Thrust changes induced by ground and ceiling planes on a rotor in hover

The thrust produced by a helicopter motor in hover has been studied by measuring the thrust on a model rotor 0.234 meters in diameter operating between ground and ceiling planes. The distance between the two planes and the rotor disk was in the range 0.08-6.0 rotor diameters. It was found that the confining surfaces changed the rotor thrust almost linearly with the logarithm of the distance from the confining surface. When both planes were near the rotor the variation was no longer linear. The measured thrust of the rotor was compared to predictions based on the theoretical calculations of Rossow (1985), and the results are given in a table.