Abstract
Icing is one of the leading causes of fatal aircraft accidents worldwide. Encountering icing conditions, dynamic characteristics of the aircraft will be damaged, thereby greatly affecting flight safety. Research on real-time estimations of the safety envelope under icing conditions is critical to improve flight safety. In order to determine the safety envelope, the reachability analysis based on the level set method is presented. The reachable set is obtained via computing the Hamilton-Jacobi partial differential equation (HJPDE), which is based on optimal control and is used in the landing phase of an aircraft. The results show that icing will shrink the safety envelope. Particularly under severe icing conditions, the stall speed of the aircraft will increase, and dynamic behavior will be more sensitive. A slight change of command by the pilot may contribute to the flight state moving outside the safety envelope. Furthermore, the effect of flap deflection was considered, which positively impacts the expanding safety envelope during the landing phase. Finally, a maneuvering coping strategy based on safety envelope is proposed. Examples are provided using the NASA’s generic transport model (GTM), and the results can be applied to flight safety risk assessment, providing theoretical guidance for the design of envelope protection systems.
Highlights
Aircraft accidents caused by ice continue to occur
The safety envelope estimation based on reachability analysis is proposed in this study, which can guarantee safety of an aircraft encountering icing conditions
The longitudinal nonlinear dynamic model of the aircraft is established based on the equations of motion and aerodynamics force and moment affected by icing
Summary
Aircraft accidents caused by ice continue to occur. Icing affects the aerodynamic performance, and degrades the control of aircraft, leading to catastrophic crashes [1]. It is shown that the stability boundary of the nonlinear dynamic system consists of the union of the stable manifolds of all equilibrium points and/or closed orbits on the stability boundary This method could determine an accuracy envelope, it relies too much on the precision of the model and number of the dimensions cannot exceed three. The reachability analysis [14, 15] based on the level set method has been proposed to estimate the safety envelope of the aircraft under icing conditions during landing. This allows us to predict, to some extent, the states that can be reached with a given control authority from a trim condition.
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