Soft Walls: Modifying Flight Control Systems to Limit the Flight Space of Commercial Aircraft.


Researchers: Adam Cataldo, Xiaojun Liu, and Zhongning Chen
Advisor:Edward A. Lee

The Soft Walls project is a technological response to the September 11, 2001 tragedy [1]. The project goal is to design an aircraft control system to enforce government-mandated no-fly zones. The no-fly zones will include major cities, government centers, military installations, chemical and nuclear plants, and critical infrastructure centers. As an aircraft approaches a no-fly zone, the flight control system will force the aircraft away, giving the pilot a sensation of an external force. The no-fly zone boundaries are called Soft Walls, because aircraft are gently diverted as they approach these zones.

In the future, all aircraft are likely to use fly-by-wire systems, where pilot controls are mediated by computers, rather than being mechanically or hydraulically connected to the aircraft control surfaces. We are designing our control system for fly-by-wire aircraft. The aircraft will carry a three-dimensional model of the earth’s surface, augmented with the no-fly zones. The model will change only when the no-fly zones change.  One of our design principles is to give the pilot as much control as possible, subject to the constraint that the aircraft can never enter the no-fly zone.

We have developed a control algorithm for two-dimensional infinite wall [2]. This algorithm uses a simplified model of the aircraft dynamics and adds a bias to the pilot's control as the aircraft gets near the no-fly zone. The bias is increased and decreased gradually, and the algorithm is provably safe, that is, the aircraft can never enter the no-fly zone. Our next goal is to find a control algorithm which works for any convex, two-dimensional no-fly zone.

For more information, see the Soft Walls website at http://ptolemy.eecs.berkeley.edu/projects/softwalls/

[1] Edward A. Lee, "Soft Walls - Modifying Flight Control Systems to Limit the Flight Space of Commercial Aircraft (Draft 2),"Revised from Technical Memorandum UCB/ERL M01/31, University of California, Berkeley, CA 94720, October 3, 2001.

[2] J. Adam Cataldo, Edward A. Lee, and Xiaojun Liu, "Preliminary Version of a Two-Dimensional Technical Specification for Softwalls," Technical Memorandum UCB/ERL M02/9, University of California, Berkeley, CA 94720, April 17, 2002.

Last updated 11/18/02