Effects of structural failure on the safe flight envelope of aircraft

The research presented in this paper focuses on the effects of structural failures on the safe flight envelope of an aircraft, which is the set of all the states in which safe maneuver of the aircraft can be assured. Nonlinear reachability analysis basedonan optimal control formulation is performed to estimate the safe flight envelope using actual aircraft control surface inputs. This approach uses the physical model of an aircraft, where the aerodynamic stability and control derivatives are calculated using Digital Datcom. Symmetrical damages to a Cessna Citation II are considered with 25, 50, 75, and 100% spanwise vertical tail tip losses, leading to gradual shrinkage in the safe flight envelope. Based on the estimated safe flight envelopes, a discussion on the effects of structural damages and different flight conditions on the safe flight envelope is presented. In particular, the interpolatibility of the resulting safe flight envelopes is demonstrated. This property is essential for a novel database-driven flight envelope prediction method, where a database of safe flight envelopes is created offline to be accessed later in real time.