Flight Control Law Clearance using Optimal Control Theory

Avriel Herrmann
Work towards M.Sc. degree under the supervision of Prof. J. Z. Ben-Asher
Faculty of Aerospace Engineering
Technion – Israel Institute of Technology

Flight control law clearance is the practice of ensuring the safety of an aircraft for all admissible time-varying pilot inputs under all possible operational conditions. To date, the method used in industry is to divide the parameter space into a grid and test the flight control law for a finite number of maneuvers. An alternative approach is optimization; instead of showing that a flight control law is valid under all possible conditions, the worst possible aircraft behavior is sought, and if it can be demonstrated that the behavior is within acceptable limits, then the flight control law is valid. A number of studies have already utilized this method with various optimization techniques, such as genetic algorithms, differential evolution and adaptive simulated annealing, however these techniques essentially use brute force to find a solution and tend to be very computationally intensive.

The purpose of this work is to determine whether optimal control techniques can be applied to flight control law clearance, in order to solve the problem in a more complete and efficient manner. The focus is on Angle-of-Attack (AoA) limit exceedance, given the trimmed and linearized pitch dynamics of the aircraft. Using optimal control theory and General Pseudospectral Optimal Control Software (GPOPS), it is shown that the unbounded system achieves a maximum AoA with a ‘bang-bang’ pilot input, while the system with bounds on the angular speed of the elevator has a ‘bang-singular-bang’ worst case pilot input. Approximating the singular regions with linear functions, both inputs are tested in the Aero-Data Model in a Research Environment (ADMIRE) simulation. For a small number of specific duty cycles and periods the ‘bang-bang’ input achieves a higher AoA, but overall the results show that on average the ‘bang-singular-bang’ input produces the worst aircraft behavior.

The talk will be given in English

Wed, 19-03-2014, 16:30 (Gathering at 16:00)

Classroom, ground floor, library, Aerospace Eng.

Light refreshments will be served before the lecture

Flight Control Law Clearance using Optimal Control Theory