Measurement Around A Rotor Blade Excited In Pitch, Part 2: Unsteady Surface Pressure.

Mihir K. Lal, S. G. Liou, G. A. Pierce, N. M. Komerath.

Journal of the American Helicopter Society, Vol. 39, No.2, p.13-20, April 1994.

Abstract: This paper describes measurements of chordwise distributions of unsteady pressure at three radial locations on a stiff two-bladed teetering model helicopter rotor in hover, with the blades executing simple harmonic pitch oscillations about the quarter-chord pitch axis. The objective of the present work is to provide a data base to correlate the measured unsteady blade pressure distributions with dynamic inflow to establish the validity or deficiencies of available analytical methods for predictions of unsteady aerodynamic phenomena. The effect of dynamic inflow on rotor unsteady surface pressure has been extensively documented. Two means of changing inflow velocity have been employed, first by an appropriate combination of rotor speed and forcing frequency, and second by mean pitch angle. The reduced frequency effect and the tip effect on the perturbation lifting surface pressure have been demonstrated.