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

Adam Cataldo, Xiaojun Liu, and Zhongning Chen1
(Professor Edward A. Lee)
NASA

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 such 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 a 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.

[1]
E. A. Lee, Soft Walls: Modifying Flight Control Systems to Limit the Flight Space of Commercial Aircraft, UC Berkeley Electronics Research Laboratory Memorandum No. UCB/ERL M001/31, September 2001.
[2]
J. A. Cataldo, E. A. Lee, and X. Liu, Preliminary Version of a Two-Dimensional Technical Specification for Softwalls, UC Berkeley Electronics Research Laboratory Memorandum No. UCB/ERL M02/9, April 2002.
1Undergraduate (EECS)

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