Par 4-97 Page 4-84 the same replacement tube diameter as the original. As an aid to installing the replacement tube, squarely cut the original damaged tube leaving a minimum short stub equal to 2-1/2-tube diameters on one end and a minimum long stub equal to 4-1/2-tube diameters on the other end.
Select a length of steel tube of the same material and at least the same wall thickness, having an inside diameter approximately equal to the outside diameter of the damaged tube. Fit this replacement tube material snugly around the original tube with a maximum diameter difference of 1/16 inch. From this replacement tube material, cut a section of tubing diagonally (or fishmouth) of such a length that each end of the tube is a minimum distance of 1-1/2-tube diameters from the end of the cut on the original tube. Use a fishmouth cut replacement tube wherever possible. Deburr the edges of the replacement tube and original tube stubs. If a fishmouth cut is used, file out the sharp radius of the cut with a small round file. Spring the long stub of the original tube from the normal position, slip the replacement tube over the long stub, and then back over the short stub. Center the replacement tube between the stubs of the original tube. Tack weld one end of the replacement tube in several places, then weld completely around the end. In order to prevent distortion, allow the weld to cool completely, then weld the remaining end of the replacement tube to the original tube.
FIGURE 4-40. SPLICING USING LARGER DIAMETER REPLACEMENT TUBE
4-98. REPAIRS AT BUILT-IN FUSELAGE FITTINGS. Make splices in accordance with the methods described in paragraphs 4-86 through 4-92. Repair built-in fuselage fittings in the manner shown in Figure 4-41. The following paragraphs outline the different methods as shown in Figure 4-41.
Par 4-98 Page 4-85 FIGURE 4-41. REPAIRS AT BUILT-IN FUSELAGE FITTINGS
a.
Tube of Larger Diameter Than Original. A tube (sleeve) of larger diameter than the original is used in the method shown in Figure 4-41, image (A). The forward splice is a 30-degree scarf splice. Cut the rear longeron (right) approximately 4 inches from the centerline of the joint and fit a 1 inch long spacer over the longeron, and edge weld this spacer and longeron. Make a tapered “V” cut approximately 2 inches long in the aft end of the outer sleeve, and swage the end of the outer sleeve to fit the longeron and weld.
b. Tube of Same Diameter as Original. In the method shown in Figure 4-41, image (B), the new section is the same size as the longeron forward (left) of the fitting. The rear end (right) of the tube is cut at 30 degrees and forms the outside sleeve of the scarf splice. A sleeve is centered over the forward joint as indicated.
c. Simple Sleeve. In Figure 4-41, image (C), it is assumed the longeron is the same size on each side of the fitting. It is repaired by a sleeve of larger diameter than the longeron.
Par 4-98 Page 4-86
d. Large Difference in Longeron Diameter Each Side of Fitting. Figure 4-41, image (D) assumes that there is 1/4-inch difference in the diameter of the longeron on the two sides of the fitting. The section of longeron forward (left) of the fitting is cut at 30 degrees, and a section of tubing of the same size as the tube and of such length as to extend well to the rear (right) of the fitting is slipped through it. One end is cut at 30 degrees to fit the 30-degree scarf at left, and the other end fishmouthed. This makes it possible to insert a tube of proper diameter to form an inside sleeve for the tube on the left of the fitting and an outside sleeve for the tube on the right of the fitting.
4-99. ENGINE-MOUNT REPAIRS. All welding on an engine mount must be of the highest quality, since vibration tends to accentuate any minor defect. Engine-mount members should preferably be repaired by using a larger diameter replacement tube, telescoped over the stub of the original member, and using fishmouth and rosette welds. However, 30-degree scarf welds in place of the fishmouth welds will be considered acceptable for engine-mount repair work.
a. Repaired engine mounts must be checked for accurate alignment. When tubes are used to replace bent or damaged ones, the original alignment of the structure must be maintained.
When drawings are not available, this can be done by measuring the distance between points of corresponding members that have not been distorted.
b. Grind out all cracked welds.
c. Use only high-grade metallurgically controlled (mc) welding rods for engine-mount repairs.
d. If all members are out of alignment, reject the engine mount and replace with one supplied by the manufacturer or one which was built to conform to the manufacturer’s drawings.
The method of checking the alignment of the fuselage or nacelle points should be requested from the manufacturer.
e. Repair minor damage, such as a crack adjacent to an engine-attachment lug, by rewelding the ring and extending a gusset or a mounting lug past the damaged area.
Engine-mount rings which are extensively damaged must not be repaired, unless the method of repair is specifically approved by the FAA, or the repair is accomplished in accordance with FAA-approved instructions.
f. If the manufacturer stress relieved the engine mount after welding it, the engine mount should be re-stress relieved after the weld repairs are made.
4-100. BUILT-UP TUBULAR WING OR TAIL-SPARS. Repair built-up tubular wing or tail-spars by using any of the applicable splices and methods of repair shown in Figure 4-35 through Figure 4-45, provided the spars are not heat treated. In the case of heat-treated spars, the entire spar assembly would have to be reheat treated to the manufacturer’s specifications after completion of the repair. In general, this will be found less practicable than replacing the spar with one furnished by the manufacturer or holder of the Parts Manufacturer Approval (PMA) for the part.
FIGURE 4-42. STREAMLINE TUBE SPLICE USING ROUND TUBE (APPLICABLE
TO LANDING GEAR) , GAP E WELD,
FORM INSIDE AT LEAST AT LEAST TUBE TO FIT. • 30.
A- Slot Width (Original Tube).
B- Outside Diameter (Insert Tube).
C- Streamline Tube Length of Major Axis.
S.L. Size A B D 1" 375 563 1.340 .496 1-¼ .375 -688 1.670 .619 1-½ .500 .875 2.005 .743 1-¾ .500 1.000 2.339 .867 2 .500 1.125 2.670 991 2-¼ .500 1.250 3.008 1.115 2-½ _500 1.375 3.342 1.239
ROUND INSERT TUBE (B) SHOULD BE AT LEAST OF SAME MATERIAL AND ONE GAUGE THICKER THAN ORIGINAL STREAMLINE TUBE (C).
Par 4-100 Page 4-87
FIGURE 4-43. STREAMLINE TUBE SPLICE USING SPLIT SLEEVE (APPLICABLE
TO WING AND TAIL SURFACE BRACE STRUTS AND OTHER MEMBERS)
SAW SLEEVE ALONG OPEN OUT ' ORIGINAL
TUBE AND WELD
OUT TONG AS CIGINAL OR USE
TUBING OF AT LEAST A- Minimum Length of Sleeve.
B- Streamline Tube Length of Minor Axis.
C- Streamline Tube Length of Major Axis.
S.L. Size B c 1" 7.324 .572 1.340 1-¼ 9.128 .714 1.670 1-½ 10.960 858 2.005 1-¾ 12.784 1.000 2.339
14.594 1.144 2.670 2-¼ 16.442 1.286 3.008 2-½ 18.268 1.430 3.342 Par 4-100 Page 4-88
FIGURE 4-44. STREAMLINE TUBE SPLICE USING SPLIT INSERT (APPLICABLE
TO LANDING GEAR) SIZE OF ROSETTES = WELD. GAP S 14C. DRILL OUTSIDE TUBES ONLY.
2A B 2A L = MAXIMUM INSERT LENGTH SAW .08 C OFF OF T.E. AND WELD INSERT TUBE IS OF SAME STREAMLINE TUBING AS ORIGINAL.
A- Is ⅓ B.
B- Is Minor Axis Length of Original Streamline Tube.
C- Is Major Axis Length of Original Streamline Tube.
S.L. Size L 1" .382 572 1.340 5.160 1-¾ .476 .714 1.670 6.430 1-½ .572 -858 2.005 7.720 1-¾ .667 1.000 2.339 9.000 2 _763 1.144 2.670 10.300 2-¼ .858 1.286 3.008 11.580 2-½ .954 1.430 3.342 12.880 Par 4-100 Page 4-89
FIGURE 4-45. STREAMLINE TUBE SPLICE USING PLATES (APPLICABLE TO
LANDING GEAR) ЗА A- Streamline Tube Length of Minor Axis, Plate Widths.
B- Distance of First Plate From Leading Edge, ⅓ A.
C- Streamline Tube Length of Major Axis.
S.L. Size B 6A 1" .572 .382 1.340 3.430 1-¼ .714 .476 1.670 4.280 1-2 858 .572 2.005 5.150 1-¾ 1.000 .667 2.339 6.000
1.144 .762 2.670 6.860 2-¾ 1.286 .858 3.008 7.720 2-½ 1.430 .954 3.342 8.580
4-101. WING-BRACE STRUTS AND TAIL-BRACE STRUTS. In general, it will be found advantageous to replace damaged wing-brace struts made either from rounded or streamlined tubing with new members purchased from the original manufacturer. However, there is no objection, from an airworthiness point of view, to repairing such members in a proper manner.
An acceptable method of repair, if streamlined tubing is used, will be found in Figure 4-43.
Repair similar members made of round tubes using a standard splice, as shown in Figure 4-35, Figure 4-37, or Figure 4-38.
a. Location of Splices. Steel-brace struts may be spliced at any point along the length of the strut, provided the splice does not overlap part of an end fitting. The jury-strut attachment is not considered an end fitting; therefore, a splice may be made at this point. The repair procedure and workmanship minimize distortion due to welding and the necessity for subsequent straightening operations. Observe every repaired strut carefully during initial flights to ascertain that the vibration characteristics of the strut and attaching components are not adversely affected by the repair. A wide range of speed and engine-power combination must be covered during this check.
Par 4-100 Page 4-90
Par 4-101 Page 4-91
b. Fit and Alignment. When making repairs to wing and tail surface brace members, ensure repairs are properly fit and aligned to avoid distortion.
4-102. LANDING GEAR REPAIR.
a. Round Tube Construction. Repair landing gears made of round tubing using standard repairs and splices as shown in Figure 4-35 and Figure 4-41.
b. Streamline Tube Construction. Repair landing gears made of streamlined tubing by either one of the methods shown in Figure 4-42, Figure 4-44, or Figure 4-45.
c. Axle Assemblies. Representative types of repairable and nonrepairable landing gear axle assemblies are shown in Figures 4-46 and 4-47. The types as shown in Figure 4-46, images (A), (B), and (C) are formed from steel tubing and may be repaired by the applicable method shown in Figure 4-35 through Figure 4-45. However, it will always be necessary to ascertain whether or not the members are heat treated. The axle assembly as shown in Figure 4-47 is, in general, of a nonrepairable type for the following reasons.
FIGURE 4-46. REPRESENTATIVE TYPES OF REPAIRABLE AXLE ASSEMBLIES
Par 4-102 Page 4-92 FIGURE 4-47. LANDING GEAR ASSEMBLIES THAT CANNOT BE REPAIRED
BY WELDING (
1) The axle stub is usually made from a highly heat-treated nickel alloy steel and carefully machined to close tolerances. These stubs are usually replaceable and must be replaced if damaged.
(2) The oleo portion of the structure is generally heat treated after welding, and is perfectly machined to ensure proper functioning of the shock absorber. These parts would be distorted by welding after machining.
4-103. REPAIRS TO WELDED ASSEMBLIES. These repairs may be made by the following methods.
a. A welded joint may be repaired by cutting out the welded joint and replacing it with one properly gusseted. Standard splicing procedures should be followed.
Par 4-103 Page 4-93
b. Replacing weld deposit by chipping out the metal deposited by the welding process and rewelding after properly reinforcing the joint by means of inserts or external gussets.
4-104. STAINLESS STEEL STRUCTURE. Repair structural components made from stainless steel, particularly the “18-8” variety (18 percent chromium, 8 percent nickel), joined by spot welding, in accordance with the instructions furnished by the manufacturer, a Designated Engineering Representative (DER), or the FAA. Substitution of bolted or riveted connections for spot-welded joints are to be specifically approved by a DER or the FAA. Repair secondary structural and nonstructural elements such as tip bows or leading and trailing edge tip strips of wing and control surfaces by soldering with a 50-50 lead-tin solder or a 60-40 lead-tin solder.
For best results, use a flux of phosphoric acid (syrup). Since the purpose of flux is to attack the metal so that the soldering will be effective, remove excess flux by washing the joint. Due to the high heat conductivity of the stainless steel, use a soldering iron large enough to do the work properly.
4-105.–4-110. [RESERVED.]
Par 4-111 Page 4-94 SECTION 6. WELDING AND BRAZING SAFETY
4-111. GENERAL. A number of inherent hazards exist in the use of oxy-fuel welding and cutting apparatus. It is necessary that proper safety and operating procedures are understood. A thorough understanding of the proper safety and operating procedures minimizes the hazards involved and adds to the pleasure and efficiency of your work.
4-112. FIRE AND EXPLOSION SAFETY. Fires occur in welding areas because flammables are left where they can be ignited by welding sparks or gas welding flames. Before welding, clear the welding area of all flammables such as rags, paper, wood, paint cans, solvent, and trash containers. Do not weld in areas where flammables are present.
a. Unless absolutely necessary, never weld any tank or radiator that has had a flammable in it, including gasoline, Aviation Gasoline (AVGAS), motor oil, hydraulic fluid, or any other liquid that could ignite if the vapor and temperature reach a flashpoint. Explosions often occur when empty tanks are being welded or cut open with a torch.
b. If welding such tanks or radiator coolers is absolutely necessary, the tank must first be washed with a caustic-based, water-soluble liquid, rinsed with plenty of clear water, and then dried. Before welding, the tank or container should be thoroughly purged with argon, or other inert gas, while the welding is in process.
4-113. WELDING WORK AREA.
a. The work area must have a fireproof floor; concrete floors are recommend.
b. Use heat-resistant shields to protect nearby walls or unprotected flooring from sparks and hot metal.
c. Maintain an adequate suction ventilation system to prevent the concentration of oxygen/fuel gas, flammable gases, and/or toxic fumes. It is important to remember that oxygen will not burn. The presence of oxygen, however, serves to accelerate combustion, and causes materials to burn with great intensity.
CAUTION: Oil and grease in the presence of oxygen can ignite and burn violently.
d. A completely clean welding shop area with white walls, ceiling, and floor; and with plenty of light, is better for welding. The better the lighting conditions, the easier it is to see the weld puddle and make excellent aircraft-quality welds.
e. During oxy-fuel processes, use work benches or tables with fireproof tops. Fire bricks commonly top these surfaces and support the work.
f. Chain or otherwise secure oxygen and fuel gas cylinders to a wall, bench, post, cylinder cart, etc. This will protect them from falling and hold them upright.
Par 4-114 Page 4-95
4-114. FIRE PROTECTION. Practice fire prevention techniques whenever oxy-fuel operations are in progress. Simple precautions prevent most fires, and minimize damage in the event that a fire does occur. Always practice the following rules and safety procedures.
a. Inspect oxy-fuel apparatus for oil, grease, or damaged parts. DO NOT use the oxy-fuel apparatus if oil or grease is present or if damage is evident. Have the oxy-fuel apparatus cleaned and/or repaired by a qualified repair technician before it is used.
b. Never use oil or grease on or around any oxy-fuel apparatus. Even a trace of oil or grease can ignite and burn violently in the presence of oxygen.
c. Keep flames, heat, and sparks away from cylinders and boxes.
d. Flying sparks can travel as much as 35 feet. Move combustibles a safe distance away from areas where oxy-fuel operations are performed.
e. Use approved heat-resistant shields to protect nearby walls, floor, and ceiling.
f. Have a fire extinguisher of the proper class (ABC) and size in the work area. Inspect it regularly to ensure that it is in proper working order. Know how it is used.
g. Use oxy-fuel equipment only with the gases for which it is intended.
h. DO NOT open an acetylene cylinder valve more than approximately 1-1/2 turns and preferably no more than 3/4 of a turn. Keep the cylinder wrench, if one is required, on the cylinder valve so, if necessary, the cylinder may be turned off quickly.
i. On all gases except acetylene, open the cylinder valve completely to seal the cylinder back-seal packing.
j. NEVER TEST FOR GAS LEAKS WITH A FLAME. Use an approved leak-detector solution.
k. When work is complete, inspect the area for possible fires or smoldering materials.
l. Special care should be taken when welding structural tubing that has been coated on the inside with linseed oil. Smoke and fire may be generated by the heat of the torch. Ensure that an observer with a fire extinguisher is close.
4-115. PROTECTIVE APPAREL.
a. Protect yourself from sparks, flying slag, and flame brilliance at all times.
(1) For gas welding and brazing, use number 3 or 4 green-shaded tempered lenses.
(2) When gas welding aluminum, use cobalt-blue tint lenses.
(3) When arc welding, including TIG, MIG, and plasma cutting; use number 9 to 12 green lenses and a full face-and-neck covering helmet.