This is a Significant Technology milestone.
The tests by Bousman provided evidence that air responds to the motion of the rotor as a a whole, which is described well by simple dynamic inflow models for a rotor. This provided confidence in the use of dynamic inflow models for rotor response modelling.
Bousman, W. G.: An Experimental Investigation of the Effects of Aeroelastic Couplings on Aeromechanical Stability of a Hingeless Rotor Helicopter. Journal of the American Helicopter Society, vol. 26, no. 1, Jan. 1981, pp. 46–54
(Note: Only the month and year for this milestone are valid)