several dimensions, and then figure the bend allowance
according to the repair diagram. If the damage is within
for the material consumed in each bend before you are
the limits of negligible damage, it may be disregarded
able to lay out the overall length or width of a part.
unless it is necessary to close the hole for aerodynamic
smoothness. If the damage exceeds the limits of
On very accurate layouts, a magnifying glass is
negligible damage, it must be repaired according to the
frequently used as an aid to precision work. A
repair diagram or replaced.
magnifying glass enlarges the graduations on a scale
and makes them easier to read. It helps locate center
Layout for Repair
punch marks, and it allows a close inspection of the
accuracy of the completed layout.
Information needed to fabricate replacement parts
is usually found on blueprints, while information
Use the same layout procedures to lay out material
concerning repairs may be found in the aircraft
for repairs that you used for sheet metal repairs. In the
structural repair manual. The manual contains
layout of a part, you should plan the bending and
information on extrusions and the necessary data for
forming operations so that each step is made in the
the fabrication of various sheet metal equivalents.
proper sequence. If the steps are not made in the proper
sequence, the part may become so bulky that it will be
The aircraft structural repair manual will indicate
impossible to insert in the brake to make the final bend.
the type of material to be used in each repair. If the
correct material is not available, the General Manual
Since layout of replacement parts involves the
for Structural Repair, NAVAIR 01-1A-1, should be
interpretation of blueprints, you should review
checked for an acceptable substitute.
Blueprint Reading and Sketching, NAVEDTRA 14040.
The fabrication of sheet metal parts for internal
TYPES OF REPAIRS
structural repair requires careful adherence to the
accepted standards of aircraft sheet metal work. This
The type of repair to be made will depend on the
includes accurate calculation of bend allowance and
materials, tools, amount of time available, accessibility
careful layout of all dimensions. Layout is the
to the damaged area, and maintenance level. The types
interpreting and transcribing of information from
of repair are permanent, temporary, and one-time flight
blueprints, drawings, or written instructions for the
(ferry). Repairs are also classified as either internal or
metal that will be made into a part for an aircraft.
external.
If several parts are to be fabricated, the dimensions
A permanent repair is one that restores the strength
may be transferred to a template. Working from a
of the repaired structure equal to or greater than its
template ensures a higher degree of uniformity and
original strength and satisfies aerodynamic, thermal,
speeds production.
and interchangeability requirements. This ensures the
designed capabilities of the aircraft.
The procedure for making a layout either for a
template or for the actual part is essentially the same.
The temporary repair restores the load-carrying
Layout of a part or a template consists principally of
ability of the structure but is not aerodynamically
marking the flat sheet so that all drilling, cutting,
smooth or able to satisfy interchangeability
bending, and forming operations are indicated on the
requirements. This repair should be replaced by a
sheet. It is a comparable level 3 drawing that has been
permanent type as soon as possible in order for the
marked up in sufficient detail to clearly indicate the
aircraft to be restored to its normal condition.
fabrication requirements for each piece/part.
The one-time flight repair restores a limited
The sheet metal layout may be made from printed
load-carrying ability to the damaged structure in order
instructions, but it is more often made directly from the
to fly the aircraft to a depot maintenance activity for a
blueprint. Accuracy in all details is essential. You
permanent repair. When this type of repair is made, the
should not transfer dimensions directly from the
aircraft cockpit should be placarded to limit the
blueprint to the layout because the print material may
performance of the aircraft.
have stretched or shrunk, which causes minor distortion
of the dimensions. Measurements indicated on the
External Repair
blueprint are made on the layout.
After the damage has been inspected and classified
Details are often left out and must be developed in
on external surfaces, the structural repair manual for the
the shop. You may, for example, find that you must add
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