Many hover tests performed in the past on similar, relatively simple configurations produced significantly different results concerning jet-induced lift in ground effect. This report presents an investigation performed at NASA Ames Research Center to clarify the reasons for these differences. The test parameters investigated are the effects of the gap size between the model and a single nozzle, the shape of the outer edge of the model, the jet impingement angle to the ground, the size of the ground plane relative to the model, and the effect of large surfaces, other than the ground plane, close to the model. Although no single parameter explains the differences between previous data sets, it has become evident that certain parameters are important when testing small-scale hover models. Results indicate that the size of the ground plane needs to be only as large as the model. However, gap size, edge shape, and test-chamber size are parameters that had a measurable effect on negative jet-induced lift forces and therefore must be chosen and documented appropriately. Other observations and recommendations are made concerning the testing of small-scale hover models.
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Levin et al. (1997) studied this question.