Service and Repair Manual

l/8 inch of the length of the damage as seen in a vertical cross section of the longerons. For sections aft of bulkhead No. 5 use one for each 5/18 inch of damage. The width of the patch should be at least 25 percent greater than the cross-sectional length of the damage and should be formed with a flange if a corner or bent part of the longeron is damaged. Rivet the flange of the patch to the longeron.

     Small damages to the back of the longeron may be neglected if after cutting away the damaged material the adjacent corners or legs are undamaged. Replace any damaged reinforcements, fittings, and gussets and use the rivet patterns given in figure 31 to attach new sections of the cabin track.

     c. Repair of Lower Longeron. - The extruded angle which is attached to the lower edge of the fuselage may be spliced between stations 3 and 4 as shown in figures 15 and 32. Minor damages to this member may be patched or reinforced with 3/18-inch 24ST sheet stock attached by one 3/16-inch A17ST rivet at each end of the damage for each 1/8-inch length of damage as seen lna vertical cross section. The cross section of each patch should be at least 25 percent greater than the maximum cross section of the damage.

     The extruded "T" section which is attached to the upper surface of the wing cannot be repaired.

     Any damage which exceeds that caused by the bolt and rivet holes ln adjacent cross sections will necessitate complete replacement of this extrusion. Any damage to the gusset straps which reinforce the lower edges of the skin above the wing should be repaired by patching with 24ST sheet of the same gage as the damaged gusset using one 3/ 18-inch Al? ST rivet for each 5/16 inch of damage measured along the cross section of the gusset or three rows of 3/16-inch rivets at 1-inch spacing around the damage.

     6. Bulkheads,

     a. General. - All bulkheads are designated by numbers counting aft from the fire wall. (See figure 10.) Each bulkhead is splotched on the horizontal reference line. The outer flange face of the bulkheads is cut out so as to clear the stringers. Due to the variation of design, the bulkheads or formed channels are individually paragraphed. When effecting a repair to the bulkheads, follow the procedure outlined for each specific case. in general the bulkheads are accessible. However, in some cases, the location of the damage may necessitate the dismantling of surrounding flutings and the stripping of the structure. All damaged fittings, clips, gussets, etc., should be replaced. Bulkhead patches and splice plates should be formed from sheet stock of the same gage and material as the damaged bulkhead. Splice plates should be formed with flanges as channels and inserted into the bulkhead. Rivet or bolt patterns are given for each bulkhead in the paragraphs which follow. A distinction is maintained between attachment to webs and attachment to flanges.

     b. Types of Damage.

     (1) Negligible Damage. - Small smooth isolated dents may be neglected provided the dents are free from cracks, abrasions, and sharp corners, and the adjacent rivets and bolts are not disturbed. Small holes tn webs which after clean-up do not exceed an inch in diameter and are at least 1/2 inch from the nearest hole, edge of sheet, or inside flange may be neglected except in bulkhead sections which are reinforced.

     (2) Cracks. - All cracks located in any part of the bulkhead structure must be drilled at the ends to prevent them from spreading. Use a l/8-inch drill, whether the crack is considered negligible or otherwise. Cracks up to 1 inch in length and 1/2 inch from the inside flange or nearest rivet hole may be neglected.

     c. Bulkhead No. 1.

     (1) Bulkhead Frame. - The channel sections which form the frame around this bulkhead (figure 32A), should tn general be replaced lf damaged because of the low design margins and the difficulty of attaching repair material. (See figure 14.)

     (2) Vertical Channels. - Minor repairs to the vertical channels may be effected in some cases by adding 24ST patches of the same gage as the damaged material. The design stresses in the flanges and in the bent material at the corners between the flanges and the back of the channels is such that the patch material must be attached with at least one 3/16-inch Al7ST rivet above and below the damage for each 1/8 inch of damage measured horizontally after t.he damaged material has been cleaned away. For damage to the back of a channel use one 3/16-inch rivet above and below for each 3/18 inch of damage. The patching material should have at least 25 percent more cross-sectional area than the horizontal cross section of the damaged material and should be formed with a flange if the corner of the channel is damaged. Use the original rivet spacing and where possible the original rivet holes in attaching all reinforcing material.

     (3) Lower Cross Member. ~ Minor repairs to either leg or to the back of the lower cross channel may be made using the data given tn figure 33. For more extensive damage or damage requiring the use of more than two such patches the channel should be replaced as in figure 14.

     (4) Upper Cross Member. - The hat section forming the upper cross member may be spliced as shown in figure 34 to facilitate the insertion of a new section. Minor damage to a leg or flange may be patched with an .081-inch 24ST angle attached with sixteen 3/16-inch Al7ST rivets or four in each leg at each end of the damage plus those which are necessary in the damaged area. Use the existing rivet spacing.