split and inserted or rotated into position.
In flush patches, the
filler must be of the same gage and material as the original skin,
and the doubler generally must be one gage heavier.
Repairs on hulls and floats must be watertight, and pressurized
compartment repairs must be sealed against pressure loss.
Whenever
possible, the manufacturer's sealing method must be used.
A
recommended method includes cleaning contact surfaces, removing any
burrs and chips, using zinc-chromate tape and paste, and bringing the
mating surfaces together with machine screws and nuts to complete the
seal.
Installing flush access doors is an easy and efficient way to repair
internal structures and some skin areas.
Such doors consist of a
doubler and a stressed access coverplate. The doubler is riveted to
the skin, and the plate is attached to the doubler with nut plates
and machine screws.
The number of patches or repairs can be so numerous or the skin
damage so extensive that panel replacement is required.
Inspecting
such areas includes a careful examination of internal structures.
Bent, fractured, or wrinkled members must be repaired or replaced.
Rivets in the vicinity must be inspected for failure. The technical
manual for the particular aircraft must be consulted to determine the
rivet inspection procedure.
The gage and alloy for the replacement panel is shown in the
applicable manual for the specific aircraft. Either of two ways can
be used to determine the new panel's size.
Dimensions can be
measured during inspection, or the old skin can be used as a
template. The latter method is more accurate and is preferred. The
new sheet is drilled near the center using the holes in the old sheet
as a guide.
The two sheets are held together with sheet metal
fasteners as the holes are drilled outward from the center. Lacking
a template the holes in the reinforcing members are used as guides to
drill the new holes. Sheet metal fasteners are used here as with a
template. Because most ribs, stringers, and bulkheads depend on the
skin for some of their rigidity, duplicating holes from the frame or
reinforcing members must be done with care.
Drilling pressure can
force the skin away from the frame and make the holes out of
alignment. A wood block held firmly against the skin while drilling
can prevent this. Unless the drill is held at a 90 angle, the holes
will be out-of-round. Where a straight drill cannot be inserted, an
angle attachment or flexible-shaft drill is necessary.
New hole
locations can be marked with a soft pencil, a prick punch, or a hole
finder.
71
AL0992
A straight bucking bar is preferred because its weight can be applied
in a direct line with the rivet's shaft.
Where internal structural
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