H-1 Upgrades Height-Velocity Diagram Development Through Flight Test and Trajectory Optimization

This article presents the use of an analytical methodology combined with flight tests to define the height-velocity diagram for the AH-1Z and UH-1Y helicopters. The methodology involves a longitudinal helicopter simulation math model and a trajectory optimization scheme. The model accounts for helicopter height and forward distance, forward and vertical speeds and wind, main rotor rpm, and power supplied by each of the two engines. The control variables of the model are main rotor thrust coefficient and tip-path-plane angle. The optimization methodology is a direct approach utilizing collocation and the nonlinear program SNOPT. The problem formulation seeks to minimize the size of the H-V diagram while constraining the solution to realistic flight as executed by pilots. The analysis was used to develop pre-test estimate H-V diagrams for the AH-1Z and UH-1Y in order to improve test efficiency and safety. Post-test correlation validated the analysis and its use with limited UH-1Y data.