Hi-fidelity simulation and prediction of helicopter single point external load stabilization

Abstract

The helicopter has been used since its early development for external transport of large or bulky loads to small austere locations. Among the problems encountered as lift capability and airspeeds increased was that of divergent load oscillations due to load aerodynamics The most problematic are the single point external loads displaying unsteady aerodynamics and coupled yawpendulum modes accounting for the instability of cargo containers. However, a lack of simulation models for unsteady aerodynamics renders simulation and analysis incapable of predicting the critical speeds at which such loads become unstable. This thesis attempts to provide a stabilization system for controlling the yaw degree of freedom for the single point external load. Empirical models of the yaw resistance at the hook and of the yaw moments due to vortex shedding were developed and tuned using flight test data and lab measurements. Several load stabilization systems were considered, and a horizontal and vertical tail fin assembly was selected This thesis presents simulation model improvements required for a simulation to match flight results for the load yaw, along with the design, modeling and optimization of the fin stabilization system, and a simulation assessment of the envelope expansion obtained from both passive and active stabilization.