b.Mass Balancing.. - The procedure for checking static balance should consist of rebalancing the aileron on its end bearings in an inverted horizontal position by attaching small weight, in a manner similar to that employed for the elevator. (See figure 98.) After completing the repairs replace the balancing weight at the same point, in the same manner as the original attachment and add sufficient lead sheet to the leading edge to bring the trailing edge up to its original prebalance position.      c. Negligible Damage. - Smooth dents, free from cracks, abrasion and sharp corners may be neglected provided the adjacent rivets and Internal structure are intact. Do not neglect dents in the nose skin which tend to buckle when the aileron is twisted or warped by hand. Where accessible, negligible dents should be restored to shape taking care to avoid the formation of cracks.      d. Reparable Damage.      (1) Nose Skin. - The nose skin may be repaired or reinforced by using external patches which extend to the upper and lower edges of the nose skin as shown in figure 99. The patch must cover the damage and extend to the nearest ribs. Use .025-inch 24ST stock for the patch and attach it with 1/8- inch solid rivets in the beam flanges and 1/8-inch blind rivets in the rib flanges. Use rivet spacing as illustrated in figure 99. Damage to the skin aft of the beam web should be reinforced with .025- inch 24ST sheet of sufficient size to take one row of 1/8- inch blind rivets al 1/ 2-inch spacing around the damage forward of the beam plus at least three of the original AN442AD-4 rivets in the beam flange at each end of the damage. Use a .025-inch shim between the reinforcement and beam flange where the skin patches should be well rounded to prevent their cutting through the fabric.      (2) Nose Ribs. - Damaged nose ribs should be replaced using the same size rivets and pattern where accessible. if blind rivets must be used, use two of the same diameter for each original solid rivet.      (3) Nose Beam Web. - The nose beam web may be patched with .032-inch gage 24ST stock attached by two rows of 1/ 8-inch blind rivets arranged around the damage at 1-inch spacing between rivets and 3/4 inch between rows. (See figure 100.) If the damage is too near a flange to obtain the required rivet pattern, form a 3/4-inch flange on the patch which is long enough to take the existing 1/ Bs inch rivets in the flange, next to the damage, plus two additional rivets at each

end of the damage. If only the flange is damaged reinforce it with a .032-inch gage 3/4-inch by 3/4-inch 24ST angle long enough to take four of the original 1/8-inch rivets in the beam flange at each end of the damage plus four 1/8-inch blind rivets in the back of the channel. To splice the beam use a nestled channel of .032-inch 24ST stock with 3/4-inch flanges approximately 5 inches long and attach this splice channel with four AN442AD-4 rivets in each flange on each side of the cut plus three 1/8-inch blind rivets on each side of the cut in the web of the beam and three 1/8-inch rivets at each end of the splice in the web of the channel. (See figure 100.)      (4) Rib Webs. - Damage to the web of any rib aft of the main beam should be patched with .025-inch gage 24ST sheet using one row of AN442AD-4 rivets at 3/4-inch spacing around the damage. If the damage extends into the radius of either flange add a flange to the patch and use at least two AN442AD-4 rivets-in the rib cap strip at each end of the damage, Damage to the rib flange alone should be reinforced with a .025-inch gage 24ST angle formed to fit into the flange of the rib and pick up the cap strip rivets. (See figure 101.) Use at least two AN442AD-5 rivets through the cap strip approximately 1/2 inch apart at each end of the damage plus any existing intermediate rivets. To splice the rib use a nestled channel (figure 101) of .025-inch gage 24ST aluminum alloy attached with etght AN442AD-5 rivets, four in each cap strip, two on each side of the cut. If the cap strip is damaged replace or insert a new section and splice with a strip of .032-inch gage 24ST using two AN442AD-5 rivets on each side of the cut at 1/2-inch minimum spacing.      (5) Tab Mechanism. - The tab mechanism must be rigidly supported. Any damaged parts should be replaced, and any damaged supporting structure must be carefully reinforced to prevent flutter of the aileron in flight.      (6) Trailing Edge. - For general repair of the trailing edge see figure 102. 10. Wing Tip. Each wing tip is attached by screws and can be easily removed. (See figures 56 and 64.) Wing tips should generally be replaced if damaged. Minor repairs may be effected using blind rivets and following the procedures outlined for repair of the fin and stabilizer. For aerodynamic reasons patches forward of spar No. 3 should be made flush with the skin. For a general repair to the wing tip joint see figure 103.