NASA and the U.S. Air Force unveiled a
jet-powered aircraft equipped with state-of-the-art flight control technologies
at a briefing in Oshkosh, Wis. on August 2, 1996. The 8-foot 4-inch aircraft was
built to demonstrate a computerized flight control system that learns as it
flies -- especially important for the demands of ultra high speed flight.
The "LoFLYTE" aircraft has been developed
by Accurate Automation Corporation in Chattanooga, Tenn., for NASA and the Air
Force. Technologies being implemented in the LoFLYTE program could eventually
find their way into commercial, general aviation, and military aircraft.
The experimental LoFLYTE aircraft will be
used to explore new flight control techniques involving neural networks, which
allow the aircraft control system to learn by mimicking the pilot.
The model is a Mach 5 waverider design
which is a futuristic hypersonic aircraft configuration that actually cruises on
top of its shockwave. Waverider aircraft powered by airbreathing hypersonic
engines, would fly at speeds above Mach 4, LoFLYTE represents the first known
flying waverider vehicle configuration, but in upcoming flight tests at NASA's
Dryden Flight Research Center in California it will be flown at subsonic speeds
to explore take-off and landing control issues.
The remotely-piloted aircraft has been
designed to demonstrate that neural network flight controls are superior to
conventional flight controls. Neural networks are computer systems that actually
learn by doing. The computer network consists of many interconnected control
systems, or nodes, similar to neurons in the brain. Each node assigns a value to
the input from each of its counterparts. As these values are changed, the
network can adjust the way it responds.
The LoFLYTE aircraft's flight controller
consists of a network of multiple-instruction, multiple-data neural chips. The
network will be able to continually alter the aircraft's control laws in order
to optimize flight performance and take the pilot's responses into
consideration. Over time, the neural network system could be trained to control
the aircraft. The use of neural networks in flight would help pilots fly in
quick-decision situations and help damaged aircraft land safely even when
controls are partially destroyed.
The main objective of LoFLYTE is to
demonstrate the ability of such a flight control system that learns through
experience, said Robert Pegg of Langley's Hypersonic Vehicles Office. In
addition to experimenting with neural networks, the flight of the model is also
key as a low-speed demonstration of a hypersonic vehicle. "We're very interested
in both outcomes, both the neural net technology and the flight
characteristics," Pegg said.
"We see a big advantage to using this type
of control system in a hypersonic vehicle," Pegg said. "At those high speeds,
things happen so quickly that the pilot cannot control the aircraft as easily as
at subsonic speeds."
The initial configuration for the aircraft
was developed at NASA Langley and then Accurate Automation Corporation
integrated the neural network technology into the Langley design. Successful
tests of the waverider concept in Langley's 12-foot Low-Speed Wind Tunnel and
30- by 60-foot Full Scale Tunnel preceded the development of this model
The construction of the model was
completed at SWB Turbines of Appleton, Wis. This company provided the small
turbine engine that powers the model. The shell of the model was made at
Mississippi State's Raspet Flight Research Laboratory and then shipped to SWB
Turbines so that the radio control gear and the engine could be installed.
The waverider was chosen as the testbed
for the neural networks because the configuration has an inherently high
hypersonic lift-to-drag ratio. If neural networks can control this "worst-case
scenario" configuration, then they should be able to handle any other desired
configuration. The waverider configuration was also chosen because it allows for
long hypersonic cruise ranges of up to 8,000 miles. At an altitude of 90,000
feet the Mach 5 waverider would be able to fly at a rate of one mile per second.
The program contracts are being
administered through the NASA Langley Research Center in Hampton, Va. and the
Air Force Wright Laboratory in Dayton, Ohio, under the Small Business Innovative
Research (SBIR) program.
Pegg also added another positive
implication that LoFLYTE could have. "We want to make the public aware that the
government is getting a good return on its SBIR-invested money," he said. "We
hope this project will help us further demonstrate to the public that the SBIR
program is a viable investment for the American people."
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