EFFECTS OF BLADE STALL ON HELICOPTER ROTOR BLADE BENDING AND TORSIONAL LOADS.
HUGHES TOOL CO CULVER CITY CALIF AIRCRAFT DIV
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The highest blade dynamic loads tend to occur under conditions of retreating blade stall. An investigation is made to compare measured and calculated blade bending loads under such conditions. The analysis is based on the use of normal modes and the numerical solution of the differential equations of motion which eliminates the limitations caused by using harmonics of airloads. It also permits more accurate allowance for aerodynamic nonlinearities in the stalled region. The analysis also includes negative aerodynamic torsional damping when blade stall occurs, as well as the effects of blade bending and torsional deformations on airloads. Finally, the analysis includes an investigation of the effect of hysteresis of the lift coefficientangle of at8tack relationship in stall. It is concluded that, in order to accurately calculate blade loads under conditions of retreating blade stall, the effects of lift hysteresis and negative aerodynamic torsional damping must be included, in addition to the usual nonlinearities in lift and moment coefficients. It is further concluded that a numerical integration of the differential equation as opposed to a solution utilizing harmonics of airload and inclusion of the effects of blade deformation are essential to achieve accurate definition of the airloads. Author