EXPERIMENTAL INVESTIGATION OF VERTICAL CG POSITION CHANGES ON QUADROTOR'S PERFORMANCE VIA FREQUENCY-DOMAIN IDENTIFICATION TECHNIQUES

Payload placement on quad-rotor (QR) is a subject of considerable importance during its flight and maneuvering phases. In this sense, any changes in the payload position, especially along the vertical axis, could significantly affect the QR center of gravity (CG) position and, in turn, its performance, dramatically. The current experimental study investigates the effect of payload vertical positioning on the performance and stability characteristics of a typical QR. The QR is test flown for more than eighty times with different payload positions, whose recorded flight data (RFD) are filtered using extended Kalman filter and subsequently utilized for QR frequency domain analysis. The RFDs are used to identify the QR longitudinal and lateral modes. In addition, the mode changes trend against the center of gravity location has led to the determination of the CG position at which instability occurs. The experimental results show that as the QR CG moves up along its vertical axis, its dynamics modes move towards the origin on the real axis taking the QR closer to borderline dynamic instability. Moreover, the damping behavior of the longitudinal and lateral modes with respect to CG has been extracted that in turn can lead to CG based techniques for QR damping control. In addition, in order to generalize the present results to be useful for other QRs, the QR parameters have been nondimensionalized, and an effective nondimensional parameter through which results can be extended to other QRs is determined. The newly introduced nondimensional parameter is used against another set of data, extracted from a different QR for verification and comparative purposes. Finally, to account for uncertainties and stochastic noise in the RFD measures, each experimental stage is repeated four times; and the results of the mean behavior are reported, too.