Safe Flight Envelope Estimation for Rotorcraft: A Reachability Approach

This paper considers the application of a reachability approach to estimating a safe flight envelope for rotorcraft. The flight envelope estimation problem is solved backward in time as it is formulated as an optimal control problem that involves finding a viscosity solution to the Hamilton-Jacobi-Isaacs equation with a terminal condition. The viscosity solution and its zero sub-level set computed based on the level set method is used to estimate the safe flight envelope in terms of a backward reachable set. This approach is demonstrated via an example of determining the backward reachable set for a helicopter flying forward in the longitudinal plane.