laminated with plies arranged in various directions to
Q5-9. What type of coating is frequently used to
give the structure strength and stiffness.
protect frontal surfaces of reinforced plastics
exposed to high speeds?
The much stiffer fibers of boron, graphite, and
KevlarŪ have given composite materials structural
A hole, break, or crack in one or both facings,
properties superior in strength to the metal alloys that
resulting in damage to the honeycomb/core, is
they have replaced. Specific applications of advanced
referred to as what type of damage?
composite materials and approximate percentages of
What type of repair patch is normally used to
total aircraft structures for some of our modern-day
ensure aerodynamic smoothness on aircraft
aircraft are shown in table 5-1.
Composites are attractive structural materials
TYPES OF ADVANCED COMPOSITE
because they provide a high strength-to-weight ratio
and offer design flexibility. The function of a composite
is to replace heavy/dense metals with stronger, lighter
The reduced availability of natural resources, the
weight structural components, allowing lightweight
increasing costs of production, and the apparent limit to
aircraft to carry payloads farther distances using less
our ability to fabricate high strength-to-weight metallic
fuel. In contrast to traditional materials of construction,
components necessitated the development of new
these materials can be adjusted to more efficiently
materials to meet the demands of aerospace technology.
match the requirements of specific applications.
In the following text, you will be introduced to the
These materials are highly susceptible to impact
materials that provide high-performance capability
damage, with the extent of damage being visually
now, with great expectations for the future. These
difficult to determine. A nondestructive inspection
materials are called advanced composite materials and
(NDI) is required to analyze the extent of damage and
will be used to replace some of the metals currently
effectiveness of repairs.
used in aircraft construction.
Composites are classed by the type of reinforcing
Advanced composites are materials that consist of
elements. These elements may be fibers, particle, flake,
a combination of high-strength stiff fibers embedded in
or laminar materials. They are further classified by the
a common matrix (binder) material, generally
Table 5-1.--Aircraft Advanced Composite Application Usage
Advanced Composite Application
Wings, Horizontal and Vertical Stabilizers, and
Wings, Horizontal Stabilizers, Overwing Fairing,
Forward Fuselage, and Control Surfaces
Gearbox, Transmission Pylon, Drive Shaft and Nose
Rotor Blade Trailing Edge and Scarf Joints
Upper and Lower Canopy, and Drive Shaft Cover