Reducing Blade Element Model Configuration Data Requirements Using System Identification and Optimization

This paper presents a systematic helicopter simulation development method that enables a blade element model to simulate accurate stability and control characteristics for high fidelity pilot training with limited knowledge of the helicopter aeromechanical configuration data. This method combines system identification and numerical optimization to embed stability and control validation within the model development process. Control and stability derivatives are first identified from flight test data within a 6-DoF state space model. Selected identified derivatives are then treated as targets within an objective function for a numerical optimization of blade element model variables, which can be chosen based on the availability of aeromechanical configuration data. This new method is demonstrated using a full envelope simulation of a light twin-engine helicopter of which the aerodynamic coefficients were known, but the rotor hub and flap hinge mechanical properties were unknown. The unknown variables were optimized to match flight test identified control derivatives for two blade element inflow model structures. Aerodynamic model parameters were specified to match the identified static and dynamic stability derivatives. The optimized blade element models were validated against flight test data for cyclic step and doublet responses in hover and forward flight. The optimization procedure yielded comparable results for both blade element model structures. It was possible to select a physically realistic set of blade element model design values to obtain accurate control response without relying on manual tuning.