Flight envelope limit detection and avoidance

New advanced algorithms, control laws, and pilot cueing methods were developed to provide flight envelope limit protection on rotorcraft and fixed-wing aircraft. The envelope limiting systems were designed to detect an approaching limit boundary and then provide force-feel cues on the control stick so that the pilot can avoid violations of structural and controllability limits. The limit detection algorithms were designed to predict the future response of a limited parameter in order to give an adequate time margin for corrective action. The dynamic trim estimation method, which uses a neural network to estimate the quasi-steady response of the aircraft based on stick position and measured flight data, was applied to provide torque and V-n envelope protection on the XV-15 tilt-rotor aircraft and demonstrated in simulations with a pilot model. This system was also applied to provide angle-of-attack and load factor protection on the V-22 tilt-rotor aircraft and demonstrated using real-time piloted simulation. The adaptive dynamic trim estimation method extended this approach by using sensor data history to adapt to model uncertainties. The peak response limiting algorithm, which is used to detect and prevent limit violations that occur in the transient response, was applied to provide longitudinal flapping limiting on the XV-15 and demonstrated in batch simulations. Simulation results showed that the dynamic trim estimation scheme has the potential to effectively expand an aircraft's flight envelope by allowing the pilot to safely fly near limit boundaries. An adaptive algorithm was used to adjust to variations in the mass properties of the aircraft, but improvements to the adaptation method are warranted. The peak response limiting system was shown to be effective in determining rate and position constraints on the stick travel to ensure that flapping limits are not violated.