FAA Advisory Circular 43.13-1B
Acceptable Methods, Techniques, and Practices
Aircraft Inspection and Repair
AC 43.13-1B | 1. Wood Structure | 4. Repairs | 1-51. Types of Patches
9/8/98
TABLE 1-2. Minimum recommended bend radii for aircraft plywood.
PLYWOOD
CHARACTERISTICS
10 PERCENT MOISTURE
CONTENT, BENT ON COLD
MANDRELS
AT 90� TO
FACE GRAIN
AT 0� OR 45�
TO FACE
GRAIN
AC 43.13-1B
THOROUGHLY SOAKED IN HOT
WATER AND BENT ON COLD
MANDRELS
AT 90� TO
FACE GRAIN
AT 0�0R 45°
TO FACE
GRAIN
THICKNESS
(INCHES)
.035
.070
.100
.125
.155
.185
.160
.190
.225
.250
.315
.375
NUMBER
OF PLIES
3
3
3
3
3
3
5
5
5
5
5
5
MINIMUM BEND RADIUS (INCHES)
2.0
1.1
5.2
3.2
8.6
5.2
12
7.1
16
10
20
13
17
11
21
14
27
17
31
20
43
28
54
36
0.5
0.1
1.5
0.4
2.6
0.8
3.8
1.2
5.3
1.8
7.1
2.6
6
2
7
3
10
4
12
5
16
7
21
10
1-51. TYPES OF PATCHES. There are
four types of patches: splayed patch, surface
(or overlay) patch, scarf patch, and plug patch.
They are all acceptable for repairing plywood
skins.
of the taper. The difference between the radii
is 5T (5 times the thickness of the skin). If one
leg of the dividers has been sharpened to a
chisel edge, the dividers may be used to cut the
inner circle.
a. Splayed Patch. Small holes with their
largest dimensions not over 15 times the skin
thickness, in skins not more than 1/10 inch in
thickness, may be repaired by using a circular
splayed patch as illustrated in figure 1-13. The
term “splayed” is used to denote that the edges
of the patch are tapered, but the slope is
steeper than is allowed in scarfing operations.
(1) Lay out the patch according to fig-
ure 1-13. Tack a small piece of plywood over
the hole for a center point and draw two circles
with a divider, the inner circle to be the size of
the hole and the outer circle marking the limits
(2) Taper the hole evenly to the outer
mark with a chisel, knife, or rasp.
(3) Prepare a circular tapered patch to
fit the prepared hole, and bond the patch into
place with face-grain direction matching that
of the original surface.
(4) Use waxed paper or plastic wrap,
(cut larger than the size of the patch) between
the patch and the plywood pressure plate. This
prevents excess adhesive from bonding the
pressure plate to the skin. Center the pressure
plate carefully over the patch.
Par 1-50
Page 1-25