given. Study the examples shown in figure 2-17. The dimensions given for fits signify the amount of clearance allowable between moving parts. A positive allowance is indicated for a part that is to slide or revolve upon another part. A negative allowance is one given for a force fit. Whenever possible, the tolerance and allowances. for desired fits conform to those set up in the American Standard for Tolerances, Allowances, and Gages for Metal Fits. The classes of fits specified in the standard may be indicated on assembly drawings. ·, -~ ### Page 53 CE:\TER LINE Till:\ DU.fEi\:SION TIil:\ LEADER THI/\ BHEAK (LONG) 'J;1, ii THIX BHEAK I SHORT) THICK Pl!AXTOM THIX SECTIO:\INC: TIIIX I IIDDEN \IEDl\'M STITCH LIXE --- - - - - -- - - - - -- - - -- - -- - - -- ------ \IEDIU~f 01.'TLIXE OR VISIBLE L!XE DAT\'~! L!:\E Cl 1TTl'.\C PI.A:\'E i C\'TTl:\C: PLAXE FOR COMPLEX OH OFFSET V!E\\'S r ---, TllICK THICK i EXTHA T!IICK I EXTRA T!IICK 4irlt' - - -...., EXTRA TIIICK FIGURE 2-15. The meaning of lines. Phantom i-line ,,--- ' ' -- ~ : ' ' ---r::-- Dimension line Center line " ,, ( ') . : \ , I -----t--------'-L._ __ _y- { '-"·· Outline Hidden line A Cutting plane !me FIG-URE 2-16. Correct uses of lines. 44 Extension line Leader line Sectioning line **SECTION AA** ### Page 54 .312t5 DRILL ~ • 3217 REAM_) •• __ / 1/4 DRILL ¥ 7/16 C' BORE 1/8 DEEP 2 HOLES , •• 2560 DR~ 3/16 DRILL ao0 c'stc TO 6/16 DIA 1/8 Df!EP, 3 HOLES FIGURE 2-17. Dimensioning holes. Leader Lines Leaders are solid Jines with one arrowhead and indicate a part or portion to which a note, number, or other reference applies. Break Lines Break lines indicate that a portion of the object is not shown on the drawing. Short breaks are made by solid, freehand lines. For long breaks, solid ruled lines with zigzags are used. Shafts~ rods, tubes, and other such parts which have a portion of their length broken out, have the ends of the break drawn as indicated in figure 2-16. Phantom Lines Phar1tom lines indicate the alternate position of parts of the object or the relative position of a missing part. Phantom lines are composed of one long and two short evenly spaced dashes. Sectioning Lines Sectioning lines indicate the exposed surfaces of an object in sectional view. They are generally thin, full lines, hut may vary with the kind of material shown in section. 45 Hidden Lines Hidden lines indicate invisible edges or con­ tours. Hidden lines consist of short dashes evenly spaced and are frequently referred to as dash lines. Outline or Visible Lines The outline or visible line is used for all lines on the drawing representing visible lines on the object . Stitch Lines Stitch lines indicate stitching or sewing lines and consist of a series of evenly spaced dashes. Cutting Plane and Viewing Plane Lines Cutting plane lines indicate the plane in which a sectional view of the object is taken. In figure 2-16, plane line A-A indicates the plane in which section A-A is taken. Viewing plane lines indicate the plane from which a surface is viewed. READING DRAWINGS A drawing cannot be read all at once any more than a whole page of print can be read at a glance. Both must be read a line at a time. To read a drawing effectively, follow a systematic procedure. Upon opening a drawing, read the drawing number and the description of the article. Next, check the model affected, the latest change letter, and the next assembly listed. Having determined that the drawing is the correct one, proceed to read the illustration(s). In reading a multiview drawing, first get a general idea of the shape of the object by scanning all the views; then select one view for a more careful study. By referring hack and forth to the adjacent view, it will be possible to determine what each line represents. Each line on a view represents a change in the direction of a surface, hut another view must be consulted to determine what the change is. For example, a cirde on one view may mean either a hole or a protruding boss, as in the top view of the object in figure 2-18. Looking at the top view, we see two circles; however, the other view must be consulted to determine what each circle repre­ sents. A glance at the other view tells us that the smaller circle represents a hole, and the larger ### Page 55 I : : I ' ' I I I I I I : I : L_t_.J I _j ~----+- F.wm:u: 2--18. Reading views. circle represenH~ a protruding .bo~s. Jn the same way, the top vie\v must he t'On$u.!t,·d to : referred to as caH out:;, and ,:,en'<' t(1 ideniHy t:>.ach component. fos·wllati0r dia~nn.nC" arr:: rn,;ed extensively in aircraft maintcnann~ and repair manuals and arc invahwbl(' in idt~ntif:~iug and locating com. fH>nents an,1 1.m< 100 = 80 20 X 100 = 25% 80 FIGURE 3-5. Finding percent of MAC. is the figure used when the fuel load musl' Le re­ duced to obtain the most critical loading on the e.g. limit being investigated. Either of 2 formulas may be used. Formula 1: Minimum fuel= ~']_2 gallons per horsepower. hpXY, 2 X6 lb. 1200 X :Y,2 X 6 = 1200 X Y,2 X 6 = 600 lb. fuel. Formula 2: Minimum Juel==Y2 lb. per cngme horsepower. hpX Y2 =minimum fuel. 1200 X \/2 = 600 lb. fuel. This will be the minimum pounds of fuel requfred for the forward or rearward weight check. For turbine-engine powered aircraft 1 the mini­ mum fuel load is specified by the aircraft manu· facturer. The fuel tank location in relation to the e.g. limit affected by the computation determines the use of minimum fuel. For example, when a forward weight check is performed, if the fuel tanks arc located forward of the forward e.g. limit, they are assumed to be full. If they are located aft of the forward e.g. limit, they are assumed to be empty. If the minimum fuel required for a particular air­ craft exceeds the capacity of the tanks located forward of the forward e.g. limit, the excess fuel must be loaded in the tanks that are aft of the forward e.g. limit. When a rearward weight check is conducted, the fuel loading conditions are oppo­ site to those used for the forward check. 59 Full Oil Full oil is the quantity of oil shown as oil capacity in the Aircraft Specifications. When weighing an aircraft, the oil tank may either contain the number of gaHons of oil specified or be drained. When an aircraft with full oil tanks is weighed, the weight· of the oil must be subtracted from the recorded readings to arrive at the actual empty weight. The weight and balance report must show whether weights include full oil or if the oil tanks were drained. Tare Weight Tare includes the weight of all extra items, such as jacks, blocks, and chocks on the weighing scale platform, except that of the item being weighed. The weight of these items, when included in the scale reading, is deducted to obtain the actual weight of the aircraft. AIRCRAFT WEIGHING PROCEDURE Before beginning a study of aircraft weighing procedure or attempting the actual weighing of an aircraft, it is necessary to become familiar with the weight and balance information in the ap­ plicable Aircraft Specification or Type Certificate Data Sheet. The .-:pecification for Taylorcraft, model BC and BCS airplanes, illustrated in figure 3-6 has been reproduced in its f'ntircty. A few of the items need explaining; the rest are self-explanatory. The designation 2 PCLM is read ~~2-place, closed land monoplane" and indicates that the airplane seats two persons, has an enclosed cock­ pit, can be operated from the solid part of the earth's surface, and has only one wing. Two PCS11 indicates that the airplane is a ff2-place, closed sea monoplane." It should be noted that the e.g. range, EWCG range, and the maximum weight are different for the landplane and the seaplane. The location of the seats indicates a side-by-side arrangement. The datum and the leveJing means are shown in the portion of the specification that is pertinent to aI1 rnode}s. Since the datum and the leveling means are directly connected to weight and balance, they would be among the first items referred to in planning the weighing operation. Although the location or arrangrment of the ·'>. ### Page 69 ··.~ Type Certificate Holder. **DEPARTMENT OF TRANSPORTATION** FEDERAL AVIATION ADMINISTRATION AIRCRAFT SPECIFICATION NO. A-696 Taylorcraft Aviation Corporation 104 Prospect Street Alliance, Ohio 44601 BC BCS BC-65 BCS-65 A-696 Revision 16 TAYLORCRAFT BCS12-D BC12-Dl BCS12-Dl BC12-65 ( Army L-2H) BCS12-65 BC12D-85 BCS12D-85 BC12D-4-85 BCS12D-4-85 BC12-D 9 September 1969 I-Model BC, 2 PCLM, Approved August 24, 1938; Model BCS, 2 PCSM, Approved April 5, 1939 Engine. Fuel. Engine Limits. Propeller Limits. Airspeed Limits. ( True Ind.) Center of Gravity { C.G.) Range. Empty '-"' eight C.G. Range. Maximum \\'eight. Number of Seats. Maximum Baggage. Fuel Capacity. Oil Capacity. Control Surface Movements. Serial No. Eligible. Required Equipment. Continental A-50-1 (see item 114(a) for optional engines) 73 min. grade aviation gasoline For all operations, 1900 r.p.m. ( 50 hp.) Diameter: Maximum 83 in. Land plane: Level flight or climb 105 m.p.h. Glide or dive 131 m.p.h. Seaplane: Level flight or climb 95 m.p.h. Glide or dive 129 m.p.h. Landplane: ( +14.5) to (+19.7) Seaplane: ( + 15.1) to ( +19.4) Landplane: ( +15.3) to ( +18.5) Seaplane: ( +15.9) to (+18.3) (91 knots) ( 114 knots) (83 knots) ( 112 knots) V\lhcn empty weight C.G. falls within pertinent range, computation of critical for and aft C.G. positions is unnecessary. Ranges are not valid for non-standard arrangements. Landplanc: llOO Ih. (S/N 1407 and up are eligible at 1150 lb.) Seaplane: 1228 lb. 2 ( +23) 30 lb. (+40) 12 gal. ( ~9). See item 115 for auxiliary tank. 4 quart. Elevators; Rudders: (-21) Ailerons: 1001 and up Lan , d - 0 V 400 360 0 320 ;z 0 vv ,i- c.>:· :,,, o"' ~ f'" , , ~ 280 ":v ;._ fv' "¢~· 'l."-' L <{;, ,ff:, V , 9.,<1-' , ,,.0 ~ 240 ~ :wo w 160 ii: 120 ~ F i? I/ F I,< '/IO~ C? ".,I- I '/ ) ) 30 ' , / i,.f'.l. 20- /I ~c,'i- ,,.. 'l>~c,O . ', ! I I I ,,. . ~. ### Page 79 ) J. I I I I I ' 2401 2300 2200 2100 2000 1900 1800 1700 1600 1500 1400 = ~ENTER ~F dRAV;TY ~NV~LO~E / - / / / / / ~ / / / / / / / / , , / / / I / / Any point falling with- - / / in the envelope meets - / all Balance require- _ ments. - I / . ' / / I I 40 50 60 70 80 90 100 l!() MOMENT IN THOUSANDS OF POPXD-INCHES FIGURE 3-14. Center of gravity envelope. number 'for the empty weight of the aircraft is developed by dividing the empty-weight moment by 1,000. This gives an index number of 52.8 for the airplane's empty-weight moment. Load the aircraft to determine whether the e.g. will fall within the diagonal lines of figure 3-14. Arrange item weights and index numbers in an orderly form to facilitate adding. :Moment Weight (thousands Item (lhs.) of lb.-in.) Acft. EW 1,386.0 52.8 Oil 19.0 - 0.4 Pilot & copilot 340.0 12.2 Rear passengers (two) 340.0 24.1 Baggage 20.0 1.9 Fuel 245.0 11.8 Total 2,350.0 102.4 The total airplane weight in pounds is 2,350.0, and the moment is 102.4. Locate this point (2,350 @ 102.4) on the e.g. envelope illustrated in figure 3-14. Since the point falls within the diagonal lines, the loading arrangement meets all weight-and-balance requirements. ELECTRONIC WEIGHING EQUIPMENT Electronic weighing equipment greatly sirilpli­ fied the mechanics of weighing large, heavy air­ craft. Figure 3-15 shows one type of electronic scales. The complete weighing kit is contained in a portable carrier. Included in the kit are a steel tape, plumb bobs, spirit level, straightedge, hy­ drometer (for determining the fuel specific gravity) and the load cells. The load cells are actually strain gages that reflect the load imposed upon them by the aircraft in terms of voltage change. This change is indicated on a scale that is cali­ brated to read in pounds. One load cell is placed between the jack-pad and the jack at each weighing point. Each load cell must he balanced or ~'zeroed" before applying any load to the cell. After completing the weighing operation, remove all load from the cells and check to see if the cell reading is still zero. Any deviation from zero is referred to as the ••zero scale shift" and constitutes the tare when using electronic weighing scales. The direction of shift is the factor that .determines whether the tare is added to or subtracted from the scale reading. Always follow the instructions of the manufacture whose scales you are using. HELICOPTER WEIGHT AND BALANCE The weight and balance principles and proce­ dures that have been described apply generally to ### Page 80 D D FIGURE 3-15. Aircraft electronjc weighing kit. helicopters. Each model helicopter is certificated for a specific maximum gross weight. However, it cannot be operated at this ma~imum weight under all conditions. Combinations of high altitude, high temperature, and high humidity determine the density altitude at a particuh1r location. This, in turn, critically affects the hovering. takeoff, climb, autorotation, and landing performa,nce of a heli­ copter. A heavily loaded helicopter has less ability to withstand shocks and additional loads caused by turbulent air. The hel:!v~er the load, the less the margin of safety for the S\J.pporting structures, such as the main rotor, fu~elage, landing gear, etc. Most helicopters h~ve a much more restricted e.g. range than do airpl{lnes. In some cases this range is less than 3 in1,Jhe;,~ The exact location and 71 length of the e.g. range is specified for each heli­ copter and usually extends a short distance fore and aft of the main rotor mast or the centroid of a dual rotor system. Ideally, the helicopter should have such perfect balance that the fuselage re­ mains horizontal while in a hover, and the only cyclic adjustment required should be that niade necessary by the wind. The fuselage acts as a pendulum suspended from the rotor. Any change in the center of gravity changes the angle at which it hangs from this point of support. More recently designed helicopters have loading com­ partments and fuel tanks located at or near the balance point. If ·the helicopter is not loaded properly and the e.g. is not very near the balance point~ the fuselage does not hang horizontaJly in a hover. If the e.g. is too far aft, the nose tilts up, and excessive forward cyclic control is required to maintain a stationary hover. Conversely, if the e.g. is too far forward, the nose tilts down and excessive aft cyclic control is required. In extreme out-of-balance conditions, full fore or aft cyclic control may be insufficient to maintain control. Similar lateral balance problems may be en­ countered if external loads are carried. Upon delivery by the manufacturer, the empty weight, empty weight e.g., and the useful load are noted on the weight and balance data sheet in the helicopter flight manual. If, after delivery, additional fixed equipment is added or removed, or if a major repair or alteration is made, which may affect the empty weight, empty weight e.g., or useful load, the weight and balance data must be revised. All weight and balance changes should be entered in the appropriate aircraft record. ### Page 81 GENERAL Fuel is a substance that, when combined with oxygen, will burn and produce heat. Fuels may be classified according to their physical state as solid, gaseous, or liquid. Solid Fuels Solid fuels are used extensively for external­ combustion engines, such as a steam engine, where the burning takes place under boilers or in furnaces. They include such fuels as wood and coal. Solid fuels are not used in reciprocating engines, where the burning takes place inside the cylinder, because of their slow rate of burning, low heat value, and numerous other disadvantages. Gaseous Fuels Gaseous fuels are used to some extent for internal-combustion engines, where a large supply of combustible gas is readily available. Natural gas and liquefied petroleum gas are two of the more common types. Gaseous fuels can be dis­ regarded for use in aircraft engines. The large space they occupy limits the supply of fuel that can he carried. Liquid Fuels Liquid fuels, in many respects, are the ideal fuel for use in internal-combustion engines. Liquid fuels are classified as either nonvolatile or volatile. The nonvolatile fuels are the heavy oils used in diesel engines. The volatile class includes those fuels that are commonly used with a fuel metering device and are carried into the engine cylinder or combustion chamber in a vaporized or partially vaporized condition. Among these are alcohol, benzol, kerosene, and gasoline. Aviation fuel is a liquid containing chemical energy that, through combustion, is released as heat energy and then converted to mechanical 73 CHAPTER 4 FUELS AND FUEL SYSTEMS energy by the engine. This mechanical energy is used to produce thrust, which propels the aircraft. Gasoline and kerosene are the two most widely used aviation fuels, **CHARACTERISTICS AND PROPERTIES OF** AVIATION GASOLINE Aviation gasoline consists almost entirely of hydrocarbons, namely 1 compounds consisting of hydrogen and carbon. Some impurities ju the form of sulphur and dissolv1;d water will be present. The water cannot be avoided, since the gasoline is exposed to moisture in the at­ mosphere. A small amount of sulphur, always present in crude petroleum, is left in the process of manufacture. Tetraethyl lead (TEL) is added to the gasoline to improve its performance in the engine. Organic bromides and chlorides are mixed with TEL so that during combustion volatile lead halides will be formed. These then are exhausted with the combustion products. TEL, if added alone, would burn to a solid lead oxide and remain in the engine cylinder. Inhibitors are added to gasoline to suppress the formation of substances that would be left as solids when the gasoline evaporates. Certain properties of the fuel affect engine per­ formance. These properties are volatility, the manner in which the fuel burns during the com­ bustion process, and the heating value of the fuel. Also important is the corrosiveness of the gasoline as well as its tendency to form deposits in the engine during use. These latter two factors are. important because of their effect on general cleanli­ ness, which has a bearing on the time between engine overhauls. Volatility Volatility is a measure of the tendency of a liquid substance to vaporize under given con~ ditions. Gasoline is a complex blend of volatile ### Page 82 1---Gage ----Bomb ____ Sample container FIGVRE 4-1. Vapor pressure test apparatus. hydrocarbon compounds that have a wide range of boiling points and vapor pressures. It is blended in such a way that a straight chain of boiling points is obtained. This is necessary to obtain the required starting, acceleration, power, and fuel mixture characteristics for the engine. If the gasoline vaporizes too readily, fuel lines may become filled with vapor and cause decreased fuel flow. If the fuel does not vaporize readily enough, it can result in hard ·starting, slow warm­ up, poor acceleration, uneven fuel distribution to cylinders, and excessive crankcase dilution. The lower grades of automobile fuel are not held within the tolerances required for aviation gasoline and usually contain a considerable amount of cracked gasoline, which may form excessive gum deposits. For these reasons, auto­ mobile fuels should not be used in aircraft engines, especially air-cooled engines operating at high cylinder temperatures. Vapor Lock Vaporization of gasoline in fuel lines results in a reduced supply of gasoline to the engine. In severe cases, it may result in engine stoppage. 74 This phenomenon is referred to as vapor locking. A measure of a gasoline's tendency to vapor lock is obtained from the Reid vapor pressure test. In this test a sample of the fuel is sealed in a "bomb" equipped with a pressure gage. The apparatus (see figure 4-1) is then immersed in a constant­ temperature bath and the indicated pressure is noted. The higher the corrected vapor pressure of the sample under test, the more susceptible it is to vapor locking. Aviation gasolines are limited to a maximum of 7 p.s.i. because of their increased tendency to vapor lock at high altitudes. Carburetor Icing Carburetor icing is also related to volatility. When the fuel changes from a liquid to a vapor state, it extracts heat from its surroundings to make this change. The more volatile the fuel, the more rapid the heat extraction will be. As the gasoline leaving the carburetor discharge nozzle vaporizes, it can freeze water vapor con­ tained in the incoming air. The moisture freezes on the walls of the induction system, the venturi throat, and the throttle valves. This type of ice formation restricts the fuel and air passages of the carburetor. It causes loss of power and, if not eliminated, eventual engine stoppage. Ex­ treme icing conditions can make operation of the throttle controls impossible. This icing condition is most severe in the temperature range of 30° to 40° F. out;:;ide air temperature. Aromatic Fuels Some fuels may contain considerable quantities of aromatic hydrocarbons, which are added to increase the rich mixture performance rating of the fuel. Such fuels, known as aromatic fuels, have a strong solvent and swelling action on some types of hose and other rubber parts of the fuel system. For this reason, aromatic-resistant hose and rubber parts have been developed for use with aromatic fuels. Detonation In an engine that is operating in a normal man .. ner, the flame front traverses the charge at a steady velocity of about 100 feet per second until the charge is consumed. When detonation occurs, the first portion of the charge bums in a normal manner but the last portion bums almost instan­ taneously, creating an excessive momentary pres~ ### Page 83 sure unbalance in the cootbustion chamber. This abnormal type of combustion is called detonation. This tremendous increase in the speed of burning causes the cylinder head temperature to rise. In severe cases, the increase in burning speed will decrease engine efficiency and may cause structural damage to the cylinder head or piston. During normal combustion, the expansion of the burning gases presses the head of the piston down firmly and smoothly without excessive shock. The increased pressure of detonation ex­ erted in a short period of time produces a heavy shock load to the walls of the combustion chamber and the piston head. It is this shock to the combustion chamber that is heard as ·an audible knock in an automobile engine. If other sounds could be filtered out, the knock would be equally audible in an aircraft engine. Generally, it is necessary to depend upon instruments to detect detonation in an aircraft engine. Surface Ignition Ignition of the fuel/ air mixture by hot spots or surfaces in the combustion chamber is called surface ignition. If this occurs before the normal ignition event, the phenomenon is referred to as preignition. When it is prevalent, the result is power loss and engine roughness. Preignition is generally attributed to overheating of such parts as spark ph~g electrodes, exhaust valves, carbon deposits, etc. Where preignition is present, an engine may continue to operate even though the ignition has been turned off. Present information indicates that gasoline high in aromatic hydrocarbon content is much more likely to cause surface ignition than fuels with a low content. Octane and Performance Number Rating Octane and performance numbers designate the antiknock value of the fuel mixture in an engine cylinder. Aircraft engines of high power output have been made possible principally as a result of blending to produce fuels of high octane ratings. The use of such fuels has permitted increases in compression ratio and manifold pressure, resulting in improved engine power and efficiency. However, even the high-octane fuels will detonate under severe operating conditiobs and when certain engine controls are improperly operated. Antiknock qualities of aviation fuel are desig­ nated by grades. The higher the grade, the more 75 compression the fuel can stand without detonating. For fuels that have two numbers, the first number indicates the lean-mixture rating and the second the rich-mixture rating. Thus, grade 100/130 fuel has a lean-mixture rating of 100 and a rich­ mixture rating of 130. Two different scales are used to designate fuel grade. For fuels below grade 100, octane numbers are used to designate grade. The octane number system is based on a comparison of any fuel with mixtures of iso-octane and normal heptane. The octane number of a fuel is the percentage of iso-octane in the mixture that duplicates the knock characteristics of the particular fuel being rated. Thus, grade 91 fuel has the same knock -characteristics as a blend of 91 percent iso-octane and 9 percent normal hep­ tane. With the advent of fuels having antiknock characteristics superior to iso-octane, another scale was adopted to designate the grade of fuels above the 100-octane number. This scale repre­ sents the performance rating of the fuel-its knock-free power available as compared with that available with pure iso-octane. Jt is arbitrarily assumed that 100 percent power is obtained from iso-octane alone. An engine that has a knock­ limited horsepower of 1,000 with 100-octane fuel will have a knock-limited horsepower of 1.3 times as much (1,300 horsepower) with 130 performance number fuel. The grade of an aviation gasoline is no indi­ cation of its fire hazard. Grade 91/96 gasoline is as easy to ignite as grade 115/145 and explodes with as much force. The grade indicates only the gasoline's performance in the aircraft's engine. A convenien·t means of improving the antiknock characteristics of a fuel is to add a knock inhibitor. Such a fluid must have a minimum of corrosive or other undesirable qualities, and probably the best available inhibitor in general use at present is TEL (tetraethyl lead). The few difficulties en­ countered because of the corrosion tendencies of ethylized gasoline are insignificant when compared with the results obtained from the high antiknock value of the fuel. For most aviation fuels the ad­ dition of more than 6 ml. per gallon is not per­ mitted. Amounts in excess of this have little effect on the antiknock value, hut increase cor• rosion and spark plug trouble. There are two distinct types of corrosion caused by the use of ethyl gasoline. The first is caused by the rtaction of the lead bromide with hot metaUic surfaces, and occurs when the engine is ### Page 84 . ·.,. in operation; the second is caused by the con­ densed products of combustion, chiefly hydro­ hromic acid, when the engine is not running. Purity Aviation fuels must he free of impurities that would interfere with the operation of the engine or the units in the fuel and induction system. Even though all precautions are observed in storing and handling gasoline, it is not uncommon to find a small amount of water and sediment in an aircraft fuel system. A small amount of such contamination is usually retained in the strainers in the fuel system. Generally, this is not con­ sidered a source of great danger, provided the strainers are drained and cleaned at frequent intervals. However, the water can present a serious problem because it settles to the bottom of the fuel tank and can then be circulated through the fuel system. A small quantity of water will flow with the gasoline through the carburetor metering jets and will not be especially harmful. An ex­ cessive amount of water will displace the fuel passing through the jets and restrict the flow of fuel; it will cause loss of power and can result in engine stoppage. Under certain conditions of temperature and humidity, condensation of moisture (from ihe air) occurs on the inner surfaces of the fuel tanks. Since this condensation occurs on the portion of the tank above the fuel level, it is obvious that the practice of servicing an airplane immediately after flight will do much to minimize this hazard. Fuel ldentitlcation Gasolines containing TEL must be colored to conform with the Jaw. In addition, gasoline may be colored.--for purposes of identification. For ex­ ample, grade 100 low lead aviation gasoline is blue, grade 100 is green and grade 80 is red. See figure 4-2. 100/130 gasoline is manufactured (1975) in two grades-high-lead, up to 4.6 milliliters of lead per gallon and low-lead1 not over 2.0 milliliters per gallon. The purpose being to eliminate two grades of lower octane fuel ( 80 /87) and 91/96) . The high-lead will continue to be colored green whereas the low-lead will be blue. The low-lead will replace the 80/87 and 91/96 octane fuels as they are phased out. Engine manu­ facturers have prepared instructions to be followed in making adjustments necessary for changeover to the 100 octane fuel. A change in color of an aviation gasoline usually indicates contamination with another product or a loss of fuel quality. A color change can also be caused by a chemical reaction that has weakened the lighter dye component. This color change in itself may not affect the quality of the fuel. A color change can also be caused by the pre­ servative in a new hose. Grade 115/145 gasoline that has been trapped for a short period of time in new hose may appear green. Flushing a smaII amount of gasoline through the hose usually re­ moves all traces of color change. Military or Sp<.><,ia[ u~e Civilian Civilian FIGURE 4-2. Identification of avgas. ### Page 85 JET A ( Kerosene-40•F) JET A•I (Ker<»em:-S8'FI JET B ( Naptha•Kerosene- 76' FI Civilian Military FIGURE 4-3. Identification of jet fuels. t-uel Identification Markings The most positive method of identifying the type and grade of fuel includes the following: l. Marking of Hose. A color band not less than one foot wide painted adjacent to the fitting on each end of hose used to dispense fuel. The bands completely encircle the hose, and the name and grade of the product is stenciled longitudinally in one-inch letters of a contrasting color over the color band. 2. Marking of Fuel Carriers, Pits and Fill Stands. Tags identifying the name and grade of the product permanently affixed to each discharge meter and fill pipe. Porcelain tags (4"X6") carrying the same information permanently bolted to the outside of the rear compartment of fuel servicing equipment. The delivery pipes of truck fill stands are banded with colors corresponding to that used on the dispensing hose. TURBINE ENGINE FUELS The aircraft gas turbine is designed to operate on a distillate fuel, commonly called jet fuel. Jet fuels are also composed of hydrocarbons with a little more carbon and usually a higher sulphur content than gasoline. Inhibitors may be added to reduce corrosion and oxidation. Anti-icing additives are also being blended to prevent fuel icing. Two types of jet fuel in common use today are: (1) Kerosene grade turbine fuel, now named Jet A; and (2) a blend of gasoline and.kerosene fractions designated Jet B. There is a third type, called Jet A-I, which is made for operation at extremely low temperatures. See figure 4-3. 77 There is very little physical difference between Jet A (JP-5) fuel and commercial kerosene. Jet A was developed as a heavy kerosene having a higher flash point and lower freezing point than most kerosenes. It has a very low vapor pressure, so there is little loss of fuel from evaporation or boil­ off at higher altitudes. It contains more heat energy per gallon than does Jet B (JP-4). Jet Bis similar to Jet A. It is a blend of gasoline and kerosene fractions. Most commercial turbine engines will operate on either Jet A or Jet B fuel. However, the difference in the specific gravity of the fuels may require fuel control adjustments. Therefore, the fuels cannot always he considered interchangeable. Both Jet A and Jet B fuels are blends of heavy distillates and tend to absorb water. The specific gravity of jet fuels, especially kerosene, is closer to water than is aviation gasoline; thus, any water introduced into the fuel, either through refueling or condensation, wiJI take an appreciable time to settle out. At high altitudes, where low temperatures are encountered, water droplets com~ bine with the fuel to form a frozen substance referred to as Hgel." The mass of ttgel" or tticing" that may be generated from moisture held in suspension in jet fuel can be much greater than in gasoline. Volatility One of the most important characteristics of a jet fuel is its volatility. It must, of necessity, be a compromise between several opposing factors. A highly volatile fuel is desirable to aid in starting in cold weather and to make aerial restarts easier and surer. Low volatility is desirable to reduce ### Page 86 " s -§ > >-..c • ~ -0 = " u " " .. 10 0 L_ _ _J_ __ .i:::::.._ ___ __J OF 50F IOOF Temperature 150F 200F FIGURE 4--4. Vaporization of aviation fuels at atmospheric pressure. the possibility of vapor lock and to reduce fuel losses by evaporation. At normal temperatures, gasoline in a closed container or tank can give off so much vapor that the fuel/air mixture may be too rich to burn. Under the same conditions, the vapor given off by Jet B fuel can be in the flammable or explosive range. Jet A fuel has such a low volatility that at normal temperatures it gives off very little vapor and does not form flammable or explosive fuel/ air mixtures. Figure 4-4 shows the vaporization of aviation fuels at atmospheric pressure. Identification Because jet fuels are not dyed, there is no on­ sight identification for them. They range in color from a colorless liquid to a straw-colored (amber) liquid, depending on age or the crude petroleum source. Jet fuel numbers are type numbers and have no relation to the fuel's performance in the aircraft engine. FUEL SYSTEM CONTAMINATION There are several forms of contamination in aviation fuel. The higher the viscosity Of the fuel, the greater is its ability to hold contaminants in suspension. For this reason, jet fuels having a high viscosity are more susceptible to contami­ nation than aviation gasoline. The principal con­ taminants that reduce the quality of both gasoline 78 and turbine fuels are other petroleum products, water, rust or scale, and dirt. Water Water can be present in the fuel in two forms: (I) Dissolved in the fuel or (2) entrained or suspended in the fuel. Entrained water can be detected with the naked eye. The finely divided droplets reflect light and in high concentrations give the .fuel a dull, hazy, or cloudy appearance. Particles of entrained water may unite to form droplets of free water. Fuel can be cloudy for a number of reasons. If the fuel is cloudy and the cloud disappears at the bottom, air is present. If the cloud disappears at the top, water is present. A cloud usually indi­ cates a water-in-fuel suspension. Free water can cause icing of the aircraft fuel system, usually in the aircraft boost-pump screens and low-pressure filters. Fuel gage readings may become erratic because the water short-circuits the aircrafts elec­ trical fuel cell quantity probe. Large amounts of water can cause engine stoppage. If the free water is saline, it can cause corrosion of the fuel system components. Foreign Particles Most foreign particles are found as sediment in the fuel. They are composed of almost any material with which the fuel comes into contact. The most common types are rust, sand, aluminum and magnesium compounds, brass shavings, and rubber. Rust is found in two forms: (I) Red rust, which is nonmagnetic and (2) black rust, which is mag­ netic. They appear in the fuel as red or black powder (which may resemble a dye), rouge, or grains. San.d or dust appears in the fuel in a crystalline, granular, or glasslike form. Aluminum or magnesium compounds appear in the fuel as a form of white or gray rowder or paste. This powder or paste becomes very sticky or gelatinous when water is present. Brass is found in the fuel as bright gold-colored chips or dust. Rubber appears in the fuel as fairly large irregular bits. All of these forms of contamination can cau~e sticking or malfunctions of fuel metering devices, flow dividers, pumps, and nozzles. Contamination with Other Types or Grades of Fuel The unintentional mixing of petroleum products can result in fuels that give unacceptable per- ### Page 87 formance in the aircraft. An aircraft engine is designed to operate most efficiently on fuel of definite specifications. The use of fuels that differ from these specifications reduces operating effi­ ciency and can lead to complete engine failure. Operators of turbine-powered aircraft are some­ times forced by circumstances to mix fuels. Such mixing, however, has very definite disadvantages. When av{ation gasoline is mixed with jet fuel, the TEL in the gasoline forms deposits on the turbine blades and vanes. Continuous use of mixed fuels may cause a loss in engine efficiency. How­ ever, on a limited usage basis, they will have no detrimental effects on the engine. Aviation gasoline containing by volume more than 0.5 percent of jet fuel may be reduced below the allowable limits in knock rating. Gasoline contaminated with turbine fuel is unsafe for use in reciprocating engines. Microbial Growth Microbial growth is produced by various forms of micro-organisms that live and multiply in the water interfaces of jet fuels. These organisms may form a slime similar in appearance to the deposits found in stagnent water. The color of this slime growth may be red, brown, gray, or black. If not properly controlled by frequent removal of free water, the growth of these organisms can become extensive. The organisms feed on the hydrocarbons that are found in fuels, hut they need free water in order to multiply. Micro-organisms have a tendency to mat, gener­ ally appearing as a brown blanket which acts as a blotter to absorb more moisture. This mixture or mat accelerates the growth of micro-organisms. The buildup of micro-organisms not only can in­ terfere with fuel flow and quantity indication, but, more important, it can start electrolytic corrosive action. Sediment Sediment appears as dust, powder, fibrous ma· terial, grains, flakes, or stain. Specks or granules of sediment indicate particles in the visible size range, i.e., approximately 4,0 microns or larger in size. (See figure 4--5.) The presence of any appreciable number of such particles indicates either a malfunction of the filter/separators or a source of contamination downstream of the filter/ separator, or else an improperly cleaned sample container. Even with the most efficient filter/ separators and careful fuel handling, an occasional 79 AVGAS CLEAN FUEL 5-MlCRON PARTICLES TIME: I HOUR JP-4 5-MICRON PARTICLES JP·5 FIGURE 4-5. Comparison of particle's rate of settling in three types of fuel. visible particle will be encountered. These strays are usually due to particle migration through the filter media and may represent no particular prob­ lem to the engine or fuel control. The sediment ordinarily encountered is an extremely fine powder, rouge, or silt. The two principle components of this fine sediment are normally sand and rust. Sediment includes both organic and inorganic matter. The presence of appreciable quantities of fibrous materials ( close to naked eye visibility) is usually indicative of filter element breakdown, either because of a ruptured element or mechanical disintegration of a component in the system. Usually, high metal content of relatively large par­ ticles suggest a mechanical failure somewhere in the system which is necessarily not limited to a metallic filter failure. In a clean sample of fuel, sediment should not be visible except upon the most meticulous inspec­ tion. Persistent presence of sediment is suspect and requires that appropriate surveillance tests and corrective measures be applied to the fuel handling system. Sediment or solid contamination can be separated into two categories: (1) coarse sediment and (2) fine sediment. Course Sediment Sediment that can be seen and that easily settles out of fuel or can be removed by adequate filtera­ tion is coarse sediment. Ordinarily, particles 10 microns in size and larger are regarded as coarse sediment. (See figure 4--6.) ### Page 88 **0 40- MICRON** PARTICLE "HUMAN HAIR IS ABOUT 100 MICRONS IN **DIAMETER 0 10-MICRON** **PARTICLE** • 5-MICRON PARTICLE 25,400 MICRONS• I INCH FIGURE 4-6. Enlargement of small particles and comparison to human hair. Coarse particles clog orifices and wedge in slid­ ing valve clearances and shoulders, causing mal­ functions and excessive wear of fuel controls and metering equipment. They are also effective in clogging nozzle screens and other fine screens throughout the aircraft fuel system. Fine Sediment Particles smaller than 10 microns may be de­ fined as fine sediment. (See figure 4-6.) Ninety eight percent of the fine sediment in fuel can be removed by proper settling, filtration, and centri­ fuging. Particles in this range accumulate through­ out fuel controls, appearing as a dark shellac-like surface on sliding valves, and may also be centri­ fuged out in rotating chambers as sludge-like mat­ ter, causing sluggish operation of fuel metering equipment. Fine particles are not visible to the naked eye as distinct or separate particles; they will, however, scatter light and may appear as point flashes of light or a slight haze in fuel. Maximum possible settling time shoul-d be al­ lowed in fuel tanks after filling to allow reasonable settlement of water and sediment. 80 Contamination Detection Coarse contamination can be detected visually. The major criterion for contamination detection is that the fuel he clean, bright, and contain no perceptible free water. Clean means the absence of any readily visible sediment or entrained water. Bright refers to the shiny appearance of clean, dry fuels. Free water is indicated by a cloud, haze, or a water slug. A cloud may or may not be present when the fuel is saturated with water. Perfectly clear fuel can contain as much as three times the volume of water considered to tolerable. Several field methods for checking water content have been devised. One is the adding of a food color that is soluble in water, but not in fuel. Co]orless fuel samples acquire a definite tint if water is present. Another method uses a gray chemical powder that changes color to pink through purple, if 30 or more p. p.m. (parts per million) of water arc present in a fuel sample. In a third method a hypodermic needle is used to draw a fuel sample through a chemically treated filter. If the sample changes the color of the filter from yellow to blue, the fuel contains at least 30 p.p.m. of water. Since fuel drained from tank sumps may have been cold-soaked, it should be realized that no method of water detection can he accurate while the fuel entrained water is frozen into ice crystals. There is a good chance that water will not be drained or detected if the sumps are drained while the fuel is below 32° F. after being cooled in flight. The reason for this is that the sump drains may not be at the lowest point in the fuel tank while the airplane is in a flight attitude, and water may accumulate and freeze on other areas of the tank where it will remain undetected until it thaws. Draining will be more effective if it is done after the fuel has been undisturbed for a period of time during which the free water can precipitate and settle to the drain point. The benefits of a settling period will be lost, however, unless the accumulated water is removed from the drains before the fuel is disturbed by internal pumps. ### Page 89 Contamination Control The aircraft fuel system can be considered as being divided into three parts when discussing clean fuel. The manufacturer produces cle.an fuel. Contamination can occur at any time after the fuel is produced. The first part of the fuel system is the delivery and storage system between the re­ finery and the airport fuel service truck. Although this system is not physically a part of the aircraft, it is of equal importance in controlling contami­ nation. Anytime fuel is transferred it is susceptible to contamination. Therefore. all aviation maintenance personnel should be familiar with the following means of contamination control. Fundamental in the control of contamination of turbine fuels are the methods followed by the in· dustry in receiving and storing any bulk shipment of a petroleum product. These methods have long been established as sound, and they are too well known to need repetition here. The refueling fa. cilities used by operators of turbine powered air­ craft should incorporate the following features: I. Fuel being pumped into airport storage should pass through a filter-separator. The filter should meet the requirements of U.S. Government Specification MIL-F-8508A. 2. Turbine fuels should be allowed to settle for a period of one hour per foot of depth of the fuel before being withdrawn for use. This means that ordinarily more than one storage tank must be provided for each grade of product. 3. Storage tanks should be checked with litmus paper after each new load of fuel is received and the fuel has settled. The litmus paper should re­ main submerged for a minimum of 15 seconds. During periods of heavy rain underground tanks should be checked with litmus paper more fre­ quently. 4. Suction lines should be a minimum of 6 inches from the bottom of the tank. Kerosene storage tanks should be equipped with floating type suction lines. Floating suction does not remove the bottom product, which may not have settled suf­ ficiently. It also prevents reintroduction into the fuel of any contamination at the bottom of the 81 tank. Floating suction is the only logical way to take full advantage of gravity in removing water and particulate matter contamination. Its import­ ance must not be minimized. 5. Fuel being withdrawn from storage should be passed through a filter-separator meeting the speci­ fication MIL-F-8508A. 6. Great care should be exercised in loading mobile fuelers to exclude airborne dust and dirt, rain or other foreign material. 7. To lessen the likelihood of rust and scale the tanks of mobile fuelers should be constructed of either stainless steel, nonferrous material or steel coated with a reliable, inert material. 8. As turbine fuel is being dispensed into the aircraft from truck or hydrant it should be filtered to a degree of 5 microns for solid particles and contain no more than 0.0015 per cent of free and entrained water. Bypass valves around the filter should not be permitted. 9. All the quality control procedures usually followed in handling aviation gasoline should be employed. These include regular and frequent check of filter-separators; frequent quality check such as the "clear and bright" test; and continual emphasis on cleanliness. Examples: "Don't let the hose nozzle drag on the apron." "Keep the dust cap on the nozzle at all times when nozzle is not in use." FUEL SYSTEM The aircraft fuel system stores fuel and delivers the proper amount of clean fuel at the right pres· sure to meet the demands of the engine. A well­ designed fuel system ensures positive and reliable fuel flow throughout all phases of flight, which include changes in altitude, violent maneuvers and sudden acceleration and deceleration. Further­ more, the system must be reasonably free from tendency to vapor lock, which can result from changes in ground and in-flight climatic conditions. Such indicators as fuel pressure gages, warning signals, and tank quantity gages are provided to give continuous indications of how the system is functioning. ### Page 90 To priming c:onnection Hight tauk FIGURE 4-7. Gravity feed fuel system. The simplest type of fuel system is the gravity feed, which is still in use on many low-powered airplanes. A gravity feed system is shown in figure 4-7. The fuel tanks arc mounted above the carburetor, with gravity causing the fuel to flow from the tanks to the carburetor. A selector valve is provided to stop the fuel flow or to select a par­ ticular tank in the system from which to ·draw fuel. A strainer filters the fuel before it reaches the carburetor. A drnin is provided for removing water and sediment trapped at the strainer. A primer furnishes the additional fuel required for pngine starting. Airplanes equipped with a high-output engine require a fuel system that supplies fuel to the carburetor at a positive pressure. The basic source for this pressure is an engi~e-driven fuel pump, but auxiliary fuel pumps or booster pumps are required in every prPssure frrd system to: (I) supply fuel prt'ssurc for starting the engine; ( 2) supply fuel to the primn system; and (3) to serve as an emergency pump in case thf' engine-driven pump fails. FUEL SYSTEM COMPONENTS The basic components of a fuel system include tanks, lines, valves, pumps, filtering units, gages, warning signal, and primer. Some systems will include central refueling provisions, fuel dump valves, and a means for transferring fuel. In order to clarify the operating principles of complex air­ craft fuel systems, the various units are discussed in the following paragraphs. 82 Fuel Tanks The location, size, shape, and construction of fuel tanks vary with the type and intended use of the aircraft. In some aircraft, the fuel tanks are integral \y·ith the wing or other structural portions of the aircraft. Fuel tanks are made of materials that will not react chemically with any aviation fuel. Aluminum alJoy is widely used, and synthetic rubber bladder. type .fuel cells are used in some installations. Usually a sump and a drain are provided at the lowE'st point in the tank as shown in figure 4-8. When a sump or low point is provided in the tank, the main fuel supply is not drawn from the bottom of the sump, but from a higher point in the tank. The top of each tank is vented to the outside air in order to maintain atmospheric pressure within the tank. Air vents are designed to min. imize the possibility of their stoppage by dirt and ice formation. In order to permit rapid changes in internal air pressure, the size of the vent is proportional to the size of the tank, thus preventing the collapse of the tank in a steep dive or glide. All except the very smallest of tanks are fitted with internal baffles to resist fuel surging caused by changes in the attitude of the aircraft. Usually an expansion space is provided in fuel tanks to aHow for an increase in fuel volume due to expansion. The filler neck and cap are usually located in a recessed welJ, equipped with a scupper and ### Page 91 .----- Vents '-.... Scupper Overboard drain line '---- Baffle platt>s / Standpipe FIG\JRE 4---8. A typical metal fuel tank. drain. The scupper is designed to prevent over­ flowing fuel from entering the win·~ or fuselage structure. Fuel caps have provisipn,~ for locking devices to prevent acciden~al loss during flight. Filler openings are clearly inarked with the word HFUEL", the tank capacity, and the type of fuel to be used. Information concerning the capacity of each tank is usually posted near th.e fuel se­ lector valves, as well as on the tank filler caps. Some fuel tanks are equipped with dµmp valves that make it possible to jettiso:r:i fuel (luring flight in order tO reduce the weight of the ~irpraft to its specified maximum landing weighL l:p aircraft equipped with dump valves, th~ operating control is located within reach of th~ pilot, copilot, or · flight engineer. Dump valves are designed and installed to afford safe, rapid discharge of fuel. Fuel Cells Present day aircraft may be equipped with one or more of the following types of fuel cells: the bladder-type fuel cell and the integral fuel cell. Bladder-Type Fuel Cells The bladder-type fuel cell is a nonself-sealing cell that is used to reduce weight. It depends en­ tirely upon the structure of the cavity in which it sits to support the weight of the fuel within it. For this reason, the cell is made slightly larger 83 than the cavity. The bladder cells in use are made either of rubber or of nylon. Integral Fuel Cells Since integral fuel cells are usually built into the wings of the aircraft structure, they are not removable. An integral cell is a part of the aircraft structure, which has been so built that after the seams, structural fasteners, and access doors have been properly sealed, the cell will hold fuel without leaking. This type of construction is usually re­ ferred to as a Hwet wing." Fuel Lines and Fittings In an aircraft fuel system, the various tanks and other components are usually joined together by fuel lines made of metal tubing connected, where flexibility is necessary, by lengths of flexible hose. The metal tubing usual1y is made of aluminum alloy, and the flexible hose is made of synthetic rubber or Teflon. The diameter of the tubing is governed by the fuel flow require­ ments of the engine. Each fuel line is identified by a color-coded band near each end. Except for short lines be­ tween flexible connections, tubing should be prop­ erly supported by clamping to structural members of the aircraft. A special heat-resistant hose is used where the ### Page 92 . '.,· ~ cover Clamp Thumb nut FIGl;RE 4-9. Main fuels.trainer for light aircraft. flexible lines will be subjected to intense heat. For all flexible fuel lines located forward of the firewall, fire-resistant hose is used. In many installations, the fuel lines are designed to be located within the tanks. Therefore, minor leaks occurring within the tank are cJassified as internal leaks and v,·ill not cause fire hazards. Fuel Strainers Strainers are installed in the tank outlets and frequently in the tank filler necks. These are of fairly coarse mesh and prevent only the larger particles from entering the fuel system. Other, fine-mesh, strainers are provided in the carburetor fuel inlets and in the fuel lines. The function of the main strainer is important: it not only prevents foreign matter from entering the carburetor, but also, because of its location at the low point of the fuel system, traps any small amount of water that may be present in the system. In multiengine aircraft, one main strainer is usually installed in each engine nacelle. A main fuel strainer for a light airplane is shown in figure 4----9. It consists of a cast metal top, a screen, and a glass bowl. The bowl is attached to the cover by a clamp and thumb nut. Fuel enters the unit through the inlet port, filters through the screen, and exits through the outlet port. At regular intervals the glass bowl is drained. and the screen is removed for inspection and cleaning. The main fuel strainer shown in figure 4-10 is so 84 Fuel outlet Fuel inlet In - Drain cock Fuel flow through strainer element FIGURE 4-10. Main fuel strainer. installed that the fuel flows through it before reaching the engine-driven pump. It is located at the lowest point in the fuel system. The shape and construction of the fine-mesh screen provides ### Page 93 OFF FIGURE 4--11. Centrifugal fuel booster pump. a large screening surface encased in a compact housing. Reinforcing the screen is a coarse, heavy­ wire mesh. Auxiliary Fuel Pumps The electrically driven centrifugal booster pump, shown in figure 4----11, supplies fuel under pressure to the inlet of the engine-driven fuel pump. This type of pump is an essential part of the fuel system, particularly at high altitudes, to keep the pressure on the suction side of the engine-driven pump from becoming low enough to permit the fuel to boil. This booster pump is also used to transfer fuel from one tank to another, to supply fuel under pressure for priming when starting the engine, and, as an emergency unit, to supply fuel to the carburetor in case the engine­ driven pump fails. To increase the capacity of the pump under emergency conditions, many pumps are equipped with a two-speed or variable-speed control so that the recommended fuel inlet pres­ sure to the carburetor can be maintained. As a precautionary measure, the booster pump is al­ ways turned on during takeoffs and landings to ensure a positive supply of fuel. The booster pump is mounted at the tank outlet 85 within a detachable sump or is submerged in fuel at the bottom of the fuel tank. The seals between the impeller and the power section of the pump prevent leakage of fuel or fumes into the motor. If any liquid or vapor should leak past the seal, it is vented overboard through a drain. As an added precaution in nonsubmerged-type pumps, air is allowed to circulate around the motor to remove dangerous fuel vapor. As fuel enters the pump from the tank, a high­ speed impeller throws the fuel outward in all directions at high velocity. The high rotational speed swirls the fuel and produces a centrifuge action that separates air and vapor from the fuel before it enters th-e fuel line to the carburetor. This results in practically vapor-free fuel delivery to the carburetor and permits the separated vapors to rise through the fuel tank and escape through the tank vents. Since a centrifugal-type pump is not a positive-displacement pump, no relief valve is necessary. Although the centrifugal type is the most common type of booster pump, there are still a few sliding-vane-type booster pumps in service. This type, too, is driven by an electric motor. Unlike the centrifugal type, it does not have the advantage of the centrifuge action to separate the vapor from the fuel. Since it is a positive­ displacement-type pump, it must have a relief valve to prevent excessive pressure. I ts construc­ tion and operation are identical to the engine­ driven pump. Hand Pump The hand, or wobble, pump is frequently used on light aircraft. It is generally located near other fuel system components and operated from the cockpit by suitable controls. A diagram of a wobble pump is shown in figure 4--12. When the handle attached to the central blade is operated, the low pressure created on the chamber below the upward moving blade, permits the incoming fuel pressure to lift the lower flapper and allows fuel to flow into this chamber. At the same time fuel flows through a drilled passageway to fill the chamber above the downward moving blade. As the blade moves downward, the lower flapper closes, preventing fuel from escaping back into the inlet line. The fuel below the downward mov­ ing blade flows through a passageway into another chamber and is discharged through an outlet flapper valve to the carburetor. The cycle is re- ### Page 94 Fuel outlet Blade Fuel inlet r I ' ' ~ Inlet fuel ~:,\;::.-.j Discharge fuel FIGURE 4-12. Schematic diagram of a wobble pump. peated each time the handle is moved m either direction. Engine-Driven Fuel Pump The purpose Of the engine-driven fuel pump is to deliver a continuous supply of foe) at the proper pressure at all times during engine oper­ ation. The pump widely used at the present ti'me is the positive-displacement, rotary-vane-type pump. A schematic diagram of a typical engine-driven pump (vane-type) is shown in figure 4-13. Regard­ less of variations in design, the operating principle of all vane-type fuel pumps is the same. A. [KJ Booster pump }Jressure m Engine-driven pump pressure Balance line C. B. Pump inlet Pump outlet FIGURE 4-13. Engine-driven fu('I pump (pressure delivery). 86 B D r:J] Booster pump pressure A. Balance line C. Pump inlet B. Pump outlet D. Bypass valve FIGL'RE 4-14. Engine-driven fuel pump (bypass flow). C The engine-driven pump· is usualJy mounted on the accessory section of the engine. The rotor, with its sliding vanes, is driven by the crankshaft through the accessory gearing. Note how the vanes carry fuel from the inlet to the outlet as the rotor turns in the direction indicated. A seal prevents leakage at the point where the drive shaft enters the pump hody, an-H D L-=-f+-tt~~+I E 1------' Power supply FIGURE 4--20. Schematic of a turbine engine fuel flow indicating system. 91 28VDC .; ' ### Page 100 \\ 1111/1,, ' 'I o , ' 50 100 // ,'\ F 150 ,k ' 0 01Lc:,JfJ11 / 200 I I I "'' 200 ' ' ..,, OIL FUEL -::-100 -O•---..; ... 10....::_ ; ; /, I I I PSI , ,' 0 0 ,,,' I I I I\ FIGUR'E 4-21. Engine gage unit. thorough! y in the Powerplant Handbook, and is mentioned at this time only because the fuel pressure indicator provides a means for a check on the operation of other fuel system units. In small aircraft the fuel pressure gage may be actuated by a Bourdon tube (an instrument that converts changes in pressure to mechanical mo­ tion), or an aneroid and bellows type, installed with a pressure line leading directly from the carburetor to the indicator. On larger aircraft, where the fuel pressure gage is located some dis­ tance from the carburetor, a transmitter is usually installed. The pressure transmitter may be a simple cast metal ceJI that is divided into two chambers by a flexible diaphragm. Pressure ap­ plied by the fuel source to the transmitter inlet pushes against the diaphragm and builds up an equal pressure to a thin fluid (highly refined kerosene), which transfers the pressure to the indicator mechanism. Some installations, however, use electrical transmitters to register fuel pressure on the gage. In this electrical arrangement, the pressure-indicating unit is contained in the trans­ niitter. Fuel pressure, acting upon the aneroid and bellows portion of the unit, causes motion of one part of an electrical unit (the synchro transmitter). As the unit turns, it causes a similar movement of a corresponding unit (the synchro motor). This receiving unit actuates the indicator on the instrument panel. These pressure and electrical arrangements make it unnecessary for combustible fuel to enter the cockpit or flight deck, thereby reducing fire risk. 92 A fuel pressure gage often used with fuel in­ jection systems on light aircraft engines is illus­ trated in figure 4-23. A gage of this type registers metered fuel pressure at the fuel injection unit distributor valve and is a direct indication of engine power output when installed in a fuel injection system for light aircraft engines. The dial of the gage is marked to indicate percent of power. The gage does not indicate either the engine-driven pump or the boost pump pressure. Pressure Warning Signal In an aircraft with several tanks, there is always the possible danger of allowing the fuel supply in one tank to become exhausted before the selector valve is switched to another. To prevent this, pressure-warning signals are installed in some aircraft. The complete installation, shown in figure 4-22, consists of a pressure-sensitive mechanism and a warning light. The warning mechanism has both a fuel and an air connection. The connection marked ''fuel" is connected to the fuel pressure line of the carburetor. The air connection is vented to either atmospheric or carburetor air inlet pressure. This arrangement prevents the warning mechanism from acting in response to changes in the absolute pressure of the fuel. If, for example, the absolute pressure of the fuel decreases because of a change in atmospheric or carburetor air inlet pressure, the change is also reflected at the warning mechanism, which then cancels the effects of the change. Normal fuel pressure against the power surface of the dia­ phragm holds the electrical contacts apart. When the fuel pressure drops below specified limits, the contacts close and the warning light is turned on. This alerts the operator to take whatever action is necessary to boost the fuel pressure. Valve-In-Transit Indicator Lights On large multiengine aircraft, each of the fuel crossfeed and line valves may be provided with a valve~in-transit indicator light. This light is on only during the time the valve is in motion and is off when movement is complete. Fuel Temperature Indicator A means for checking the temperature of the fuel in the tanks and at the engine is provided on some turbine-powered aircraft. During ex­ treme cold, especially at altitude, the gage can ### Page 101 r--~ Warning light Electrical connec:tions to warning light Pressure gage Inlet from fuel pump Warning Location of units in the system dilution valve A B~ Y t:onnection Contacts Adjustment screw Pressure warning mechanism FIGURE 4-22. Fuel pressure-indicating system. be checked to determine when fuel temperatures are approaching those at which there may be danger of ice crystals forming in the fuel. MUL TIENGINE FUEL SYSTEMS The design of the fuel system for an .. n:raft having two or more engines presents p1obiems not normally encountered in single-engine fuel systems. A large number of tanks are often re­ quired to carry the necessary fuel. These tanks may be located in widely separated parts of the aircraft, such as the fuselage and the inboard and outboard sections of the wings. The individual engine fuel systems must he interconnected so FIGURE 4-23. Fuel pressure gage for fuel-injection system. 93 that fuel can be fed from the various tanks to any engine. In case of engine failure, the fuel normally supplied to the inoperative engine must be made available to the others. Crossfeed System The twin-engine fuel system ilJustrated in figure 4-24 is the simple crossfeed type. As shown, the tank selector valves are set to supply fuel from the main tanks to the engines. These valves can also be positioned to sripply fuel from the auxiliary tanks. The crossfeed valve is shown in the off position. It can also he set to supply fuel from the fuselage tank to either or both engines and to crossfeed. A few of the numerous combinations in which the three valves can be set are also illustrated. Manifold System The main feature of the four-engine system shown in figure 4-25 is the fuel manifold. This fuel manifold system is actuaBy a variation of the crossfeed. As shown~ fuel is being supplied from the main tanks directly to the engines. The mani­ fold valves can also be set so that all tanks feed into the manifold and each engine receives its fuel supply from this line. The auxiliary fuel supply can be delivered to the engines only through the manifold. The main advantage of this system is its flexibility. Should an engine fail, its fuel is immediately available to the other engines. If a tank is damaged, the corresponding engine can be supplied with fuel from the manifold. Another advantage of this system is that all fuel tanks can be serviced at the same time through a single Jine manifold connection. This ### Page 102 ' Left engine Filter~ Main tank valve Auxiliary tank Auxiliary tank Right engine Crossfeed valve Main tank Boost pump Aux. Main/ ! Aux. Main/ Auxiliary tanks to engines Right main tank to both engines Fuselage tank to left engine Aux. Fuselage tank to both engines FIGURF. 4-24. Twin-engine crossfeed system schematic. method of fuel serv1cmg has greatly reduced servicing time on large aircraft because fuel can be introduced into the fueling manifold under high pressure. FUEL JETTISON SYSTEMS A fuel jettison system is required for transport category and general aviation ·aircraft if the maxi­ mum take-off weight exceeds the maximum landing weight. The maximum take-off and landing weights are design specifications and may be found in the Aircraft Type Certificate data sheets. A fuel jettison system must be able to jettison enough fuel within 10 minutes for general aviation, or 15 minutes for transport category aircraft, to meet the requirements of the specifications and Federal Air Regulations. It must be operable- un­ der the conditions encountered during all opera­ tions of the aircraft. Design requirements are that fuel jettisoning must be stopped with a minimum o.f fuel for 45 minutes of cruise at maximum continuous power for reciprocating engines. Turbine powered air­ craft require enough fuel for take-off and landing and 45 minutes cruising time. 94 The fuel jettisoning system is usually divided into two separate, independent systems, one for each wing, so that lateral stability can be main­ tained by jettisoning fuel from the "heavy" wing if it is necessary to do so. Normally, if an unbal­ anced fuel load exists, fuel will be used from the "heavy" wing by supplying fuel to engines on the opposite wing. The system consists of lines, valves, dump chutes and chute-operating mechanisms. Each wing con­ tains either a fixed or an extendable dump chute depending upon system design. In either case the fuel must discharge clear of the airplane. TROUBLESHOOTING THE FUEL SYSTEM In order to become proficient at the art of troubleshooting, one must be familiar with the complete system. To do this, one can become familiar with the schematics of various portions of the system, the nomenclature of the units, and their particular function within the system by studying aircraft and engine maintenance manuals. ### Page 103 Engine No. l Engine No. 2 Engine No. 3 Refueling receptacle ~ Engine No. 4 Engine-driven pump No. 1 tank No. 2 tank Auxiliary tank No. 3 tank No. 4 tank j;·:·.;.:;.:".£:.-1 Flow to engine ~ F1ow blocked FIGURE 4--25. A typical manifold crossfeed system. Location of Leaks and Defects The location of leaks and defects within the internal portions of the fuel system is usually a matter of observation of the pressure gage and operation of the selector valves to deteri:nine where the trouble lies. Troubleshooting of the internal fuel system can he aided by visualizing the pa th of flow of the fuel from the fuel tank to the fuel-metering device, noting the location of the pump(s), selector valves, emergency shutoff valves, etc. The location of leaks or defects in the external portions of the fuel system involves very little time in comparison to locating leaks within the internal system. Usually, fuel leaks are evidenced by stains or wet spots, if they are newly developed, and by the presence of fuel odor. The plumbing, clamps, gaskets, supports, etc., are to be examined carefully at each inspection period. Any defect or leak in the internal or external fuel system is a potential hazard. Replacement of Gaskets, Seals, and Packings In order to prevent leakage of fuel, it is of utmost importance that aH gaskets, seals, and packings be properly installed. Listed below are some of the general precautions that should always be observed. 95 When replacing units of the fuel system, it is necessary to check each part for cleanliness, ensure that all of the old gasket material is removed, and ensure that none of the old seal remains in the groove seat. Always replace old gaskets and seals with new ones, check the new gaskets and seals for cleanliness and integrity, and ensure that it is the right part for the job. Mating surfaces should be perfectly flat so that the gasket can do the job for which it is designed. Screws, nuts, and bolts that hold units together should be evenly tightened or torqued to prevent leakage past the gasket or seal. FUEL TANK REPAIRS There are three basic type fuel cells used in air; craft. ~Telded sheet metal integral and fuel celL No fuel system is airworthy if it will not contain fuel. Inspection of the fuel tank bays or aircraft structure for evidence of fuel leaks is a very im­ portant part of the preflight inspection. Welded Steel Tanks Welded tanks are most common in the smaller single and twin engine aircraft. If the access plates to the fuel tank compartment are discolored the tank should be inspected for leaks. When leaks are found, the tank must be drained and inerted. Fuel will be drained in accordance with .. ,~. ### Page 104 local instructions and the manufacturer's recom­ mendations. Inerting the tank may be accom­ plished by slowly discharging a CO, fire extinguisher ( 5 lb. minimum size) into the tank. Dry nitrogen inay be used if it is available. If the tank is to be welded, removal is necessary. Before welding, the tank must be steamed for a minimum of 8 hours. This is to remove all traces of fueL Air pressure not over 'l'.2 psi may he used to detect the leaking area. Liquid soap or bubble solution brushed in the suspected area may identify the leak. Aluminum tanks are fabricated from weldable alloys. After riveting patches in place, the rivets may he welded to insure no leaks from that area. Pressure checks should be per­ formed after repairs are completed to assure that all leaks were corrected. Fuel Cells Fuel cell leaks will usually appear on the lower skin of the aircraft. A fuel stain in any area should be investigated immediately. Fuel cells suspected of leaking should be drained, removed from the aircraft and pressure checked. When performing a pressure check, lf1 to 'l'.2 psi air pres­ ure is adequate. All fuel cell maintenance must be accomplished in accordance with the manufac­ turer's specifications. 3/4[~ A-SLOW SEEP 3D!A C- HEAVY SEEP Integral Fuel Tanks The integral tank is a nonremovable part of the aircraft. Because of the nature of an integral tank, some leaks allow fuel to escape directly to the atmosphere. This makes it completely feasible to disregard certain minute leaks that do not repre­ sent a fire hazard or too great a loss of fuel. In order to standardize ·the procedures for integral tank fuel storage maintenance, the various rates of fuel leakage are classified. Fuel Leak Classification The size of the surface area that a fuel leak moistens in a 30-rninute period is used as the classification standard. Wipe the leak area com­ pletely dry with clean cotton cloths. Compressed air may also be used to dry the leak areas that are difficult to wipe. Wear goggles when using com­ pressed air to dry the leak area. Dust the leak area with dyed red talcum powder. The talcum powder turns red as the fuel wets it, making the wet area easier to see. At the end of 30 minutes, each leak is classified into one of four classes of leaks: slow seep, seep, heavy seep, or running leak. The four classes of leaks are shown in figure 1-26. A slow seep is a leak in which the fuel wets an area around the **D- RUNNING LEAK** **AREA WHERE FUEL** **APPEARS TO FLOW** **OR RUN, FOLLOWING** **CONTOUR OF SKIN** **WHEN THIS AREA IS WIPED DRY.** FIGURE 4-26. Fuel leak classification. ### Page 105 leak source not over % of an inch in diameter. A seep is a leak that wets an area from % inches to l)".2 inches in ·diameter. A heavy seep is a fuel leak that wets an area around the leak source from 1¥2 inches to 3 inches in diameter. In none of these three leak classifications does the fuel run, flow, drip, or resemble any of these conditions at the end of the 30-minute time period. The last classification, a running leak, is the most severe and the most dangerous. It may drip from the aircraft surface, it may run down vertical surfaces, or it may even run down your finger when you touch the wet area. The aircraft is un­ safe for flight and must be grounded for repair. When possible, the fuel from the leaking tank should be removed after you mark the leak location. If it is impossible to defuel the tank immediately, the aircraft should be isolated in an approved area. Place appropriate warning signs around the air­ craft until qualified personnel can defuel the leak­ ing tank. Grounding of the aircraft for slow seeps, seeps, and heavy seeps, is determined by the applicable aircraft handbook. This determination may de­ pend on the location of the fuel leak. For example, can the leakage progress to a potential fire source? The number of fuel leaks in a given area is also a contributing factor. There is no rule of thumb for determining if the aircraft is to be grounded. Running leaks ground the aircraft regardless of location. You may only have to make appropriate entries on the aircraft forms and periodically observe the progress of the fuel leak if it is determined that the aircraft is airworthy and no repair is required. When repair is required, you must find the cause of the fuel leak and make an effective repair. Leak Repairs Repair of leaks m integral fuel tanks must be accomplished in accordance with the aircraft manufacturer's specifications. No attempt will be made in this handbook to discuss integral tank repairs further. 97 Fire Safety The first and most difficult step in the achieve­ ment of fire safety is to correct the misconceptions about the "safety" of turbine fuels. At the time these fuels were first introduced many people said, "fire problems in aircraft are over, turbine fuel is completely safe." This is obviously nonsense but it has been persistent nonsense. FJight line personnel have agreed that aviation gasoline will burn, and therefore they have exer­ cised reasonable care and caution in handling it. However, it has been difficult to convince them that under some circumstances turbine fuels are just as dangerous from the fire standpoint. The characteristics of turbine fuel do vary from those of gasoline. Kerosene, for example, has a slow flame propagation and burning rate, which makes it less hazardous in the event of spill or a ground accident. However, it does ignite readily when vaporized or when misted, as when sprayed through a small leak in a service hose. One disadvantage of the low volatility fuels is that they will not evaporate readily and completely if spilled on the ramp, so special treatment of the spill area is required. Small spills of kerosene should be removed with a commercial absorb­ ent cleaning agent. On large spills it is better to apply an approved emulsifier and then flush away the resulting mixture with large volumes of water. This will prevent or appreciably lessen any oily residue. Just as with gasoline, an electrostatic charge may be built up in pumping turbine fuel through a service hose. In fact, the amount of the charge is higher in kerosene because of the higher specific gravity and wider boiling range. Also, the amount of the charge increases with high linear rate of fuel flow, such as is required for servicing turbine powered aircraft. In consequence, all of the fire safety precautions observed in the handling of gasoline must be fol­ lowed with equal care in the handling of turbine fuels. These precautions are well known and have been detailed by the National Fire Protection Association in its bulletin No. 407. It is recom­ mended that this bulletin be made required read­ ing for all personnel handling turbine fuel. ### Page 106 GENERAL The term H airer.aft plumbing" refers not only to the hose, tubing, fittings, and connectors used in the aircraft, hut also to the processes of forming and installing them. Occasionally it may be necessary to repair or replace damaged aircraft plumbing lines. Very often the repair can be made simply by replacing the tubing. However, if replacements are not available, the needed parts may have to he fabri­ cated. Replacement tubing should be of the same size and material as the original line. All tubing is pressure tested prior to initial instal1ation, and is designed to withstand several times the normal operating pressure to which it will be subjected. If a tube bursts or cracks, it is generally the result of excessive vibration, improper installation, or damage caused by collision with an object. All tubing failures should be carefully studied and the cause of the failure determined. PLUMBING LINES Aircraft plumbing lines usually are made of metal tubing and fittings or of flexible hose. Metal tubing is widely used in aircraft for fuel, oil, cool­ ant, oxygen, instrument, and hydraulic lines. Flexible hose is generally used with moving parts or where the hose is subject to considerable vibra­ tion. Generally, aluminum ailoy or corrosion-resistant steel tubing have replaced copper tubing. The high fatigue factor of copper tubing is the chief reason for its replacement. It becomes hard and brittle from vibration and finally breaks, however it may be restored to its soft annealed state by heating it red hot and quenching it in cold water. Cooling in air will result in a degree of softness but not equal to that obtained with the cold water quench. This annealing process must be accom­ plished if copper tubing is removed for any reason. Inspection of copper tubing for cracks, hardness, brittleness and general condition should be accom­ plished at regular intervals to preclude failure. The workability, resistance to corrosion, and lightweight of aluminum alloy are major factors in its adop­ tion for aircraft plumbing. **99 CHAPTER 5** FLUID LINES AND FITTINGS In some special high-pressure (3,000 p.s.i.) hydraulic installations, corrosion-resistant steel tub­ ing, either annealed or 1/4.-hard, is used. Corrosion­ resistant steel tubing does not have to be annealed for flaring or form_ing; in fact, the flared section is somewhat strengthened by the cold working and strain hardening during the flaring process. Its higher tensile strength permits the use of tubing with thinner walls; consequently the final installa­ tion weight is not much greater than that of the thicker-wall aluminum alloy tubing. IDENTIFICATION OF MATERIALS Before making repairs to any aircraft plumbing, it is important to make accurate identification of plumbing materials. Aluminum alloy or steel tub­ ing can be identified readily by sight where it is used as the basic plumbing material. However, it is difficult to determine whether a material is carbon steel or stainless steel, or whether it is 1100, 3003. 5052-0, or 2024-T aluminum alloy. It may be necessary to test samples of the ma­ terial for hardness by filing or scratching with a scriber. The magnet test is the simplest method for distinguishing between the annealed austenitic and the ferritic stainless steels. The austenitic types are nonmagnetic unless heavily cold worked, whereas the straight chromium carbon and low alloy steels are strongly magnetic. Figure 5-1 gives the methods for identifying five common Material Carbon steel __ 18-8 ________ _ Pure nickel_ __ _ MoneL __ . ___ _ Nickel steel_ __ Magnet test Nitric acid test Strongly Slow chemical magnetic. action, brown. Nonmagnetic. No action. Strongly Slow action, magnetic. pale green. Slightly Rapid action, magnetic. greenish blue. Nonmagnetic. Rapid action, greenish blu~. FIGURE 5-1. Identification of metallic materials. ### Page 107 metallic materials by using the magnet and concen­ trated nitric acid tests. By comparing code markings of the replacement tubing with the original markings on the tubing being replaced, it is possible to identify definitely the material used in the original installation. The alloy designation is stamped on the surface of large aluminum alloy tubin-g. On small alumi­ num alloy tubing, the designation may be stamped on the surface, but more often it is shown by a color code. Bands of the color co·de, not more than 4 inches in ,width, are painted at the two ends and approximately midway between the ends of some tubing. When the band consists of two colors, one-half the width is used for each color. Painted color codes used to identify aluminum alloy tubing are: Aluminum alloy number llOO 3003 2014 2024 5052 6053 6061 7075 Color of band White Green Gray Red Purple Black Blue and Yellow Brown and Yellow Aluminum alloy tubing, llOO (Y,,-hard) or 3003 (Y,,-hard), is used for general purpose lines of low or negligible fluid pressures, such as instrument lines and ventilating conduits. The 2024--T and 5052-0 aluminum alloy materials are used in gen­ eral purpose systems of low and medium pressures, such as hydraulic and pneumatic 1,000 to 1,500 p.s.i. systems and fuel and oil lines. Occasionally, these materials are used in high-pressure (3,000 p.s.i.) systems. Tubing made from 2024-T and 5052-0 materials will withstand a fairly high pressure before burst­ ing. These materials are easily flared and are soft enough _ to be formed with handtools. They must be handled with care to prevent scratches, dents, and nicks. Corrosion-resistant steel tubing, either annealed or 11,i-hard, is used extensively in high-pressure hydraulic systems for the operation of landing gear, flaps, brakes, and the like. External brake lines should always be made of corrosion-resistant steel to minimize damage from rocks thrown by the tires during takeoff and landing, and from careless ground handling. Although identification markings for steel tubing differ, each usually includes the manufacturer's name or trademark, the SAE num­ ber, and the physical condition of the metal. Metal tubing is sized by outside diameter, which is measured fractionally in sixteenths of an inch. Thus Number 6 tubing is o/,_6 (or % inch) and Number 8 tubing is o/,_6 ( or Y,, inch), etc. In addition to other classification or means of identification, tubing is manufactured in various wall thicknesses. Thus, it is important when in­ stalling tubing to know not only the material and outside diameter, but also the thickness of the wall. FLEXIBLE HOSE Flexible hose is used in aircraft plumbing to connect moving parts with stationary parts in locations subject to vibration or where a great amount of flexibility is needed. It can also serve as a connector in metal tubing systems. Synthetics Synthetic materials most commonly used in the manufacture of flexible hose are: Buna-N, Neo­ prene, Butyl and Teflon ( trademark of DuPont Corp.). Buna-N is a synthetic rubber compound which has excellent resistance to petroleum pro­ ducts. Do not confuse with Buna-S. Dp not use for phosphate ester base hydraulic fluid (Skyrol ®). Neoprene is a synthetic rubber compound which has an acetylene base. Its resistance to petroleum products is not aS good as ,Buna-N but has better abrasive resistance. Do not use for phosphate ester base hydraulic fluid (Skydrol ® ) . Butyl is a syn­ thetic rubber compound made from petroleum raw materials. It is an excellent material to use with phosphate ester based hydraulic fluid ( Skydrol ® ) . Do not use with petroleum products. Teflon is the DuPont trade name for tetrafluoroethylene resin. It has a broad operating temperature range ( -65° F. to +450° F.). It is compatible with nearly every substance or agent used. It offers little re­ sistance to flow; sticky viscous materials will not adhere to it. It has less volumetric expansion than rubber and the shelf and service life is practically limitless. Rubber Hose Flexible rubber hose consists of a seamless syn - thetic rubber inner tube covered with layers of cotton braid and wire braid, and an outer layer of rubber-impregnated cotton braid. This type of hose is suitable for use in fu.el, oil, coolant, and hydraulic systems. The types of hose are normally classified by the amount of pressure they are de­ signed to withstand under normal operating con­ ditions. 1. Low pressure, any pressure below 250 p.s.i. Fabric braid reinforcement. ### Page 108 Two cotton braids - impregnated --­ with synthetic compound Single wire braid ----.../ Synthetic inner tube -------' A. Flame- and aromatic-resistant hose White numerals, letters and stripe 7 (Views showing opposite sides of hose) B. Nonself-sealing, Aromatic and Heat-resistant hose \__ Red numerals and letters C. Flame-, Aromatic-, and Oil-resistant hose Yellow numerals, letters and stripe Red numerals, letters and stripe D. Nonself-sealing, Aromatic-resistant hose. E. Self-sealing, Aromatic-resistant hose FtcURE 5-2. Hose identification markings. ### Page 109 2. Medium pressure, pressures up to 3,000 p.s.1. One wire braid reinforcement. Sm~ller sizes carry pressure up to 3,000 p.s.1. Larger sizes carry pressure up to 1,500 p.s.i. 3. High pressure ( all sizes up to 3,000 p.s.i. operating pressures) . Identification markings consisting of lines, letters, and numbers are printed on the hose. (See figure 5-2.) These code markings show such informa. tion as hose size, manufacturer, ,date of manufac. ture, and pressure and temperature limits. Code markings assist in replacing a hose with one of the same specification or a ·recommended substitute. Hose suitable for use with phosphate ester base hydraulic fluid will be marked "Skydrol R use". In some instances several types of hose may be suitable for the same use. Therefore, in order to make the correct hose selection, always refer to the maintenance or parts manual for the particular airplane. Teflon Hose Teflon hose is a flexible hose designed to meet the requirements of higher operating temperatures and pressures in present aircraft systems. It can generally be used in the same manner as rubber hose. Teflon hose is processed and extruded into tube shape to a desired size. It is covered with stainless steel wire, which is braided over the tube for strength and protection. Teflon hose is unaffected by any known fuel, petroleum, or synthetic base oils, alcohol, coolants, or solvents commonly used in aircraft. Although it is highly resistant to vibration and fatigue, the principle advantage of this hose is its operating strength. Size Designation The size of flexible hose is determined by its inside diameter. Sizes are in one-sixteenth-inch increments and are identical to corresponding sizes of rigid tubing, with which it can be used. Identification of Fluid Lines Fluid lines in aircraft are often identified by markers made up of color codes, words, and geo­ metric symbols. These markers identify ea,ch line's function, content, and primary hazard, as well as the direction of fluid flow. Figure 5-3 illustrates the various color codes and symbols used to desig­ nate the type of system and its contents. In most instances, fluid lines are marked with I-inch tape or decals, as shown in figure 5-4 (A). **LUBRICATION 0 D** WBRICATION D LUBRICATIO! r WARNING SYMBOL 0 0 0 FIGURE 5-3. Identification of aircraft fluid lines. On lines 4 inches in diameter ( or larger), lines in oily environment, hot lines, and on some cold lines, ste!el tags may be used in place of tape or decals, as shown in figure 5-4 (B). Paint is used on lines in engine compartments, where there is the possibility of tapes, decals, or tags being drawn into the engine induction system. ### Page 110 Red (A) 01------1e 8 FUEL e 8 0 Red FLAM (B) FIGURE 5-4. Fluid line identification using: (A) tape and decals and (B) metal tags. In addition to the above-mentioned markings, certain lines may be further identified as to spe­ cific function within a system; for example, DRAIN, VENT, PRESSURE, or RETURN. Lines conveying fuel may he marked FLAM; lines containing toxic materials are marked TOXIC in place of FLAM. Lines containing physically dangerous materials, such as oxygen, nitrogen, or freon, are marked PHDAN. The aircraft and engine manufacturers are re­ sponsible for the original installation of identifi­ cation markers, but the aviation mechanic is re- AN sponsible for their replacement when it becomes necessary. Generally, tapes and decals are placed on both ends of a line and at least once in each compart­ ment through which the line runs. In addition, identification markers are placed immediately ad­ jacent to each valve, regulator, filter, or other accessory within a line. Where paint or tags are used, location requirements are the same as for tapes and decals. PLUMBING CONNECTORS Plumbing connectors, or fittings, attach one piece of tubing to _another or to system units. There are four types: (1) Flared fitting, (2) flare• less fitting, (3) head and clamp, and (4) swaged. The amount of pressure that the system carries is usually the deciding factor in selecting a con .. nector. The beaded type of joint, which requires a head and a section of hose and hose clamps, is AN818 nut sleeve Tubing FIGURE 5-5. Flared-tube fitting. T AN FEATURE AC T 37° ANGLE 35° :,: YES RECESS NO :,: .... .... '-' COARSER THREADS FINER '-' z z "' "' ..., BLUE GRAY ..., ;,. ;,. 0 OR COLOR OR 0 0 0 "' BLACK YELLOW "' l_ J_ LONGER BODY SHORTER LENGTH BLUE OR BLACK GRAY OR YELLOW FIGURE 5-6. AN and AC fitting differences. ### Page 111 used only in low- or medium-pressure systems, such as vacuum and coolant systems. The flared, flareless, and swaged types may be used as con­ nectors in all systems, regardless of the pressure. Flared-Tube Fittings A flared-tube fitting consists of a sleeve and a nut, as shown in figure 5-5. The nut fits over the sleeve and, when tightened, draws the sleeve and tubing flare tightly against a male fitting to form a seal. Tubing used with this type of fitting must be flared before installation. The male fitting has a cone-shaped surface with the same angle as the inside of the flare. The sleeve supports the tube so that vibration does not concentrate at the edge of the flare, and distributes the shearing action over a wider area for added strength. Tube flaring and the instal­ lation of flared-tube fittings are discussed in detail later in this chapter. The AC (Air Corps) flared-tube fittings have been replaced by the AN (Army/Navy) Standard and MS (Military Standard) fittings. However, since AC fittings are still in use in some of the older aircraft, it is important to be able to identify them. The AN fitting has a shoulder between the end of the threads and the flare cone. (See figure 5-6.) The AC fitting does not have this shoulder. Other differences between the AC and AN :fittings include the sleeve design, the AC sleeve being noticeably longer than the AN sleeve of the same size. Although certain flared-tube fittings are interchangeable, the pitch of the threads is different in most cases. Figure 5-7 shows the AN and AC811 fittings that can be safely inter­ changed. Combinations of end connections, nuts, Tube Sizes OD All Sizes 1 All Sizes 2 All Sizes All Sizes All Sizes All Sizes All Sizes All Sizes Ys,:J.{5,>4,§{5,1%,2 78, }{5, >i, §{5, 1%, 2 Ys, :J.{5, >4, }fo, l %, 2 Ys, ~6, >4, §{5, 1%, 2 Type End Type Connection Nut Type (Male (Female Sleeve Thread) Thread) AN' AN' AN' 81!2 81!2 81I2 AN AN AN AN AN 811 AN AN 811 8ll 811 811 811 811 AN 8ll 811 AN AN 811 AN AN 811 AN AN 811 811 AN 811 811 1 This is the normal assembly of AN fittings. 2 This is the normal assembly of AC811 fittings. Type Tube Flare AN1 81I2 811 811 AN AN AN 811 811 AN AN AN FIGURE 5-7a. Interchangeability of AN and AC811 fittings. 1-•·1~~;~~ lµw 1 \!A~I ~f . ·_ LpTYP1CAL CONNECTION ..!. BT LI HT CT JT RT ·@ A ET FIGURE 5-7 b. AC811 solderless fittings. ### Page 112 Material: Aluminum alloy Steel. .............. ---········-----·-·······-··- Brass ......... -----....... -·--........ -· ..... . Aluminum bronze .............................. . Size: -- AN744 to AN932 -- ...................... (code D) ...................... ( code, absence of Jetter) ............ (code B) ·············--·-··-··· ( code Z-for AN819 sleeve) The dash number following the AN number indicates the size of 1:he tubing ( or hose) for which the fitting is made, in I6ths of an inch. This size measures the 0. D. of tubing and the I. D. of hose. Fittings having pipe threads are coded by a dash number, indicating the pipe size in 8ths of an inch. The material code letter, as noted above, fol lows the dash number. BOLT AN774 TEE AN779 ADAPTOR AN807 ~om NUT AN817 NUT AN818 ---r------:-i I '---, • I ,-·, \ I : ) I I 1 ~. --! :___i~,: ' '' --, ______ 1-· ELBOW AN777 ~~,-----, •' r~-----r r r r----Ht- ' I I, TEE AN804 • ,------. _/1. \ : ]" -- ----. -~+-----/ : : j I ~ -~, r-_, _____ ,;.,, ELBOW AN8!1 , _____ --'--({ ____ ,'-' , . .._ ___ ..,~, ELBOW ANHi ELBOW ANau FIGURE 5-8. AN plumbing fittings. 105 \ ' : i \-- -- ---"-rJ , _______ ., ' ' ·c .. ~:.:i **TEE ANIH** ### Page 113 ' ' \....,1 ___ .1._.,., '-i - - . -,- , ';····· TEE AN8116 UNION AN832 • ___ ;_ /'' .. >' ELBOW AN837 .. ~-· -1 HOSE NIPPLE AN841 ELBOW AN838 * CROSS ,'f: - -: )- :'-"-· .. -H , _____ _,__u- AN8U ,---- -,~ -, 1 ; -- ·-, -,,--,- , ___ ::,_:--~-- -- :,,• TEE AN834 AN840 HOSE NIPPLE HOSE ELBOW AN8411 HOSE ELBOW AN845 ELBOW AN846 CONNECTOR AN849 * Inactive for new design. ~ * AN867 ~ *ANB71 AN843 **HOSE ELBOW AN844 ELBOW AN848** BUSHING AN893 BUSHING AN894 FIGURE 5-8. AN plumbing fittings.~Continued 106 ### Page 114 COUPLING AM910 NIPPLE AN911 BUSHING PLUG AM913 AN912 ELBOW AN914 ELBOW AN915 ELBOW AN916 TEE AH917 ' :\:~, ~ . -··:;-),- - ' : : ,' ; : : ,; J : I_. : -< :- .. -- . '.'"· - ',J _ -- .. : - - - ,l, REDUCER AM919 CROSS AN918 NUT AM924 TEE AN9t6 ELBOWAN9!7 CROSS AN9!s ~ ~ ELBOW AN928 PLUG AN93! CAPAM9ff FIGURE 5-8. AN plumbing fittings.-Continued sleeves, and tube flares are allowed to make up a complete fitting assembly. The use of dissimiJar metals should be avoided since their contact will cause corrosion. When combining AC and AN end connections, nuts, sleeves, or tube flares, if the nut will not ~ove more than two threads by hand, stop and investigate for possible trouble. The AN standard fitting is the most commonly used flared-tubing assembly for attaching the tubing to the various fittings required in aircraft plumbing systems. The AN standard fittings in­ clude the AN818 nut and AN819 sleeve. (See figure 5-8.) The AN819 sleeve is used with the AN818 coupling nut. All these fittings have straight threads, but they have different pitch for the various types. Flared-tube fittings are made of aluminum alloy, steel, or copper base alloys. For identifi­ cation purposes, all AN steel fittings are colored black, and all AN aluminum alloy fittings are colored blue. The AN 819 aluminum bronze sleeves are cadmium plated and are not colored. The size of these fittings is given in dash numbers, which equal the nominal tube outside diameter (0.D.) in sixteenths of an inch. Threaded flared-tube fittings have two types of ends, referred to as male and female. The male end of a fitting is externally threaded~ where­ as the female end of a fitting is internally threaded. ### Page 115 Cone angle Sleeve pilot Tube shoulder Sleeve cutting edge Sleeve Bevel Tube Nut .FIGURE 5-9. Flareless-tube fitting. Flareless-tube Fittings The MS (Military Standard) flareless-tube fit­ tings are finding wide application in aircraft plumbing systems. Using this type fitting elimi­ nates all tube flaring, yet provides a safe, strong, dependable tube connection. The fitting consists of three parts: a body, a sleeve, and a nut. The body has a counterbored shoulder, against which the end of the tube rests. (See figure 5-9.) The angle of the counterbore causes the cutting edge of the s1eeve to cut into the outside of the tube when the two are joined. Installation of flareless­ tube fittings is discussed later in this chapter. Quick-disconnect Couplings Quick-disconnect coup]ings of the self-sea1ing type are used. at various points in many fluid systems. The couplings are installed at locations where frequent uncoupling of the lines is required for inspection and maintenance. Quick-disconnect couplings provide a means of quickly disconnecting a line without loss of fluid or entrance of air into the system. Each coupling assembly consists of two halves, held together by a union nut. Each half contains a valve that is hel_d open when the coupling is connected, allowing flmd to flow through the coupling in either di­ rection. When the coupling is disconnected, a spring in each half closes the valve, preventing the loss of fluid and entrance of air. The union nut has a quick-lead thread which permits connecting or disconnecting the coupling by turning the nut. The amount the nut must be turned varies with different style couplings. One style requires a quarter turn of the union nut to lock or unloek the coupling while another style requires a full turn. Some couplings require wrench tightening; others are connected and disconnected by hand. The design of some couplings is such that they must be safetied with safety wire. Others do not require lock wiring, the positive locking being assured by the teeth on the loeking spring, which engage ratchet teeth on the union nut when the coupling is fully engaged. The lock spring auto­ matically disengages when the union nut is un­ screwed. Because of individual differences all ~uick di.sconnects should be installed accordi~g to mstruct1ons in the aircraft maintenance manual. Flexible Connectors Flexible connectors may be equipped with either swaged fittings or detachable fittings, or they may be used with beads and hose clamps. Those equipped with swaged :fittings are ordered by correct length from the manufacturer and ordi~ narily cannot be assembled by the mechanic. They are swaged and tested at the factory and are equipped with standard fittings. The fittings on detachable connectors can be detached and reused if they are not damaged; otherwise new fittings must be used. The bead and hose clamp connector is often used for connecting oil, coolant, and low-pressure fuel system tubing. The bead, a slightly raised ridge around the tubing or the fitting, gives a good gripping edge that aids in holding the clamp and hose in place. The bead may appear near the end of the metal tubing or on one end of a fitting. TUBE FORMING PROCESSES Damaged tubing and fluid lines should be re­ placed with new parts whenever possible. Some­ times replacement is impractical and repair is necessary. Scratches, abrasions, and minor cor~ rosion on the outside of fluid lines may be con­ sidered negligible and can be smoothed out with a burnishing tool or aluminum wool. Limitations on the amount of damage that can be repaired in this manner are discussed later in this chapter under ''Repair of Metal Tube Lines." If a fluid line assembly is to be replaced, the fittings can often be salvaged; then the repair will involve only tube forming and replacement. 108 Tube forming consists of four processes: (1) Cutting. (2) bending, (3) flaring, and (4) beading. If the tubing is small and of soft material, the assembly can be formed by hand bending during installation. If the tubing is ;i-inch diameter, or larger. hand bending without the aid of tools is impractical. Tube Cutting When cutting tubing, it is important to produce a square end, free of burrs. Tubing may be cut with a tube cutter or a hacksaw. The cutter can be used with any soft metal tubing, such as copper, aluminum, or aluminum alloy. Correct use of the tube cutter is shown in figure 5-10. ### Page 116 ·.,4 ,' ,~ -- ·-, I 1,' Clean cut FIGURE 5-10. Tube cutt;ng. A new piece of tubing should be cut approxi­ mately 10 percent longer than the tube to be re­ placed to provide for minor vari{ltions in bending. Place the fobing in the cutting tool, with the cutting wheel at the· point where the cut is to be made. Rotate the cutter around the tubing, applying a light pressure to the cutting wheel by intermit­ tently twisting the thumbscrew, Too much pressure on the cutting wheel at one time could deform the tubing or cause excessive burring. After cutting the tubing, carefully remove any burrs from inside and outside the tube. Use a knife or the burring edge attached to the tube cutter. When performing the deburring operation use extreme care that the wall thickness of the end of the tubing is not reduced or fractured. Very slight damage of this type can lead to fractured flares or defective flares which will not seal properly. A fine tooth file can be used to file th~ end square and smooth. If a tube cutter is not available, or if tubing of hard material is to be cut, use a fine-tooth hacksaw, preferably one having 32 teeth per inch. The use of a saw will decrease the amount of work harden· ing of the tubing during the cutting operation. After sawing, file the end of the tube square and smooth, removing all burrs. An easy way to hold small-diameter tubing, when cutting it, is to place the tube in a combination flaring tool and clamp the tool in ~ vise. Make the cut about one-half inch from the flaring tool. This procedure keeps sawing vibrations to a minimum and prevents damage to the tubing if it is acci­ dentally hit with the hacksaw fra!Jle or file handle while cutting. Be sure all filings and cuttings are removed from the tube. Tube Bending The objective in tube bending is to obtain a smooth bend ~ithout flattening the tube. Tubing 109 under one-fourth inch in diameter usually can be bent without the use of a bending tool. For larger sizes, a hand tube bender similar to that shown in figure 5-11 is usually used. To bend tubing with the hand tube bender, insert the tubing by raising the slide bar handle as far as it will go. Adjust the handle so that the full length of the groove in the slide bar is in contact with the tubing. The zero mark on the radius block and the mark on the slide bar must align. Make the bend by rotating the handle until the desired angle of bend is obtained, as indicated on the radius block. Bend the tubing carefully to avoid excessive flattening, kinking, or wrink]ing. A small amount of flattening in bends is acceptable, but the small diameter of the flattened portion must not he less than 75 percent of the original outside di­ ameter. Tubing with flattened, wrinkled, or ir­ regular bends should not be installed. Wrinkled bends usually result from trying to bend thin-wall tubing without using a tube bender. Examples of correct and incorrect tubing bends are shown in figure 5-12. Tube bending machines for all types of tubing are generally used in repair stations and large maintenance shops. w·ith such equipment, proper bends can be made on large diameter tubing and on tubing made from hard material. The pro­ duction tube bender is an example of this type of machine. The ordinary production tube bender wm ac­ commodate tubing ranging from Yz-inch to lYz­ inch outside diameter. Benders for larger sizes are available, and the principle of their operation is similar to that of the hand tube bender. The radius blocks are so constructed that the radius of bend will vary with the tubing diameter. The radius of bend is usually stamped on the block. When hand or production tube benders are not available or are not suitable for a particular bending operation, a filler of metallic composition or of dry sand may be used to faciJitate bending. When using this method, cut the tube slightly longer than is required. The extra length is for inserting a plug (which may be wooden) in .each end. After plugging one end, fill and pack the tube with fine, dry sand and plug tightly. Both plugs must be tight so they will not he forced out when the bend is made. The tube can also be closed by flattening the ends or by soldering metal disks in them. After the ends are closed, bend the tubing ### Page 117 - ·:,, Note: This bender can be slipped over partially conne<-1:ed tubes M it is applied at dire<.1 point of hend. Left hand :1. Drop dip over tube ...... ___ _ -- . ! Left hand To remove hent tube. lift slide bar handle to original po.~ition and raise dip Left hand Xote: Zero mark ('Oincides with mark on bloc-k )' ' / ;,--~~~~----!'Ji 4. With right hand (·ontinue to bend tube to desired anp;le by pressinii:: handle as shown below. / --- Right hand FIGURE 5-11. Tube bending. over a forming hlock shaped to the specified radius. In a modified version of the filler method, a fusible alloy is used instead of sand. In this method, the tube is filled under hot water with a fusible alloy that melts at 160° F. The alloy-filled tubing is then removed from the water, allowed to cool,.and bent slowly by hand around a forming llO block or with a tube bender. After the bend is made, the alloy is again melted under hot water and removed from the tubing. When using either filler method, make certain that all particles of the filler are removed so that none will he carried into the system in which the tubing is installed. Store the fusible alloy filler where it will he free from dust or dirt. It can he ### Page 118 I ' ' ' , ' GOOD Perfect bend , .,, ..:-·~--- -, r' ) ' Wrinkled bend ' ' , ,---- Flattened bend ,----... .,,-, ' -----,' ,,,,, I I ' I I i Kinked bend FIGURE S~l2. Correct and incorrect tubing bends. re-melted and re-used as often as desired. Never heat this filler in any other than the prescribed method, as the alloy will stick to the inside of the tubing, making them both unusable. Tube Flaring Two kinds of flares are generaIIy used in aircraft plumbing systems, the single flare and the double flare. Flares are frequently subiected to extremely high pressures; therefore, the flare on the tubing must be properly shaped or the connection will leak or fail. A flare made too small produces a weak joint, which may leak or pull apart; if made too large it interferes with the proper engagement of the screw thread on the fitting and will cause leakage. A crooked flare is the result of the tubing not being cut squarely. If a flare is not made properly, flaws cannot be corrected by applying additional torque when tightening the fitting. The flare and tubing must be free from cracks, dents, nicks, scratches, or any <'ther defects. The Haring tool used for aircraft tubing , has male and female dies ground to produce a flare of 35° to 37°. Under no circumstances is it per­ missible to use an automotive type flaring tool which produces a flare of 45°. Single Flare A hand flaring tool similar to that shown in figure 5~ 13 is used for flaring tubing. The tool 111 FIGURE 5-13. Hand flaring tool (single flare). consists of a flaring block or grip die, a yoke, and a flaring pin. The flaring block is a hinged double bar with holes corresponding to various sizes of tubing. These holes are countersunk on one end to form the outside support against which the flare is formed. The yoke is used to center the flaring pin over the end of the tube to be flared. To prepare a tube for flaring, cut the tube squarely and remove all burrs. Slip the fitting nut and sleeve on the tube and place the tube in the proper size hole in the flaring tool. Center the plunger or flaring pin over the end of the tube. Then project the end of the tubing slightly from the top of the flaring tool, about the thickness of a dime, and tighten the clamp bar securely to prevent slippage. Make the flare by striking the plunger several light blows with a lightweight hammer or mallet. Turn the plunger a half turn after each blow and be sure it seats properly before removing the tube from the flaring tool. Check the flare hy sliding the sleeve into position over the flare. The outside diameter oJ the flare should extend approximately onc-s_ixteenth inch beyond the end of the sieeve, but /should not he larger than the major outside diameter of the sleeve. Double Flare A double flare should be used on 5052-0 and 6061-T aluminum alloy tubing for all sizes from Ys- to %-inch outside diameter. This is necessary to prevent cutting off the flare and failure of the tube assembly under operating pressures. Doub]e flaring is not necessary on steel tubing. See figure 5-14 for an illustration of single- and double­ flared tubing. The double flare is smoother and more concentric than the single flare and, there­ fore, seals better. It is also more resistant to the shearing effect of torque. ### Page 119 A. Single-flared end B. Double-flared end FIGURE 5-14. Cutaway view of single- and double-flared tube ends. To make the double flare, separate the clamp blocks of the double-flaring tool and insert and clamp the tubing with the burred end flush with the top of the clamp. Insert the starting pin into the flaring pin guide and strike the pin sharply with a hammer until the shoulder of the pin stops against the clamp blocks. Remove the starting pin and insert the :finishing pin; hammer it until its shoulder rests on the clamp block. Beading Tubing may be beaded with a hand-beading tool, with machine-beading rolls, or with grip dies. The method to be used depends on the diameter and wall thickness of the tube and the material from which it was made. The hand-beading tool is used with tubing having X- to 1-inch outside diameter. The bead is formed by using the header frame with the proper rollers attached. The inside and outside of the tube is lubricated with light oil to reduce the friction between the rollers during heading. The sizes, marked in sixteenths of an inch on the rollers, are for the outside diameter of the tubing that can be beaded with the rollers. Separate rollers are required for the inside of each tubing size, and care must be taken to use the correct parts when beading. The hand-beading tool works somewhat like the tube cutter in that the roller is screwed down intermittently while rotating the beading tool around the tubing. In addition, a small vise ( tube holder) is furnished with the kit. Other methods and types of beading tools and machines are available, but the hand-beading tool is used most often As a rule, beading machines are limited to us,. with large-diameter tubing, over 119{s inch, unh ss special rollers are supplied. The grip-die method of beading is confined to small tubing. Flareless-Tube Assemblies Although the use of flareless-tube fittings elimi­ nates all tube flaring, another operation, referred to as presetting, is necessary prior to installation of a new flareless-tube assembly. Figure 5-15 (steps 1, 2, and 3) illustrates the presetting oper­ ation, which is performed as follows: (a.) Cut the tube to the correct length, with the ends perfectly square. Deburr the inside and outside of the tube. Slip the nut, then the sleeve, over the tube (step 1). (b.) Lubricate the threads of the fitting and nut with hydraulic fluid. Place the fitting in a vise (step 2), and hold the tubing firmly and squarely on the seat in the fitting. (Tube must bottom firmly in the fitting.) Tighten the nut until the cutting edge of the sleeve grips the tube. Thi_s point is determined by slowly turning the tube back and forth while tightening the nut. When the tube no longer turns, the nut is ready for final tightening. (c.) Final tightening depends upon the tub­ ing. For aluminum alloy tubing up tO and in~ eluding Yz-inch outside diaffieter, tighten the nut from one to one and one-sixth turns. For steel tubing and aluminum alloy tubing over Yz·inch outside diameter, tighten from one and one-sixth to one and one-half turns. After presetting the sleeve, disconnect the tub­ ing from the fitting and check the following points ### Page 120 Step 1 Step 2 3/32 to 1/8 inch a Sleeve cutting edge Slight deformation permissible 1------ .005 inch maximum - aluminum alloy tubing ' ...... ___ .015 inch maximum - corrosion resistant steel tubing FIGURE 5-15. Presetting flareless-tuhe assembly. (illustrated in step 3): (a.) The tube should extend %, to Ys inch beyond the sleeve pilot; otherwise hlowoff may occur. (h.) The sleeve pilot should contact the tube or have a maximum clearance of 0.005 inch 113 for aluminum alloy tubing or 0.015 inch for steel tubing. (c.) A slight collapse of the tube at the sleeve cut is permissible. No movement of the sleeve pilot, except rotation, is permissible. REPAIR OF MET AL TUBE LINES Scratches or nicks no deeper than 10 percent of the wall thickness in aluminum alloy tubing may he repaired, if they are not in the heel of a bend. Replace lines with severe die marks, seams, or splits in the tube. Any crack or de­ formity in a flare is also unacceptable and is cause for rejection. A dent of less than 20 percent of the tube diameter is not objectionable, unless it is in the heel of a bend. Dents can be removed by drawing a bullet of proper size through the tube by means of a length of cable. A severely damaged line should he replaced. However, the line can he repaired by cutting out the damaged section and inserting a tube section of the same size and material. Flare both ends of the undamaged and replacement tube sections and make the connection by using standard unions, sleeves, and tube nuts. If the damaged portion is short enough, omit the insert tube and repair by using one union and two sets of con­ necting :fittings. When repairing a damaged line, he very careful to remove all chips and burrs. Any open line that is to he left unattended for some time should he sealed, using metal, wood, rubber, or plastic plugs or caps. When repairing a low-pressure line using a flexible fluid connection assembly, position the hose clamps carefully in order to prevent overhang of the clamp hands or chafing of the tightening screws on adjacent parts. If chafing can occur, the hose clamps should he repositioned on the hose. Figure 5-16 illustrates the design of a flexible fluid connection assembly and gives the maximum allowable angular and dimensional offset. Layout of Lines Remove the damaged or worn assembly, taking care not_ to further damage or distort it, and use it as a forming template for the new part. If the old length of tubing cannot be used as a pattern, make a wire template, bending the pattern by hand as required for the new assembly. Then bend the tubing to match the wire pattern. Never select a path that does not require bends ### Page 121 .. . Min. l/4" -j -:"b " I " ' -/J-' Fitting 1/ 16'' Max offset \ Hose I Tubing 3° Max. ~deviation ~-23 Minimum gap 'G" shall be 1/2" or Tube 00/4, whichever is greater. Maximum gap "G" is not limited except on suction lines using other than self-sealing hose. On such suction lines, maximum G ~hall be 1-1/2 inch or one tube diameter, whichever is greater. FIGURE 5-16. Flexible fluid connection assembly. in the tubing. A tube cannot be cut or flared accurately enough so that it can be installed without bending and still be free from mechanical strain. Bends are also necessary to permit the tubing to expand or contract under temperature changes and to absorb vibration. If the tube is small (under one-fourth inch) and can be hand formed, casual bends may be made to allow for this. If the tube must be machine formed, definite bends must be made to avoid a straight assembly. Start all bends a reasonable distance from the fittings, because the sleeves and nuts must he slipped back during the fabrication of flares and during inspections. In all cases the new tube as­ sembly should be so formed prior to installation that it will not be necessary to pull or deflect the assembly into alignment by means of the coupling nuts. **FABRICATION AND REPLACEMENT OF** FLEXIBLE HOSE Hose and hose assemblies should be checked for deterioration at each inspection period. Leakage, separation of the cover or braid from the inner tube, cracks, hardening, lack of flexibility, and I Socket Nipple l FIGURE 5-17. Sleeve-type fittings. excessive ttcold flow" are apparent signs of de­ terioration and reaSon for replacement. The term ttcold flow" describes the deep, permanent im­ pressions in the hose produced by the pressure of hose clamps or supports. When failure occurs in a flexible hose equipped with swaged end fittings, the entire assembly must be replaced. Obtain a new hose assembly of the correct size and length, complete with factory­ installed end fittings. When failure occurs in hose equipped with reusable end fittings, a replacement line can he fabricated with the use of such tooling as may be necessary to comply with the assembly instruc­ tions of the manufacturer. Assembly of Sleeve-Type Fittings 114 Sleeve-type end fittings for flexible hose are detachable and may be reused if determined to be serviceable. The inside diameter of the fitting is the same as the inside diameter of the hose to which it is attached. Common sleeve-type fittings are shown in figure 5-17. To make a hose assembly, select the proper size hose and end fittings. Cut the hose to the correct length using a fine-tooth hacksaw. Place the socket in a vise. Screw the hose into the socket counterclockwise until the hose bottoms on the shoulder of the socket (figure 5-18); then back off one-quarter turn. Lubricate in:side of hose and nipple threads liberally. Mark the hose position ### Page 122 A C D E FIGURE 5-18. Assembly of MS fitting to flexible hose. around the hose at the rear of the socket using a grease pencil or painted line. Insert the nipple into the nut and tighten the nipple and nut on the assembly tool. If an assembly tool is not available, a mating AN815 adapter may he used. Using a wrench on the assembly tool, screw the nipple into the socket and hose. A %2· to ){,;-inch clearance between the nut and sleeve is required so that the nut will swivel freely when the as­ sembly tool is removed. After assembly, always make sure a11 foreign matter is removed from inside the hose by blowing out with compressed air. Proof-test After Assembly All flexible hose must he proof-tested after as­ sembly by plugging or capping one end of the hose and applying pressure to the inside of the hose assembly. The proof-test medium may he a liquid or a gas. For example, hydraulic, fuel, and oil lines are generally tested using hydraulic oil or water, whereas air or instrument lines are tested with dry, oil-free air or nitrogen. When testing with .a liquid, all trapped air is hied from the assembly prior to tightening the cap or plug. Hose tests, using a gas~ are conducted underwater. In all cases follow the hose manufacturer's in­ structions for proof-test pressure and fluid to be used when testing a specific hose assembly. Place the hose assembly in a horizontal position and observe for leakage while maintaining the test pressure. Proof-test pressures should be main­ tained for at least 30 seconds. Installation of Flexible Hose Assemblies Flexible hose must not be twisted on instal­ lation, since this reduces the life of the hose con­ siderably and may also loosen the fittings. Twist­ ing of the hose can be determined from the identifi­ cation stripe running along its length. This stripe should not spiral around the hose. Flexible hose should he protected from chafing by wrapping it with tape, but only where neces­ sary. The minimum bend radius for flexible hose varies according to size and construction of the hose and the pressure under which the hose is to operate. Bends that are too sharp will reduce the bursting pressure of flexible hose considerably below its rated value (figure 5-19). Flexible hose should he installed so that it will be subject to a minimum of :flexing during oper­ ation. Although hose must he supported at least every 24 inches, closer supports are desirable. A flexible hose must never be stretched tightly be­ tween two fittings. From 5 percent to 8 percent of its total length must he allowed for freedom of movement under pressure. When under pressure, flexible hose contracts in length and expands in diameter. Protect all flexible hose from excessive temper­ atures, either by locating the lines so they wil1 not be affected or by installing shrouds around them. INSTALLATION OF RIGID TUBING Before installing a line assembly in an aircraft, inspect the line carefuUy. Remove dents and scratches, and be sure all nuts and sleeves are snugly mated and securely fitted by proper flaring of the tubing. The line assembly should he clean and free of all foreign matter. Connection and Torque Never apply compound to the faces of the fitting or the flare, for it will destroy the metal-to-metal contact between the fitting and flare, a contact 115 ### Page 123 PLANNING HOSE LINE INSTALLATIONS WRONG -3 I RIGHT 1 ... provide slack or bend in the hose line to provide for changes in length that will occur when pressure is applied. WRONG RIGHT 3 ... relieve sharp bends, avoid strain or hose collapse and make cleaner installations by using Aeroquip elbows or other adapter fittings. Provide as large a bend radius as possible. Never use less than the recommended minimum bend radius specified for the hose. 2 ... observe linear stripe. The hose must not be twisted. High pressures applied to a twisted hose may cause failure or loosen the nut. ,U, .. -, ' ' ~1----r ' I ' I r).(, ' ' ' ' ·----~ ' ' I I 4 ... provide additional bend radius when lines are subject to flexing and remember that the metal end fittings are not flexible. Place line support clamps so as not to restrict hose flexing. FIGURE 5-19. Flexible hose installation. 1 ~ ~:.::: ·:.:" :.::::;e Incorrect - Will damage flare y _J or threads, or cause sleeve to "'f!!!:7- crack under vibration if tight­ened Ioconect - May pull off or distort flare if tightened Correctly fitted and tightened .025 clearance between :':::'.--cf--,- Flare and shoulder before tightening FIGURE 5-20. Correct and incorrect methods of tightening flared fittings. 116 which is necessary to produce the seal. Be sure that the line assembly is properly aligned before tightening the fittings. Do not pull the installation into place with torque on the nut. Correct and incorrect methods of installing flared-tube assem­ blies are illustrated in figure 5-20. Proper torque values are given in figure 5-21. It must be re­ membered that these torque values are for flared­ type fittings only. Always tighten fittings to the correct torque value when installing a tube assem­ bly. Overtightening a fitting may badly damage or completely cut off the tube flare, or it may ruin the sleeve or fitting nut. Failure to tighten suf­ ficiently also can be serious, as this condition may allow the line to blow out of the assembly or to leak under system pressure. The use of torque wrenches and the prescribed torque values prevents overtightening or under­ tightening. If a tube fitting assembly is tightened properly, it can be removed and retightened many times before re-flaring is necessary. ### Page 124 Aluminum Alloy Tubing, Bolt, Steel Tubing, Bolt Fitting or Nut Fitting or Nut Tubing Fittin[! Bolt Torque Torque 0.0. or Nut Size :nch-lhs. inch-lbs. J/8 -2 20-30 3/16 -.1 30-40 90- 100 !/4 -4 40-65 l."35- JS() 5/16 -5 60-85 IA0-200 3/8 -6 75-125 270- 300 !/2 -S 150- 250 450- 500 518 -"IO 200- 350 650- 700 3/4 -J:2 300- 500 900- 1000 1/8 -14 500- 600 1000 - I 100 -16 500-700 1200- 1400 1-1/4 -20 600- 900 1200- 1400 1-1/2 -24 600--· 900 1500- 1800 1-3/4 -28 850 -- 1050 2 -3:2 950-1150 Hose End Fittings and Hose Assemblies MS28740 or Equivalent End Fitting Minimum M"aximum 70 120 100 250 21() 420 3()() 480 500 850 700 1150 Minimum bend radii ( inches) Alum. alloy ll00-Hl4 5052-0 Steel 3/8 7/16 21/32 9/16 7/8 3/4 l 1/8 15/16 1 5/16 1 1/4 I 3/4 ! 1/2 1 3/16 l 3/4 2 5/8 3 3 l/2 3 3/4 4 3/8 5 5 1/4 1 6 1/8 8 7 FrcvRE 5-21. Flared fitting data. Flareless Tube Installation Tighten the nut by hand until an increase in resistance to turning is encountered. Should it be impossible to run the nut down with the fingers, use a wrench, but be alert for the first signs of bottoming. It is important that the final tightening commence at the point where the nut just begins to bottom. With a wrench, turn the nut VE,, turn ( one flat on a hex nut). Use a wrench on the connector to prevent it from turnin·g while tightening the nut. After the tube assembly is installed, the system should be pressure tested. Should a connection leak, it is permissible to tighten the nut an addi­ tional V,; turn ( making a total of Ya turn). If, after tightening the nut a total of Vs turn, leakage still exists, the assembly should be removed and the components of the assembly inspected for scores, cracks, presence of foreign material, or damage from overtightening. NOTE: Overtightening a flareless-tube nut drives the cutting edge of the sleeve deeply into the tube, causing the tube to be weakened to the point where normal in-flight vibration could cause the tube to shear. After inspection (if no discrepancies are found), reassemble the connections and repeat' the pressure test procedures. CAUTION: Do not in any case tighten the nut beyond VJ turn (two flats on the hex nut); this is the maximum the fitting may be tightened without the possibility of permanently damaging the sleeve and nut. 117 Common faults are: 1. Flare distorted into nut threads. 2. Sleeve cracked. 3. Flare cracked or split. 4. Flare out of round. 5. Inside of flare rough or scratched. 6. Fitting cone rough or scratched. 7. Threads of nut or union dirty, damaged or broken. Some manufacturers service instructions will spec­ ify wrench torque values for flareless tubing in­ stallations ( e.g., see figure 5-22). PLUMBING ASSEMBLY PRECAUTIONS Make certain that the material in the fittings used is similar to that of the tubing; for example, use steel fittings with steel tubing and aluminum alloy fittings with aluminum alloy tubing. Brass fitti.Pgs plated with cadmium may be used with p.luminum alloy tubing. For corrosion prevention, altiminum alloy lines ~nd fittings are usually anodized. Steel lines and fittings, if not stainless steel, are plated to prevent rusting or corroding. Brass and steel fittings are usµally cadmium plated, although some may come plated with nickel, chromium, or tin. To ensure proper sealing of hose connections and to prevent breaking hose clamps or damaging the hose, follow the hose clamp tightening instructions carefully. When available, use the hose damp torque-limiting wrench. These wrenches are avail­ able in calibrations of 15 and 25 inch-pounds. In the absence of torque-limiting wrenches, the finger­ tight-plus-turns method should be followed. Be- ### Page 125 WRENCH TORQUE FOR 304 1/8 H STEEL TUBES Tube Outside Diameter Wall Thickness Wrench Torque Inch-Pounds l l 3/16 3/16 1/4 1/4 5/16 3/8 3/8 1/2 1/2 1/2 5/8 5/8 5/8 3/4 3/4 0.016 0.020 0.016 0.020 0.020 0.020 0.028 0.020 0.028 0.035 0.020 0.035 0.042 0.028 0.049 0.020 0.065 90 -110 90- 110 110-140 110-140 100- 120 170- 230 200- 250 300 - 400 400-500 500 - 600 300- 400 600- 700 700- 850 650 - 800 800- 960 800 - 950 1(10-1750 WRENCH TORQUE FOR 304-lA or 3471A STEEL T TBES 3/8 1/2 1/2 0.042 0.028 0.049 0.035 145- 175 300 - 400 500 - 600 750 - 900 WRE1'CH TORQUE FOR 6061-T6 OR T4 TUBES 1/4 3/8 1/2 1/2 5/8 5/8 .1/4 114 0.035 0.035 0.035 0.049 0.03.5 0.049 0.035 0.035 0.035 110 - 140 145- 175 270- 330 320 -380 .360- 440 425 -- 525 380- 470 750- 900 900 - 1100 FIGURE 5-22. Torque values for flareless fittings. Hose damp tightening, finger-tight-phi\ tllrns method Initial installation only S\•lf sealing hosc­ ,ipprmdmat\'ly 15 inch-pounds All oth{'r aircraft hos(' \\'orm screw type damp 10 thn•ads per inch Fin.~(·r-ti,ght-ph1s :2 <'omplde tllrns Clamp,-rn0 M.,.c~F:TICAl.l.Y ORA'-CF-DYf:J) CLF.VIS BOI.T llFWOllKFD BOLT I.OW STllFr-:CTI! JNSl'l'CTED MACNCT!C l'.\S. \lATF.!llAL BOLT FIGURE 6--1. Aircraft bolt identification. A Class 4 fit requires a wrench to turn the nut onto a bolt, whereas a Class 1 fit can easily be turned with the fingers. Generally, aircraft screws are manufactured with a Class 2 thread fit for ease of assembly. Bolts and nuts are also produced with right­ hand and left-hand threads. A right-hand thread tightens when turned clockwise; a left-hand thread tightens when turned counterclockwise. AIRCRAFT BOLTS Aircraft bolts are fabricated from cadmium- or zinc-plated corrosion-resistant steel, unplated cor­ rosion-resistant steel, and anodized aluminum alloys. Most bolts used in aircraft structures are either general-purpose, AN bolts, or NAS internal­ wrenching or close-tolerance bolts, or MS bolts. In certain cases, aircraft manufacturers make bolts of different dimensions or greater strength 122 than the standard types. Such bolts ~re made for a particular application, and it is of extreme importance to use like bolts in replacement. Special bolts are usually identified by the letter ~~s" stamped on the head. AN bolts come in three head styles-hex-head, clevis, and eyebolt (see figure 6-1). NAS bolts are available in hex-head, internal-wrenching, and countersunk head styles. MS bolts come in hex­ head and internal-wrenching styles. General-Purpose Bolts The hex-head aircraft bolt (AN-3 through AN-20) is an all-purpose structural bolt used for general applications involving tension or shear loads where a light-drive fit is permissible (.006- inch clearance for a %-inch hole, and other sizes in proportion). Alloy steel bolts smaller than No. 10--32 and ### Page 129 aluminum alloy bolts smaller than U-inch di­ ameter are not used in primary structures. Alumi­ num alloy bolts and nuts are not used where they will he repeatedly removed for purposes of main­ tenance and inspection. Aluminum alloy nuts may be used with cadmium-plated steel bolts loaded in shear on land airplanes, but are not used on seaplanes due to the increased possibility of dis­ similar-metal corrosion. The AN-73 drilled-head bolt is similar to the standard hex-bolt, but has a deeper head which is drilled to receive wire for safetying. The AN-3 and the AN-73 series bolts are interchangeable, for aU practical purposes, from the standpoint of tension and shear strengths. Close-Tolercance Bolts This type of bolt is machined more accurately than the general-purpose bolt. Close-tolerance bolts may be hex-headed (AN-173 through AN- 186) or have a 100° countersunk head (NAS-80 through NAS-86). They are used in applications where a tight-drive fit is required ( the bolt will move into position only when struck with a 12- to 14-ounce hammer). Internal-Wrenching Bolts These bolts, (MS-20004 through MS-20024 or NAS-495) are fabricated from high-strength steel and are suitable for use in both tension and shear applications. When they are used in steel parts, the bolthole must be slightly countersunk to seat the large corner radius of the shank at the head. In Dural material, a special heat-treated washer must he used to provide an adequate hearing surface for the head. The head of the internal­ wrenching bolt is recessed to allow the insertion of an internal wrench when installing or removing the bolt. Special high-strength nuts are used on these bolts. Replace an internal-wrenching bolt with another internal-wrenching bolt. Standard AN hex-head bolts and washers cannot be substi­ tuted for them as they do not have the required strength. Identification and Coding Bolts are manufactured in many shapes and varieties. A clear-cut method of classification is difficult. Bolts can be identified by the shape of the head, method of securing, material used in fabrication, or the expected usage. 123 AN -type aircraft bolts can be identified by the code markings on the boltheads. The markings generally denote the bolt manufacturer, the ma­ terial of which the bolt is made, and whether the bolt is a standard AN-type or a special-purpose bolt. AN standard steel bolts are marked with either a raised dash or asterisk; corrosion-resistant steel is indicated by a single raised dash; and AN aluminum alloy bolts are marked with two raised dashes. Additional information, such as bolt diameter, bolt length, and grip length may be obtained from the bolt part number. For example, in the bolt part number AN3DD5A, the HAN" designates that it is an Air Force-Navy Standard bolt, the ''3" indicates the diameter in sixteenths of an inch (U6), the ''DD'' indicates the material is 2024 aluminum alloy. The letter HC" in place of the ''DD" would indicate corrosion-resistant steel, and the absence of the letters would indicate cadmium-plated steel. The ''5" indicates the length in eighths of an inch(%), and the "A" indicates that the shank is undrilled. If the letter ''H" preceded the ''5" in addition to the ''A" following it, the head would be drilled for safetying. Close-tolerance NAS bolts are marked with either a raised or recessed triangle. The material markings for NAS bolts are the same as for AN bolts, except that they may be either raised or recessed. Bolts inspected magnetically (Magna­ flux) or by fluorescent means (Zyglo) are identified by means of colored lacquer, ot a head marking of a distinctive type. SPECIAL-PURPOSE BOLTS Bolts designed for a particular application or use are classified as special-purpose bolts. Clevis bolts, eyebolts, Jo-bolts, and lock bolts are special­ purpose bolts. Clevis Bolts The head of a clevis bolt is round and is either slotted to receive a common screwdriver or re­ cessed to receive a crosspoint screwdriver. This type of bolt is used only where shear loads occur and never in tension. It is often inserted as a mechanical pin in a control system. Eyebolt This type of special-purpose bolt is used where external tension loads are to be applied. The eye ### Page 130 is designed for the attachment of such devices as the fork of a turnbuckle, a clevis, or a cable shackle. The threaded end may or may not be drilled for safetying. Jo-Bolt Jo-bolt is a trade name for an internally threaded three-piece rivet. The Jo-bolt consists of three parts-a threaded steel alloy bolt, a threaded steel nut, and an expandable stainless steel sleeve. The parts are factory preassembled. As the Jo-bolt is installed, the bolt is turned while the nut is held. This causes the sleeve to expand over the end of the nut, forming the blind head and clamping against the work. When driving is complete, a portion of the bolt breaks off. The high-shear and tensile strength of the Jo-bolt makes it suitable for use in cases of high stresses where some of the other blind fasteners would not be practical. Jo-bolts are often a part of the permanent structure of late-model aircraft. They are used in areas which are not often subjected to replacement or servicing. (Because it is a three­ part fastener, it should not he used where any part, in becoming loose, could be drawn into the engine air intake.) Other advantages of using Jo-bolts are their excellent resistance to vibration, weight saving, and fast installation by one person. Presently, Jo-bolts are available in four diam­ eters: The 200 series, approxiniately ?1'6-inch in diameter; the 260 series, approximately 7,4-inch in diameter; the 312 series, approximately :Ytfi-inch in diameter; and the 375 series, approximately %-inch in diameter. Jo-bolts are available in three head styles which are: F(flush), P(hex-head), and FA(flush millable). Lockbolts The lockbolt combines the features of a high­ strength bolt and rivet, but it has advantages over both. The lockbolt is generally used in wing-splice fittings, landing-gear fittings, fuel-cell fittings, longerons, beams, skin-splice plates, and other major structural attachments. It is more easily and quickly installed than the conventional rivet or bolt and eliminates the use of Iockwashers, cotter pins, and special nuts. Like the rivet, the lockbolt requires a pneumatic hammer or "pull gun" for installation; when installed, it is rigidly and perma­ nently locked in place. Three types of lockbolts are commonly used, the pull type, the stump type, and the blind type. (See figure 6-2.) Pull type. Pull-type lockbolts are used mainly in aircraft primary and secondary structures. They 124 II Pull type Stump type Blind type FlGURE 6-2. Lockbolt types. are installed very rapidly and have approximately one-half the weight of equivalent AN steel bolts and nuts. A special pneumatic "pull gun" is re· quired to install this type of lockbolt. Installation can be accomplished by one person since bucking is not required. Stump type. Stump-type lockbolts, although they do not have the extended stem with pull grooves, are companion fasteners to pull-type lockbolts. They are used primarily where clearance will not permit installation of the pull-type lockbolt. A standard pneumatic riveting hammer ( with a hammer set attached for swaging the collar into the pin-locking grooves) and a bucking bar are tools necessary for the installation of stump-type lockbolts. Blind type. Blind-type lockbolts come as com­ plete units or assemblies. They have exceptional strength and sheet pull-together characteristics. Blind lockbolts are used where only one side of the work is accessible and, generally, where it is diffi­ cult to drive a conventional rivet. This type of lockbolt is installed in the same manner as the pull­ type lockbolt. Common features. Common features of the three types of lockbolts are the annular locking grooves on the pin and the locking collar which is swaged into the pin's lock grooves to lock the pin in tension. The pins of the pull- and blind-type lockbolts are extended for pull installation. The extension is provided with pulling grooves and a tension breakoff groove. ### Page 131 Composition. The pins of pull- and stump-type lockbolts are made of heat-treated alloy steel or high-strength aluminum alloy. Companion collars are made of aluminum alloy or mild steel. The blind lockbolt consists of a heat-treated alloy steel pin, blind sleeve and filler sleeve, mild steel collar, and carbon steel washer. Substitution. Alloy steel lockbolts may be used to replace steel hi-shear rivets, solid steel rivets, or AN bolts of the same diameter and head type. Aluminum alloy lockbolts may be used to replace solid aluminum alloy rivets of the same diameter and head type. Steel and aluminum alloy lock­ bolts may also be used to replace steel and 2024T aluminum alloy bolts, respectively, of the same diameter. Blind lockbolts may be used to replace solid aluminum alloy rivets, stainless steel rivets, or all blind rivets of the same diameter. Numbering system. The numbering systems for the various types of lockbolts are explained by the following breakouts ( see figure 6--4) . Pull-type loekbolt- ALPP H T 8 8 16ths of an 1 Tcrip 1ength in inch. Body diameter in 32nds of all inch. Pin materials- E = 75S-T6 aluminum alloy. T = heat-treated alloy r,;,teel. Class fit- ][ = hole filling (interference fit). N = non-hole filling (dearancc fit). Head type- ACT 509 = dose tolerance head. ALPP = pan head. ALPJl = brazier head. AN .S09 C-sink ALP509 = standard AN- 509 C-sink head. ALP426 = standard AN-426 C-sink head. Blind-type Ioekholt­ BL 8 4 I T Lcrip length in 16ths of an inch, ±){i inch. Diameter in 32nds of an ineh. lllind Jorkbolt. GRIP GlllP RANGE GRIP GRIP RANGE NO. NO. Min. Max. Min. Max. 1 .031 .094 17 1.031 1.094 2 .094 .156 18 1.094 1.156 3 .156 .219 19 1.156 1.219 4 .219 .281 20 1.219 1.281 5 .281 .344 21 1.281 1.344 6 .344 .406 22 1.344 1.406 7 .406 .469 23 1.406 1.469 8 .469 .531 24 1.469 1.531 9 .531 .594 25 1.531 1.594 10 .594 .656 26 1.594 1.656 11 .656 . 718 27 1.656 1.718 12 .718 .781 28 1.718 1.781 13 .781 .843 29 1.781 1.843 14 .843 .906 30 1.843 1.906 15 .906 .968 31 1.906 1.968 16 .968 1.031 32 1.968 2.031 33 2.031 2.094 FIGURE 6-3. Pull- and stump-type lockbolt grip Lol'kbolt eollar­ LC C 8 ranges. l TDiameter of pin in 32nds of an inch. i\1aterial- C = 24ST aluminum aHoy (green color). F = 61ST aluminum alloy (plain color). R = mild steel (cadmium plated). Loekbolt collar. * l1st· 25ST aluminum alloy with heat-treated alloy lo('kholts only. Lse 61ST aluminum alloy with 75ST aluminum alloy lockholts only. ' Us,· mild steel \\ ith ht·at-treatrd alloy steel lockbolts for high temperatLJrc applications onfy. Stump-type lockbolt­ ALSF I:: 8 8 1 T Tcrip 1eng11i in 161hs of an inch. Body diameter in 32nds of an inch. Pin material- E = 75S--T6 aluminmn alloy. T = heat-treated alloy steel. Head type- ASCT509 = elosc tolerance AN-509 C-sink head. ALSF = flat head type. ALS509 = standard AN-509 C-sink head. ALS426 = standard AN-426 C-sink head. FIG!JRE 6--4. Lockbolt numbering system. ### Page 132 ·..:.:'. .!,!-inch Diameter %-inch Diameter **GRIP GRIP RANGE GRIP GRIP RANGE NO. NO.** Min. Max. Min. Max. 1 .031 .094 2 .094 .156 2 .094 .156 3 .156 .219 3 .156 .219 4 .219 .281 4 .219 .281 5 .281 .344 5 .281 .344 6 .344 .406 6 .344 .406 7 .406 .469 7 .406 .469 8 .469 .531 8 .469 .531 9 .531 .594 9 .531 .594 10 .594 .656 10 .594 .656 11 .656 . 718 11 .656 . 718 12 .718 .781 12 . 718 .781 13 .781 .843 13 .781 .843 14 .843 .906 14 .843 .906 15 . 906 .968 15 .906 .968 16 .968 1.031 16 .968 1.031 17 1.031 1.094 17 1.031 1.094 18 1.094 1.156 18 1.094 I:156 19 1.156 1.219 19 1.156 1.219 20 1.219 1.281 20 1.219 1.281 21 1.281 1.343 21 1.281 1.343 22 1.343 1.406 22 1.343 1.406 23 1.406 1.469 23 1.406 1.469 24 1.460 1.531 24 1.469 1.531 25 1.531 1.594 FIGURE 6--5. Blind-type lockbolt grip ranges. Grip Range. The bolt grip range required for any application should be determined by measuring the thickness of the material with a hook scale inserted through the hole. Once this measurement is determined the correct grip range can he selected by referring to the charts provided by the rivet manufacturer. Examples of grip-range charts are shown in figures 6-3 and 6-5. When installed, the lockholt collar should he •waged substantially throughout the complete length of the collar. The tolerance of the broken end of the pin relative to the top of the collar must be within the following dimensions: Pin Tolerance diameter Below Above %; .079 to .032 :l...: .079 to .050 %', .079 to .050 % .079 to .060 When removal of a lockbolt becomes necessary, remove the collar by splitting it axially with a sharp, cold chisel. Be careful not to break out or deform the hole. The use of a backup bar on the opposite side of the collar being split is recom- 126 mended; The pin may then he driven out with a drift punch. AIRCRAFT NUTS Aircraft nuts are made in a variety of shapes and sizes. They are made of cadmium-plated carbon steel, stainless steel, or anodized 2024T aluminum alloy, and may he obtained with either right- or left-hand threads. No identifying marking or lettering appears on nuts. They can be identified only by the characteristic metallic luster or color of the aluminum, brass, or the insert when the nut is of the self-locking type. They can he further identified by their construction . Aircraft nuts can he divided into two general groups: Non-self-locking and self-locking nuts. No?--self-locking nuts are those that must be safetied by external locking devices, such as cotter pins, safety wire, or locknuts. Self-locking nuts contain the locking feature as an integral part. Non-self-locking Nuts Most of the familiar types of nuts, including the plain nut, the castle nut, the castellated shear nut, the plain hex nut, the light hex nut, and the plain check nut are the non-self-locking type. ( See figure 6-6.) The castle nut, AN310, is used with drilled­ shank AN hex head bolts, clevis bolts, eyeholts, drilled head bolts, or studs. It is fairly rugged and can withstand large tensional loads. Slots (called castellations) in the nut are designed to accommodate a cotter pin or Jock wire for safety. The castellated shear nut, AN320, is designed for use with devices (such as drilled clevis bolts and threaded taper pins) which are normally sub­ jected to shearing stress only. Like the castle nut, it is castellated for safetying. Note, however, that the nut is not as deep or as strong as the castle nut; also that the castellations are not as deep as those in the castle nut. The plain hex nut, AN315 and AN335 (fine and coarse thread), is of rugged construction. This makes it suitable for carrying large tensional loads. However, since it requires an auxiliary locking device such as a check nut or lockwasher, its use on aircraft structures is somewhat limited. The light hex nut, AN340 and AN345 (fine and coarse thread), is a much lighter nut than the plain hex nut and must be locked by an auxiliary ### Page 133 AN310 AN315 AN335 @-------A ~ AN345 w m -------- AN316 AN350 FIGURE 6-6. l\'on-self-locking nuts. device. It is used for miscellaneous 1ight-tension requirements. The plain check nut, AN316, is employed as a locking device for plain nuts, set screws, threaded rod ends, and other devices. The wing nut, AN350, is intended for use where the desired tightness can he obtained with the fingers and where the assembly is frequently removed. Self-Locking Nuts As their name implies, self-locking nuts need no auxiliary means of safetying but have a safetying feature included as an integral part of their con­ struction. Many types of self-locking nuts have been designed and their use has become quite widespread. Common applications are: ( 1) At­ tachment of antifriction hearings and control pulleys; (2) Attachment of accessories, anchor nuts around inspection holes and small tank instailation openings; and ( 3) Attachment of rocker box covers and exhaust stacks. Self-locking nuts are accept­ able for use on certificated aircraft subject to the restrictions of the manufacturer. Self-locking nuts are used on aircraft to provide tight connections which will not shake loose under 127 severe vibration. Do not use self-locking nuts at joints which subject either the nut or bolt to rota­ tion. They may be used with antifriction bearings and control pulleys, provided the inner race of the bearing is clamped to the supporting structure by the nut and bolt. Plates must be attached to the structure in a positive manner to eliminate rotation or misalignment when tightening the bolts or screws. The two general types of self-locking nuts cur­ rently in use are the all-metal type and the fiber­ lock type. For the sake of simplicity, only three typical kinds of self-locking nuts are considered in this handbook: The Boots self-locking and the stainless steel self.locking nuts, representing the all-metal types; and the dastic stop nut, represent­ ing the fiber-insert type. Boots Self-Locking Nut The Boots self-locking nut is of one-piece, all­ metal construction, designed to hold tight in spite of severe vibration. Note in figure 6--7 that it has two sections and is essentially two nuts in one, a locking nut and a load-carrying nut. The two sections are connected with a spring which is an integral part of the nut. The spring keeps the locking and Ioad-car~ying sections such a distance ### Page 134 6$§.tft … IL Boots aircraft nut Elastic anchor nut Flex:loc nut Fiber locknut Elastic stop nut FIGURE 6-7. Self-locking nuts. apart that the two sets of threads are out-of-phase; that is, so spaced that a bolt which has been screwed through the load-carrying section must push the lockino- section outward against the force of the spring 0 to engage the threads of the locking section properly. Thus, the spring, thro1Jgh the medium of the locking section, exerts a constant locking force on the bolt in the same direction as a force that_ would tie:hten the nut. In this nut, the load-carrying sec­ ti;n has the thread strength of a standard nut of comparable size, while the locking section presses against the threads of the bolt and locks the nut firmly in position. Only a wrench applied to the nut will loosen it. The nut can be removed and reused without impairing its efficiency. Boots self-locking nuts are made with three dif­ ferent spring styles and in various shapes and sizes. The wing type, which is the most common, ranges in size for No. 6 up to 1/i inch, the Roi-top ranges from 114 inch to %6 inch, and the bellows type ranges in size from No. 8 up to o/s inch. Wing­ type nuts are made of anodized aluminum alloy, cadmium plated carbon steel, or stainless steel. The Rol-top nut is cadmium-plated steel, and the bellows type is made of aluminum a11oy only. Stainless Steel Self-Locking Nut The stainless steel self-locking nut may be spun on and off with the fingers, as its locking action takes place only when the nut is seated against a solid surface and tightened. The nut consists of two parts; a case with a beveled lo<:king shoulder and key, and a threaded insert with a lockin_g shoulder and slotted keyway. Until the nut rs tightened it spins on the bolt easily, because the threaded insert is the proper size for the bolt. How­ ever, when the nut is seated against a solid surface and tightened, the locking shoulder of the insert is pulled downward and wedged against the locking shoulder of the case. This action compresses the threaded insert and causes it to clench the bolt tightly. The cross-sectional view in figure 6-8 shows how the key of the case fits into the slotted keyway of the insert so that when the case is turned the threaded insert is turned with it. Note that the slot is wider than the key. This permits the slot to be narrowed and the insert to be compressed when the nut is tightened. Elastic Stop Nut The elastic stop nut is a standard nut with the height incteased to accommodate a fiber-locking collar. This fiber collar is very tough and durable and is unaffected by immersion in hot or cold water or ordinary solvents such as ether, carbon tetrachloride, oils, and gasoline. It will not dam­ a~e bolt threads or piatin~. As shown in figure 6--9, the fiber-locking collar is not threaded and its inside diameter is smaller than the largest diameter of the threaded portion or the outside diameter of a corresponding bolt. When the nut is screwed onto a bolt, it acts as an ordinary nut until the bolt reaches the fiber collar. When the bolt is screwed into the fiber collar, how­ ever, friction ( or drag) causes the fiber to be pushed upward. This creates a heavy downward. pressure on the load-carrying part and automatic­ ally throws the load-carrying sides of the nut and bolt threads into positive contact. After the bolt Jras been forced all the way through the fiber collar, the downward pressure remains constant. This pressure locks and holds the nut securely in place even under severe vibration. Nut case Untightened nut Keyway Tightened nut FIGURE 6-8. Stainless steel self-locking nut. ### Page 135 Fiber collar FIGURE 6--9. Elastic stop nut. Nearly all elastic stop nuts are steel or aluminum alloy. However, such nuts are available in prac­ tically any kind of metal. Aluminum alloy elastic stop nuts are supplied with an anodized finish. Steel nuts are cadmium plated. Normally, elastic stop nuts can be used many times with complete safety and without detriment to their locking efficiency. When reusing elastic stop nuts, be sure the fiber has not lost its locking friction or become brittle. If a nut can be turned with the fingers, replace it. After the nut has been tightened, make sure the rounded or chamfered end of the bolts, studs, or screws extends at least the full round or chamfer through the nut. Flat end bolts, studs, or screws should extend at least ¥32 inch through the nut. Bolts of %6-inch diameter and over with cotter pin holes may he used with self-locking nuts, but only if free from burrs around the holes. Bolts with damaged threads and rough ends are not acceptable. Do not tap the fiber-locking insert. The self-locking action of the elastic stop nut is the result of having the bolt threads impress themselves into the untapped fiber. Do not install elastic stop nuts in places where the temperature is higher than 250° F., because the effectiveness of the self-locking action is reduced beyond this point. Self-locking nuts may be used on aircraft engines and accessories when their use is specified by the engine manufacturer. Self-locking nut bases are ma