This lesson, divided into five parts, discusses general repair
principles, structural repair, stressed skin repairs, internal
structure repair, and structural sealing.
Because the discussions
are general and describe typical repairs made in maintaining Army
aircraft, specific repairs for specific aircraft must be made
according to the applicable technical manual (TM).
PRINCIPLES OF REPAIR
This section covers maintaining original (design) strength, original
contour, and minimum weight: the bases for airframe repairs. Again,
the discussion in this section is basic.
It is comparable to the
form into which concrete will be poured to make a good foundation.
This section is closely tied to damage assessment in the next
Without a firm basis on which a valid assessment can be
made, no worthwhile repair can be made.
MAINTAIN ORIGINAL STRENGTH
In so far as aviation maintenance is concerned, any repair must
maintain the repaired member's original strength.
maintain this strength can put a weakening strain on another member
The paragraphs that follow discuss five basic
considerations in maintaining original strength.
Compression or Bending. If a member or fuselage skin is subject to
compression and needs patching, put the patch on the outside to
ensure higher resistance to compression or bending loads.
patch cannot be placed on the outside, use material one gage thicker
than the original material, and put the patch on the inside.
patch must have a cross-sectional area equal to, or greater than, the
original damaged section.
The general rule here is to regain, as
near as possible, the original strength.
Circular or oval patches must be used to reduce the
danger of cracks starting at the corners.
If a rectangular patch
must be used, make the curvature radius at each corner no smaller
than 1/2 inch.
Buckled or bent members must be replaced or
reinforced by putting splices over the affected areas.
Similarity of Material. Be certain that all replacement
or reinforcement material used is similar to the original
material used. If substitutions are necessary, use material
of a gage heavy enough to give an equivalent cross-sectional
strength. Substituting a lighter gage but stronger material for the