resistance to cyclic stressing if it is in a corrosive environment.
CORROSION INSPECTIONS
At periodic inspections all equipment must be examined for corrosion.
Without such examinations and removal of any corrosion found, an
aircraft can be seriously damaged.
Locations to examine include
unpainted aluminum surfaces, skin seams, and lap joints.
Nicks and
crevices where traces of cleaning compound may have accumulated and
unexposed areas where moisture can accumulate must also be inspected
for corrosion.
Locations where corrosion can form and that require
examination include possibly plugged drain holes, structures under
floorboards, and jointed surfaces.
Fittings, braces, and compound parts inside the aircraft must be
inspected for corrosion because of possibly faulty drainage or
disposal outlets.
Inspections for corrosion must be made where
dissimilar metals contact or where spot welds, piano-type hinges, and
exhaust-gas paths are located.
Wheel wells, landing gear, dive
brakes and similar areas, heavy or tapered aluminum skin surfaces,
battery boxes and components, and relief tube outlets must also be
inspected as possible sites for corrosion.
STRUCTURAL MEMBER STRESSES
An aircraft at rest or in flight is subject to applied forces
throughout its entire structure.
At rest, the weight (pull of
gravity) of the wings, fuselage, engines, and empennage causes forces
to act downward on the wing and stabilizer tips, along the spars and
stringers, and on the bulkheads and formers. These forces are passed
from member to member causing bending (tension and compression),
twisting (torsion), compression, and shearing.
The five stresses in an aircraft are tension, compression, shear,
bending, and torsion. The first three of these forces are generally
called the basic stresses, and the last two are called the
combination stresses.
Stresses rarely act singly.
Their action is
usually combined.
In airframe repair, the stresses most frequently
encountered are bending, torsion, and shear.
The paragraphs that
follow describe the application of these forces.
Tension. Tension in airframe repair is the force that
stretches a structural member. Notice in Figure 2-1 the
conditions of the metal strap under the applied force.
Under
tension, the top of the metal strap is being pulled and
the underneath side is being pushed together (compressive force).
Some of the strap's material was removed by drilling a hole in
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