Square Square is the product obtained by multiplying a number by itself: 1X1=1, 2X2=4, 17X17=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: 1X1X1=1, 2X2X2=8, 13X13X13=2,197. Cubing may be considered specialized form of volumn computation:
Volume= Length multiplied by Width by Heighth, V=LXW×H.
Square Root Square root is the opposite of a "squared" number. The square root of a number is, that number which when multiplied by itself (squared) will produce the original or desired number: For example, the square root of 1 is 1, 1X1=1. 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 when multiplied by itself (cubed) will produce the original or desired number. The cube root of 1 is 1, 1X1X]=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 by their diameter.
circumference = 3.1416, Di- 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 (7) Xr'=a,
(7) multiplied by the radius squared equals area.
The radius is equal to one half the diameter. For example, diameter =2, radius =1. 3.1416X1=
3.1416 square units in a circle which has a diameter of 2. Another example, diameter =4, radius=
2. 3.1416X2°=3.1416X4=12.5664 square units.
lion micrograms.
33 ......
CHAPTER 2
AIRCRAFT DRAWINGS 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 misunderstanding and misinterpretation arose frequently. 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, industry uses drawings to describe objects. For this reason, drawing is called the Draftsman's Lan- 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 symbols that are used in a drawing. (See especially "The Meaning of Lines" section of this chapter.)
Prints are the link between the engineers who design an aircraft and the men who build, maintain, 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.
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 drawings, 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 lines, 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 small, 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 2-1.
It describes the object by giving, in a general way, the size and shape. Its primary purpose is to show the relationship of the various parts. An assembly drawing is usually more complex than a detail drawing, and is often accompanied by detail drawings of various parts.
Installation Drawing An installation drawing is one which includes 3/4~ NOTE: all necessary information for a part or an assembly
- ALL BEND RADII 3/16 of parts in the final position in the aircraft. It -RADIUS OF CUT OUT shows the dimensions necessary for the location
- IS 1/4 of specific parts with relation to the other parts
- L.H. IS SHOWN and reference dimensions that are helpful in later 4 3/8 -R.H. - / OPPOSITE work in the shop. (See installation drawing at the bottom of figure 2-1.)
DETAILS MATERIAL
- 024 24ST ALCLAD
CARE AND USE OF DRAWINGS Drawings are both expensive and valuable;
- 2-3/18 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.
5/16 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 unclean matter than can soil or smudge 4 1/8 ASSEMBL 3 1/2 the print. Never make notes 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 5/16 sign and date any changes they make.
SYM. When finished with a drawing, fold and return it to its proper place. Prints are folded originally B1219AD4 RIVETS I2 REQ in a proper size for filing, and care should be taken
- 2 PLATE .064 24ST ALCLAD | REQ. so that the original folds are always used.
36-31290 SIDE | REQ 36-31290 SIDE | REQ.
TITLE BLOCKS FORWARD Every print must have some means of identification. This is provided by a title block (see 9/16 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- INSTALLATION 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:
28 TO FUS. RL. (REF)
1. A drawing number to identify the print for filing purposes and to prevent confusing it FIGURE 2-1. Working drawings. with any other print.
the title block. Above the title block will be found AERONAUTICAL CENTER FEDERAL AVIATION ADMIN. OKLAHOMA CITY, OKLA. a notation such as: 470204-1LH shown; 470204- 2RH opposite. Both parts carry the same number, N° 1ADF "T" ANTENNA but the part called for is distinguished by a dash LOCATION A DETAILS number. Some prints have odd numbers for left- SCALE: FULL SIZE hand parts and even numbers for right-hand parts.
APPROVED: SUBMITTED JOSEPH DOE B.B. BLACK DR.BY: HBF СК.BY: TDY DATE 4-8-68 DR. AC-A-735 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.
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 system to conform to their particular needs. Letters may be used instead of numbers. The letter or number depicting the standard drawing size may be prefixed to the number, separated from it by a dash. Other numbering systems provide a separate box preceding the drawing number for the drawing size identifier.
In other modification of this system the part number of the depicted assembly is assigned as the drawing number.
SIZE 2 4 5 LENGTH 17" 22" INDEFINITE (ROLL) WIDTH 8-1/2" 17" 17,22,25,50,34, and 36 inches FIGURE 2-3. Standard blueprint paper sizes.
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 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
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 bill 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 connecting the number with the item assists in locating it in the bill of material.
BILL OF MATERIAL ITEM PART NO. REQUIRED • SOURCE CONNECTOR UG-21D/U 2 STOCK FIGURE 2-4. A typical bill of material.
OTHER DATA Revision Block Revisions to a drawing are 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 All changes to approved drawings must be carefully noted on all existing prints of the When drawings contain such corrections, attention 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 corrected drawing from its previous version, many firms are including, as part of the title block, a space for entering the appropriate symbol to designate that the drawing has been changed or revised.
2 CHANGED PART NO. 5 E.O. 1 2/3/70 B.K.
REVISED DIMENSIONS • J. L.M. 7/1/69 E.K.P.
NO. REVISION AUTH. DATE SIGN.
FIGURE 2-5. Revision block.
Notes Notes are added to drawings for various reasons. Some of these notes refer to methods of attachment or construction. Others give alternatives, 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 only when the information cannot be conveyed in the conventional manner or when it is desirable to avoid crowding the drawing. Figure 2-1 illustrates 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 drawings are similar to the numbers and letters printed on the borders of a map. They are 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 intersect is the area sought.
Use the same method to locate parts, sections, and views on large drawings, particularly assembly drawings. Parts numbered in the title block can be located on the drawing by finding the numbers in squares along the lower border.
Zone numbers read from right to left.
Station Numbers A numbering system is used on large assemblies for aircraft to locate stations such as fuselage frames. Fuselage Frame-Sta 185 indicates that the frame is 185 inches from the datum of the aircraft. The measurement is usually 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 closer 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.
0000 FIGURE 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 tolerance. For example, using .225 + .0025 - .0005, the plus and minus figures indicate the part will be 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 allowances 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 allowances are sufficient when close dimensions are not required. Standard tolerances of -.010 or -⅔2 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 pictorial 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.
Orthographic Projection Drawings In 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 orthographic 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 the box opened as shown in (b), then laid flat as shown in (c), the result is a sixview orthographic projection.
It is seldom necessary to show all six views to portray an object clearly; therefore, only those views necessary to illustrate the required characteristics of the object are drawn. One-view, twoview, and three-view drawings are the most common. Regardless of the number of views used, the arrangement is generally as shown in figure 2-7, with the front view being the principal one.
If the right-side view is shown, it 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 objects 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 half views, as illustrated in figure 2-9.
Aircraft drawings seldom show more than two principal, or complete, views of an object. Instead, generally there will be 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 principal 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 39
(a) Obiect
(b) Kotated TOP
LEFT SIDE FRONT RIGHT SIDE REAR BOTTOM
(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 are shown by the use of section (cross-hatching) lines.
Sectional views are used when the interior construction or hidden features of an object cannot 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 40
.032 THICK FIGURE 2-9. Symmetrical object with exterior half view.
FIGURE 2-8. One-view drawing.
59R 1000 32 OSR (TYP) 28- .56 B
DETAIL B FIGURE 2-10. Detail view.
PLUG BODY WASHER - GASKET — CLAMP NUT • 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 exterior 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 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 sections. 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 larger 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 standardized 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.
QUICK
DISCONNECT COUPLING FIGURE 2-12. Half section.
SEC. A B-B 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 small 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 indications, 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 are is given in terms of its radius and is marked with the letter R following the dimension. Parallel dimensions are placed so that the longest dimension is farthest from the outline and the shortest dimension is closest to 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 machining 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 diameters 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.
CENTER LINE THIN DIMENSION → THIN
LEADER THIN
BREAK (LONG) THIN BREAK (SHORT) • THICK
PHANTOM THIN
SECTIONING THIN
HIDDEN MEDIUM
STITCH LINE MEDIUM
OUTLINE OR THICK
VISIBLE LINE
DATUM LINE THICK
CUTTING PLANE EXTRA THICK
VIEMING PLANE EXTRA THICK
CUTTING PLANE FOR
COMPLEX OR OFFSET EXTRA THICK VIEW'S FIGURE 2-15. The meaning of lines.
- Extension line Dimension line - Phantom line Leader line
•Center line Sectioning fine -Break line
SECTION AA Outline Hidden line Cutting plane line FIGURE 2-16. Correct uses of lines.
Hidden Lines Hidden lines indicate invisible edges or contours. 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 3/16 DRILL .3125 DRILL on the drawing representing visible lines on the 3 HOLES .3217 REAM object.
EQUALLY SPACED 3/16 DRILL 80° C'Sk Stifch Lines 7/16 C' BORE 1/4 DRILL TO 5/16 DIA Stitch lines indicate stitching or sewing lines 1/8 DEEP and consist of a series of evenly spaced dashes.
2 HOLES 80°_ 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.
.2560 DRI 1/4 DRILL 3/8 C'BORE Viewing plane lines indicate the plane from 1/8 DEEP, 3 HOLES which a surface is viewed.
FIGURE 2-17. Dimensioning holes.
Leader Lines Leaders are solid lines 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 Phantom 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, but may vary with the kind of material shown in section.
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 back 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, but another view must be consulted to determine what the change is. For example, a circle 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 represents. A glance at the other view tells us that the smaller circle represents a hole, and the larger 45