Chap 12 1972 AC 43.13-1A
REFERENCE EDGE OF TEMPLATE,
PENCIL LINE DRAWN ON BLADE AT
SELECTED STATION FOR TEMPLATE
OUTLINE OF NEW REFERENCE TIP.
PLAN VIEW OF BLADE WITH DAMAGED TIP.
SHEET ALUMINUM LEADING EDGE
TIP TEMPLATE, ALLI
BLADES ON THE SAME
PROPELLER MUST BE
SHORTENED EXACTLY THE SAME.
ENLARGED SIDE VIEW OF TIP OF BLADE
•DOTTED LINE SHOWS SIDE VIEW OF NEW TIP AFTER CUTTING DOWN.
FIGURE 12.5.—Method of repairing damaged tip of aluminum alloy propellers.
Page 228 AC 43.13-1A 1972
ANGLE OF BEND
THICKNESS OF BLADE MEASURE AT A POINT OF TANGENCY TAKEN ONE INCH EACH SIDE C.L. OF BEND FIGURE 12.6.-Protractor and method of measuring angle of bend in aluminum alloy propellers.
Par 585 Chap 12
AC 43.13-1A 1972 with it and keep such sets of blades together (see figure 12.5 for acceptable methods). Mark the shortened blades to correspond with the manufacturer's system of model designation to indicate propeller diameter. In making the repair, it is not permissible to reduce the propeller diameter below the minimum diameter limit shown on the pertinent airplane specification.
c. Straightening Propeller Blades. Repair bent blades in accordance with the manufacturer's instructions. Carefully check the extent of a bend in face alinement by means of a protractor similar to the one illustrated in figure 12.6.
Only bends not exceeding 20° at 0.15-inch blade thickness to 0 degrees at 1.1-inch blade thickness may be cold straightened. Straighten blades with bends exceeding these values only upon recommendation of the manufacturer, and only at facilities having proper heat-treatment equipment. In all cases, inspect the blades (as discussed in paragraph 605) for cracks and other injuries both before and after straightening.
586. REPAIR TOLERANCES. The following tolerances are those listed in the blade manufacturing specification for aluminum alloy blades and govern the width and thickness of new blades.
These tolerances are to be used with the pertinent blade drawing to determine the minimum original blade dimensions to which the reduction of figure 12.4 may be applied. When repairs reduce the width or thickness of the blade below these limits, reject the blade. The face alignment or track of the propeller should fall within the limits recommended by the manufacturer for new propellers.
Basic diameter less than 10 feet 6 inches:
Blade width-from shank to 24-inch station + 3/64 from 24-inch station to tip $ 1/82 Blade thickness + 0.025 Basic diameter 10 feet 6 inches to less than 14 feet 0 inches:
Blade width-from shank to 24-inch station ÷ 1/16 Chap 12 Page 229 from 30-inch station to tip ÷ 1/82 Blade thickness--from shank to 24-inch station .. ...- $ 0.030 from 80-inch station to tip ‡ 0.025 Basic diameter 14 feet 0 inches and over:
Blade width-from shank to 30-inch station - ÷ 8/82 from 86-inch station to tip .. ‡ 1/16 Blade thickness-from shank to 80-inch station . + 0.040 from 86-inch station to tip .. . ... +0.085
a. No repairs are permitted to the shanks (roots or hub ends) of aluminum alloy adjustable pitch blades. The shanks must be within manufacturer's tolerances.
587. PROPELLER BALANCE. Upon completion of repairs, check horizontal and vertical balance and correct any unbalance as recommended by the manufacturer. A coaxial hole is drilled in the butt end of certain aluminum alloy detachable blades for the application of lead to obtain static horizontal balance. The size of this hole must not be increased by the repair agency.
To effect vertical balance, follow the manufacturer's specific instructions. The outside of an eccentric hole must not be closer than 1/4 inch to the nearest external blade surface. As an alternate to drilling the two holes mentioned above, the manufacturer may have drilled a single eccentric hole having a diameter and depth conforming to the eccentric hole dimensions given in the table for application of lead. The outer edge of the hole must not be closer than 1 inch to the nearest external blade surface. Finish the ends of all balancing holes with a full sized drill having a spherical end to eliminate sharp corners. Remove the sharp edges of all holes by a 1/32-inch chamfer. The following table is included for inspection information only:
Par 585
Page 230 AC 43.13-1A 1972 Size and depth of balancing holes. be used: (1) safety bolt and castellated nut, Shank centrie hole Max. con- contrle hole max. con- hole depth die. Max. eccentric (2) safety bolt (drilled head) and threaded bushing, or (3) undrilled bolt and self-locking size diameter depth inch max.
(inch) (inches) (inches) nut. Where it is desirable to use oversized 00 2% 2¼ bolts, obtain suitable aircraft standard bolts 0-V2 1/32 8% 1/16 inch larger than the original bolts. En- 1 1¾o 8 % 4¾ 4 % 4½ large the crankshaft propeller flange holes and the propeller hub holes sufficiently to accomo- 2 date the new bolts without more than 0.005- 81⅓2 6 inch clearance. Such reboring will be permitted only once. Further repairs of boltholes may be steel hubs and parts must be accomplished only 588. STEEL HUBS AND HUB PARTS. Repairs to in accordance with the methods (A) or (B) of figure 12.7.
in accordance with the manufacturer's recom- NoTe: Methods (A) or (B) are preferred over the mendations. Welding and remachining is per- oversized bolt method, because a propeller hub flange missible only when covered by manufacturer's service bulletins. redrilled in accordance with this latter method will alwavs require the redrilling of all new propellers subsequently used with the redrilled fiange.
589. PROPELLER HUB AND FLANGE REPAIR.
When the propeller boltholes in a hub or crankshaft flange for fixed-pitch propellers become damaged or oversized, it is permissible to make repairs by methods (A) or (B) in figure
12.7, or by use of aircraft standard bolts 1/16 inch larger than the original bolts. Make the repairs in accordance with the recommendations of the propeller metal hub manufacturer or the engine manufacturer as applicable. Obtain from the engine or propeller hub manufacturer suitable flange bushings with threaded or smooth bores, as illustrated in methods (A) or (B) of figure 12.7. Drill the flange and insert the bushings as recommended by the engine manufacturer. Drill the rear face of the propeller to accommodate the bushings, and protect the holes with 2 coats of aluminum paint or other high moisture-resistant coating.
Use bolts of the same size as those originally used. Any of the following combinations may
590. CONTROL SYSTEMS. Components used to control the operation of certificated propellers should be inspected, repaired, assembled, and/or tested in accordance with the manufacturer's recommendations. Only those repairs which are covered by the manufacturer's recommendations should be made, and only those replacement parts which are approved under FAR Part 21 should be used.
591, DEICING SYSTEMS. Components used in propeller deicing systems should be inspected, repaired, assembled, and/or tested in accordance with the manufacturer's recommendations. Only those repairs which are covered by the manufacturer's recommendations should be made, and only those replacement parts which are approved under FAR Part 21 should be
592.-602. RESERVED.
Par 587 Chap 12
AC 43.13-1A Page 177 1972 FrOURE 11.1.-Wire and circult protector chart. (a) High In-rush. Circuits containing incandescent lamps can draw an initial current which is 16 times greater than the continuous sauge copper Wire AN breaker amp. Circuit Fuse amp. current. Contact burning or welding may occur when switch is closed.
22 (b) Inductive. Magnetic energy stored in
7.5 solenoid coils or relays is released when the 10 control switch is opened and may appear as an 16 14 12 25 (80) 20 arc. (c) Motors. Direct current motors will 10 85 (40) draw several times their rated current during 8 50 starting, and magnetic energy stored in their 80 armature and field coils is released when the 100 control switch is opened.
125 1 (2) Switch Selection. Figure 11.2 provides 150 an approximate method for selecting the prop- Figures in parentheses may be substituted where protectors of the indicated rating are not available.
Basis of chart:
(1) Wire bundles in 185° F. ambient and altitudes up to 80,000 feet.
(2) Wire bundles of 15 or more wires, with wires carrying no more than 20 percent of the total currentcarrying capacity of the bundle as given in Specification MIL-W-5088 (A8G).
(8) Protectors in 75° to 85° P. amblent.
(4) Copper wire Specification MIL-W-5088 (A8G) or equivalent.
er nominal switch rating when the continuous load current is known. The procedure is essentially a derating to obtain reasonable switch efficiency and service life.
(3) Switch Installation. Hazardous errors in switch operation may be avoided by logical and consistent installation. Mount "on-off" two position switches so that the "on" position is reached by an upward or forward movement of the toggle. When the switch controls movable aircraft elements, such as landing gear or
(5) Circuit breakers to Specification MIL-C-6809 or FIOURE 11.2.-Switch derating factors.
equivalent.
(6) Fuses to Specification MIL-F-15160 or equivalent.
Nominal system Derating voltage Type of load factor malfunction can be hazardous, use a switch specifically designed for aircraft service. These 24 V.D.C. Lamp switches are of rugged construction and have sufficient contact capacity to break, make, and 24 V.D.C. 24 V.D.C. Inductive Relative (Beater) (Relay-Bolenold) 2 carry continuously the connected load current. 24 V.D.O. Motor 8 Snap-action design is generally preferred to 12 V.D.C. Lamp obtain rapid opening and closing of contacts ir- 12 V.D.O. Inductive respective of the speed of the operating toggle or plunger, thereby minimizing contact arcing. 12 V.D:C. 12 V.D.C. Motor Reslstive (Heater) (Relay-Solenold) 2 1 2
b. Switch Ratings.
(1) Nominal Rating. The nominal current rating of the conventional aircraft switch is usually stamped on the switch housing and represents the continuous current rating with the contacts closed. Derate switches from their nominal current rating for the following types of circuits:
NOTES :
1. To find the nominal rating of a switch to operate a given device, multiply the continuous load current required by the device by the derating factor corresponding to the voltage and type of load.
2. To find the continuous load current that a switch of a given nominal rating will handle efficiently, divide the switch nominal rating by the derating factor corresponding to the voltage and type of load.
Chap 11 Par 430
flaps, the toggle should move in the same direction as the desired motion. Inadvertent operation of switches can be prevented by mounting suitable guards over the switches.
(4) Relays, Relays are used as a switching device where a weight reduction can be achieved, or to simplify electrical controls. It Par 430 AC 43.13-18 1972 should be remembered that the relay is an electrically operated switch, and therefore subject to dropout under low system voltage conditions. Concerning contact ratings, the discussion of switch ratings in paragraph 480b (1) is generally applicable to relays,
431.-441. RESERVED.
Chap 11
WOOD HUB OF PROPELLER WOOD HUB OF PROPELLER {2) (1) 0 = 1/4" LARGER
THAN BOLT SIZE
METHOD (A) METHOD (B)
REPAIR OF DAMAGED OR ELONGATED BOLTHOLES IN REPAIR OF ELONGATED BOLTHOLES PROPELLER HUB FLANGES. IN PROPELLER.
(I) DRILLED BOLT WITH CASTELATED NUT OR UNDRILLED BOLT WITH SELF- LOCKING NUT.
(2) BOLT WITH HEAD DRILLED FOR SAFETY WIRING.
NOTE: PROPELLER HUS THESE REPAIRS ARE PERMITTED ONLY ON THE DRIVING FLANGE OF THE PROPELLER HUB AND THE ADJACENT FACE OF THE PROPELLER.
FIGURE 12.7.-Repair of fixed-pitch hub and propeller with elongated or damaged boltholes.
Page 332 AC 43.13-1A 1972 Section 4. OVERHAUL OF PROPELLERS 603, HUB AND HUB PARTS. Disassemble propellers submitted for overhaul and clean all hub parts in accordance with the manufacturer's recommendations. Make an inspection of the parts to determine that the critical dimensions are within the manufacturer's specified tolerances. Take particular care to check the 90° relation between shaft bore and blade socket centerline and track of the blade sockets, as these are the dimensions which are most likely to be affected by accidents. Reject and replace any hub which is sprung, worn, or damaged.
Stress risers such as cuts, nicks, or tool marks must be carefully stoned or the part rejected Carefully inspect splines and cone seats for signs of wear, and check splines with a single key "no-go" gauge made to plus 0.002 inch of the base drawing dimensions for spline land width. If the gauge enters more than 20 percent of the spline area, reject the hub. Cones and cone seats may show discoloration, pitting, and corrosion. Generally, corrosion and discolored spots may be removed by light lapping.
Pitting is not grounds for rejection, if 75 percent of the bearing area is not affected and the pitted areas are well dispersed about the cone bearing area. After cleaning, minutely inspect steel hubs and parts for cracks by the wet or dry magnetic particle method at every major overhaul period. It is not necessary to remove the plating or special external finish for this inspection unless so specified in the manufacturer's recommended practice.
Steel hubs which adapt fixed-pitch propellers to all taper crankshafts are susceptible to cracks along the keyway which often extend into the flange lightening holes. Carefully inspect these hubs by the magnetic particle method at engine overhaul periods. Any crack is cause for rejection.
604. PLATING FOR HUBS AND PARTS. Replate hubs and parts from which the plating has been removed after they have been satisfactorily inspected. All replating must be of the same material as the original plating and be done in accordance with the manufacturer's recommendations. Chrome or nickel plating is not an acceptable substitute for cadmium or zinc plating. The use of zinc chromate primer on the external surfaces followed by a coating of aluminum lacquer in lieu of cadmium plating is considered acceptable where recommended by the manufacturer. However, this type of finish will require replacement more frequently than cadmium plating.
605. INSPECTION OF ALUMINUM PROPELLERS AND BLADES. Carefully inspect aluminum propellers and blades for cracks and other injuries. A transverse (chordwise) crack or flaw of any size is cause for rejection. Refer any unusual condition or appearance revealed by these inspections to the manufacturer. Acceptable inspection methods are the acid-etching process, the anodizing process, the fluorescent penetrant process, or the dye penetrant process.
Where applicable, supplement one process with another. Etching is accomplished by immersing the blade in a warm 20 percent caustic soda solution and cleaning with a warm 20 percent nitric acid solution, with a warm water rinse between the caustic bath and the acid bath, and also a warm water rinse following the acid bath. Remove all effects of the etching by polishing. Maintain the caustic and acid solution at a temperature of from 160° F. to 180° F. Some blades incorporate parts made of steel and other materials, and the caustic soda and the nitric acid must not be allowed to come in contact with these parts. The blade surfaces are then examined with a magnifying glass of at least three-power. A crack will appear as a distinct black line. The fluorescent penetrant method is recommended as a supplement to the caustic etch for the inspection of Par 603 Chap 12
AC 43.13-1A 1972 the shanks (roots or hub ends) of adjustable pitch blades.
a. Suspected cracks or defects should be repeatedly local etched until their nature is determined. With a No. 00 sandpaper, or fine crocus cloth, clean and smooth the area containing the apparent crack. Apply a small quantity of caustic solution to the suspected area with a swab or brush. After the area is well darkened, thoroughly wipe it with a clean (dampened) cloth. Too much water may entirely remove the solution from a crack and spoil the test. If a crack, extending into the metal exists, it will appear as a dark line or mark, and by using a magnifying glass, small bubbles may be seen forming in the line or mark. Immediately upon completion of the final checks, remove all traces of the caustic solution by use of the nitric acid solution. Wash the blade thoroughly with clean (fresh) water.
b. The chromic acid anodizing process is superior to caustic etching for the detection of cracks and flaws and should therefore be used, whenever it is available, for general inspection of blades, for material defects, and for final checking of repairs performed during overhaul. Immerse the blades in the anodizing bath as far as possible, but all parts not made of Chap 12 Page 233 aluminum alloy must be kept out of the chromic acid bath or be separated from the blade by nonconductive wedges or hooks. Follow the anodizing treatment by a rinse in clear, cold, running water from 8 to 5 minutes, and dry the blades as quickly as possible, preferably with an air blast. Allow the dried blades to stand for at least 15 minutes before examination. Flaws (cold shuts or inclusions) will appear as fine black lines. Cracks will appear as brown stains caused by chromic acid bleeding out onto the surface. The blades may be sealed for improved corrosion resistance by immersing them in hot water (180° F. to 212° F.) for one-half hour. In no case, immerse the blades in hot water before the examination for cracks, since heat expands cracks and allows the chromic acid to be washed away.
606. ASSEMBLY. Accomplish the assembly of the propeller hub and blade in accordance with the manufacturer's recommendations. Replace clevis pins, bolts, and nuts which show wear or distortion. Never use cotter pins and safety wire a second time. The use of self-locking nuts is permissible only where originally used or approved by the manufacturer.
607-617. RESERVED.
Par 605
Page 224 AC 43.72-1A 1972 Section 5. ASSEMBLY OF PROPELLER TO ENGINE
618. FIXED-PITCH PROPELLERS. Loose hub bolts and bolts installed through the lightening holes in the integral hub flange of certain engine crankshafts cause the majority of the serious difficultles experienced with fixed-pitch propellers. Either of the conditions, if not corrected, will ultimately cause the loss of the propeller.
o. Loose hub bolts cause elongated boltholes and damage to the hub bolts. When not corrected, the bolts break off, or friction causes enough heat to affect the glue and chars the wood. After successive running, checks start at the boltholes. These checks are caused, or at least accentuated, by shrinkage of the wood due to the excessive heat generated. If allowed to progress, the propeller usually flies apart or catches on fire.
b. On some engines equipped with a crankshaft having an integral propeller hub flange, the outer edge of the lightening holes are at the same radius as the corresponding edge of the propeller hub boltholes. When inserting the bolts through the propeller, care must be exercised so that the bolts are inserted through the proper holes in the flange. Cases have been reported where the bolts were inserted through the larger lightening holes and, accordingly, the bolt nuts bore only on the outer edges of the lightening holes. In such cases, continuous running of the propeller may cause the boltheads or nuts to slip off the flange and through the large openings in the flange, resulting in the subsequent loss of the propeller.
c. Both the conditions discussed above are very easy to detect, and must be corrected immediately. In case the hub flange is integral with the crankshaft, frst ascertain the bolts are properly installed, then make the inspection for bolt tightness in the same manner as for any other propeller hub. Use an open-end wrench to determine hub bolt tightness; and, if the nuts can be turned, remove the cotter keys and retorque the nuts to the desired setting.
Tighten hub bolts, preferably with a torque wrench, to the recommended values which usually range from 15 to 24 foot-pounds. If no torque wrench is available, an ordinary socket wrench may be used. This socket wrench should have a 1-foot extension lever and the wrench pulled up with the recommended force 12 inches away from the center of the bolt which is being tightened. The tightening is best accomplished by tightening each bolt a litthe at a time, being sure to tighten alternate bolts which are diametrically opposite. Exercise care not to overtighten the hub bolts, thereby damaging the wood underneath the hub flanges. Avoid the practice of overtightening bolts to draw a propeller into track. Safety the nuts by means of cotter keys of proper size or heavy safety wire twisted between each nut.
A continuous length of single safety wire is not acceptable, as wire failure will result in all nuts becoming unsafetied.
619,-629. RESERVED.
Par 618 Chap 12
AC 43.13-18 Page 233 1972 Section 6. PRECAUTIONS
630. BLADE-TIP IDENTIFICATION. Many persons have been fatally injured walking into whirling propellers. Painting a warning strip on the propeller serves to reduce chances of such injuries. Cover approximately 4 inches of the propeller tips on both sides with an orange-yellow nonreflecting paint or lacquer. Open the drain holes in the metal tipping of wood blades after the tips have been painted.
631. GROUND-HANDLING PRACTICES, Wood propellers are especially susceptible to damage from improper handling. When moving an airplane, avoid bumping the propeller. The practice of pushing or pulling on a propeller blade to move an airplane should be avoided; it is extremely easy to impose forces on a blade in excess of those for which the blade is designed. It is continually necessary to ascertain that the glue joints are in good condition, and that the finish on the entire propeller will protect the propeller from absorbing moisture. Place twobladed wood propellers, whether on or off an airplane, in a horizontal position to prevent unbalance from moisture absorption. A good precaution is to cover the propeller with a well-fitted waterproof cover when not in use.
It is very important to protect the shank section of wood blades from moisture changes to prevent swelling and subsequent loosening in the metal sleeve. In the case of varnished blades, it is advisable to occasiona ly apply varnish around the shank at the junction or wood and metal. In the case of the plastic-covered blade, repair cement may be applied around the same joint.
632. COMPOSITION PROPELLER SERVICE LIMITS.
In certain cases where the blade has been manufactured from laminated planks of composition material, longitudinal cracks or splitting between laminations have been observed after several hundred hours of operation. Do not permit these cracks to progress beyond the limits established by the manufacturer.
633.-643. RESERVED.
Chap 12 Par 630
Page 236 AC 43.13-1A 1972 Section 7. MAINTENANCE OF ROTOR BLADES
644. GENERAL. The design, materials, construction, and performance requirements for rotorcraft main and tail rotor blades vary considerably from those used in the manufacture and operation of airplane propellers. Major dissimilarities also exist among the blades fabricated for the various makes and models of rotorcraft currently in operation. For these reasons, it is of utmost importance that the specific maintenance requirements of each rotorcraft manufacturer be consulted prior to performing any maintenance. In all instances, the restoration of blades will be determined by the repair limitations provided in the blade manufacturer's current service and maintenance manual data.
The information in this section may serve as a general guide for maintaining the airworthiness of rotorcraft blades.
a. Leading Edge Strip. Examine leading edge abrasion strips (A in figures 12.8, 12.9 and
12.10) for nicks, cuts, gouges, or worn spots resulting from abrasion. Damage of this type can usually be considered minor provided the injuries are not concentrated in one area, do a fed tho not penetrate the strip, or do not affect the aerodynamic performance of the blade.
rations or edge voids (B in Figure 12.8) are es- a pid by The limits for leading edge strip bond sepatablished by the blade manufacturer. When a separation is suspected, carefully examine the blade assembly and determine whether it is within the manufacturer's tolerances for continued operation. If it is permissible for the blade to remain in service, recheck that blade area at frequent intervals thereafter to assure that the separation is not progressing beyond allowable limits.
Inspect the rotor blade for evidence of paint deterioration in the area where the aft edge of the leading edge metal strip terminates. If the surface of the paint in this area is cracked, blistered, or missing, carefully examine the metal surface of the blade for evidence of electrolytic corrosion or pitting (C in Figure 12.8).
Treat minor cases of localized corrosion promptly by cleaning and coating the area with a preservative that will arrest further surface deterioration until the blade can be completely refinished. When the area of corrosion appears to be extensive or pitting is deep, remove the blade for complete evaluation of the damage.
b. Blade Surface. Examine the blade upper and lower surfaces between the leading edge strip and the trailing edge for evidence of cracks (B in figures 12.9 and 12.10). Cracks of any magnitude in this area are cause for blade removal if allowable crack limitations are not prescribed by the blade manufacturer.
Trailing edge cracks in blades having bonded trailing edges are also cause for removing the blade for service. Blades incorporating rivets along the trailing edge that have cracks at the edge (C in figures 12.9 and 12.10) which terminate at a rivet hole or cracks that extend between two adjacent rivets (D in figures 12.9 and 12.10) are not permissible and the blade should be removed from further service until repairs are made.
Inspect the adhesive bonding at the blade root end doublers (E in figures 12.9 and
12.10), skin to spar joint (A in figure 12.11), and the trailing edge (C in figure 12.11) for evidence of bond separation. This may initially appear as a hairline crack and any indication of a separation is cause for removing the blade from service to thoroughly examine and evaluate the condition prior to attempting repair.
Check the entire bonded (honeycomb core) area of the blade for evidence of bond separations or voids (B in figure 12.11). In many instances these can be detected by a difference in sound heard while the surface of the blade is being tapped with a light object such as a coin.
A dull or dead sound is indicative of a void or separation. The acceptability of voids or sepa- Par 644 Chap 12