Par 4-58 Page 4-35 forming of 7075-T6 can cause cracking; therefore, it may be advisable to limit this processing to minor cold straightening.
c. Wing and Tail Surface Ribs. Damaged aluminum alloy ribs either of the stamped sheet-metal type or the built-up type employing special sections, square or round tubing, may be repaired by the addition of suitable reinforcement. (Acceptable methods of repair are shown in Figure 4-13 and Figure 4-14.) These examples deal with types of ribs commonly found in smalland 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.
d. Trailing and Leading Edges and Tip Strips. Repairs to wing, control surface trailing 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.
e. 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 two manufactured seams are different, the stronger one will be copied. (See Figure 4-16 for typical acceptable methods of repairs.)
FIGURE 4-13. TYPICAL REPAIR FOR BUCKLED OR CRACKED METAL WING RIB
CAP STRIPS
- D CRACK 0 30 30 3020203030,30 D
AT LEAST AS THICK
AS ORIGINAL
ORIGINAL
REINFORCEMENT MaTERIaL — DURAL.OR 2117-AD RIVETS ALUMINUM ALLOY USED IN 3/32" DIA. MIN.
ORIGINAL CONSTRUCTION.
SCALE - TWICE SIZE SECTION A-A
SCALE - TWICE SIZE
- 2017-T3 D SQ. ROD 30_ 30 3D 3D 30, 30 30 3D 30 • 2117-AD RIVETS 1/8" DIA: MIN.
NOTE: FOR MINIMUM NUMBER OF RIVETS REQUIRED, SEE PARAGRAPH 4-58g AND SUBSEQUENT.
Par 4-58 Page 4-36
FIGURE 4-14. TYPICAL METAL RIB REPAIRS (USUALLY FOUND ON SMALL-
AND MEDIUM-SIZE AIRCRAFT)
SEE (C) SEE (D) 1000 OTO (A) + SEE (E) (B) D = RIVET DIA.
ROX.) (MINIMUM 3/32") TER.
BEND RADI TO FIT
ORIGINAL RIB.
(G) 3/16 PLYWOOD TO STIFFEN BENT RIBS.
- D - MACHINE SCREW OR RIVET.
• 1.5 ₺ (APPROX.)
- PEEN (E) 2030_30 2020130|30.22 (D) NOTE: FOR MINIMUM NUMBER OF RIVETS REQUIRED, SEE PARAGRAPH 4-58g AND SUBSEQUENT.
Par 4-58 Page 4-37
FIGURE 4-15. TYPICAL REPAIRS OF TRAILING EDGES "А" "B" 2024-T3 SPLICE BAR 040" 2017-T3 SPACER "Д" 20,30 30 202030,30 20 I-+i "В" - 8 030001 2117-AD RIVETS →4-0 3/32" DIA. MIN. CRACK 2117-AD RIVETS 3/32" DIA. MIN. « Д→
- ЗА ЗА I. STRAIGHTEN CRIMPED OVER PORTION. - CRACK
2. INSERT HARDWOOD (ASH) INSERT SHAPED.
TO CONFORM TO T.E. PIECE.
2117-AD RIVETS 20 20 2D D 3/32" DIA. MIN.
FLATTEN HEADS (APPROX. 1.5 t ) OUTSIDE I. STRAIGHTEN CRIMPED PORTION. - CRACK
2. USE SAME AL. ALLOY AS IN ORIGINAL.
Par 4-58 Page 4-38
FIGURE 4-16. TYPICAL REPAIRS OF STRESSED SHEET METAL COVERINGS (SEE TABLES 4-9, 4-10, AND 4-11 TO CALCULATE NUMBER OF RIVETS TO BE USED) (A) ADDED
STIFFENERS TO →15; 2 EACH BACK UP SEAM | 24-5/32" REQ'D OF PATCH.
2117-T4 BACKED PATCH PLATE
BY SAME TO BE OF SAME 3" HOLE MAX. DIA. JRIVETS 2" HOLE MAX DIA |22=112 MATERIAL AS ORIGINAL AND SAME OR NEXT HEAVIER GAUGE.
16-5/32" RIVET SIZE, 2117-T4 RIVETS 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" 5" 7-12" SMOOTHLY AS DIA. INNER RIVET CIRCLE 1-3/4" 3" 4" INDICATED BY DIA. OUTER RIVET CIRCLE 4" 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 QF SAME
•1" HOLE MATERIAL AS 8-5/32" 2117-T4 MAX DIA. ORIGINAL AND
RIVETS SAME OR NEXT
HEAVIER GAUGE CRACK — NOT LESS THAN 2 TIMES LENGTH SPORTION OF SKIN REPLACED. OF CRACK ORIGINAL SKISEET 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 Par 4-58 Page 4-39
Par 4-58 Page 4-40
f. 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.
g. 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 splice must be designed as illustrated in the following examples.
(1) Material: Clad 2024 sheet, 0.032 inch thickness. Width of sheet (i.e., length at splice) = “W” = 10 inches.
(2) Determine rivet size and pattern for a single-lap joint similar to Figure 4-5.
(a) Use rivet diameter of approximately three times the sheet thickness:
3 × 0.032 = 0.096 inch. Use 1/8-inch 2117-T4 (AD) rivets (5/32-inch 2117-T4 (AD) would be satisfactory).
(b) Use the number of rivets required per inch of width “W” from Table 4-10.
(Number per inch: 4.9 × .75 = 3.7 or the total number of rivets required = 10 × 3.7 or 37 rivets.)
See notes in Table 4-10.
Par 4-58 Page 4-41 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” No. of Bolts Rivet Size 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 .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 percent of the number shown may be used.
c. For single lap sheet joints, 75 percent of the number shown may be used.
ENGINEERING NOTES:
a. The load per inch of width of material was calculated 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 above 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 pounds per square inch (psi) and a bolt allowable single shear load of 2,126 pounds.
Par 4-58 Page 4-42 TABLE 4-10. NUMBER OF RIVETS REQUIRED FOR SPLICES (SINGLE-LAP JOINT) IN 2017, 1017 ALCLAD, 2024-T3 ALCLAD SHEET, PLATE, BAR, ROD, TUBE,
AND EXTRUSIONS Thickness “t” in Inches No. of 2117-T4 (AD) Protruding Head Rivets Required Per Inch of Width “W” No. of Bolts Rivet Size 3/32 1/8 5/32 3/16 1/4 AN-3 .016 6.5 4.9 .020 6.5 4.9 3.9 .025 6.9 4.9 3.9 .032 8.9 4.9 3.9 3.3 .036 10.0 5.6 3.9 3.3 2.4 .040 11.1 6.2 4.0 3.3 2.4 .051 7.9 5.1 3.6 2.4 3.3 .064 9.9 6.5 4.5 2.5 3.3 .081 12.5 8.1 5.7 3.1 3.3 .091 9.1 6.3 3.5 3.3 .102 10.3 7.1 3.9 3.3 .128 12.9 8.9 4.9 3.3 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 percent of the number shown may be used.
c. For single lap sheet joints, 75 percent of the number shown may be used.
ENGINEERING NOTES:
a. The load per inch of width of material was calculated 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 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 hole diameters for rivets.
c. Combinations of sheet thickness and rivet size above 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 55,000 psi and a bolt allowable single shear load of 2,126 pounds.
Par 4-58 Page 4-43
(c) Lay out rivet pattern with spacing not less than shown in Figure 4-5. Referring to Figure 4-5, item (A), it seems that a double row pattern with the minimum spacing will give a total of 40 rivets. However, as only 37 rivets are required, two rows of 19 rivets each equally spaced over the 10 inches will result in a satisfactory splice.
h. 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.
i. Local Heating. Do not apply local heating to facilitate bending, swaging, flattening, 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.
j. 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.
FIGURE 4-17. TYPICAL STRINGER AND FLANGE SPLICES
TAPERED SPLICE MEMBER NOTE: UNSHADED SECTIONS ARE ORIGINAL AND/OR REPLACEMENT SECTIONS. SHADED SECTIONS ARE CONNECTING OR REINFORCING SECTIONS.
+Wз→ NOTE: FOR MINIMUM NUMBER OF RIVETS REQUIRED, SEE PARAGRAPH 4-58g AND SUBSEQUENT.
Par 4-58 Page 4-44
FIGURE 4-18. EXAMPLE OF STRINGER SPLICE (MATERIAL: 2017 ALLOY)
CUT IN STRINGER , TAPERED SPLICE MEMBER 000 0 01
ON LOWER SURFACE OF WING, MAKE END RIVET SAME SIZE AS SKIN ATTACHING RIVETS.
2d2, MINIMUM A → 3d2, MINIMUM
THE NUMBER OF BOLTS REQUIRED IN THE "BULB" LEG OF THE STRINGER IS DETERMINED FROM TABLE 4-9 FOR 2017-T3 AS FOLLOWS:
tz = 1/16" (Use "064) de= „190" (AN3 bolt) NO. OF BOLTS PER INCH OF WIOTH FROM TABLE = 3.3.
ACTUAL NO. OF BOLTS ON EACH SIDE OF CUT = 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.
0.0 -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 CUT = 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.
(1.0)
- "8" SPLICE BAR. SHADED AREA SPLICE ANGLE "A" GREATER THAN W, Xt,.
GREATER THAN W2xt2. SHADED AREA - STRINGER
AREA REPRESENTING BULB
SECTION A-A Par 4-58 Page 4-45
Par 4-58 Page 4-46 FIGURE 4-19. APPLICATION OF TYPICAL FLANGE SPLICES
AND REINFORCEMENT (
1) 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.
(2) 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.