Evaluation of Cryogenic Force Balance Calibration Methodologies Relative to Wind Tunnel Results

Independent tests of the NASA Common Research Model at NASA's National Transonic Facility and the European Transonic Windtunnel reveal differences at low operating temperatures and high Reynolds numbers that warrant further investigation. Since each facility used their own wind tunnel balance for their tunnel entry, one suggestion for the differences was the temperature compensation methodology developed and applied for each balance. This hypothesis is explored through simulation and experiment. Independent calibrations of NASA's NTF-118A balance at NASA Langley Research Center and European Transonic Windtunnel reveal differences in the thermal compensation of the normal force and pitching moment primary sensitivities with temperature, while the axial force primary sensitivities are in good agreement. The application of the balance calibrations performed at NASA and European Transonic Windtunnel to the prior wind tunnel data suggests that the thermal compensation differences are an order of magnitude lower than the differences observed between the wind tunnel aerodynamic coefficients. Thus, the balance temperature compensation methodologies used by NASA and European Transonic Windtunnel are not a major contributor to the wind tunnel differences.