CHAPTER 2
AIRCRAFT CONSTRUCTION AND MATERIALS
and other equipment. Fuselages of naval aircraft have
INTRODUCTION
much in common from the standpoint of construction
The Aviation Structural Mechanic is required to be
and design. They vary mainly in size and arrangement
familiar with the various terms related to aircraft
of the different compartments. Designs vary with the
construction. Aircraft maintenance is the primary
manufacturers and the requirements for the types of
responsibility of the Aviation Structural Mechanic
service the aircraft must perform.
(AM) rating. Therefore, you should be familiar with the
The fuselage of most naval aircraft are of all-metal
principal aircraft structural units and flight control
construction assembled in a modification of the
systems of fixed and rotary-wing aircraft. The
monocoque design. The monocoque design relies
maintenance of the airframe is primarily the
largely on the strength of the skin or shell (covering) to
responsibility of the AM rating.
carry the various loads. This design may be divided into
Each naval aircraft is built to meet certain specified
three classes: monocoque, semimonocoque, and
requirements. These requirements must be selected in
reinforced shell, and different portions of the same
such a way that they can be built into one machine. It is
fuselage may belong to any of these classes. The
not possible for one aircraft to have all characteristics.
monocoque has its only reinforcement vertical rings,
The type and class of an aircraft determine how strong
station webs, and bulkheads. In the semimonocoque
it will be built. A Navy fighter, for example, must be
design, in addition to these the skin is reinforced by
fast, maneuverable, and equipped for both attack and
longitudinal members, that is, stringers and longerons,
defense. To meet these requirements, the aircraft is
but has no diagonal web members. The reinforced shell
highly powered and has a very strong structure.
has the shell reinforced by a complete framework of
structural members. The cross sectional shape is
AIRCRAFT CONSTRUCTION
derived from bulkheads, station webs, and rings. The
longitudinal contour is developed with longerons,
LEARNING OBJECTIVE: Identify the
formers, and stringers. The skin (covering), which is
principal structural units of fixed-wing and
fastened to all these members, carries primarily the
rotary-wing aircraft.
shear load and, together with the longitudinal members,
The airframe of a fixed-wing aircraft consists of
the loads of tension and bending stresses. Station webs
five principal units. These units include the fuselage,
are built up assemblies located at intervals to carry
wings, stabilizers, flight control surfaces, and landing
concentrated loads and at points where fittings are used
gear. A rotary-wing aircraft consists of the fuselage,
to attach external parts such as wings alighting gear,
landing gear, main rotor assembly, and tail rotor. The
and engine mounts. Formers and stringers may be
following text describes the purpose, location, and
single pieces of built-up sections.
construction features of each unit.
The semimonocoque fuselage is constructed
primarily of aluminum alloy; however, on newer
FIXED-WING AIRCRAFT
aircraft graphite epoxy composite material is often
used. Steel and titanium are found in areas subject to
There are nine principal structural units of a
high temperatures. Primary bending loads are absorbed
fixed-wing (conventional) aircraft: the fuselage, engine
by the "longerons," which usually extend across several
mount, nacelle, wings, stabilizers, flight control
points of support. The longerons are supplemented by
surfaces, landing gear, arresting gear, and catapult
other longitudinal members, called "stringers."
equipment.
Stringers are lighter in weight and are used more
extensively than longerons. The vertical structural
Fuselage
members are referred to as "bulkheads, frames, and
formers." These vertical members are grouped at
The fuselage is the main structure or body of the
intervals to carry concentrated loads and at points
aircraft to which all other units attach. It provides space
where fittings are used to attach other units, such as the
for the crew, passengers, cargo, most of the accessories,
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