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Technology update
Ultralight flying wing takes to the sky at NASA Dryden
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The remote-piloted Helios Prototype flying wing made its maiden flight from NASA Dryden Flight Research Center, Edwards, CA. The aircraft, which has a maximum altitude of 100,000 ft, can remain at a 50,000-ft altitude for a period of four days.
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Making its maiden flight out of NASA's Dryden Flight Research Center, Edwards, CA, the remote-piloted Helios Prototype was aloft for one hour and 15 minutes over Rogers Dry Lake, which is adjacent to the center. The Helios Prototype is a slow-flying, ultralight flying wing designed for long-duration, high-altitude Earth science or telecommunications relay missions. It is one of several technology demonstrators developed under NASA's Environmental Research Aircraft and Sensor Technology (ERAST) program. Developed by Aero Vironment, Inc., of Monrovia, CA, the unique aircraft is intended to demonstrate two key missions: the ability to reach and sustain horizontal flight at 100,000 ft altitude for at least a day, and to maintain flight above 50,000 ft altitude for at least four days, both on electrical power derived from solar energy.
During the test flight, controllers performed a variety of functional checkouts including data collection on the aircraft's handling qualities, stability and control, and overall performance. Although the aircraft was designed to be powered by a complex array of high-efficiency solar cells that cover the upper surface of the large wing, initial flight testing is being conducted on battery power.
According to project officials, about 95% of the flight's primary test points and objectives were met. However, an unexpected deployment of a small parachute designed to keep the aircraft within a restricted airspace zone in case of control loss ended the flight prematurely. The flying wing descended from an altitude of about 100 ft in a gentle left turn and landed safely on the lakebed without incurring any damage. The anomaly appeared to be due to an electrical system failure, but the flight test team is conducting an investigation of the cause. It will present recommendations for any corrective action prior to the aircraft's next test flight.
The Helios Prototype is an enlarged version of the Centurion flying wing, which flew a series of test flights at Dryden in late 1998. The aircraft has a wingspan of 242 ft, 41 ft greater than the Centurion,
2 1/2 times that of the solar-powered Pathfinder flying wing, and longer than either the Boeing 747 jetliner or Lockheed Martin C-5 transport aircraft. Upgrading the Centurion to the Helios Prototype configuration, Aero Vironment added a sixth wing section and a fifth landing gear pod. The additional wingspan increases the area available for solar cell installation and improves aerodynamic efficiency, allowing the aircraft to fly higher, longer, and with a larger payload than the Centurion. Other additions to the Helios Prototype include a differential GPS system to improve navigation, an extensive turbulence monitoring system payload to record structural loads on the aircraft, and radiator plates to assist in cooling the avionics at high altitudes where there is little air to dissipate heat.
During later test flights, Aero Vironment's flight test engineers will evaluate new motor-control software designed to allow the aircraft's pitch to be controlled entirely by the motors. If successful, production versions of the aircraft could eliminate the elevators on the wing's trailing edge, which are currently used for pitch control. This will save weight and increase the amount of wing area available for solar cell installation.
The current Helios Prototype flight test program involves two phases consistent with the aircraft's two target missions. The first phase of testing, scheduled for 2001,
focuses on meeting key technology requirements of the Centurion mission to reach and sustain flight at 100,000 ft altitude. For this phase, the aircraft will use all 14 motors and minimal ballast to save weight.
The second phase, scheduled for 2003, will focus on the four-day mission above 50,000 ft. For those flights, eight motors will power the prototype and more than 500 lb of ballast will be added to simulate the weight of the energy storage system now under development. Fewer motors will be needed for this mission due to the lesser altitude requirements. The excess electrical energy generated by the solar arrays during the daytime is diverted to the energy storage system, which releases electricity to power the aircraft after dark. With other system reliability improvements, NASA expects that production versions of the Helios will be capable of flying missions lasting months at a time, becoming true "atmospheric satellites."
Other aircraft involved in the ERAST program include the Perseus B, developed by Aurora Flight Sciences of Manassas, VA; the Altus II, developed by General Atomics Aeronautical Systems of San Diego, CA; and the Proteus, developed by Scaled Composites of Mojave, CA. The Perseus B, which is also beginning a new series of developmental flight tests at Dryden, and the Altus II are conventionally powered with turbocharged piston engines, while the tandem-winged Proteus is an optionally piloted aircraft powered by twin turbofan engines.
Frank Bokulich
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