Cessna 172 Maintenance Manual page 27

1. General
A. This section provides information covering the materials used for repairs.
2. Repair Materials
A. In general, materials used in the airplane include 2024 and 7075 aluminum alloys. Sheet material
requiring little or no forming will generally be of 2024-T3 clad aluminum. Formed parts, such as ribs,
bulkheads, etc., will be of 2024-T42 clad aluminum. Forgings are of 7075-T73. Materials used in
repairs should be, where possible, of the same material and heat treated to the same temper. The
thickness should be equal to or greater than the material being repaired unless otherwise noted. If
the type of material cannot be readily determined and the forming required is not severe, 2024-T3
may be used generally, since the strength of -T3 is greater than that of -T4 or -T42 (-T4 and -T42 may
be used interchangeably, but they may not be substituted for -T3). When it is necessary to form a
part with a smaller bend radius than the standard bend radius for 2024-T3 or 2024-T4, use 2024-0,
and then heat treat to 2024-T42 after forming. In the event that the original temper was -T3, it may
be necessary to increase the material thickness sufficiently to provide strength equivalent to that of
the original part. It is often practical to cut repair pieces from service parts listed in the parts catalog.
Steel sheet material for reinforcement is 4130 steel heat treated to a minimum of 90,000 pounds per
square inch. The firewall is annealed stainless steel sheet.
3. Extrusions and Formed Sections
A. (Refer to Figure 1.) This section provides information on extrusions and formed sections. It also
provides details of equivalent built up sections for extrusions. Alternative materials are provided for
equivalent sections and formed sections.
B. Use of equivalent built up sections for extrusions are to be utilized only when the proper extrusions are
not available. They are intended to be cold formed from raw stock in sheet forms that have already
been heat treated to the required condition. But when workability is required, the parts may be formed
from 2024-0 aluminum and then heat treated to the -T42 condition before installation. When forming
the section, care must be taken to ensure that the bend radii and the cross section areas are not
reduced below the minimum shown in the diagrams. In some cases, equivalent sections are not
given because it is impractical to build them from sheet stock.
C. Illustrated Parts Catalogs do not identify the standard shape from which parts are fabricated. Detailed
measurements of damaged areas are required to determine the standard section from which parts
are fabricated.
CESSNA AIRCRAFT COMPANY
SINGLE ENGINE
STRUCTURAL REPAIR MANUAL
REPAIR MATERIALS
© Cessna Aircraft Company
51-30-00
Page 1
Jun 1/2005