Evaluation of a force balance with semiconductor strain gages in wind tunnel tests of the HB-2 standard model

Abstract

A six-component wind tunnel balance of a robust, unconventional design was produced using semiconductor strain gages on a compression-type axial-force element. The balance was designed primarily for supersonic tests of high-drag models in short-duration wind tunnels. It was first used in a short crash program to test a design of a high-drag training kinetic-energy projectile. Obtained data were useful for the development of the projectile, but a lack of reliable references to validate the performance of the balance was felt, especially in view of the different opinions on the usability of semiconductor strain gages for wind tunnel balances. This issue was dealt with when the balance was used in wind tunnel tests of a HB-2 hypervelocity-ballistic standard model at Mach numbers 1.5 to 4, in a campaign of tuning the supersonic performance of the T-38 wind tunnel in VTI. Test results were compared with the reference data and with results from an earlier test of the same model where a conventional-design balance was used. The evaluation of the balance was focused on the measurement of the axial-force coefficient. It was concluded that the balance was very convenient for the intended type of wind tunnel tests, but not for general use.