LOW-SPEED WIND-TUNNEL INVESTIGATION OF THE EFFECTSnOF PROPELLER OPERATION AT HIGH THRUST ON THE LONGITUDINAL STABILITY AND TRIM OF A TWIN-ENGINE AIRPLANE CONFIGURATION

摘要

An investigation has been made to determine the effects of dual-rotation propeller operation at high thrust on the static longitudinal stability characteristics of a semispan powered model representing a twin-engine airplane configuration with flaps retracted. The flow field behind the model was studied extensively by several techniques which provided information relating to the tail contribution to over-all sta¬bility characteristics.nStability and trim changes associated with an extreme constant power condition were found to be greatly dependent upon both tail height and vertical location of the center of gravity. Large adverse effects of power were obtained for a configuration having the center of gravity located on the thrust line and the tail in a high position. It-was found that adverse power effects could be essentially eliminated either by moving the tail down into the slipstream or by utilization of the direct-propeller-thrust moment associated with a vertical displacement of the center of gravity to provide stability.nThe lift effectiveness of the tail located in the propeller slip¬stream was found to increase with the slipstream velocity ratio to the first power rather than to increase directly with the dynamic pressure ratio.