Bell Eagle Eye TiltRotor UAV
The Bell Eagle Eye TiltRotor UAV demonstrator
was developed to validate and refine basic flying qualities
and performance characteristics of a small scale Tiltrotor
with the potential for future applications to VTOL UAV missions.
Scaled Composites was selected to design and fabricate the
composite structure for the two demonstrator airframes,
including the landing gear, and to integrate Bell-supplied
propulsion and flight control systems.
Because of its dual requirements to both hover
and to fly as a conventional aircraft, the Eagle Eye required
a very complex structural arrangement. Its gas turbine engine
(an Allison C20) is mounted in the center fuselage and is
attached to a combining transmission. Drive shafts from
the combining transmission pass through the center of the
wing and connect to transmissions at each wingtip. The wingtips
house the transmission as well as the actuator used to tilt
the wingtip transmission and rotor assemblies.
The cantilever wing box experiences very diverse
structural loads during hover and conventional forward flight.
An additional challenge was to make the wingbox a fuel tank
(wet wing), while preserving the dry integrity of the transmission
drive shaft conduits.
The composite sandwich fuselage featured three
removable sections; the nose, center section and tail. This
was done to allow for a reduction in overall length during
transport and storage. The nose section was mounted on hinges
to allow easy access to the avionics and other mission equipment.
The center section incorporated the wingbox, fuel tanks
engine and landing gear. Access to the center section is
through the removal of the entire top section of the fuselage.
The removable tail was attached with a simple lightweight
screw row. The tail contains numerous antenna and actuators
for the pitch control surfaces. All of the hard points and
mounts were installed by Scaled and all the system components
including engine, transmissions, oil coolers, avionics,
flight control systems, flaps, and control surfaces were
mounted and checked for clearance, interference and fit
in the fuselage structure before the vehicles were delivered
to Bell. Scaled Composites also manufactured and integrated
all the landing gear components for both vehicles.
The structure was static load tested with
the customer's participation (and to their satisfaction).
Also included was training to educate Bell's customer (the
U.S. Navy) on the composite structures used by Scaled.
Although the first vehicle was damaged in
an accident, the second Eagle Eye demonstrator has been
extremely successful, demonstrating all flight phases from
hover through the transition, and out to over 165 KCAS in
forward flight. This low-cost fast-paced demonstrator program
was yet another highly visible demonstration of Scaled's
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