A Computer-Controlled Video Instrument for Wind-Tunnel Testing of Lifting Parachutes

Abstract

Wind-tunnel tests of parachutes require that aerodynamic data be obtained simultaneously on both the forebody and the parachute. In particular, it is necessary to correlate the relative motion between the parachute and forebody to the loads exerted by the parachute on the forebody as a function of time during dynamic tests, disreefing, and for the full-open canopy. A computerized video instrumentation technique was developed to provide this correlation during a full-scale wind-tunnel test of a unique lifting parachute configuraton. The instrumentation consisted of a small, rugged TV camera, mounted on the forebody base, which tracked the positions of two lights attached to the inside of the parachute canopy. The positions of the lights were digitized by an on-line minicomputer and converted to yaw, pitch, and roll angles relative to the forebody. These data were obtained 30 times per second and stored on disk memory along with instantaneous values of the axial force and rolling moment exerted by the parachute on the forebody. The motion-force correlations made it possible to determine the yaw damping of the lifting parachute and provided information on the specific sources of rolling moments generated by the parachute. Test results indicate that this computer-controlled video instrumentation can be applied to free-flight tests, dynamic tests, and measurements of relative motion among multiple bodies.