ANALYSIS AND CORRELATION OF HELICOPTER ROTOR BLADE RESPONSE IN A VARIABLE INFLOW ENVIRONMENT

The program was conducted to determine the ability to predict Helicopter rotor response with a combined analysis based on the Sikorsky aeroelastic analysis and the Cornell Aeronautical Laboratory variable inflow analysis. The Sikorsky analysis is a fully coupled flatwise-edgewise-torsional dynamic analysis modified to incorporate refinements in rotor trim and airload calculation and to adapt it for use with the variable inflow analysis. Analytical results were compared with available flight data for steady level flight of the H-34 at 41, 70, and 112 knots with a neutral center of gravity C. G., and 73 knots with aft C. G., as well as the HU-1A at 113 knots with neutral C. G. Fairly good correlation with test data was obtained. The analysis gave better correlation of blade air loads and bending moments than had been obtained from constant inflow analysis. In particular, more realistic values were obtained for the higher harmonic root-shear forces needed to define airframe response. While further improvement can be obtained by refinement of the variable inflow analysis, the combined analysis developed for the program provides an improved design tool for rotor blade evaluation.