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Free oscillation techniques
Initially, free oscillation technique was developed for measurement of pitch and yaw damping derivatives. The free oscillation rig featured a crossed-flexure pivot and a spring-loaded hydraulically actuated device to trigger the model oscillations and to lock the model during tunnel starting and stopping. Design and fabrication of the flexure pivot and other parts of the rig were all carried out in-house. Earlier, the model displacement signal used to be recorded on an oscillographic recorder and the recorded motion used to be analyzed using manual measurements of amplitudes. Recently a new free oscillation rig featuring a crossed-flexure pivot and a solenoid-actuated triggering device has been built. Model displacement signal is recorded on a PC and a new digital method has been developed for determination of logarithmic decrement, which is more accurate and convenient compared to analog methods.
