The Effect of Confined Areas on Helicopter Performance

Abstract

Flight test performance of an OH-58C helicopter hovering in confined areas is discussed using a combination of pilot-recorded data cards and instrumentation data time histories. The test includes an investigation of the effects of wall height and blade loading on hover performance in close proximity to a three-walled structure forming a confined space. Hover performance for a range of altitudes far from the confined area, at the edge of the confined area, and at the center of the confined area are discussed. Significant performance penalties (i.e., up to 20% greater than the power required to hover out of ground effect) were observed at various positions within the confined space. Additionally, the pilots reported uncommanded vehicle excursions at some positions within the confined area, necessitating increased control inceptor activity. These observations are indicative of unique aerodynamic interactions that affect helicopter performance and handling qualities within confined areas.