Investigation of Practical Flight Envelope Protection Systems for Small Aircraft

Abstract

Personal air transportation utilizing small aircraft is a market that is expected to grow significantly in the future. For this segment, "stick and rudder" related accidents should be mitigated to guide this process in a safe manner. Instead of downscaling advanced and expensive fly-by-wire platforms that incorporate flight envelope protection found in commercial aircraft, a low cost solution should be considered. This paper focuses on a flight envelope protection system for small aircraft, to allow carefree maneuvering for the less experienced pilot. Preliminary results are obtained from an empirical comparison study in the time domain, between a PID based control limiting approach, a command limiting approach and a constrained Flight Control Law (FCL) approach using Model-based Predictive Control (MPC), with and without parametric model uncertainties. Investigation of the results reveals that, for this study, command limiting and MPC should be preferred over control limiting and that the practicality of command limiting outweighs the small performance increase of MPC.

Non-Iterative Adaptive Limit and Control Margin Estimation with Concurrent Learning

“…[1][2][3][4][5] For piloted aircraft, the effective estimation of allowable control travel that results in envelope limits (control margins), and the proximity of the states to envelope limits (limit margins) are critical. For unmanned or autonomous systems the estimation of command margins might be required for envelope protection.…”

Angle of Attack and Load Factor Limiting in Fighter Aircraft using Command Governors

“…While model predictive controllers have been extensively investigated for flight control applications 1-28 most of them consider reconfigurable flight control systems and only few focus on envelope protection and maneuver limiting. 7,13,17,21 Even though reference governors have been subject to research for quite some time very little research has been performed on applying reference and command governors to flight control design and maneuver limiting. 23,[29][30][31][32][33] Most of these papers consider simplified conditions with only a single linear or nonlinear system and no complex simulation environments.…”

Optimal Control Framework for Estimating Autopilot Safety Margins

“…This philosophy mandates an active role to the flight control system, as pilot control actions can be overridden to prevent aircraft from leaving certain envelope bounds. In the second philosophy, a more passive approach is taken wherein the flight control system takes a more advisory role, and where the pilot has the final authority over the aircraft [5]. Regardless of which philosophy is being followed, current FEP systems have not always helped in preventing LOC incidents and are not sophisticated enough to adapt to off-nominal conditions that alter the flight dynamical characteristics of the aircraft significantly.…”

“…FEP has been the subject of study in the recent past under various contexts. Yavrucuk et al [4] have studied automatic envelope protection systems tailored specifically for unmanned aerial vehicles, Falkena et al [5] has investigated FEP strategies for small aircraft from the general aviation category perspective, and Sharma et al [6] have looked into practical FEP schemes for commercial aircraft under icing conditions. For the commercial aircraft category, the industry dictates two philosophies in FEP; in the first philosophy, the responsibility of maintaining the aircraft within prescribed limits is given to the flight control system.…”