Background:

Loss of Control (LOC) is the primary contributor to aviation fatalities. LOC occurs when an aircraft leaves what is known as the “Safe Flight Envelope” (SFE). Hence, to prevent LOC the SFE of an aircraft must be known at all times. For nominal aircraft, the SFE can be calculated offline. However, when an aircraft undergoes structural damage or icing its physical properties change, its SFE will shrink. Predicting this shrinkage in near real-time prevents a formidable challenge for both fundamental and practical reasons. In order to meet this challenge, a revolutionary new approach towards SFE prediction based on a database lookup was developed at the C&S division.

With this new approach, SFEs for different damage cases are calculated offline using a nonlinear reachability analysis. When damage occurs to the aircraft, the SFEs in the database are interpolated to obtain an SFE that corresponds to the sustained damage or icing. This interpolated SFE is then used to increase situational awareness of the pilots, or update the operational bounds of the flight control system.

Recently, envelope shrinkage was for the first time proved for a realistic damaged aircraft model. These same results suggested, however, that the SFEs calculated using nonlinear reachability analysis, while theoretically accurate, may be practically unattainable. The reason is that the optimal control input sequences used in the nonlinear reachability analysis may be very sensitive to external disturbances such as turbulence and gusts, causing the predicted SFE to be much larger than the actual ‘realistic’ SFE, which in turn may lead to dangerous situations. For example, the predicted safe flight envelope of an aircraft after a damage event may only be reachable if the pilot (or flight control system) commands a very specific time-varying input sequence, which could be very sensitive to small deviations which in reality always occur.

Project Goal:

The goal of this graduation project is to investigate the robustness of the reachability analysis based SFE predictions to external disturbances such as turbulence. In addition, the student will research a applicability of a stochastic (Monte Carlo) reachability analysis methods for realistic damaged aircraft flight envelope estimation.