Service and Repair Manual

14. Round-head Rivet (AN430).

     For 1/8-inch diameter rivet: The formed head thickness should be .063 inch; the diameter of the formed head should be .188 inch; the extruded length of the rivet, after insertion, should be 3/18 inch.

     For 5/32-inch diameter rivet: The formed head thickness should be .078 inch; the diameter of the formed head should be .234 inch; the extruded length of the rivet, after insertion, should be 3/16 inch.

     For 3/16-inch diameter rivet: The formed head thickness should be, .093 inch; the diameter of the formed head should be .281 inch; the extruded length of the rivet after lnsertlon, should be 7/32 inch. (See figure 4.)

15. Flathead Rivet (AN442).

     Same allowance as used for round-head rivet (AN430). (See this sectlon, paragraph l4., figure 4.)

16.Rivet Clearance.

     For minimum clearances for rivet holes use the proper drill size. For example, on a 1/16-inch rivet size use a No. 52 (.0635 inch); 3/32-inch rivet use No. 41 (.096 inch); 1/8-inch rivet size use No. 30 (.1285 inch); 5/32-inch rivet use No. 22 (.l57 inch); 3/16-inch rivet size use No. 12 (.l89 inch); 1/4-inch rivet size use 1/4 size drill, etc. When aligning holes of different parts, it is essential that they be dimensioned by the same method and from a corresponding datum point.

17. Operation of Cherry Blind Riveter.

     The method of operating the Cherry blind riveter is given in A.P. 1464/D.76. Read note given in section VI, paragraph 3.5. (2). 18. Fittig Bolts.

     No steel bolts smaller than 3/ 16 inch shall be used. No commercial machine screws or bolts shall be substituted for aircraft bolts. The condition, to be obtained with standard bolts employing washers under the nuts where necessary, is that the threaded portion of a bolt must not be used to take a shear load. When replacing a bolt, the plain portion of the shank of the new bolt must be identical in length with that of the old bolt. All bolts must be suitably locked. Wherever lock wire is used, the wire must fit the hole. Care must be taken to ensure that the nuts are locked in the same manner as the original.

19. Enlarged Holes.

     Enlarged or elongated rivet holes should be drilled for the next larger diameter rivet. Slightly elongated holes can in some cases be filled by using a longer rivet of the original diameter. Elongated holes in fittings or extrusions must not be re-drilled because of the limited edge distances provided in manufacture.

20. Detecting the Presence of Cracks.

     When effecting repairs, great care must be exercised at all times to ensure that no cracks in the immediate structure remain undetected. Fine hair-size cracks in fractured sheets if undetected will open and spread under vibration. Minute cracks caused by bullet impacts should be cut away when cleaning up fractured areas for repair. However, if any doubt exists as to the presence at a crack, the part or area should be soaked in paraffin and thoroughly dried. The application of a whiting water or whiting methylated spirit paste to the surface will on drying disclose the presence of a crack by a discolored mark.

21. Marking-Off.

     When making up new part replacements of important members or fittings, care must be taken that the correct dimensions given on the drawing be marked off with crayon or soft marking pencil on the surface plate. Prevent heavy marking of the material, as deep markings or scratches may seriously weaken the material and may develop into fine hair-like cracks.

22.Prevention of Corrosion.

     All damaged surfaces should be immediately coated to prevent corrosion. Examine the metal under cracked or blistered paint. Use particular care in repairing internal structure which cannot be periodically inspected for corrosion.

     With the exception of Alclad aluminum, aluminum-covered sheets, all aluminum-alloy parts are anodically treated. Steel parts, other than those made of noncorrodible sheet or stainless steel are cadmium plated. However, in addition to these primary protective treatments, one coat of zinc chromate primer and one coat of aluminized zinc chromate primer before assembly are applied to everything except the conduit system. The elevators, ailerons, and rudder are coated with dope-resisting paint and all parts which are liable to come in contact with acid are given two coats of acid-resisting paint. Open-ended tubular and hollow parts are given a coat of primer either by filling or dipping. Closed or sealed metal tubular and hollow parts are coated with raw linseed oil forced into the parts by pressure.

     All cuts, files, or badly scratched surfaces can be treated with a zinc chromate paste, type II. Also when insulating dissimilar metals, insulate parts with a thin layer approximately 1/32 inch thick of zinc chromate 'paste, type II. Excess should be squeezed out before riveting, or on tightening the assembled parts. Form a small fillet at the edges of the joint unless this fillet is exposed to the air stream.

     For tail surfaces, a quick drying, clear cellulose nitrate dope may be used for emergency patches on fabric-covered airfoils. This dope is applied in the same manner as semipigmented dope, but in drying