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Because the forces and pressures on wind-tunnel models tested at transonic speeds are not steady, even for static aerodynamic tests, integration time is required to obtain data of acceptable accuracy. The integration time required for both static and dynamic tests is evaluated analytically and confirmed by experimental measurements. It is shown that, for static and dynamic tests, the accuracy obtained is a function of integration time, frequency of the signal, and the ratio of the dynamic amplitude to the full signal of interest. In addition, for the dynamic case, the frequency bandwidth used in analysis is important. Results of this study indicate that, for typical data accuracy desired from models in a large transonic wind tunnel (11-by 11-ft), up to the following integration times are required: static force and moment tests, 0.5 s; static pressure tests, 1 s; flutter tests, 30 to 60 s; and random-dynamic tests, 10 s.

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This paper presents results of wind tunnel and acoustic tests to investigate buffet loads on Shuttle Thermal Protection System (TPS) tiles. It also describes the application of these results to the prediction of tile buffet loads for the first Shuttle flight into orbit (STS-1). The tests were conducted in wind tunnels at transonic and supersonic Mach numbers and in a progressive wave tube. The wind tunnel tests included single tiles of various thicknesses and arrays of tiles mounted on both rigid and elastic substructures. The corresponding acoustic tests were of the single tiles only. In most cases the “test” tiles were of Orbiter qualified material and they were bonded to the panels and proof-loaded in accordance with flight-vehicle specifications. The fixtures for the panel installations in the wind tunnels were designed to simulate flow regions on the Orbiter where shock waves and related high pressure gradients and high dynamic loads would occur. The results of the wind tunnel tests indicate that significant tile buffet loads occurred due to separated flows and oscillating shocks. Separated flow excitation caused higher buffet loads than oscillating shocks for a given level of excitation, however, the highest combined steady and dynamic loads occurred when shock waves with ΔP > 1.5 psi were on tiles.