рад 262 AC 43,15-14 1972 MAKE MA-700 MODEL SCRIAL # 0000 REGISTRATION #_ N7234 DATUM IS leading odge of wing.
COMPUTE AS FOLLOWS IF AIRORAFT WEIONED
2. Main wheel weighing point la looated ( 1. Leveling means: level top longeron between friO NAR sear seats AFF) "PORWARD) (+ of datum.
3. Aotual neasured distance from the main weight point conterline to the tal. (or nose) point centerline 222"•
4. 011 over and above "ZERO" tank reading = (8. Gale.) (b.= Ibe.) (0. = In.)
ACTUAL EMPTY WEIGHT Weight Point Soale Reading - Tare Net Weight Right 564 564 Loft 565 Tail 67 27 Total Not Weight
CENTER OF GRAVITY AS WEIGHED 10" (a) Te1l wheel alro. (Item 2, 222) 0.0. relative to main wheel weighing points 100 11 40 1" + 122 =0.
¡tom 9, 1l6!
(b) Nose wheel airo. (Iten 3 - ) X (Item 8 - = CoG.
(Item 9 ° (a) Tail wheel airc. (Item 10a, + 720) C.Q. relative to datums added to (Item 2,+ 3) = + 10,6" • C.0.
(b) Nose wheel airc. (Item 10b, added to (Item 2 COMPUTE IF AIRCRAFT WEIGHED WITH OIL (Item 4) Weight ATT Moment Aircraft (9) (12 Less 011 (4b) (40) Empty Totala (a)
(b)- = (0) - • Empty weight C.O.
12. (a) REPAIR AGENCY_ DATE.
Name Number FIGuRE 18.17.—Sample weight and balance report to determine empty weight center-of-gravity.
Par 664 Chap 13
AC 43.13-1A age 263 1972
EQUIPMENT LIST "Required or Optional Iten Numbers as Shown in Aircraft Speoification 2 101 102 103 104 105 201 202 203 301 302 (в) 303 401(a) 402 Special Equipment Item Mako Model Weight Arm 3 Flares In Min. TIZ 03 25# 150" Enter above those items included in the empty weight.
WEIGHT AND BALANCE EXTREME CONDITIONS Approved fud Limit 8,5 " Approred max. weight 2100/ Approved aft limit 21,9"
TORNARD OREOK REARWARD C RECK Iton Weight I Moment Weight ArD Moment Aire, Empty + 12391 + 1169 + 10.6 + 12392 (9 0r 12a) |(11 or 120 (9 or 12a) K11 or 120) OL1 + 27 - 49 833 17 - 49 833 Pilot * 170 * 16 * 2720 + 170 + 16 2120 Fuol 83 + 22 1826 * 240 + 22 + 5280 Passenger (s) * 340 * 48 + 16320 Baggage * 100 + 75.5 * 7550 TOTAL + 143990 TH + 16104- TH + 2036=1W + 43428=1M ТУ - 16104 = +22,2" 11 = 43428 • 121231 = 1439 TH 2036 Most Forvard C.O. loontion Most rearvard C.O. location
LOADING SCHEDULE Gallons Number of Pounda oi of Fuel Passengers Baggage 40 2(R) 100 The above includes pilot and capacity o1l
EQUIPMENT CHANGE Computing New C.G.
Iten, Meke, and Model* weight Moment Airo. Empty + 1169 + 10.6 + 12391 (9 0r 12г) (11 or 120) 204 added 6 302(b) added 29 377 302(a) removed 24 → 696 303 removed NET TOTALS - 1179 = NW + 13454 = NM N1 = 13454 = + 12.4" = Now C.0. 1779 "ITEM NUMBERS WHEN LISTED IN PERTINENT AIRCRAFT SPECIFICATION MAY BE USED IN LIEU OF MITEM, MAKE, AND HODEL".
PREPARED BY DATE FIGURE 18.18.-Sample weight and balance report including an equipment change for aircraft fully loaded.
Chap 13 Par 664
Page 264 AC 43.13-1A 1972 Desired C.G. location Actual C.G. location
- × Location of ballast to D - Distance in inches desired to move C.G. of airplane. be added W - Weight of airplane as loaded.
X - Distance in inches from point where ballast is to be installed, to the desired location of the new C.G.
B - Weight of ballast required in pounds.
B = D × W Compute the new C.G. of the aircraft with ballast installed.
NOTE: If greater accuracy is desired, repeat the entire formula using the NEW aircraft weight and the NEW C.G. in the second operation.
FIGURE 18.19.-Permanent ballast computation formula.
Par 664 Chap 13
AC 43.13-1A 1972 in the form of lead plate wrapped around and/or bolted to the fuselage primary structure (tail-post, longerons, or bulkhead members).
Permanent ballast invariably constitutes a concentrated load; therefore, the strength of the local structure and the attachment of the ballast thereto should be investigated for the design loading conditions pertinent to the particular aircraft. Placard permanent ballast "Permanent ballast-do not remove." It is not desirable to install permanent ballast by pouring melted lead into the tail-post or longerons, due to difficulties that may be encountered in subsequent welding repair operations. It should be noted that the installation of permanent ballast results in an increase of aircraft empty weight. See figure 18.19 for ballast computation. When disposable ballast is carried, the local strength of the compartment in which the ballast is carried and the effect of the bal- Chap 13 Page 265 last on aircraft balance and weight should be investigated.
665. LOADING SCHEDULE. The loading schedule should be kept with the aircraft and usually forms a part of the airplane flight manual. It includes instructions on the proper load distribution, such as filling of fuel and oil tanks, passenger seating, restrictions of passenger movement; distribution of cargo, etc.
a. Other means of determining safe loading conditions, such as the use of a graphical index, load adjuster, etc., are acceptable and may be used in lieu of the information in paragraph 661.
b. Compute a separate loading condition when the aircraft is to be loaded in other than the specified conditions shown in the loading
666.-676. RESERVED.
Par 664
AC 49.13-14 Fage 267 1973 Chapter 14. ENGINES AND FUEL SYSTEMS Section 1. ENGINES
677. GENERAL, Persons should avail themselves of the manufacturer's manuals, service bulletins, and instruction books regarding the repair and overhaul, inspection, installation, and maintenance of aircraft engines. The repair and overhaul of engines are too many and varled for the different types and models of engines to mention here in specific detail.
678. INSPECTION. All moving and/or highlystressed parts and those subjected to high temperature should have a critical visual inspection at the time of overhaul. It is often necessary to supplement the visual inspection by employing one of the following procedures:
occur whenever an aircraft powerplant has been subjected to sudden deceleration or stoppage.
To fully evaluate any unsatisfactory findings resulting from this type of inspection, it will be necessary to refer to the applicable manu- to sad facturer's service and overhaul data. In addition, many of the prime aeronautical engine manufacturers now have specific recommendations on the subject of sudden stoppage involving their products. To assure continued airworthiness and reliability, it is essential that such data be used. In the event the manufacturer has not specified an instruction to follow, the following may be used as a guideline.
a. Wet or dry magnetic dust inspection of magnetic materials,
b. Wet or dry penetrant inspection of nonmagnetic materials,
c. X-ray or sonic inspection of any material, or
d. Hydrostatic inspection testing of fluid lines and internal passages and assemblies such as cylinder heads.
679. POWERPLANT SUDDEN STOPPAGE. For the purpose of this section, powerplant sudden stoppage refers to any momentary slowdown or complete stoppage of the main shaft of an aircraft powerplant; when the stoppage of a reciprocating or turboprop engine is the result of the rotating propeller striking a foreign object; or when the stoppage of a turbine engine is the result of ingestion of foreign objects or material. Any aircraft powerplant that has been subjected to sudden stoppage should be inspected to the extent necessary to assure continued safe operation. These procedures will serve as a guide for locating damage that may
a. Reciprocating Engine (Direct Drive).
(1) Powerpiant Exterior Inspection. Remove the engine cowling and examine the engine for visible external damage and audible internal damage.
(a) Rotate the propeller shaft to determine any evidence of abnormal grinding or sounds.
(b) With the propeller removed, inspect the crankshaft flange or splines for signs of twisting, cracks, or other deformation. Remove the thrust-bearing nut and seal and thoroughly inspect the threaded area of the shaft for evidence of cracks.
(c) Rotate the shaft slowly in 90° increments while using a dial indicator or an equivalent instrument to check the concentricity of the shaft.
(d) Remove the oil sump drain plug and check for metal chips and foreign material.
(e) Remove and inspect the oil screens for metal particles and contamination.
(f) Visually inspect engine case exterior for signs of oil leakage and cracks. Give particular attention to the propeller thrust-bearing area of the nose case section.
Chap 14 Par 677
(g) Inspect cylinders and cylinder holddown area for cracks and oil leaks. Thoroughly investigate any indication of cracks, oll leaks or other damage.
(2) Powerpiant Internal Inspection.
(a) On engines equipped with crankshaft vibration dampers, remove the cylinders necessary to inspect the dampers and inspect in accordance with the engine manufacturer's inspection and overhaul manual. When engine design permits, remove the damper pins, and examine the pins and damper liners for signs of nicks or brinelling.
(b) After removing the engine-driven accessories remove the accessory drive case and examine the accessory and supercharger drive gear train, couplings, and drive case for evidence of damage.
1. Check for cracks in the case in the area of accessory mount pads and gear shaft bosses.
2. Check the gear train for signs of cracked, broken, or brinelled teeth.
3. Check the accessory drive shaft couplings for twisted splines, misalignment and runout.
(3) Accessory and Drive Inspection. Check the drive shaft of each accessory, l.e., magnetos, generators, external supercharger, and pumps for evidence of damage.
(4) Engine Mount Inspection.
(a) Examine the engine flex mounts when applicable for looseness, distortion, or signs of tear.
(b) Inspect the engine mount structure for bent, cracked, or buckled tubes.
(c) Check the adjacent airframe structure for cracks, distortion, or wrinkles.
(d) Remove engine mount bolts and mount holddown bolts and inspect for shear, cracks, or distortion.
(5) Exhaust-driven Supercharger (Turbo) Inspection. Sudden stoppage of the powerplant can cause the heat in turbine parts to heat soak the turbine seals and bearings. This excessive heat causes carbon to develop in the seal area and varnish to form on the turbine bearings and journals.
Par 679 AC 43.13-1A 1972
(a) Inspect all air ducts and connections for air leaks, warpage, or cracks.
(b) Remove compressor housing and check the turbine wheel for rubbing or binding.
(6) Propeller Inspection Repair. Any propeller that has struck a foreign object during service should be promptly inspected in accordance with the propeller manufacturer's prescribed procedures for possible damage resulting from this contact with the foreign object and, if necessary, repaired according to the manufacturer's instructions. If the propeller is damaged beyond the repair limits established by the propeller manufacturer and a replacement is necessary, install the same make/model or alternate approved for this installation. Refer to the aircraft manufacturer's optional equipment list, applicable FAA Aircraft Specification, Data Sheet, or Supplemental Type Certificate Data.
b. Reciprocating Engine (Geared Drive). Inspect the engine, propeller and components as in preceding paragraphs.
(1) Remove the propeller reduction gear housing and inspect for:
(al Loose, sheared, or spalled cap screws or bolts.
(b) Cracks in the case.
(2) Disassemble the gear train and inspect the propeller shaft, reduction gears and accessory drive gears for nicks, cracks, or spalling.
c. Turbine, Engine, Ingestion Inspection. When the components of the compressor assembly or turbine section are subjected to ingestion damage, refer to the engine manufacturer's inspection and overhaul manual for specific inspection procedures and allowable tolerances. In general, an inspection after ingestion of foreign materials consista of the following areas:
(1) Inspect the external areas of the engine cases, attached parts and engine mounts for cracks, distortion, or other damage.
(2) Inspect the turbine disc for warpage or distortion.
(3) Inspect turbine disc seal for damage from rubbing or improper clearance.
(4) Inspect compressor rotor blades and stators for nicks, cracks, or distortion.
Chap 14
AC 43.13-1A 1972
(5) Check rotor and main shaft for misalignment.
(6) Inspect shaft bearing area for oil leaks.
(7) Inspect the hot section for cracks or hot spots.
(8) Inspect the accessory drives as prescribed under paragraph a (2) (b).
NOTE: Turbine disc seal rubbing ia not unusual and may be a normal condition. Consult the engine manufacturer's inspection procedures and table of limits.
d. Turboprop Engine Inspection.
(1) When sudden stoppage is the result of compressor ingestion of foreign material, inspect the engine as follows:
(a) Inspect the powerplant as described in paragraph c, "Turbine Engine, Ingestion Inspection."
(b) Inspect the reduction gear section as described in paragraph b(1) and b(2) where reduction gear damage is suspected.
12) When sudden stoppage is the result of the propeller striking foreign objects, inspect the engine as follow:
(a) Inspect the reduction gear section as described in paragraph b(1) and b(2).
(b) Inspect mainline shafts and coupling shafts for runout and spiral cracks.
(c) Inspect bearings for brinelling.
(d) Inspect engine compressor and turbine blades for tip clearance.
e. Approval for Returning Engine to Service.
(1) Correct all discrepancies found in the foregoing inspection in accordance with the engine manufacturer's service instructions.
(2) Test run the engine to determine that the engine, propeller, and accessories are functioning properly.
(3) After shutdown, check the engine for oil leak and check oil screens for signs of contaminants.
(4) If everything is normal the engine is ready for preflight runup and test flight.
680. CRANKSHAFTS. Carefully inspect for misalignment and replace if bent beyond the manufacturer's permissible service limit. Make no attempt to straighten crankshafts damaged in service without consulting the engine manu- Chap 14 Page 269 facturer for appropriate instructions. Worn journals may be repaired by regrinding in accordance with manufacturers' instructions. It is recommended that grinding operations be performed by appropriately rated repair stations or the original engine manufacturer to assure adherence to aeronautical standards.
Common errors that occur in crankshaft grinding are the removal of nitrided journal surface, improper journal radii, unsatisfactory surfaces, and grinding tool marks on the journals. If the fillets are altered, do not reduce their radii. Polish the reworked surfaces to assure removal of all tool marks. Most opposed engines have nitrided crankshafts and manufacturers specify that these crankshafts must be nitrided after grinding.
681. REPLACEMENT PARTS IN CERTIFICATED EN- GINES. Only those parts which are approved under FAR Part 21 should be used. Serviceable parts obtained from the engine manufacturer, his authorized service facility, and those which are FAA/PMA approved meet the requirements of FAR Part 21 and are acceptable for use as replacement parts. It is suggested that the latest type parts as reflected on the current parts list be obtained. Parts from military surplus stocks, which are applicable to the specific engine may be used provided they were originally accepted under the military procurement agency's standards, are found to be serviceable, and are not prohibited from use by the Administrator.
a. Parts for obsolete engines for which new parts are no longer obtainable from the original manufacturer or his successor are sometimes fabricated locally. When it becomes necessary to do this, physical tests and careful measurements of the old part may provide adequate technical information. This procedure is usually regarded as a major change which requires engine testing and is not recommended except as a last alternative.
b. Parts from certain military surplus tank or ground power unit engines are used on engines used in restricted aircraft and amateur-built aircraft. Users of such parts are cautioned to determine that they do not exceed the design Par 679
limits of the engine. For example, a particular tank engine utilized a piston design that developed a compression ratio well in excess of the crankshaft absorption rate of the aircraft engine counterpart-result, crankshaft failure.
682. CYLINDER HOLDDOWN NUTS AND CAP- SCREWS. Great care is required in tightening cylinder holddown nuts and capscrews. They must be tightened to recommended torque limits to prevent improper stressing and to insure even loading on the cylinder flange. The installation of baffies, brackets, clips, and other extraneous parts under nuts and capscrews is not considered good practice and should be discouraged. If these baffles, brackets, etc., are not properly fabricated or made of suitable material, they may cause loosening of the nuts or capscrews even though the nuts or capscrews were properly tightened and locked at installation. Either improper prestressing or loosening of any one of these nuts or capscrews will introduce the danger of progressive stud failure with the possible loss of the engine cylinder in flight. Do not install parts made from aluminum alloy or other soft metals under cylinder holddown nuts or capscrews.
683. REUSE OF SAFETYING DEVICES. Do not use cotter pins and safety wire a second time. Flat steel-type wristpin retainers and thin lockwashers likewise should be replaced at overhaul unless the manufacturer's recommendations permit their reuse.
684. SELF-LOCKING NUTS FOR AIRCRAFT ENGINES AND ACCESSORIES. Self-locking nuts may be used on aircraft engines provided the following criteria are met:
a. Where their use is specified by the engine manufacturer in his assembly drawing, parts list, and bills of material,
b. When the nuts will not fall inside the engine should they loosen and come off,
c. When there is at least one full thread protruding beyond the nut,
d. When the edges of cotter pin or lockwire holes are well rounded to preclude damage to the locknut, Par 681 AC 49.13-1A 1972
•. Prior to reuse, the effectiveness of the selflocking feature is found to be satisfactory,
f. Where the temperature will not exceed the maximum limits established for the self-locking material used in the nut. On many engines the cylinder baffles, rocker box covers, drive covers and pads, and accessory and supercharger housings are fastened with fiber insert locknuts which are limited to a maximum temperature of 250° F. Above this temperature the fiber insert will usually char and consequently lose its locking characteristic. For locations such as the exhaust pipe attachment to the cylinder, a locknut which has good locking features at elevated temperatures will give invaluable service. In a few instances, fiber insert locknuts have been approved for use on cylinder holddown studs. This practice is not generally recommended, since especially tight stud fits to the crankcase must be provided, and extremely good cooling must prevail so that low temperatures exist at this location on the specific engine for which such use is approved.
g. All proposed applications of new types of locknuts or new applications of currently used self-locking nuts must be investigated since many engines require specifically designed nuts. Such specifically designed nuts are usually required for one or more of the following reasons to provide:
(1) Heat resistance,
(2) Adequate clearance for installation and removal,
(3) For the required degree of tightening or locking ability which sometimes requires a stronger, specifically heat-treated material, a heavier cross-section, or a special locking means,
(4) Ample bearing area under the nut to reduce unit loading on softer metals, and
(5) To prevent loosening of studs when nuts are removed.
h. Information concerning approved self-locking nuta and their use on specific engines is usually found in engine manufacturer's manuals or bulletins. If the desired information is not available, it is suggested that the engine manufacturer be contacted.
Chap 14
AC 49.13-1А Page 271 1972
685. WELDING OF HIGHLY STRESSED ENGINE a. Dense chromium plating of the crankpin and PARTS. In general, welding of highly-stressed main journals of some small engine crankengine parts is not recommended for parts that shafts has been found satisfactory, except were not originally welded. However, under the where the crankshaft is already marginal in conditions given below, welding may be accom- strength. Plating to restore worn low-stress plished if it can be reasonably expected that the engine parts such as accessory driven shafts welded repair will not adversely affect the air- and splines, propeller shaft ends, and seating worthiness of the engine when: surfaces of roller- and ball-type bearing races
a. The weld is externally situated and can be is acceptable.
inspected easily, b. Porous chromium plated walls of cylinder * b. The part has been cracked or broken as barrels have been found to be satisfactory for practically all types of engines. Dense or the result of unusual loads not encountered in smooth chromium plating without roughened normal operation, surfaces, on the other hand, has not been found
c. A new replacement part of obsolete type to be generally satisfactory.
engine is not available, (1) Cylinder barrel pregrinding and chro-
employed will insure a first-quality weld in the type of material to be repaired and will insure military approved facilities engaged in doing are considered acceptable for all engines, and restoration of the original heat treat in heat- this work in accordance with military specifition on process details. treated parts. Refer to Chapter 2 for informa- Aviation Administration. cations are eligible for approval by the Federal
(2) Chromium plated cylinder barrels have
686. WELDING OF MINOR ENGINE PARTS. Many been required for some time to be identified in minor parts not subjected to high stresses may such a manner that the markings are visible be safely repaired by welding. Mounting lugs, with the cylinder installed. Military processed originally fabricated by welding are in this cowl lugs, cylinder fins, covers, and many parts cylinders are banded with orange enamel above the mounting flange. It has been the practice to category. The welded part should be suitably etch on either the flange edge or on the barrel stress-relieved after welding. skirt the processer's initials and cylinder oversize. Most plating facilities use the orange
687. METALLIZING. Metallizing internal parts of aircraft engines is not acceptable unless it is marks. band as well as the permanent identification proven to the Federal Aviation Administration (3) A current list of engine and maximum that the metallized part will not adversely af- permissible cylinder barrel oversize follows:
fect the airworthiness of the engine. Metalliz- Махітит ing the finned surfaces of steel cylinder barrels Engine manufacturer Enrine serles Oversize (in.)
with aluminum is acceptable, since many engines are originally manufactured in this man- Air Cooled Motors (Franklin). No oversize for sleeved cylinders.
Solid cylinders 0.020 Continental Motors - R-670, W-670, R94 0.020
688. PLATING. Restore plating on engine parts All others . 0.015 in accordance with the manufacturer's instruc- Jacobs All 0.020 tions. In general, chromium plating should not Kinner All 0.015 Pigman, LeBlond, All 0.025 be applied to highly stressed engine parts. Cer- Rearwin, Ken tain applications of this nature have been Hoyce.
found to be satisfactory; however, engineering Lycoming AlI 0.015 evaluation of the details for the processes used Menasco 0.010 should be obtained. (Table continues on next pare.)
Chap 14 Par 685
Page 272 AC 43.13-1А 1972 Pratt & Whitney R-2800B, C, CA, CB 0.025 691. ENGINE RUN-IN. After an aircraft engine *R-985 and R-1880 0.080 has been overhauled, it is recommended the Ranger All others 6-410 early yls. 6-890 - 6-410 late cyls. 6-440 0.020 0.010 0.020 in instructions be followed. Observe the manu- pertinent aircraft engine manufacturer's run- (L-440) series. facturer's recommendations concerning engine Warner All 0.015 temperatures and other criteria.
Wright All 0.020 Repair processes employed during overhaul *(The above oversize limits correspond to the manufacturer's re- often necessitate amending the manufacturquirements, except for PAW R-985 and R-1880 serles engines.)
(4) The following is a list of known agencies, and their identifying initials, performing cylinder barrel plating for the military service.
Agencies Initiale Hol-Chrome Corporation НСС San Antonio Air Materiel Area SAX Koppers Co. (American Hammered Piston er's run-in procedures. Follow the approved amended run-in procedures in such instances.
692. COMPRESSION TESTING OF AIRCRAFT EN- GINE CYLINDERS. The purpose of testing cylinder compression is to determine the internal condition of the combustion chamber by ascertaining if any appreciable leakage is occurring.
McQuay-Norris MQN VanDer Horst Corporation VDH Terry Industries TIX Lement Chromium LC Pennington Channel Chrome PCC Spar-Tan Engineering Company . SEC Superior Aero Chrome SAC
(5) Cylinder barrels which have been plated by an agency whose process is approved by the FAA and which have not been preground beyond maximum permissible limits will be considered acceptable for installation on certificated engines. It will be the responsibility of the owner or the repairing agency to provide this proof. In some cases, it may be necessary to remove cylinders to determine the amount of oversize since this information may be etched on the mating surface of the cylinder base flange.
689. ENGINE ACCESSORIES. Overhaul and repair of engine accessories in accord with the engine and the accessory manufacturers' instructions are recommended.
690. CORROSION. Accomplish corrosion preventive measures for temporary and dead storage in accord with the instructions issued by the pertinent engine manufacturer. Avoid the use of strong solutions which contain strong caustic compounds and all solutions, polishes, cleaners, abrasives, etc., which might possibly promote corrosive action. (Refer to Chapter
a. Types of Compression Testers. The two basic types of compression testers currently in use are the direct compression and the differential pressure type testers. The optimum procedure would be to utilize both types of testers when checking the compression of aircraft cylinders.
in this respect, it is suggested that the direct compression method be used first and the findings substantiated with the differential pressure method. This provides a cross-reference to validate the readings obtained by each method and tends to assure that the cylinder is defective before it is removed. Before beginning a compression test, consider the following points:
(1) When the spark plugs are removed, identify them to coincide with the cylinder.
Close examination of the plugs will reveal the actual operating conditions and aid in diagnosing problems within the cylinder. Paragraph 693d. of this section contains more information on this subject.
(2) The operating and maintenance records of the engine should be reviewed. Records of previous compression tests are of assistance in determining progressive wear conditions and help to establish the necessary maintenance ac-
(3) Before beginning a compression check, precautions should be taken to prevent the accidental starting of the engine.
b. Direct Compression Check. This type of compression test indicates the actual pressures Par 688 Chop 14
AC 43.12-1A Page 273 1972 within the cylinder. Although the particular defective component within the cylinder is difficult to determine with this method, the consistency of the readings for all cylinders is an indication of the condition of the engine as a whole. The following are suggested guidelines for performing a direct compression test.
(1) Thoroughly warm up the engine to operating temperatures and perform the test as soon as possible after shutdown.
(2) Remove the most accessible spark plug from each cylinder.
(3) Rotate the engine with the starter to expel any excess oil or loose carbon in the cylinders.
(4) If a complete set of compression testers is available, install one tester in each cylinder;
however, if only one tester is being used, check each cylinder in turn.
(5) Rotate the engine at least three complete revolutions using the engine starter and record the compression reading.
NOTE: It is recommended that an external power source be used, If possible, as a low battery will result in a slow engine-turning rate and lower readings. This will noticeably affect the validity of the second engine test on a twin-engine aircraft.
(6) Recheck any cylinder which shows an abnormal reading when compared with the others. Any cylinder having a reading approximately 15 p.s.i. lower than the others should be suspected of being defective.
(7) If a compression tester is suspected of being defective, replace it with one known to be accurate, and recheck the compression of the affected cylinders.
ment .040 orifice diameter,..250 inch long, 60° approach angle.
2. Engines in excess of 1,000 cubic inch displacement .060 orifice diameter, .250 inch long, 60° approach angle.
A typical schematic diagram of the differential pressure tester is shown in figure 14.1.
As the regulated air pressure is applied to one side of the restrictor orifice with the air valve closed, there will be no leakage on the other side of the orifice and both pressure gauges will read the same. However, when the air valve is opened and leakage through the cylinder increases, the cylinder pressure gauge will record a proportionally lower reading.
(1) Performing the Check, The following procedures are listed to outline the principles in-
CYLINDER
ADAPTER AIR VALVE
CYLINDER
PRESSURE GUAGE
RESTRICTOR CYLINDER ORFICE
REGULATOR
PRESSURE GUAGE
c. Differential Pressure Compression Check, The differential pressure tester is designed to check the compression of aircraft engines by measur- PRESSURE REGULATOR ing the leakage through the cylinders caused by worn or damaged components. The operation of the compression tester is based on the principle that, for any given airflow through a fixed orifice, a constant pressure drop across that orifice will result. The restrictor orifice dimensions in the differential pressure tester COMPRESSED should be sized for the particular engine as fol- AIR SOURCE lows: FIGURE 14.1.-Schematic of typical differential pres-
1. Engines up to 1,000 cubic inch displace- eure compression tester.
Chap 14 Par 692
volved, and are intended to supplement the manufacturer's instructions for the particular tester being utilized.
(a) Perform the compression test as soon as possible after the engine is shut down to ensure that the piston rings, cylinder walls, and other engine parts are well lubricated.
(b) Remove the most accessible spark plug from each cylinder.
(c) With the air valve closed, apply an external source of clean air (approximately 100 to 120 p.s.i.) to the tester.
(d) Install an adapter in the spark plug bushing and connect the compression tester to the cylinder.
(e) Adjust the pressure regulator to obtain a reading of 80 p.s.i. on the regulator pressure gauge. At this time, the cylinder pressure gauge should also register 80 p.s.i.
(f) Turn the crankshaft by hand in the direction of rotation until the piston (in the cylinder being checked) is coming up on its compression stroke. Slowly open the air valve and pressurize the cylinder to approximately 20 p.s.i.
CAUTION Care must be exercised in opening the air valve since sufficient air pressure will have built up in the cylinder to cause it to rotate the crankshaft if the piston is not at TDC.
Continue rotating the engine against this pres- (TDC). Reaching TDC is indicated by a flat spot or sudden decrease in force required to tated too far, back up at least one-half revolution and start over again to eliminate the effect of backlash in the valve operating mechanism and to keep piston rings seated on the lower ring lands.
(g) Open the air valve completely. Check the regulated pressure and adjust, if necessary, to 80 p.s.i.
(h) Observe the pressure indication on the cylinder pressure gauge. The difference between this pressure and the pressure shown by the regulator pressure gauge is the amount of leakage through the cylinder. A loss in excess of 25 percent of the input air pressure is cause to suspect the cylinder of being defective; how- Par 692 AC 43.13-TA 1972 ever, recheck the readings after operating the engine for at least 8 minutes to allow for sealing of the rings with oil.
i) If leakage is still occurring after a recheck, it may be possible to correct a low reading. This is accomplished by placing a fiber drift on the rocker arm directly over the valve stem and tapping the drift several times with a hammer to dislodge any foreign material between the valve face and seat.
NoTE: When correcting a low reading in this manner, rotate the propeller so the piston will not be at TDC.
This is necessary to prevent the valve from striking the top of the piston in some engines. Rotate the engine before rechecking compression to reseat the valves in the normal manner,
693. SPARK PLUGS. The spark plug provides the high voltage electrical spark to ignite the fuel/air mixture in the cylinder. The types of spark plugs used in different engines will vary in regard to heat range, reach, thread size and other characteristics required by the particular installation.
a. Heat Range. The heat range of a spark plug is a measure of its ability to transfer heat to the cylinder head. The plug must operate hot enough to burn off the residue deposits which can cause fouling, yet remain cool enough to prevent a preignition condition from occurring.
The length of the nose core is the principal factor in establishing the plug's heat range.
"Hot" plugs have a long insulator nose thereby creating a long heat transfer path, whereas "cold" plugs have a relatively short insulator to provide a rapid transfer of heat to the cylinder head. (See figure 14.2.)
HOT COLD FIGURE 14.2.-Spark plug heat ranges.
Chap 14