The Evolution of the Variable Geometry Rotor

The systematic program has been undertaken to study the problem of blade/wake geometry and to design a rotor which capitalizes on this problem. The outcome has been the Variable Geometry Rotor (VGR). The paper presents a compilation of research efforts on the VGR, from its conception through the analytical studies, to recent fullscale hover tests. The VGR matrix is described, including theoretical studies with a freelydeformed wake, flow visualization and model-scale hover and forward-flight studies, analytical investigations during simulated maneuvers and a full-scale hover program. The experimental and theoretical information from the VGR work indicates that when the conventional geometric design criteria of coplanar blades, equal-azimuth spacing, equal blade radius, and equal collective pitch are systematically altered, benefits in rotor performance, acoustics, vibration, and blade loads are possible.