The Effects of Control System Stiffness Models on the Dynamic Stall ~ehavior of a Helicopter

The control system stiffness of a n UH-60A helicopter was n~easured. A description of the measurements and the results is provided. The measured control system stiffness values mere used within a comprehensive analysis, CAMRAD 11, to establish a baseline calculation of the rotor system during an extreme thrust condition causing dynamic stall on the rotor. A I validation of the baseline CAMRAD I1 model mas made by comparing to measured blade shake test data and level-flight, high-thrust, flight-test data also showing dynamic stall from the UH-60A Airloads Program. Finally, an evaluation of the sensitivity of the rotor system response to different control system stiffness models was made. The calculated results indicate a moderate level of sensitivity to changes of control system stiffness in the presence of dynamic stall. This finding in itself is a n important determination, as this paper narrows the range of possibilities, which are assumed to be important to dynamic stall predictions by demonstrating the effects of control system stiffness on predictions and thereby moving researchers to focus on other attributes such as three-dimensional aerodynamics. Notation number of blades weight coefficient, blade chord, ft aircraft gross weight, lb structural stiffness, ft-lbldeg. rotor radius, ft radial location, ft advance ratio air density, slug/ft3 rotor solidity, bc/nR rotor speed, raqse