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The fuselage includes the cabin and/or cockpit, which
contains seats for the occupants and the controls for
the airplane. In addition, the fuselage may also
provide room for cargo and attachment points for the
other major airplane components. Some aircraft utilize
an open truss structure. The truss-type fuselage is
constructed of steel or aluminum tubing. Strength and
rigidity is achieved by welding the tubing together
into a series of triangular shapes, called trusses.

Aircraft Stuctures
[Figure 1-2 The Warren truss]

Construction of the Warren truss features longerons,
as well as diagonal and vertical web members. To
reduce weight, small airplanes generally utilize
aluminum alloy tubing, which may be riveted or
bolted into one piece with cross-bracing members.

As technology progressed, aircraft designers began to
enclose the truss members to streamline the airplane
and improve performance. This was originally accomplished with cloth fabric, which eventually gave way to lightweight metals such as aluminum. In some cases,
the outside skin can support all or a major portion of
the flight loads. Most modern aircraft use a form of this
stressed skin structure known as monocoque or semimonocoque construction.

The monocoque design uses stressed skin to support
almost all imposed loads. This structure can be very
strong but cannot tolerate dents or deformation of the
surface. This characteristic is easily demonstrated by a
thin aluminum beverage can. You can exert considerable
force to the ends of the can without causing any damage.
However, if the side of the can is dented only slightly,
the can will collapse easily. The true monocoque construction mainly consists of the skin, formers, and
bulkheads. The formers and bulkheads provide shape
for the fuselage.


[Figure 1-3 Monocoque fuselage design.]

Since no bracing members are present, the skin must be
strong enough to keep the fuselage rigid. Thus, a
significant problem involved in monocoque construction
is maintaining enough strength while keeping the
weight within allowable limits. Due to the limitations of
the monocoque design, a semi-monocoque structure is
used on many of today’s aircraft.

The semi-monocoque system uses a substructure to
which the airplane’s skin is attached. The substructure,
which consists of bulkheads and/or formers of various
sizes and stringers, reinforces the stressed skin by
taking some of the bending stress from the fuselage.
The main section of the fuselage also includes wing
attachment points and a firewall.


[Figure 1-4 Semi-monocoque construction. ]

Truss—A fuselage design made up of supporting structural members that resist deformation by applied loads.

Monocoque—A shell-like fuselage design in which the stressed outer skin is used to support the majority of imposed stresses. Monocoque fuselage design may include bulkheads but not stringers. Skin Former Bulkhead
Figure 1-3. Monocoque fuselage design. Bulkheads and/or Formers Stressed Skin Wing Attachment Points Firewall
Stringers Figure 1-4. Semi-monocoque construction.

Semi-Monocoque—A fuselage design that includes a substructure of bulkheads and/or formers, along with stringers, to support flight loads and stresses imposed on the fuselage.

On single-engine airplanes, the engine is usually
attached to the front of the fuselage. There is a fireproof
partition between the rear of the engine and the cockpit
or cabin to protect the pilot and passengers from
accidental engine fires. This partition is called a
firewall and is usually made of heat-resistant material
such as stainless steel