A high-pressure air feed system, suitable for use with blowing models mounted on a six-component virtual-centre balance, is described. Air is supplied to the balance by a flexible ring-main feed so that no air is lost as with an air-bearing system. Constraints on the balance are very low;at an internal pressure of 30 p.s.i.g. gauge with a mass flow of 0.5 lbs/sec. all force corrections were less than 1 lb., and the pitching moment correction less than 0.5lb.ft. Rolling and yawing moment corrections were 2.0lb.ft and 2.7lb.ft respectively. The constraints were measured using a calibrator which enabled the desired mass flow to be passed through the system without additional constraints.
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