Hover Performance of a Two-Bladed Model Rotor in Confined Areas

Abstract

The present study investigated the performance of a teetering rotor hovering in ground effect inside of confined areas. A teetering rotor with blades 1:13.24 the scale of OH-58C blades was positioned over a six degree-of-freedom motion platform. Hover power and thrust were measured for collective blade pitches of 0◦, 4◦, 8◦, and 10◦ at 45 heights ranging from hub heights, z, of 0.8-3.0R. This process was completed in the presence of four wall orientations including parallel, L-shape, and U-shape configurations spaced 1.5R from the vertical axis of the rotor hub as well as a U-shaped configuration spaced 2.36R from the rotor hub axis to match full-scale flight tests. Configurations with spacing of 1.5R were tested for wall heights of 0.25, 0.5, 1.0, and 1.5R. The configuration scaled to flight test conditions was tested at wall heights equal to 0.61, 1.08, 1.56 and 2.08R. Rotor performance measurements were also collected out of ground effect at blade collective pitches of 0◦ and 4-10◦ in order to make comparisons between in-ground-effect and out-of-ground effect hover performance. Hover within confined areas was found to have up to a 20% increase in power required compared to hover out of ground effect. In all but four configurations, the variation in the magnitude of the maximum penalty across a blade loading range from 0.06 to 0.1 was greater than or equal to 1%, so the results were repeatable and consistent. When wall heights were greater than or equal to 1.0R, the maximum power penalty typically occurred at a hub height between 83% and 90% of the wall height. Penalties associated with the confined area appeared to be influenced by changes in blade loading, wall orientation, wall height, and wall configuration.