An Investigation of Sting Interference Effects on an Oscillating Cone in Transonic Flow

Wind tunnel sting support interference effects on dynamic stability derivatives, static pitching moment and base pressure of a blunt, 7-deg cone were investigated at subsonic and transonic Mach numbers. The cone was tested with sting configurations having a variable effective sting length ranging from 1 to 3.3 model base diameters, at angles of attack ranging from 0 to 30 deg. A forced-oscillation system was utilized to obtain data at a frequency of oscillation of approximately 5.3 Hz, and at an amplitude of 1 deg. The Reynolds number, based on model base diameter, was nominally 1.8 million, which produced a turbulent boundary layer over the aft portion of the model. The nature of the causes of these interference effects is discussed and analyzed with respect to sting length, type of measurement, and Mach number, with emphasis on defining critical sting length and on predicting minimal interference sting configurations for dynamic stability testing. The results showed that the critical sting length depended on the type of measurement used as the interference indicator, Mach number, and angle of attack. A critical sting length of three model diameters was determined to be suitable for all test conditions for the ratio of sting diameter-to-model base diameter (0.22) investigated. Prepared in cooperation with ARO, Inc., Tullahoma, TN.