Effect of Ground Proximity on Aerodynamic Characteristics of Two Horizontal-Attitude Jet Vertical-Take-Off-and-Landing Airplane Models

An investigation has been made to study the effect of ground proximity on the aerodynamic characteristics of two jet vertical-take-off-and-landing airplane models in which the fuselage remains in a horizontal attitude for the take-off and landing. The first model (called the tilt-wing model) had a tilting wing-engine assembly which was set at 90 degree incidence for the take-off and landing. The second model (called the deflected-jet model) had a cascade of retractable turning vanes to deflect the exhaust of the horizontally mounted Jet engines downward for vertical take-off and landing while the entire model remained in a horizontal attitude. With the models at various heights above the ground in the take-off and landing configuration, the llft, drag, and pitching moment were measured and tuft surveys were made to determine the flow field caused by the Jet exhaust. The tilt-wing model experienced a loss of lift of less than 3 percent near the ground. The deflected-Jet model, however, suffered losses in lift as high as 45 percent near the ground because of a low pressure region under the model caused by the entrainment of air by the jet exhaust as it spread out along the ground. This loss in lift for the deflected Jet configuration could probably be reduced to less than 5 percent by the use of a longer landing gear and a high wing location.