Design and Conduct of a Flight Test to Investigate Hover In-Ground-Effect Performance over Sloped Terrain

This paper presents flight test results from a research investigation into the effect of sloping terrain on hover power required. The investigation involved flight test data that were collected for a UH-72A Lakota helicopter while hovering inside ground effect above sloped terrain of varied gradients, in several aircraft orientations and multiple heights above the ground. Performance data were collected over a range of thrust coefficients by varying aircraft weight, rotor speed and environmental conditions over two sorties. The data are compared and contrasted to provide specific insight into the effects of slope magnitude, slope orientation, and rotor hub height. The results demonstrate that hovering over sloping terrain yields performance effects that are both non-intuitive and operationally significant. In particular, the effect of the sloping terrain was seen, in some conditions, to cause power requirements that exceed those for hover out-of-ground-effect, a traditional worst-case value for pre-mission performance planning.