Design and Performance Prediction of Swashplateless Helicopter Rotors with Trailing Edge Flaps and Tabs

Abstract

This work studies the design of trailing edge controls for swashplateless helicopter primary control, and examines the impact of those controls on the performance of the rotor. The objective is to develop a comprehensive aeroelastic analysis for swashplateless rotors in steady level flight. The two key issues to be solved for this swashplateless control concept are actuation of the trailing edge controls and evaluating the performance of the swashplateless rotor compared to conventionally controlled helicopters. Solving the first requires simultaneous minimization of trailing flap control angles and hinge moments to reduce actuation power. The second issue requires not only the accurate assessment of swashplateless rotor power, but also similar or improved performance compared to conventional rotors. The analysis consists of two major parts, the structural model and the aerodynamic model. The inertial contributions of the trailing edge flap and tab are derived and added to the system equations in the structural model. Two different aerodynamic models are used in the analysis, a quasi-steady thin airfoil theory that includes arbitrary hinge positions for the flap and the tab, and an unsteady lifting line model with airfoil table lookup based on wind tunnel test data and computational fluid dynamics simulation.

The predicted swashplateless rotor power is sensitive to the pattern of trailed vorticity from the rotor blade. Trailed vortices are added at the inboard and outboard boundaries of the trailing edge flap, and the flap deflection is used to calculate an effective angle of attack for the calculation of the near and far wake. This wake model predicts the swashplateless rotor requires less main rotor power than the conventional UH-60A helicopter from hover to &mu = 0.25. As the forward flight speed increases, the swashplateless predicted power increases above the conventional rotor, and the rotor lift-to-drag ratio decreases below that of the conventional rotor.