Venusian Probes Subsonic Drag Determination from Flight Data

Abstract

Subsonic drag coefficients have been obtained from flight data for the Pioneer Venus multiprobes. The technique used to extract the information from the data consisted of utilizing in situ pressure and temperature measurements. Analysis of the major model parameter error sources indicates overall error levels of 5% or less in the flight values of CD. Comparisons of the flight coefficients with preflight wind-tunnel test data showed generally good agreement for the five configurations investigated, although all flight-derived values are slightly larger than preflight wind-tunnel test values. Additional wind-tunnel tests were performed on the Sounder descent probe as a control experiment on the data extraction technique. A special attempt was made to accurately duplicate the probe geometry for tests in a high Reynolds number environment in order to achieve as realistic model and flight conditions as practical. Results from this testing in the NASA Langley low-turbulence pressure tunnel produced CD =0.68 at a~0 deg which is within the expected accuracy limits of the flight derived CD value of 0.72 ±0.04.