TM 1-1520-240-BD
(7)
Insert coin patch in cutout from inside
skin. Drill rivet holes through backing plate and skin.
NOTE
Use rivets MS20470AD4, for 0.025-
inch
thick
skin,
and
rivets
MS20470AD5, for skin 0.03 inch or
thicker. Rivet pitch should be
approximately 3/4 inch.
(8)
Remove coin patch from cutout after
establishing a rivet pattern and seal faying surfaces of
cutout and coin patch.
(9)
If damage is less than 1/2 inch and larger
than 3/16 inch and located over an undamaged frame or
stiffener, repair damage by omitting backing plate.
Rivet coin patch to frame or stiffener.
(10)
Install and set rivets.
NOTE
Repair magnesium skin as directed
in
preceding
steps,
providing
dissimilar metals are insulated. Use
rivets MS20470B.
b.
Backing Plate Repair for Webs. This repair is
intended for damage occurring in webs, such as holes,
tears or sharp dents that can be cut out. It must be
repaired within an area not to exceed 1-1/2-inch
diameter. When repaired, it must clear adjacent
structure by 1/8 inch. Not more than two repairs are
permitted in any web.
(1)
Remove damage by cutting or drilling.
The diameter of cutout should not be less than 3/16
inch.
(2)
Smooth edges of cutout with a file.
(3)
If damage can be removed by drilling, drill
a 3/16-inch-diameter hole or smaller. Insert a rivet
MS20470-AD and install a washer AN960D of a size to
fit shank of rivet. Set rivet.
(4)
If diameter of cutout is larger than 3/16
inch, make a circular backing plate from same material
as web, in next heavier thickness.
NOTE
The backing plate must be large
enough to cover cutout and overlap
web a minimum of four times
diameter of rivet. If backing plate
cannot be circular, all comers must
have a minimum radius of 1/4 inch.
(5)
Smooth edges of backing plate with a file.
(6)
Center backing plate over cutout. Drill a
rivet pattern having a pitch of 1/2 to 3/4 inch. The
number of rivet holes will be determined by size of
backing plate. Maintain a pattern that will allow a
minimum edge distance of two-times diameter of rivet.
Use rivets MS20470AD4, for webs not thicker than
0.025 inch. Use rivets MS20470AD5, for webs 0.03 inch
or thicker. Use monel rivets for corrosion-resistant steel
webs.
(7)
Apply a thin even coat of primer (item
113, Appendix C) to faying surfaces of backing plate
and web. Allow primer to dry.
(8)
Assemble backing plate to web by
installing and setting rivets.
2-60
