TM 1-1520-240-BD
2-3. AIRFRAME. The airframe structure consists of two
parts the primary structure and the secondary structure.
Both are made mostly of high-strength aluminum alloy.
(See Figure 2-28).
a.
Primary Structure. The primary structure is the
skeleton framework that gives the helicopter its shape.
Stringers and longerons extend fore and aft. They are
supported by frames and bulkheads that extend across
the width of the fuselage. Formers and beams are used
where needed to support loads such as power-plants,
transmissions, and landing gear.
b.
Secondary Structure. (Figure 2-29). The
secondary structure is made up of aluminum panels that
are riveted to the primary structure. The panels are
stressed to help provide strength and stiffness to the
helicopter.
Other
panels
protect
and
provide
aerodynamic fairings over components. The airframe is
built in four sections cockpit, cabin fuselage, aft
fuselage, and pylon. The cockpit is spliced to the cabin
fuselage at station 160. The aft fuselage is spliced to
the cabin fuselage at station 440. The pylon is attached
to the aft fuselage at water line 72. The cockpit and
fuselage sections cannot be separated. The pylon can
be removed if needed to transport the helicopter.
c.
Cockpit. (Figure 2-30). The cockpit section
contains controls and the fully adjustable pilot's and
copilot's seats. The forward transmission is mounted at
the top of the section; covered by a fiberglass fairing. A
hinged work platform is built into each side of the fairing.
Three self-tuning dynamic absorbers are installed in the
cockpit section. One is in the nose and two are below
the cockpit floor, under the seats. The absorbers
automatically adjust themselves to lower vibration in the
helicopter throughout its normal operating range. The
section contains three doors. A jettisonable door is next
to each seat. The main entrance door is at the aft right
side of the section. There are three windshields in the
cockpit pilot's, copilot's, and center. Each consists of
three layers. The middle layer of all windshields is
plastic. Inboard and outboard layers are either glass or
plastic. The pilot's and copilot's windshield can be
heated electrically for anti-icing or defogging. The
center windshield can be heated for defogging only.
Each windshield has a temperature sensing element to
provide automatic temperature control.
Figure 2-28. Airframe
2-33
