Critical Sting Length as Determined by the Measurement of Pitch-Damping Derivatives for Laminar, Transitional, and Turbulent Boundary Layers at Mach Number 3 for Reduced Frequencies of 0.0033 and 0.0056

A research program was initiated for the purpose of investigating some of the problem areas in regard to support interference in supersonic wind tunnels. The critical sting length at alpha = 0 was determined by the measurement of pitch-damping derivatives for laminar, transitional, and turbulent boundary layers at the model base. The effect of wedge splitter plates on sting interference was also investigated. By utilizing the small amplitude forced oscillation technique, data were obtained at Mach number 3 on a blunt 7-deg cone for reduced frequencies of 0.0033 and 0.0056. The results showed that the critical sting length with respect to sting interference on pitch-damping data was two model diameters for the two reduced frequencies investigated and was independent of the type of boundary layer at the model base. Decreasing the effective sting length from 3.3 to one model diameter increased the model base pressure substantially and the model surface pressure slightly. The critical sting length for minimal base pressure interference is 2.5 model diameters for this model and these test conditions.