Force Measurements in Short-Duration Hypersonic Facilities

Abstract : Attention is drawn to the principle whereby the aerodynamic forces on a model in a wind tunnel are determined by measuring the reactions to them. The discussion is based upon a division of such reactions into two basic classes, depending on the restraints imposed. Where no restraints exist, the model flies freely and the forces may be inferred from the accelerations, either measured directly or derived from displacement vs. time data. When the model is supported, the forces are determined from measurements of the mechanical strains induced in suitably designed supports. Hybrid techniques, where these extreme cases of no restraint or nearly complete restraint cannot be assumed, are also discussed. A detailed discussion of transducer sensing elements and their incorporation into measuring systems is given. Some particular systems are also described.