Behavior of an Extremely Flexible Rotor in Hover and Forward Flight

The increasing interest in the application of micro-aerial vehicles for military intelligence, surveillance, and reconnaissance missions encourages the design of a variable-diameter, flexible rotor for micro-helicopters. This paper describes a systematic experimental investigation of the behavior of a two-bladed, 18 inch diameter rotor with extremely flexible blades. The effect of the blade flexibility in bending and torsion, blade planform, mass distribution and materials on the stability and performance of the rotor was investigated in hover and forward flight. It was observed that rotational speed and collective pitch had a significant effect on rotor stability. A maximum Figure of Merit of 0.41 at a blade loading of 0.17 was measured for the flexible blades. Forward flight velocity was found to increase the blade stability. It is concluded that the mass and efficiency of the flexible blades are comparable to that of a rigid rotor blade.