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We propose a new thrust stand measuring thrust variation beyond the resonant frequency. The proposed method is null-balance thrust measurement method with acceleration based compensation. A controller monitors pendulum motion and adjusts a solenoid actuator in such a way that the pendulum deflection angle is kept constant. Spontaneously, acceleration and solenoid-actuator current was measured during active control. Thrust is directly determined from the current and acceleration because spring constant and damping factor originating from wires and the thrust stand can be ignored due to null-position active control. The prototype thrust stand successfully measured thrust with its variation in the frequency range from 0 to 85 Hz, whereas conventional null-position method yielded 410-% overestimation at a resonant frequency of 30 Hz. Beyond 90 Hz, the proposed method showed errors in sensitivity and phase shift. The deterioration in accuracy is caused by the translational flexibility in torsional hinge. Measurement of translational spring constant of the torsional hinge and numerical simulation with a pendulum fixed with a hinge having rotational and translational flexibility yielded a correlation between frequency and accuracy, which is similar to that of the experiment.

A New Thrust Measurement Method for Evaluating Higher Frequency Variation by Applying Acceleration Measurement to Null-balance Method