The report deals with an experimental investigation of some of the problems associated with wind tunnel testing of V/STOL type aircraft. The models used in the study were either rotors or propellers acting as a rotor. Various size and shape wind tunnel test sections were simulated by the use of inserts installed within a larger main wind tunnel test section. The study investigated the application of wind tunnel wall corrections to models with large values of downwash. A physical limit, called flow breakdown, to the size and allowable downwash for a given model-tunnel combination was also studied. (Modified author abstract).

A discussion of wind tunnel boundary corrections as they apply to VTOL model testing is presented. Conventional wall correction theory is inadequate since it fails to account for both the presence of a highly developed wake and the total lift acting on the model. Correction theories that do consider the lift and wake characteristics of VTOL designs give satisfactory results, provided there is no wake distortion due to the interference of tunnel walls. Both the Heyson and Kirkpatrick VTOL boundary correction theories are examined and their limitations discussed. A comparison of free air and tunnel results for a .165scale North American Aviation Tilt Wing design and a free air study of an early Hamilton Standard XC 142 propeller model are discussed. The propeller data agreed with theoretically predicted values, but discrepancies, particularly in drag force, appeared when the airship North American Aviation data were compared with similar tunnel results. The exact cause of the differences was not determined. The importance of the VTOL model wake is substantiated. Minimum tunnel sizes necessary to avoid wake impingement and disturbance are presented. (Author).