The Raptor Demonstrator high altitude long
endurance UAV program began with a contract award from Lawrence
Livermore National Laboratory to Scaled Composites on June
5, 1992. In order to satisfy rigorous performance criteria
of flight up to 65,000 ft and 48-hr plus endurance, a high
fuel fraction and light weight composite structure were
necessary.
In order to reach altitudes of 65,000 ft,
the Raptor used a two-stage turbocharged, 100 hp, highly
modified Rotax engine. This propulsion package was successfully
tested in an altitude chamber to over 70,000 ft altitude.
Additionally, Scaled was responsible for the design, manufacturing,
and development of the high-altitude propeller system, a
2-blade all-graphite controllable pitch unit. Initial flight
testing used an unmodified normally aspirated Rotax 912
engine with a 3-blade fixed pitch propeller. The structure
is the same type that was used on the record setting around-the-world
Voyager aircraft. The wings and fuselage were oven cured
prepreg graphite tape with honeycomb core. In order to minimize
tooling costs, the fuselage was a simple slab sided shape
cut from flat honeycomb and graphite panels.
Scaled also designed, developed, and tested
all Raptor flight controls, including autopilot, autonomous
navigation, and emergency recovery systems.
The first flight of the Raptor occurred April
27, 1993, just ten months after contract award. Funds expended
at this point were only about $800,000. During its flight
tests, the Raptor verified its low-altitude performance,
structural integrity, and control system operations.
In 1995, the Raptor program was transferred
to NASA under the Environmental Research Aircraft and Sensor
Technology program as a flying testbed for technologies
applicable to future high altitude UAVs (www.erast.com).
The airplane was flown in a manned "Safety
Piloted" configuration to allow testing of changes
to the flight control system with minimal risk to the airframe.
The safety pilot was provided manual controls which can
over-ride control system commands. This somewhat novel approach
allowed rapid development of the vehicle handling qualities
and evaluation of the flight controls at low cost and program
risk.
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