FAA Advisory Circular 43.13-1B
Acceptable Methods, Techniques, and Practices
Aircraft Inspection and Repair
AC 43.13-1B | 1. Wood Structure | 4. Repairs | 1-49. Repairs to Single Curvature Plywood Skin
AC 43.13-1B
9/8/98
A, B, C, D = ORIGINAL DIMENSIONS
FIGURE 1-8. Method of splicing box spar flanges (plate method).
shown in section B-B, is continued the full
distance between spars.
(3) Figure 1-12(C) illustrates a com-
pression rib of the “I” type with a rectangular
vertical member on each side of the web. The
method of repair is essentially the same as in
figure 1-12(A) except the plywood reinforce-
ment plates on each side, shown as striped
blocks in section C-C, are continued the full
distance between spars.
1-47. PLYWOOD SKIN REPAIR. Make
extensive repairs to damaged stressed skin
plywood structures in accordance with specific
recommendations from the aircraft manufac-
turer. It is recommended that repairs be made
by replacing the entire panel, from one struc-
tural member to the next, if damage is very
extensive. When damaged plywood skin is re-
paired, carefully inspect the adjacent internal
structure for possible hidden damage. Repair
any defective frame members prior to making
skin repairs.
1-48. DETERMINATION OF SINGLE
OR DOUBLE CURVATURE. Much of the
outside surface of plywood aircraft is curved.
On such areas, plywood used for repairs to the
skin must be similarly curved. Curved skins
are either of single curvature or of double
(compound) curvature. A simple test to de-
termine which type of curvature exists may be
made by laying a sheet of heavy paper on the
surface in question. If the sheet can be made
to conform to the surface without wrinkling,
the surface is either flat or single curvature. If
the sheet cannot be made to conform to the
surface without wrinkling, the surface is of
double curvature.
1-49. REPAIRS TO SINGLE CURVA-
TURE PLYWOOD SKIN. Repairs to single
curvature plywood skin may usually be formed
from flat plywood, either by bending it dry or
after soaking it in hot water. The degree of
curvature to which a piece of plywood can be
bent will depend upon the direction of the
grain and the thickness. Table 1-2 is a guide
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