Experimental/theoretical correlation of analysis for helicopter rotor blade/droop stop impacts

A theoretical and experimental study of the transient response of an articulated rotor blade experiencing a droop stop impact was conducted. The rotor blade is modeled using the finite element method and the droop stop is simulated using a conditional rotational spring. During an rotor blade/droop stop impact, the boundary conditions of the blade change from a hinged to a cantilevered condition. Three different methods of integrating the equations of motion in time, in physical space, in modal space without a change of the mode shapes during an impact, and in modal space with a change of the mode shapes during an impact were studied. A 1/8^th scale model articulated rotor blade was constructed. Given a range of initial flap hinge angles, drop tests of the model rotor blade were conducted at zero rotational speed. The transient response of the tip deflection, flap hinge angle, and strain at three locations were measured. Good correlation existed between the experimental data and both the physical space integration and modal space integration without a change of the mode shapes in the tests performed without a discrete damper. Marginal correlation existed between the experimental data and the modal space integration with a change of the mode shapes in the tests performed without a discrete damper. Differences in the solution methods decrease when tests are simulated with a discrete flap damper.