IN-FLIGHT MEASUREMENT OF ROTOR BLADE AIRLOADS, BENDING MOMENTS, AND MOTIONS, TOGETHER WITH ROTOR SHAFT LOADS AND FUSELAGE VIBRATION, ON A TANDEM ROTOR HELICOPTER. VOLUME 5. INVESTIGATION OF BLADE STALL CONDITIONS
BOEING CO MORTON PA VERTOL DIV
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The report describes the results of an investigation into helicopter rotor blade stall conditions. The goals of this research were to increase the comprehension of blade stall and to aid in the future design of rotor blades with greater aerodynamic efficiency. The problem of rotor blade stall is discussed, covering areas such as rotor performance limitations, static airfoil section performance, dynamic and aerodynamic effects of the rotor environment, and radial flow effects. The results of the tests are presented and described in detail they include tests at the high dynamic loads boundary, evidence of stall in rotor loads and blade motion data, coefficients of rotor airloads, and indications of negative aerodynamic damping. The test results are weighed against theoretical methods of prediction for purposes of comparison. The use of airloads measurements in the synthesis of airfoil data is investigated and a method for doing so is provided. The conclusions drawn from these tests are presented and recommendations for future research in this field are given.