Document: SLSA-MIP-5-4-0-US
Date of Issue: 05/2016
Revision: -
15-7
15.4.5.2 Repairing the skins with patches
CAUTION
The following procedure is intended for skin repairs only with max. area of the patch up to
200 cm
2
(31 in
2
) (area of the cut out skin). Before riveting the patch check the adjacent part
of the inner structure in the damaged area and find out whether its repair is needed. Place
patches on the fuselage so, that the longer patch side lies in the longitudinal plane of the
airplane (in flight direction), see Fig.15-3. Place patches on the wing so, that the longer patch
side lies in direction of transversal axis of the airplane (parallel with the wing leading edge),
see Fig. 15-3.
Fig. 15-3
Location of patches on the airplane skin
1 - Correctly located patch
2 - Incorrectly located
patch
Mark the damaged surface area (preferably by spirit felt tip) and cut out the most suitable
geometrical shape (circle, square, rectangle).
Be careful that all cracks as well as adjacent corroded areas are cut out. Corners of cut out
holes in the skin must have minimum radius of 12.7 mm (0.5 in) and their edges must be
smoothly filled off.
Size of patch overlapping depends on the cut out of skin area:
patch up to the area of 52 cm
2
(8 in
2
)
– rivet by one row of rivets, the patch edge must
overlap the edge of the cut out hole by minimum 19 mm (0.75 in).
patch with the area over 52 cm
2
(8 in
2
)
– rivet by two rows of rivets, the patch edge
must overlap the cut out hole by minimum 32 mm (1.25 in).
Both ways of patching are shown on Fig. 15-5.
If the damaged area is located near the spars and frames, choose such patch dimension so
that it covers all these elements of structure and it is possible to rivet it (Fig.15
–4).
Types of patches according to their position on the airframe structure.
Surface patches
- These can be used in the areas where surface smoothness is not
important
Sunk patches
- Use for patches on the wing, tail unit and control surfaces.
Surface patches across obstacles and stiffeners in the skin
- pay special attention
to drilling the patch together with the surrounding structure. Attach the patch in several
points and then drill holes for rivets from inner side (if possible). Use original holes in
frames and stiffeners.
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