NASA RESEARCHING ENGINE AIRFLOW CONTROLS TO IMPROVE PERFORMANCE AND FUEL EFFICIENCY August 27, 1997 Release: 97-33 Printer Friendly Version
Two NASA aeronautics research facilities are working together to develop and flight validate an ad-vanced engine airflow control system that is expected to significantly increase propulsion system perform-ance on both military and commercial aircraft turbine engines. Under the High Stability Engine Control project, NASA's Dryden Flight Research Center, Edwards, Calif., and Lewis Research Center, Cleveland, Ohio, are working together to evaluate a computerized system that can sense and then respond to high levels of engine inlet airflow turbulence or distortion, thereby preventing sudden in-flight engine compressor stalls and potential engine failures. Turbine engines used on today's military and commercial aircraft operate with a high "stall margin" as a safety feature, in order to prevent compressor stalls under adverse or turbulent airflow conditions. The built-in stall margin prevents the engines from operating at peak efficiency when the airflow is stable.
The NASA research program, however, has developed a Distortion Tolerant Control system that uses measurement-based, real-time estimates of inlet airflow turbulence to both enhance engine stability when the airflow is distorted, and increase engine performance when the flow is stable. The technology incorpo-rates a Distortion Estimation System which includes an aircraft-mounted high-speed processor that senses changes in airflow at the front of the engine. The processor, in turn, directs the aircraft's engine control computer to automatically command engine trim changes to accomodate for changing airflow distortion conditions. "The primary benefit of Distortion Tolerant Control is its ability to set the stability margin requirement on-line and in real-time," said John DeLaat, program manager at NASA Lewis. "This can allow the built-in stall margin to be reduced, which can then be traded for increased performance, decreased weight, or both. The result will be higher-performance military aircraft and more fuel-efficient airliners," he added.
The High Stability Engine Control system was flight tested at NASA Dryden on the center's Advanced Control Technology for Integrated Vehicles (ACTIVE) aircraft, a highly-modified F-15 which is explor-ing a variety of advanced control system technologies. The F-15's right engine was heavily instrumented for the experiment, while its left engine remains in the standard configuration.
"The F-15 ACTIVE aircraft is an ideal flight research testbed for advanced technologies such as this system," said John Orme, Dryden's principal investigator on the project. "The aircraft's fly-by-wire con-trol system allows for minimum modifications to integrate research systems. Additionally, propulsion testing on only one of the two engines reduces the flight safety risk inherent with most new technologies."
Flight demonstrations of the experiment were conducted in two phases. The first "open loop" phase, completed Aug. 8, focused on gathering baseline data on inlet airflow distortion. The second "closed loop" phase, which concluded Aug. 26, fed that data into a Stability Management Control device in the aircraft's electronic engine control computer which then gave trim commands to the right engine to ac-commodate for airflow distortion.
Project pilots flew the modified F-15 through a variety of maneuvers designed to create unstable or distorted airflow conditions in the engine air inlets, including nose-high angles (angle of attack) up to 25 degrees, full-rudder sideslips, wind-up turns, split-S descents, takeoffs and simulated fighter maneuvering. Test-point speeds ranged from Mach 0.3 to 1.6, and altitudes from 5,000 to 45,000 feet. "Flight testing involved some of the most aggressive maneuvering the ACTIVE aircraft has accom-plished," Orme noted. "The F100-PW-229 engine is an exceptionally stable engine with a very low inci-dence of inlet turbulence-induced stalls, so we had to operate the instrumented engine in off-design high-distortion conditions to assure we could achieve system-commanded engine trims."
The High Stability Engine Contrlol research is sponsored and managed by NASA Lewis, while NASA Dryden was in charge of the flight test phase. Also providing support were engine manufacturer Pratt & Whitney, West Palm Beach, Fla., which developed the system calculations; Boeing Phantom Works (formerly McDonnell-Douglas), St. Louis, Mo., which assisted in system integration; and the U.S. Air Force's Wright Laboratories, Wright-Patterson AFB, Ohio, which owns the aircraft. Five pilots--three NASA and one each from the Air Force and Boeing Phantom Works--flew the research missions.
--nasa-- Note to Editors: Still photos and video footage are available from the Dryden Public Affairs Office to support this re-lease. Among still photos available are: EC96-43456-1 Takeoff of F-15 ACTIVE aircraft flown in High Stability Engine Control project.
For photo prints or video dubs, please call (805) 258-3449 or (805) 258-2665. Photos are also available on the Internet under NASA Dryden Research Aircraft Photo Archive, Dry-den News and Feature Photos, URL:
/centers/dfrc/Gallery/Photo/index.html
NASA Dryden news releases are also available on the Internet at:
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