The Wind Tunnel as a Design Tool

The helicopter industry has made extensive use of available wind tunnels for years; first to test powered rotors for performance, then for rotor loads, then dynamics and rotor-airframe interaction. Designers needs eventually required that tunnels be designed expressly for rotorcraft. In 1965 two models of proposed Boeing V/STOL tunnels were built to investigate the relationship between flow qualities and tunnel features such as test section length for tandem rotor helicopters, wall height to width, slotted wall geometry and more. This included control of tunnel velocity uniformity, longitudinal pressure gradient, and test section boundary layer behavior. Panel vortex studies of slotted walls, for ex­ample, continued into the 1967-68 construction period. Based on these analytical and experimental studies and the industry's use of available tunnels, the new tunnel was developed specifically for rotorcraft testing. The Boeing Vertol wind tunnel (BVWT) has been chosen to illustrate how such a facility is used to help design full-scale rotorcraft. This paper details the features that provide the requisite capabilities necessary for rotorcraft development. Special attention has been given to the test section of the tunnel. Also described are model design requirements along with data acquisition and processing methods used to present both on-line and final data.