Drag balance for hypervelocity impulse facilities

Abstract

A new technique is described for measuring drag with 100-/*s rise time on a nonlifting model in a free piston shock tunnel. The technique involves interpretation of the stress waves propagating within the model and its support. A finite element representation and spectral methods are used to obtain a mean square optimal estimate of the time history of the aerodynamic loading. Thus, drag is measured instantaneously and the previous restriction caused by the mechanical time constant of balances is overcome. The effectiveness of the balance is demonstrated by measuring the drag on a cone with 15-deg semivertex angle in nominally Mach 5.6 flow with stagnation enthalpies from 2.6 to 33 MJ/kg. Measurement repeatability of about 10% is achieved.