Part B. Structural Repair

lack strength for use in primary structures.

Strong alloys can be

formed in their annealed state first and then heat treated, in the

desired shape, to develop their strength. When using a brake to form

metal, be sure that a thin piece of soft metal is placed on the brake

jaws to prevent marring the metal's surface.

The best method for determining the size and number of rivets to use

on a repair is to refer to the direct and general support manual

applicable to the aircraft being repaired.

This manual gives the

essential information needed to perform direct and general support

and depot maintenance on the complete airframe.

All repairs must be made so that the aircraft's original contour is

maintained.

In addition, all repairs must be kept to a minimum

weight.

This is accomplished by using patches as small as

practicable and limiting the number of rivets to what is necessary.

When weight is added in each repair, the aircraft's balance may be so

disturbed that trim and balance tabs may have to be adjusted.

A

patch on the propeller spinner requires a balancing patch to keep the

propeller assembly in balance.

PART B:

STRUCTURAL REPAIR

GENERAL

In making aircraft structural repair, the primary objective is to

restore the damaged parts to their original condition.

Frequently,

the only effective way is to replace the damaged part or parts.

However, each damage must be studied carefully to determine if

repairing or replacing is the course to follow.

If a damaged part

can be repaired, its purpose or function must be fully understood.

The reason for this is that while strength may be the principal

requirement in some structures, others might need totally different

characteristics. For example, fuel tanks, floats, and hulls must be

leak proof; however, cowlings, fairings, and similar parts must be

smooth and streamlined.

This

section

discusses

damage

assessment,

cracks,

damage

classification, corrosion control, corrosion inspection, structural

member stresses, and repair practices.

DAMAGE ASSESSMENT

While inspecting damage, remember that all damage is not obvious

or limited to an immediate location. For example, skin damage

made by shells or shell fragments may be accompanied by damage

to longerons, struts, cables, and so on. A hard landing can

overload one of the landing gears. While inspecting a sprung

shock strut, see if the damage extends to supporting structural

members. When a shock occurs at one end of a member it

is transmitted the entire length of that member. Therefore, all

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