External Noise And Downwash Measurements On The Vought XC-142a

In August 1967 the Vought XC-142A V/STOL Aircraft and the Sikorsky HH-53B and HH-3C helicopters were utilized in simulated jungle rescue mission tests at Eglin AFB, Florida. During the tests, noise and downwash measurements were made underneath and to one side of the vehicles for a number of hover heights up to an altitude of 200 feet above ground level. Data gathered for both wooded and clear test sites are summarized in this paper. A few of the problems encountered with microphone wind noise and other instrumentation difficulties are briefly discussed. Downwash measurements indicated that surface velocities well outside the rotor cylinder (90 feet from center) were essentially independent of disc loading. Beneath the aircraft, both turbulence and velocities were slightly higher for the XC-142A which had a disc loading approximately six times that of the helicopters.