Investigation of Practical Flight Envelope Protection Systems for Small Aircraft

Abstract

Personal air transportation using small aircraft is a market that is expected to grow significantly in the near future. However, seventy times more accidents occur in this segment as compared with commercial aviation. The majority of these accidents is related to handling and control problems, which are closely linked to the experience level of the pilots. In commercial aviation, the combination of fly-by-wire technology and flight envelope protection is used to prevent these types of accidents. Instead of downscaling advanced and high-cost fly-by-wire platforms, a low-cost solution should be considered for the general aviation market. This paper focuses on a flight envelope protection system for small aircraft. Preliminary results are obtained from an empirical comparison study in the time domain between a proportional-integral-derivative-based control limiting approach, a command limiting approach, a constrained flight control law approach using model-based predictive control and incremental nonlinear dynamic inversion, and a virtual control limiting approach, which also uses incremental nonlinear dynamic inversion. Comparison is done not only using a nominal model but also in cases of parametric uncertainty, sensor noise, time delays, wind gusts, and turbulence. Investigation of the results reveals that, for this study, control limiting should be avoided, and for practical implementation command limiting is the best option.