Future aircraft turbine engines, both commercial and military, will have to be able to successfully accommodate expected increased levels of steady-state and dynamic engine-face distortion. Advanced tactical aircraft are likely to use thrust vectoring for enhanced aircraft maneuverability. As a result, the engines will see more extreme distortion levels than currently encountered with present-day aircraft. Also, the mixed-compression inlets needed for the High-Speed Civil Transport (HSCT) will likely encounter disturbances similar to those seen by tactical aircraft, in addition to planar pulse, inlet buzz, and high distortion levels at low flight speed and off-design operation.
Distortion tolerant control. (Engine cutaway copyright Pratt & Whitney; used with permission.)
The current approach of incorporating sufficient component design stall margin to tolerate these expected levels of distortion would result in significant performance penalties. The objectives of NASA's High Stability Engine Control (HISTEC) program, which has reached a highly successful conclusion, were to design, develop, and flight demonstrate an advanced, high-stability, integrated engine control system that uses measurement-based real-time estimates of distortion to enhance engine stability. The resulting distortion tolerant control adjusts the stall margin requirement online in real time. This reduces the design stall margin requirement, with a corresponding increase in performance and decrease in fuel burn.
The HISTEC approach includes two major systems: a Distortion Estimation System (DES) and Stability Management Control (SMC). The DES is an aircraft-mounted, high-speed processor that estimates the amount and type of distortion present and its effect on the engine. It uses high-response pressure measurements at the engine face to calculate indicators of the type and extent of distortion in real time. From these indicators, the DES determines the effects of the distortion on the propulsion system. In addition, the DES uses maneuver information from the flight control to anticipate high distortion conditions. The DES output consists of fan and compressor pressure ratio trim commands that are passed to the SMC. The SMC performs a stability audit online by using the trims from the DES and then accommodates the distortion through the production engine actuators.
In-flight fan distortion accommodation.
Last year, the HISTEC distortion tolerant control system was flight tested on the NASA F-15 ACTIVE aircraft at the NASA Dryden Flight Research Center in Edwards, California. The flight demonstration showed closed-loop control operation with the engine fan and compressor stall margins being adjusted on the basis of estimated distortion. Project pilots flew the F-15 ACTIVE aircraft through a variety of maneuvers-such as high angle of attack flight, windup turns, and takeoff-which create distorted airflow conditions at the inlet. Detailed analysis of the flight test data performed this year verified that both the DES and SMC performed as designed. The system was able to successfully modify the engine pressure ratio (EPR) limit in response to high levels of distortion, thus temporarily moving the operating line to accommodate the lower stability condition.
F-15 ACTIVE aircraft.
The NASA Lewis Research Center conducted the HISTEC program in partnership with the NASA Dryden Flight Research Center, Pratt & Whitney, Boeing Phantom Works (formerly McDonnell Douglas), and the U.S. Air Force.
Find out more about the High Stability Engine Control distortion tolerant control technologies.
DeLaat, J.C.; Southwick, R.D.; and Gallops, G.W.: High Stability Engine Control (HISTEC). AIAA Paper 96-2586 (NASA TM-107272), 1996. (Available online: http://gltrs.grc.nasa.gov/cgi-bin/GLTRS/browse.pl?1996/TM-107272.html)
DeLaat, J.C., et al.: The High Stability Engine Control (HISTEC) Program: Flight Demonstration Phase. AIAA Paper 98-3756 (NASA TM-1998-208482), 1998. (Available online: http://gltrs.grc.nasa.gov/cgi-bin/GLTRS/browse.pl?1998/TM-1998-208482.html)
Southwick, R.D., et al.: High Stability Engine Control (HISTEC) Flight Test Results. AIAA Paper 98-3757 (NASA TM-1998-208481), 1998. (Available online: http://gltrs.grc.nasa.gov/cgi-bin/GLTRS/browse.pl?1998/TM-1998-208481.html)
Orme, J.S., et al.: Development and Testing of a High Stability Engine Control (HISTEC) System. AIAA Paper 98-3715, 1998.
DeLaat, J.C., et al.: High Stability Engine Control (HISTEC): Flight Demonstration Results. SAE Paper 985556 (NASA TM-1998-208655), 1998.
Lewis contact: Jonathan S. Litt, (216) 433-3748,
Jonathan.S.Litt@grc.nasa.gov
Author: Jonathan S. Litt
Headquarters program office: OAT
Program/Projects: Propulsion Systems R&T, PHSV, HISTEC
Special recognition: 1998 NASA Group Achievement Award
Last updated June 16, 1999, by Nancy.L.Obryan@nasa.gov
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