High Stability Engine Control

Objective

NASA is sponsoring the design, development, and flight demonstration of an advanced high stability integrated engine control system using real-time estimation of distortion to enhance engine stability. A HISTEC-enabled decrease in design stall margin requirements will significantly increase propulsion system performance and /or reduce weight.

Background

Future aircraft turbine engines, both commercial and military, must 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 propulsion system will see more extreme aircraft angle-of-attack, , and sideslip levels, . These both tend to increase engine-face distortion to greater levels than currently encountered with present-day aircraft. Also, in addition to planar pulse, inlet buzz, and high distortion levels at low flight speed and off-design operation, the mixed-compression inlets needed for the High Speed Civil Transport (HSCT) will likely encounter disturbances similar to those seen by tactical aircraft. These increased levels of distortion usually decrease propulsion systems performance; and more importantly, they reduce the stable flow range of the compressor. Current gas turbine engine design practice is to base fan and compressor stall margin requirements on a worst-case stackup of destabilizing factors. These factors include external destabilizing factors such as inlet distortion, as well as internal factors such as large tip clearances. A stability audit is defined and maintained during the development process to account for the effects of each known destabilizing factor. The stability audit totals the worst-case stall margin losses from each of the known factors, adds a margin for engine-to-engine variability, and assures that the fan and compressor have some remaining stall margin. However, this approach results in an increase in design stall margin requirement with a corresponding reduction in performance and/or increase in weight.

The NASA Glenn Research Center is currently pursuing two research approaches that were confirmed as being beneficial by NASA’s aircraft engine customers during the NASA- sponsored Advance Control Concepts study. The far-term approach is to increase the amount of operational stall margin available by actively controlling the onset of stall. This technique is known as active stall control or active stability control. The near-term approach is to increase the stall margin requirement online as engine face pressure distortion is encountered. This approach, distortion tolerant control, allows a reduction in the required design stall margin by an amount on the order of the effect of the distortion.

The Technology

The distortion tolerant control approach developed for the HISTEC program includes two major functional elements: 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 the effect on the propulsion system of that distortion. It uses a small number of high-response pressure measurements at the engine face and maneuver information from the flight control to calculate, in real-time, indicators of the type and extent of distortion. From these indicators, the DES determines the effects of the distortion on the propulsion system. 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.

The HISTEC distortion tolerant control was demonstrated in flight on the NASA F-15 ACTIVE aircraft at the Dryden Flight Research Center in Edwards, CA during the summer of 1997.

Plan

• Phase I - Algorithm development
• Phase II - Concept Validation and system development
• Phase III - Engine/Flight Demonstration

Accomplishments

• The program has been successfully accelerated to meet customer technology insertion opportunities.
• Distortion estimation algorithms have been developed and concept feasibility demonstrated.
• Instrumented inlet case has been designed, fabricated, delivered to NASA Dryden, and installed on the right-hand engine.
• Flight hardware/software systems have been selected, programmed, and functionally verified.
• Flight test planning and preparation are complete.
• Modifications to F-15 ACTIVE have been completed.
• Flight test commenced July 15, 1997.
• Flight testing was completed August 26, 1997.

Participants

• NASA Glenn - Program management
• NASA Dryden - Flight test, data reduction
• Pratt & Whitney - Concept and systems development
• McDonnell Douglas - Vehicle integration
• USAF - Flight systems, engine, vehicle assets

Publications

J.C. DeLaat, R.D. Southwick, and G.W. Gallops: "High Stability Engine Control (HISTEC)," prepared for the 32nd Joint Propulsion Conference cosponsored by AIAA, ASME, SAE, and SAE, July 1-3, 1996. NASA TM 107272, AIAA-96-2586.

Download paper

DeLaat, J.C.; Southwick, R.D.; Gallops, G.W.; and Orme, J.S.: "The High Stability Engine Control (HISTEC) Program: Flight Demonstration Phase." Prepared for the 34th Joint Propulsion Conference and Exhibit, July 13-15, 1998, NASA TM 1998-208482, AIAA-98-3756.

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Southwick, R.D.; Gallops, G.W.; Kerr, L.J.; Kielb, R.; Welsh, M.; DeLaat, J.C.; and Orme, J.S.: "High Stability Engine Control (HISTEC) Flight Test Results." Prepared for the 34th Joint Propulsion Conference and Exhibit, July 13-15, 1998, NASA TM 1998-208481, AIAA-98-3757.

Download paper

Project Contact

John DeLaat
NASA Glenn Research Center
21000 Brookpark Road, M.S. 77-1
Cleveland, Ohio 44135
Phone: (216) 433-3744
Fax: (216) 433-8643
email: jdelaat@grc.nasa.gov

responsible official: sanjay garg
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last updated: 2.29.08