Modeling DelftaCopter from Flight Test Data

Abstract

The DelftaCopter, a tilt-body tailsitter UAV, endures large gyroscopic moments due to the single helicopter rotor providing its thrust. In previous research by de Wagter et al.[1] the DelftaCopter’s attitude dynamics were modeled using a rigid rotor, as is customary for small helicopter modeling. A controller based on this model was unable to compensate coupling between pitch and roll rate caused by gyroscopic moments. In this paper, two models are compared for reproducing the attitude dynamics of the Delfta- Copter in hover. The Cylinder Dynamics (CD) model, used in the previous research, assumes a rigid rotor. The Tip-Path Plane (TPP) model incorporates flapping motion of the blades and was developed by Mettler[2]. The two models are compared by fitting each model’s parameters on flight data using chirps, sine waves with increasing frequency, as system identification maneuvers. The TPP model is shown to be much more accurate in reproducing the high-frequency attitude dynamics. An LQR controller directly based on the TPP model is shown to yield adequate tracking performance. This validates the applicability of this model to the DelftaCopter. For forward flight, an extension to the TPP hover model is proposed incorporating the aerodynamics of the wings and elevons. It is shown that with the extension, chirps in forward flight can be simulated with reasonable accuracy. This paves the way for a model-based controller in this flight state.