Multi-component force balances for conventional and cryogenic wind tunnels

Abstract

The measurement of the total forces acting on the surface of a wind tunnel model is still the most important wind tunnel measurement technology. Either the model is mounted by struts to a balance, which is located outside the test section (an `external balance'), or the balance is located inside the model and connects the model structure to the mounting sting, which in the case of aeroplane configurations protrudes from the rear fuselage (an `internal balance'). This review concerns internal balances only. The functional principle is described and some comments on the demand for high accuracy are given. The optimization of designs for strain gauge balances, the fabrication methods and the selection of materials are commented on. The calibration theory of multi-component balances is outlined and the calibration equipment is described. Examples for conventional manual calibration equipment and for an automatic calibration machine are given. Finally the specific design features of cryogenic balances and half model balances are given. This review presents the author's experiences and developments. Since there is hardly any general literature on the subject of strain gauge balances and since the balance engineers in the world have not that much contact with each other, there may be different points of view at other institutions.