Comparison of wind-tunnel and flight results on a four-propeller tilt-wing configuration

Over the years aerodynamicists have learned to rely heavily on wind­-tunnel-model results in predicting the aerodynamic characteristics of con­ventional aircraft configurations. With the development of V/STOL con­figurations which have high slipstream deflection angles. such as the
four-propeller tilt-wing XC-142A V/STOL aircraft, the reliability of small-scale wind-tunnel-model results in predicting full-scale airplane characteristics needs to be reexamined.

Extensive tests have been made by NASA on several sizes of wind-tunnel models of the XC-142A V/STOL configuration and by Ling-Temco-Vought, Inc., on the airplane. These results show that models predict the slow-speed level-flight characteristics very well but that small models underpredict the descent capability of the airplane. Larger scale wind-tunnel models of approximately half size show better agreement with the airplane descent characteristics.

It was found from smoke flow studies that small models can also pre­dict the region in which self-generated disturbances will be encountered by tilt-wing configurations in ground proximity.