AC 43.13-1A Page 215 1972 Section 2. REPAIR OF WOOD AND COMPOSITION PROPELLERS
567. GENERAL. Repair propellers in accordance with the best accepted practices and the latest techniques. Manufacturer's recommendations should in all cases be followed. It is necessary to mark the name of the manufacturer and model designation on the repaired propeller in the event original markings were removed during the repair or refiniahing operations.
filler and will not induce failure, may be filled with a mixture of glue and clean fine sawdust thoroughly worked and packed into the defect, dried, and then sanded smooth and flush with the surface of the propeller. It is very important that all loose or foreign matter be removed from the place to be filled so that a good bond of the glue to the wood is obtained.
568. REPAIR OF WOOD PROPELLERS. Carefully examine wood propellers and blades requiring repair to be sure that they can be restored to their original airworthy condition. Refer doubtful cases to the manufacturer. Carefully evaluate propellers damaged to the following extent prior to attempting a repair:
A crack or deep cut across the grain of the wood.
Split blades.
Separated laminations, except the outside laminations of fixed-pitch propellers.
More screw or rivet holes, including holes filled with dowels, than used to attach the metal leading edge strip and tip.
An appreciable warp.
An appreciable portion of wood missing.
A crack, cut, or damage to the metal shank or sleeve of blades.
Broken lag screws which attach the metal sleeve to the blade.
Oversize shaft hole in fixed-pitch propellers.
Cracks between the shaft hole and boltholes.
Cracked internal laminations.
Excessively elongated boltholes.
a. Fill small cracks parallel to the grain with glue, thoroughly worked into all portions of the cracks, dried, and then sanded smooth and flush with the surface of the propeller. This also applies to small cuts. Dents or scars which have rough surfaces, or shapes that will hold a
b. Blade Inlays. Inlays shown in figure 12.1 may be used. Make inlays of the same wood as the propeller blade; i.e., inlay a yellow birch propeller with yellow birch, not with white birch, and as near the same specific gravity as possible. Make repair joints to conform with figure 12.1 for taper of 10:1 from deepest point to feather edge or end of inlay. Measurements are taken along a straight line parallel to the grain or general slope of the surface on thrust and camber face. This rule applies also to the edge repairs. Extend grain of inlays in the same direction as the grain of the propeller laminations. Make inlays using a fishmouth, scarf, or butt joint. The permanency of the joint is in the order named, the fishmouth being preferable. Dovetail-type inlays should not be used. Do not exceed 1 large, 2 medium, or 4 small widely separated inlays per blade.
Do not overlap a trailing and a leading edge inlay more than 25 percent, as shown in figure
12.1A. Propeller blades of a thickness ratio of 12 or more may be repaired, provided the cross-grained cut does not exceed 20 percent of the chord in length and the depth of cuts does not exceed 1/8 the blade thickness at the deepest point of damage. Blades with airfoil sections less than .12 thickness ratio may be repaired if the maximum depth of damage does not exceed 1/20 of the blade section thickness at the deepest point of damage. To determine the thickness ratio for a propeller blade, divide the maximum thickness of the airfoil section by the blade chord at the 8/4 radius station.
Chap 12 Par 567
Page 216 AC 43.13-1A 1972 Example 1.
Given 6" Chord .72 Maximum thickness of airfoil section Computation .72 + 6 = .12 thickness ratio Example shows the blade thickness ratio to be 12; therefore, an inlay ⅛ of blade thickness at the point of damage may be inserted.
Example 2.
Given 4" Chord „36 Maximum thickness of airfoil section Computation .36 + 4 = .09 thickness ratio Example shows blade thickness ratio to be less than .12; therefore, an inlay 1/20 the blade thickness at the point of damage may be in-
fixed-pitched propellers which would exceed in depth a value greater than 5 percent of the difference between the hub and bore diameters are not acceptable. In the portion of the blade where it fairs into the hub, allowable depths for inlays are dependent upon the general proportions. Where the width and thickness are both very large in proportion to the hub and blade, maximum inlay depths of 71/2 percent of the section thickness at the inlay are permissible. Where the width and thickness are excessively small, maximum inlay depths of 21/2 percent of the section thickness at the center of the inlay are permissible; for propellers over 50 horsepower, cuts 2 1/2 percent deep may be filled with glue and sawdust, while for propellers under 50 horsepower, cuts 5 percent deep may be filled with glue and sawdust.
e. Propeller Tip Repairs. In order to replace the wood worn away at the end of the metal tipping, remove enough of the metal to make the minimum repair taper 10:1 each way from the deepest point. Due to the convex leading edge of the average propeller, this taper usually works out 8:1. Repairs under the metal tipping must not exceed 71/2 percent of the chord for butt or scarf joints, and 10 percent for fishmouth joints, with 8/4 inch maximum depth for any repair. Methods of repairing or replacing propeller blade metal caps or leading edge strips are contained in paragraph 569.
The scarfing of wood tips onto a propeller blade to replace a damaged tip is not considered an acceptable repair. The success of this type of repair is fully dependent upon the strength and quality of the glue joint. Since it is difficult to apply pressure evenly over the glue area, and since no satisfactory means are available for testing the strength of such jointa, it is quite possible for defective glue joints to exist and remain undected until failure occurs.
f. Lamination Repairs. Whenever the glue joint of an outside lamination of fixed-pitch propellers is open, repair the propeller by removing the loose lamination and gluing on a new lamination of kiln dried wood of the same kind as the original lamination. It is not usually economical to attempt to repair separations between other laminations. Repair outside laminations, which have been crushed at the hub due to excessive drawing up of hub bolts, by planing and sanding one hub face smooth, removing a lamination on the other hub face and replacing it with a new lamination, thus building the hub thickness up to the original thickness. It is permissible to replace both outer laminations if necessary and feasible.
d. Blade Profiling. Narrow slivers up to 1/8 inch wide broken from the trailing edge at the wider portions of the blade may be repaired by sandpapering a new trailing edge, removing the least material possible, and fairing in a new trailing edge of smooth contour. Narrow both blades by the same amount. Near the hub or tip, use an inlay which does not exceed, at its greatest depth, 5 percent of the chord.
g. Repair of Elongated Boltholes. It is permissible to repair elongated boltholes by the insertion of a steel bushing around each bolt, as illustrated in figure 12.7. Machine the inside diameter of the bushing to fit the bolt snugly, and the outside diameter approximately 1/4 inch larger than the bolt size. Make the bushing approximately 1/2 inch long. Drill the face of the hub with a hole concentric with the bolt- Par 568 Chap 12
AC 43.13-1A Page 217 1972 NOTES:
IF INLAYS OVERLAP
LENGTHWISE, DEPTH
OF EACH IS LIM- ITED TO 1/10 THICK-
OUTLINE NESS AT DEEPEST OF INLAY MAX. LENGTH POINT OF DAMAGE.
INLAY MATERIAL
SHOULD BE THE SAME
CHECK- AS THE PROPELLER OR CRACK LAMINATIONS.
TRAILING EDGE OUTLINE OF INLAY- 10 k LEADING EDGE DAMAGE
• (CHORD AT CENTER OF REPAIR) THICKNESS AT MAX.
20 % b
DEPTH OF DAMAGE MAX. DAMAGE -INLAY REPAIR k = MAX. DEPTH OF DAMAGE m = 1/20 TO 1/8 † + • THICKNESS AT DEEPEST• MAX. DEPTH OF
POINT OF DAMAGE DAMAGE (SEE TEXT) FIGURE 12.1.-Propeller repair by addition of small inlay. (See continuation.)
Chap 12 Par 568
Page 218 AC 43.13-1A 1972 NOTES:
MAXIMUM LENGTH INLAY MATERIAL SHOULD BE
THE SAME AS PROPELLER
LAMINATIONS 2 b
OUTLINE OF DAMAGE INLAY TRAILING EDGE 10 a MAX. 25% OVERLAP OUTLINE OF 10 ₫ MAXIMUM LEADING EDGE
MAXIMUM DAMAGE- INLAY- 10 ₫ MAXIMUM
- D (CHORD AT GENTER OF REPAIR) -INLAY INLAY- FIOURE 12.1A.-Propeller repair by addition of small inlay-continued.
Par 368 Chap 12
AC 49.13-1A Page 399 1972 7 1/2 % D MAXIMUM FOR BUTT OR SOARF JOINT 10 % D MAXIMUM FOR FISHMOUTH JONT 5%% MAXIMUM FOR ALL JOINTS
BUTT JOINTS b (CHORD AT OENTER OF REPAIR)
SCARF JOINTS
TRAILING EDGE SCARF JOINTS LEADING EDGE
FISHMOUTH JOINTS FIGURE 12.1B-Propeller repair by addition of small inlay-continued.
Chap 12 Pur 368
hole and only to a sufficient depth to accommodate the bushing so that it does not protrude above the surface of the wood hub. Do not drive the bushing into the hub. Fit the bushing into the hole in the hub with a clearance not exceeding .006 inch after moistureproofing.
Protect the bushing hole from moisture by two coats of aluminum paint, varnish, glue, or other moisture-resistant coating.
h. Repair of Plastic Covered Propellers and Blades. Repair small cracks, dents, scratches, and cuts in the plastic of plastic-covered wood propellers and blades by using special repair cement supplied by the manufacturer, Instructions accompany the cements. Polishes and cleaners are available for preserving the gloss finish of varnished or plastic-covered propellers and blades.
569. REPAIR OF COMPOSITION BLADE, Repair composition blades in accordance with the manufacturer's instructions. For repairs to the metal cap and leading edge strip, the methods and procedures discussed in the following paragraphs may be followed:
a. Replace fabric used to strengthen the tips of wood blades when it becomes loose or worn through. Launder the fabric (mercerized cotton airplane cloth) to remove all sizing. Cut a piece of fabric to approximate size required to cover both faces of outer portion of blade. Recover the same portion that the original fabric covered. Apply glue to the wood where the fabric is to be put, using a rather thick solution of the glue. Use resorcinol glue when the temperature of the workroom can be kept above 21° C. (70° F.). Put the fabric on glued surface, starting at the leading edge of the thrust face, and work toward the trailing edge. Fold the fabric around the trailing edge over the camber face and toward the leading edge. Make a joint on the leading edge where it will be covered by the metal tipping. As the fabric is put on, smooth it out over the wood to prevent air bubbles or uneven gluing. Fabric must be perfectly flat on the blade. Trim excess fabric off with small scissors. Under no circumstances cut or score fabric with a knife. Allow the glue under the fabric to dry about 6 hours, then Par 560 AC 43.13-1A 1972 brush two coats of nitrate dope on the fabric, allowing one-half hour for drying time. Then sand the fabric lightly and brush a coat of pigment dope over it. Lightly sand the uncovered portion of the wood and apply two coats of a good grade of moisture-resistant varnish, allowing 12 to 16 hours drying time between coats.
b. Metal Tip Replacement. Replace tipping when it cannot be properly repaired. Cracks in the narrow necks of metal between pairs of lobes of the tipping are to be expected and are not defects. All other cracka are defects that require repair or elimination by new tipping. If the propeller does not require fabric, apply two coats of varnish to the wood to be covered by the metal tipping. If new fabric has been applied, puncture it with a pointed tool at each screw and rivet hole. Apply varnish, white lead, aluminum paint, etc., to all holes, allowing the wood to absorb as much as it can. With & soft lead pencil, draw guide centerlines on the propeller extending about 4 inches from the centers of old screw and rivet holes. This procedure is followed to insure use of the original screw and rivet holes in the propeller. New holes are not to be drilled. A number of wood propeller tip failures have occurred which have been attributed to the practice of drilling new rivet and/or screw holes in the wood tips when replacing the metal tipping. To avoid continued occurrence of these failures, it is strongly recommended that the manufacturer's procedure be closely adhered to, and any procedure which involves drilling new holes in the wood tip and plugging old holes with dowels is
(1) Obtain new tips and leading-edge strips, cut to size and formed to the approximate shape of the leading edge of the propeller.
These pieces are usually supplied without holes so that the holes can be drilled in them to line up with the old screw and rivet holes in the propeller as stated below. If such material cut to shape is not available, the old tipping can be hammered flat and used as a pattern to lay off a new tip. For this purpose, use a piece of sheet metal of the same material and thickness as the old tip, and remove the burr from the cut edges of this piece.
Chap 12
AC 43.13-1A 1972
(2) Lay the cutout flat metal strip over the leading edge, and proceed to bend this metal down over the leading edge of the propeller, being careful that the metal extends an equal width on thrust and camber faces. This can be done by following the impressions of the old tipping lines. Numerous waves will occur in the metal, but these will be eliminated as the work progresses. Obtain several pieces of strong rubber tape, 4 feet long, 1/2 inch wide, and 1/16 inch thick. While forming the metal, hold it in place on the propeller by wrapping the rubber tape around the blade. Start at the tip and work inboard, being careful not to cover the pencil lines placed on the propeller which show the location of the rivet holes.
While metal is held in place, tap the leading edge with a rawhide or rubber mallet, using moderate force to make sure the metal is seated against the wood along the nose of the leading edge. Smooth the metal by hammering it with the mallet, backing up the opposite side of the blade with a laminated hardwood bucking block having an iron weight built in the center and a piece of leather fastened to the end on which the propeller bears. The block should measure about 2 by 4 inches. Start at the end of the blade and work toward the hub, moving bucking block so that it is always under the section being hammered. Continue to do this until the metal is well shaped to the profile of the propeller. Check to see that the metal has not moved from its original position.
If this happens, remove the rubber tape, reset the metal, and rewrap the rubber tape, thus forming the metal to the leading edge.
(3) With a centerpunch and a hammer, proceed to locate the old screw and rivet holes, using the pencil marks on the blade as a guide.
Punch the metal approximately 1/4 inch from the edge. After all holes have been located, remove the metal from the propeller. Drill screw and rivet holes in the metal with a 1/8-inch drill. File off burrs on the inside of the metal.
Run the drill through the original rivet holes in the propeller in order to clean them. Cut or saw slots in the metal at the original positions.
(Refer to old tipping metal for location of the slots.) Place the metal leading edges on the blades they were formed to fit, and hold them Chap 12 Page 221 in place with rubber tape. With a centerpunch as large as or slightly larger than the diameter of the screw and rivet heads, proceed to punch metal into the original countersunk holes in the wood so that the screw and rivet heads may be entered to the correct depth (not more than 1/82 inch below the surface of the metal).
Use screws and rivets of the appropriate material. Use screws one size larger than were originally in the propeller, and rivets of the solid flat countersunk-head type. Insert screws and rivets in their respective holes, and install rivets with their heads on the thrust face of the propeller. After rivets are tapped in place, cut off the excess length of the rivet, leaving 1/8 inch for heading. End cutters built up with solder to accurately measure this distance are very useful. When an assistant backs up the rivets with a steel bar 18 inches long and pointed to fit the rivet head, hammer the rivets either by hand or with a pneumatic hammer.
Screws may be driven either by hand or with an electric screwdriver.
(4) Cut the metal of the cap tip on the camber face of the propeller to the shape of the propeller tip. Bevel the edge by hand-filing and trim off flat side of metal cap so that it extends about 3/16 inch all around the tip of the propeller. Form a hardwood block to the shape of the propeller tip thrust face. Put metal tipping in place and clamp this block to the underside of the tip with a C-clamp; turn this 8/16 inch of metal up and over the camber face of the tip. Tighten and complete the lap joint.
Mount the propeller blade solidly, with the thrust face up, on a stand supporting the blade at several points along its radius. With a hammer and a flat-faced tool, proceed to smooth the metal, starting at the nose of the leading edge and working toward the edge of the metal until all wrinkles and high spots are removed.
At the edge, use a caulking tool and, in the same manner, press the metal edge tightly against the wood. Turn the propeller over and repeat this operation on the camber face. Make sure that the thin tip is supported at all times when hammering. Apply solder over rivet and screwheads and over the metal seam of the tip of the propeller. Use 50-50 solder in wire form. Use muriatic acid as flux when soldering Par 569
Page 222 АС 43.13-1A 1972 brass. Use stainless steel soldering flux when rected by the the application of finish or solder soldering stainless steel tipping. File excess to the light blade. The light blade may be solder off and check the propeller balance coated with a high grade of primer allowing while doing so. Polish the metal with a fine for a finishing coat. After allowing each coat emery cloth or an abrasive drum driven by a to dry 48 hours, recheck the balance. Then, as flexible shaft. Vent the tipping by drilling may be necessary, either the required amount three holes, No. 60 drill (.040), 3/16 inch deep of finish must be removed by carefully sandin the tip end. Drill ventholes parallel to the papering or applying an additional finishing longitudinal axis of the blade. coat. Recheck the balance and sandpaper or apply additional finish as may be required to
570. REFINISHING. After repairing a blade, it is effect final balancing. Correct vertical unbalusually necessary to refinish it. In some cases it ance in fixed-pitch propellers by applying may be necessary to completely remove the old putty to the light side of the wood hub at a finish. Apply the finish, where necessary, in ac- point on the circumference approximately 90° cordance wih the recommendations of the pro- from the longitudinal centerline of the blades.
peller manufacturer, or with a material which Weigh the putty and prepare a brass plate has satisfactory adhesion and high moisture- weighing slightly more than the putty. The resistant properties. Refinishing of plastic-cov- thickness of the plate should be from 1/16 inch ered blades requires special techniques. Some to 1/8 inch, depending on the final area, and be manufacturers make this information availa- of sufficient size to accommodate the required ble through service bulletins. Refinish or re- number of fathead attaching screws. The plate paint wood blades carefully so that the balance may be made to fit on the hub face or to fit the of the entire propeller is not disturbed. Coating shape of the light side of the wood hub, and one blade heavier than the other will produce drilled and countersunk for the required numunbalance and cause a noticeable vibration ber of screws. Attach the plate and tighten all during flight. of the screws. After the plate is finally attached to the propeller, secure the screws to
571. PROPELLER BALANCING. It is always neces- the plate by soldering the screwheads and resary to check the balance of the propeller after check the propeller balance. All edges of the any repairs or refinishing. Accomplish final plate may be beveled to reduce its weight as balance on a rigid knife-edge balancing stand necessary. The drilling of holes in the proor on a suspension-type balancer in a room free peller and the insertion of lead or other matefrom air currents. There must not be any per- rial to assist in balancing will not be permitsistent tendency to rotate from any position on the balance stand, or to tilt on the suspension balancer. Horizontal unbalance may be cor- 572.-582. RESERVED.
Par 569 Chap 12
AC 43.13-1A Pago 223 1972 Section 3. REPAIR OF METAL PROPELLERS
583. GENERAL, Reject damaged blades with model numbers which are on the manufacturer's list of blades that cannot be repaired.
Follow manufacturer's recommendations in all cases, and make repairs in accordance with latest techniques and best industry practices.
584. STEEL BLADES. Due to the critical effects of surface injuries and their repair on the fatigue life of steel blades, all repairs must be made in accordance with the manufacturer's instructions.
585. ALUMINUM PROPELLER REPAIRS, Aluminum-alloy propellers and blades with dents, cuts, scars, scratches, nicks, leading-edge pitting, etc., may be repaired, provided the removal or treatment does not materially affect the strength, weight, or performance of the blade.
Remove these damages or otherwise treat as explained below unless contrary to manufacturer's instructions or recommendations. More than one injury is not sufficient cause alone for rejection of a blade. A reasonable number of repairs per blade may be made and not necessarily result in a dangerous condition, unless their location with respect to each other is such to form a continuous line of repairs that would materially weaken the blade. Suitable sandpaper or fine-cut files may be used for removing the necessary amount of metal. In each case, the area involved will be smoothly finished with No. 00 sandpaper or crocus cloth, and each blade from which any appreciable amount of metal has been removed will be properly balanced before it is used. Etch suspected cracks and all repairs as discussed in paragraph 605. To avoid removal of an excessive amount of metal, local etching should be accomplished at intervals during the process of removing suspected cracks. Upon completion of the repair, carefully inspect the entire blade by etching or anodizing. Remove all effects of the etching process with fine emery paper. Blades identified by the manufacturer as being coldworked (shot-blasted or cold-rolled) may require peening after repair. Accomplish repair and peening operations on this type of blade in accordance with the manufacturer's instructions. However, it is not permissible in any case to peen down the edges of any injury wherein the operation will lap metal over the
a. Round out nicks, scars, cuis, etc., occurring on the leading edge of aluminum alloy blades as shown in figure 12.2 (view B). Blades that have the leading edges pitted from normal wear in service may be reworked by removing sufficient material to eliminate the pitting. In this case, remove the metal by starting well back from the edge, as shown in figure 12.8, and working forward over the edge in such a way that the contour will remain substantially the same, avoiding abrupt changes in contour or blunt edges. Trailing edges of blades may be treated in substantially the same manner. On the thrust and camber face of blades, remove the metal around any dents, cuts, scars, scratches, nicks, longitudinal surface cracks, and pits to form shallow saucer-shaped depressions as shown in figure 12.2 (view C). Exercise care to remove the deepest point of the injury and also remove any raised metal around the edges of the injury as shown in figure 12.2 (view A).
For repaired blades, the permissible reduction in width and thickness for minimum original dimensions, allowed by the blade drawing and blade manufacturing specifications are shown in figure 12.4 for locations on the blade from the shank to 90 percent of the blade radius.
Beyond the 90 percent blade radius point, the blade width and thickness may be modified as required.
b. Shortening Blades. When the removal or treatment of defects on the tip necessitates shortening a blade, shorten each blade used Chap 12 Par 583
page
CROSS - SECTION CROSS - SECTION
BEFORE REPAIR AFTER REPAIR
BEFORE REPAIR AFTER REPAIR C
SURFACE CRACK AFTER REPAIR-
BEFORE REPAIR CRACK WORKED OUT FIGURE 12.2.—Method of repairing surface cracks, nicks, etc., on aluminum alloy propellers. AC 43.13-1A 1972
MAXIMUM THICKNESS OF BLADE
SECTION IS AT A POINT APPROX- IMATELY .3 OF CHORD LENGTH AS SHOWN.
3 OF CHORD LENGTH
CORRECT METHOD -ORIGINAL
SECTION
REWORKED
DO NOT DESTROY MAXIMUM THICKNESS OF BLADE SECTION IF POSSIBLE.
NOTE - MAINTAIN ORIGINAL RADIUS. DAMAGED 8 REWORK CONTOUR TO POINT OF MAXIMUM THICKNESS. PORTION RADIUS IS TOO LARGE.
D CONTOUR IS TOO BLUNT.
INCORRECT METHOD FIGURE 12.3.Correct and incorrect method of reworking leading edge of aluminum alloy propellers.
Page 226 AC 49.12-14 BLADE RADIUS 70 FIGURE 12.4.--Repair limits to blade section width and thickness for aluminum alloy propellers.
•REDUGTIONS SHOWN ARE THE MAXIMUM ALLOWABLE BELOW THE MINIMUM DIMENSIONS REQUIRED BY. THE BLADE DRAWING AND BLADE MANUFACTURING SPEGIFIGATION REP PER CENT 50 60 RADIUS 40 Par 585 Chap 12