Determination of Rotary Wing MAV Stability Derivatives in Hover Using a Forced Oscillation Test Stand

This paper discusses the use of a forced oscillation technique to determine the stability derivatives for a rotary wing Micro Air Vehicle (MAV) in hover. The experimental setup consists of an oscillating test stand with an integrated force balance. The MAV under consideration is mounted on the force balance. The test stand oscillates the MAV along a single axis at a fixed amplitude and frequency using a scotch yoke mechanism and a precision servo drive motor. Using synchronized position data and force response measurements, the in-phase and out-of-phase reactions of the MAV to the forced oscillation can be separated. From this data, the applicable stability derivatives can be obtained. Tests show that the current test setup is capable of consistently measuring the stability derivative Xu of a generic co-axial MAV for forced oscillations between 0.5 and 1.4 Hz and peak to peak oscillation amplitudes from 4 to 7 in. The measured stability derivative Xu of a single teetering rotor was measured over a range of collective pitch angles for a constant rotor RPM. These measured stability derivatives follow the trend predicted by simple qualitative analysis.