Par 4-58 Page 4-129
FIGURE 4-11. Huck rivet.
Repairs to Aluminum Alloy Members. Make repairs to aluminum alloy members with the same material or with suitable material of higher strength. The 7075 alloy has greater tensile strength than other commonly used aluminum alloys such as 2014 and 2024, but is subject to somewhat greater notch sensitivity. In order to take advantage of its strength characteristics, pay particular attention to design of parts to avoid notches, small radii, and large or rapid changes in cross-sectional areas. In fabrication, exercise caution to avoid processing and handling defects, such as machine marks, nicks, dents, burrs, scratches, and forming cracks. Cold straightening or forming of 7075-T6 can cause cracking; therefore, it may be advisable to limit this processing to minor cold straightening.
Wing and Tail Surface Ribs. Damaged aluminum alloy ribs either of the stam ped sheet-metal type or the built-up type employing special sections, square or round tubing, may be repair ed by the addition of suitable reinforcement. (A cceptable methods of repair are shown in figures 4-13 and 4-14.) These examples deal with types of ribs commonly found in small and medium size aircraft. Repair schemes developed by the aircraft manufacturer are acceptable, but any other methods of reinforcement are major repairs and require approved data.
Trailing and Leading Edges and Tip Strips. Repairs to wing, control surface tra iling edges, leading edges, and tip strips should be made by properly executed and reinforced splices. Acceptable methods of trailing edge repairs are shown in figure 4-15.
Repair of Damaged Skin. In cases where metal skin is damaged extensively, repair by replacing an entire sheet panel from one structural member to the next. The repair seams are to lie along stiffening members, bulkheads, etc.; and each seam must be made exactly the same in regard to rivet size, splicing, and rivet pattern as the manufactured seams at the edges of the original sheet. If the tw o manufactured seams are different, the stronger one will be copied. (See figure 4-16 for typical acceptable methods of repairs.)
Patching of Small Holes. Small holes in skin panels which do not involve damage to the stiffening members may be patched by covering the hole with a patch plate in the manner shown in figure 4-16. Flush patches also may be installed in stressed-skin type construction. An acceptable and easy flush patch may be made by trimming out the damaged area and then installing a conventional patch on the underneath side or back of the sheet being repaired. A plug patch plate of the same size and skin thickness as the opening may then be inserted and riveted to the patch plate. Other types of flush patches similar to those used for patching plywood may be used. The rivet pattern used, however, must follow standard practice to maintain satisfactory strength in the sheet.
Splicing of Sheets. The method of copying the seams at the edges of a sheet may not always be satisfactory.
For example, when the sheet has cutouts, or doubler plates at an edge seam, or when other members transmit loads into the sheet, the sp lice must be designed as illustrated in the following examples.
Material: Clad 2024 sheet, 0.032 inch thickness. Width of sheet (i.e., length at splice) = “W” = 10 inches.
Determine rivet size and pattern for a single-lap joint similar to figure 4-5.
Use rivet diameter of approximately three times the sheet thickness, 3 x 0.032 = 0.096-inch. Use 1/8-inch
Par 4-58 Page 4-130 2117-T4 (AD) rivets (5/32-inch 2117-T4 (AD) would be satisfactory).
Use the number of rivets required per inch of width “W” from table 4-9 (read NOTES) (number per inch 6.2 x .75 = 4.6 or the total number of rivets required = 10 x 4.6 or 46 rivets.)
Lay out rivet pattern with spacing not less than shown in figure 4-5. Referring to figure 4-5(A), it seems that a double row pattern with the minimum spacing will give a total of 50 rivets. However, as only 46 rivets are required, two rows of 23 rivets each equally spaced over the 10 inches will result in a satisfactory splice.
Straightening of Stringers or Intermediate Frames .
Members which are slightly bent may be straightened cold and examined with a magnifying glass for cracks or tears to the material. Reinforce the straightened part to its original shape, depending upon the condition of the material and the magnitude of any remaining kinks or buckles. If any strain cracks are apparent, make complete reinforcement in sound metal beyond the damaged portion.
Local Heating. Do not apply local heating to facilitate bending, swaging, flatteni ng, or expanding operations of heat-treated aluminum alloy members, as it is difficult to control the temperatures closely enough to prevent possible damage to the metal, and it may impair its corrosion resistance.
Splicing of Stringers and Flanges. It is recommended that all splices be made in accordance with the manufacturer’s recommendations. If the manufacturer’s recommendations are not available, the typical splices for various shapes of sections are shown in figures 4-17 through 4-19. Design splices to carry both tension and compression, and use the splice shown in figure 4-18 as an example illustrating the following principles.
To avoid eccentric loading and consequent buckling in compression, place splicing or reinforcing parts as symmetrically as possible about the centerline of the member, and attach to as many elements as necessary to prevent bending in any direction.
To avoid reducing the strength in tension of the original bulb angle, the rivet holes at the ends of the splice are made small (no larger than the original skin attaching rivets), and the second row of holes (those through the bulbed leg) are staggered back from the ends. In general, arrange the rivets in the splice so that the design tensile load for the member and splice plate can be carried into the splice without failing the member at the outermost rivet holes.
•L = 20 SPACES 3 d EACH - -TOTAL NO. OF RIVETS - 18 (9 EACH SIDE OF SPLICE) A = ORIGINAL TUBE C = REPLACEMENT TUBE B = SLEEVE USE 2117-T ALUM. ALLOY RIVETS SMALL HEAD
HAMMER STANDARD SPLICES MAY BE USED ON LIGHTLY- 2dl ROUND HEAD LONGERONS OR WEB MEMBERS.
CORRECT WAY INCORRECT WAY d MUST NOT BE LESS THAN D/8.
R = 3 d
•0 30
• •. .00 100
STREAMLINE M/3 EACH (USE BASIC ROUND SIZES IN TABLE FOR SIZE OF RIVETS ETC.)
A, C * 3/4 718 1 1-1/8 1-1/4 1-/3/8 1-1/2 1-/5/8 1-3/4 1-718 .065 065 .065 .065 .058 .058 .058 .058 .058 .058 718 1-1/8 1-1/4 1-3/8 1-1/2 1-5/8 1-3/4 1-7/8 2 ALL .058 THICK RIVET DIA. 5/32 5/32 3/16 3/16 3/16 3/16 1/4 1/4 1/4 1/4 L 9-3/8 9-3/8 11-1/4 11-1/4 11-1/4 11-1/4 15 15 15 15 * INCLUDES ALL THICKNESSES UP TO AND INCLUDING MAXIMUM SHOWN.
NOTE. USE SAME MATERIAL AS ORIGINAL FOR SLEEVE AND REPLACEMENT TUBE.
FIGURE 4-12. Typical repair method for tubular members of aluminum alloy.
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- D
- A D- 30 3030.202030.30.300
AT LEAST AS THICK
AS ORIGINAL
ORIGINAL
REINFORCEMENT 2117-AD RIVETS MATERIAL - DURAL. OR ALUMINUM ALLOY USED IN 3/32" DIA. MIN.
ORIGINAL CONSTRUCTION.
SCALE - TWICE SIZE SECTION A-A
SCALE - TWICE SIZE 2017-T3
000.0000 D SQ. ROD 3D 3D 3D 3D 130|30, 30 30 130„ • 2117-AD RIVETS 1/8" DIA: MIN.
NOTE: FOR MINIMUM NUMBER OF RIVETS REQUIRED, SEE PARAGRAPH 4-58g AND SUBSEQUENT.
FIGURE 4-13. Typical repair for buckled or cracked metal wing rib capstrips.
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SEE (C) SEE (D) 000OT0 (A)
- SEE (E) (B) D = RIVET DIA.
›PROX.) (MINIMUM 3/32) +0 * BEND RADII TO FIT
ORIGINAL RIB.
(G) 1ĞPLYWOODTO STIFFEN BENT RIBS.
MACHINE SCREW D OR RIVET.
1.5 ₺ (APPROX.)
<PEEN (E) 2030. 30.202015980.39 (D) NOTE: FOR MINIMUM NUMBER OF RIVETS REQUIRED, SEE PARAGRAPH 4-58g AND SUBSEQUENT.
FIGURE 4-14. Typical metal rib repairs (usually found on small and medium-size aircraft).
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"A" .040" 2017-T3 SPACER 2D, 3D 30 202D 3D 3D 20 "B" 2024-T3 SPLICE BAR "Д" * В" ----+1 2117-AD RIVETS 3/32" DIA. MIN.
- CRACK 2117-AD RIVETS 3/32" DIA. MIN.
- ЗА ЗА I. STRAIGHTEN CRIMPED OVER PORTION. CRACK
2. INSERT HARDWOOD (ASH) INSERT SHAPED.
TO CONFORM TO T.E. PIECE.
2117-AD RIVETS 2D 20 20 2D D 3/32" DIA. MIN.
FLATTEN HEADS (APPROX. 1.5 ₺ ) OUTSIDE I. STRAIGHTEN CRIMPED PORTION. - GRACK
2. USE SAME AL. ALLOY AS IN ORIGINAL.
NOTE: FOR MINIMUM NUMBER OF RIVETS REQUIRED, SEE PARAGRAPH 4-58g AND SUBSEQUENT.
FIGURE 4-15. Typical repairs of trailing edges.
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(A) ADDED
STIFFENERS TO →15K REQD 2 EACH BACK UP SEAM 24-5/32" OF PATCH.
2117-T4 BACKED PATCH PLATE
BY SAME TO BE OF SAME PRIVETS -1 22-1/2; MATERIAL AS 3" HOLE MAX. DIA." ORIGINAL AND
E MAX DIA SAME OR NEXT "G" HEAVIER GAUGE.
16-5/32" RIVET SIZE, 2117-T4 BIVETS SPACING,
MATERIAL, AND
PATTERN "G", "H", AND "K SAME AS ARE ORIGINAL A B.
CIRCULAR PATCH PLATES. DAMAGED SKIN DIMENSIONS OF CIR. PATCH PLATES SHOULD BE DESIGNATION "K" "H" "G" CLEANED OUT DIAMETER (OUTSIDE) 2-1/2" 7-12" SMOOTHLY AS DIA. INNER RIVET CIRCLE 1-3/4" 4" INDICATED BY DIA. OUTER RIVET CIRCLE 6-1/2" CDEF.
SAME RIVET SIZE, SPACING, MATERIAL, & PATTERN AS B C.
SAME RIVET SIZE, SPACING, MATERIAL, & PATTERN AS A D.
PATCH PLATE
TO BE OF SAME
- 1" HOLE MATERIAL AS 8-5/32" 2117- MAX DIA. ORIGINAL AND RIVETS• SAME OR NEXT
HEAVIER GAUGE CRACK
DI NOT LESS THAN 2 TIMES LENGTH -PORTION OF SKIN REPLACED. . OF CRACK:
ORIGINAL SKIN SHEET. *4 RIVETS REQD. EACH SIDE
RIVET SPACING AT LEAST 3X RIVET DIA
HOLES DRILLED TO PREVENT CRACK SPREADING.
SKIN GAUGE = .028" (B) RIVET DIA. = 1/8" CRACK 2.5" LONG FIGURE 4-16. Typical repairs of stressed sheet metal coverings. (Refer to tables 4-9, 4-10, and 4-11 to calculate number of rivets to be used.)
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86/8/6 AC 43.13-1B
.0
TAPERED SPLICE MEMBER NOTE: UNSHADED SECTIONS ARE ORIGINAL AND/OR REPLACEMENT SECTIONS. SHADED SECTIONS ARE CONNECTING OR REINFORCING SECTIONS.
NOTE: FOR MINIMUM NUMBER OF RIVETS REQUIRED, SEE PARAGRAPH 4-58g AND SUBSEQUENT.
FIGURE 4-17. Typical stringer and flange splices.
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CUT IN STRINGER TAPERED SPLICE MEMBER
ON LOWER SURFACE OF WING, MAKE END RIVET SAME SIZE AS SKIN ATTACHING RIVETS.
2 dz, MINIMUM 3 dz, MINIMUM
THE NUMBER OF BOLTS REQUIRED IN THE "BULB" LEG OF THE STRINGER IS DETERMINED FROM TABLE 4-9 FOR 2017-T3 AS FOLLOWS:
+z=1/16" (Use .064") dz= .190" (AN3 bolt) NO. OF BOLTS PER INCH OF WIDTH FROM TABLE = 3.3.
ACTUAL NO. OF BOLTS ON EACH SIDE OF CUI = WX 3.3 = (1.0) × 3.3 = 3.3 BOLTS USE 4 BOLTS
WHEN BOTH RIVETS AND BOLTS
ARE USED, BOLT HOLES SHOULD BE REAMED TO SIZE.
-KEEP LARGE HOLES BACK FROM END OF SPLICE.
THE NUMBER OF RIVETS REQUIRED IN
THE UPPER LEG OF THE STRINGER IS DETERMINED FROMTABLE 4-9 FOR 2017-T3 AS FOLLOWS:
t, = 1/16" (Use „064") d, = 1/8 (2117-AD rivet) NO. OF RIVETS PER INCH OF WIDTH FROM TABLE = 9.9 ACTUAL NO. OF RIVETS ON EACH SIDE OF CUI = WIx 9.9 = (.5) × 9.9 =4.95 RIVETS. USE 5 RIVETS.
d, (1/8), RIVET DIA. PREFERABLY /2tTO 3t, BUT NOT GREATER THAN W/4.
W½
(1.0) SPLICE ANGLE "A" dz - "B" SPLICE BAR. SHADED AREA GREATER THAN W, Xt,.
SHADED AREA GREATER THAN W2xt2. t2 (T6) ~ STRINGER
- AREA REPRESENTING BULB
SECTION A-A FIGURE 4-18. Example of stringer splice (material-2017 alloy).
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Par 4-58 Page 4-138
NOTE: FOR MINIMUM NUMBER OF RIVETS REQUIRED, SEE PARAGRAPH 4-58g AND SUBSEQUENT.
NOTE: STRENGTH INVESTIGATION IS USUALLY REQUIRED FOR THIS TYPE OF REPAIR.
F IGURE 4-19. Application of typical flange splices and reinforcement.
Par 4-58 Page 4-139 To avoid concentration of load on the end rivet and consequent tendency toward progressive rivet failure, the splice is tapered at the ends by tapering the backing angle and by making it shorter than the splice bar. (See figure 4-18.)
The preceding principles are especially important in splicing stringers on the lower surface of stressed skin wings, where hightension stresses may exist. When several adjacent stringers are spliced, stagger the splices if possible.
Size of Splicing Members . When the same material is used for the splicing members as for the original member, the cross-section area (i.e., the shaded areas in figure 4-17), of the splice material will be greater than the area of the section elem ent which it splices. The area of a section element (e.g., each leg of an angle or channel) is equal to the width multiplied by the thickness. For example, the bar “B” in figure 4-18 is assumed to splice the upper leg of the stringer, and the angle “A” is assumed to splice the bulbed leg of the stringer. Since the splice bar “B” is not as wide as the adjacent leg, its thickness must be increased such that the area of bar “B” is at l east equal to the area of the upper leg of the stringer.
The Diameter of Rivets in Stringers . The diameter of rivets in stringers might preferably be between two and three times the thickness “t” of the leg, but must not be more than 1/4th the width “W” of the leg. Thus, 1/8-inch rivets are chosen in the example, figure 4-18.
If the splices were in the lower surface of a wing, the end rivets would be made the same size as the skin-attaching rivets, or 3/32 inch.
The Number of Rivets . The number of rivets required on each side of the cut in a stringer or flange may be determined from standard text books on aircraft structures, or may be found in tables 4-9 through 4-11.
In determining the number of rivets required in the example, figure 4-18, for attaching the splice bar “B” to the upper leg, the thickness “t” of the element of area being spliced is 1/16 inch (use 0.064), the rivet size is 1/8 inch, and table 4-9 shows that 9.9 rivets are required per inch of width. Since the width “W” is 1/2 inch, the actual number of rivets required to attach the splice bar to the upper leg on each side of the cut is 9.9 (rivets per inch) x 0.5 (inch width) = 4.95 (use 5 rivets).
For the bulbed leg of the stringer “t” = 1/16 inch (use 0.064); AN-3 bolts are chosen, and the number of bolts required per inch of width = 3.3. The width “W” for this leg, however, is 1 inch; and the actual number of bolts required on each side of the cut is 1 x 3.3 = 3.3 (use 4 bolts). When both rivets and bolts are used in the same splice, the bolt holes must be accurately reamed to size. It is preferable to use only one type of attachment, but in the above example, the dimensions of the legs of the bulb angle indicated rivets for the upper leg and bolts for the bulb leg.
Splicing of Intermediate Frames. The same principles used for stringer splicing may be applied to intermediate frames when the following point is considered.
Conventional frames of channel or Z sections are relatively deep and thin co mpared to stringers, and usually fail by twisting or by buckling of the free flange. Reinforce the splice joint against this type of failure by using a splice plate heavier than the frame and by splicing the free flange of the frame with a flange of the splice plate. (See figure 4-20.) Since a frame is likely to be subjected to bending loads, make the length of splice plate “L” more than twice the width “W2,” and the rivets spread out to cover the plate.
Par 4-58 Page 4-140 TABLE 4-9. Number of rivets required for splices (single-lap joint) in bare 2014-T6, 2024-T3, 2024-T36, and 7075-T6 sheet, clad 2014-T6, 2024-T3, 2024-T36, and 7075-T6 sheet, 2024-T4, and 7075-T6 plate, bar, rod, tube, and extrusions, 2014-T6 extrusions.
Thickness “t” in inches No. of 2117-T4 (AD) protruding head rivets required per inch of width “W”
Rivet size
No. of Bolts 3/32 1/8 5/32 3/16 1/4 AN-3 .016 6.5 4.9 - - - - - - - - .020 6.9 4.9 3.9 - - - - - - .025 8.6 4.9 3.9 - - - - - - .032 11.1 6.2 3.9 3.3 - - - - .036 12.5 7.0 4.5 3.3 2.4 - - .040 13.8 7.7 5.0 3.5 2.4 3.3 .051 - - 9.8 6.4 4.5 2.5 3.3 .064 - - 12.3 8.1 5.6 3.1 3.3 .081 - - - - 10.2 7.1 3.9 3.3 .091 - - - - 11.4 7.9 4.4 3.3 .102 - - - - 12.8 8.9 4.9 3.4 .128 - - - - - - 11.2 6.2 3.2
NOTES:
a. For stringers in the upper surface of a wing, or in a fuselage, 80 percent of the number of rivets shown in the table may be used.
b. For intermediate frames, 60 perc ent of the number shown may be used.
c. For single lap sheet joints, 75 per cent of the number shown may be used.
ENGINEERING NOTES:
a. The load per inch of width of material was ca lculated by assuming a strip 1 inch wide in tension.
b. Number of rivets required was calculated for 2117- T4 (AD) rivets, based on a rivet allowable shear stress equal to 40 percent of the sheet allowable tensile stress, and a sheet allowable bearing stress equal to 160 percent of the sheet allowable tensile stress, using nominal bolt diameters for rivets.
c. Combinations of sheet thickness and rivet size abov e the underlined numbers are critical in (i.e., will fail by) bearing on the sheet; those below are critical in shearing of the rivets.
d. The number of AN-3 bolts required below the underlined number was calculated based on a sheet allowable tensile stress of 70,000 psi and a bolt allowable single shear load of 2,126 pounds.