Image-based force and moment measurement in hypersonic facilities

Abstract

This article addresses the problem of force and moment measurement in short-duration hypersonic facilities. An image-based technique is described in which the motion of a free-flying model is tracked over a sequence of high-speed digital images. Force components are derived from the calculated trajectory by assuming constant acceleration during the test time. A linear version of the technique, appropriate for simple model geometries, is first outlined and the technique's precision is estimated. A nonlinear version, suitable for more generalised body shapes, is then described in the context of a series of experiments to determine the aerodynamic characteristics of the NASA Orion vehicle in the T5 hypervelocity shock tunnel. The accuracy of these measurements was adversely affected by both the choice of light source and test-gas luminosity, but these experiments nevertheless show image-based measurements to be, at the very least, a promising supplement to standard accelerometer-based techniques.

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