Scaling the Dynamics of Free-Flight Wind Tunnel Models

Abstract

UNSW Canberra has been running experiments to measure the aerodynamics coefficients and the external flow fields on free-flight models of high speed aerial vehicles in ground-based test facilities. It is found that the dynamic behaviour of the free flying models is a function of both the aerodynamics of the flow over the model and also the mass distribution of the model. A clear analytical model of the scaling of the dynamic behaviour is vital to both make sense of the measured dynamic response of the model and to select an optimum mass distribution of the model for an experiment. The shuttle orbiter was used as a candidate geometry for the scaling laws as it travels at hypersonic speeds. It was found that the scaling laws are in good agreement with real flight data. The ratio of air density between shuttle altitude to that at model altitude was an important factor when scaling the mass of the model. This affected the mass of the model and how the wind tunnel conditions are set. The altitude at which the shuttle orbiter experiments are carried out affected the sensitivity of the air density ratio.