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 4. SUMMARY AND EVALUATION OF RESULTS
BOEING CO MORTON PA VERTOL DIV
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The report describes and evaluates the results of an extensive program to measure the dynamic effects of flight on a tandem rotor helicopter. The flight test results are reviewed and then compared with theoretical predictions and with other flight test data. The airloads measurements from this program are similar to those of other flight test programs, with one major exception single lifting-rotor helicopter data differ from the forward rotor data of a tandem. The aft rotor apparently produces an upwash which gives an increase in the airloads on the inboard region of the forward rotor. This effect results in an airload distribution that is similar to that which would be obtained with an increased blade twist of the forward rotor. For most longitudinal cyclic trim settings, the oscillations of the airloads of both tandem rotors tend to be similar to those of a single rotor, with intrarotor tip vortex intersections causing the predominant disturbances. Longitudinal cyclic trim settings can be obtained experimentally with the tandem helicopter which cause large airload pressure oscillations due to the intersection of forward rotor blade vortexes by the aft rotor blades. These pressure oscillations occur rapidly and do not appear to increase blade stresses, rotor shaft loads, or airframe vibration.