Fast Thrust Response for Improved Flight/Engine Control under Emergency Conditions

Damaged aircraft have occasionally had to use differential thrust to maneuver as a consequence of losing hydraulic power needed to operate flight control surfaces. The lack of successful landings in these cases inspired research into methods of utilizing propulsion-only control more effectively. That research demonstrated that one of the major contributors to the difficulty in landing is the slow response of the engines as compared to using traditional flight control. To address this, research is being conducted into ways of making the engine more responsive under emergency conditions. This can be achieved by relaxing controller limits, adjusting schedules, and/or redesigning the regulators to increase bandwidth. Any of these methods will enable faster response at the potential expense of engine life, but there is also increased likelihood of stall. To reduce this risk, the use of a stall margin controller is proposed and discussed. It is explained why this new control mode will enable significantly faster engine response compared to standard Bill of Material control while still maintaining a safe stall margin.