Part A. Principles of Repair

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).

PART A:

PRINCIPLES OF REPAIR

GENERAL

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

section.

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.

Failure to

maintain this strength can put a weakening strain on another member

or members.

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.

If the

patch cannot be placed on the outside, use material one gage thicker

than the original material, and put the patch on the inside.

The

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.

Cracking.

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

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