System Identification of a Subscale Distributed Electric Propulsion Aircraft

Abstract

Flight testing of a 21%-scale Cirrus SR22T aircraft with a distributed electric propulsion system was performed with the goal of identifying the influence of distributed propulsion units on the aircraft flight dynamics. Stability and control derivatives for this configuration were identified for a linear aircraft model, including throttle-based control influences of a semispan-distributed array of propulsors. Unknown model parameters were identified from flight test data under unsteady excitation of control effectors using frequency-domain system-identification methods, and the resultant model was validated against independently acquired sets of flight data. The identified throttle-based control derivatives were characteristic of anticipated local thrust contributions from each propulsor and associated proportional yawing moments. Additional throttle-based control influences were also observed, through modulation in the aircraft lift, pitch, and roll characteristics. Furthermore, significant spanwise nonuniformity was observed in the aircraft lift sensitivity to throttle changes, which was linked to three-dimensional influences of the wing aerodynamics. These observations demonstrate the inherent degree of interconnectivity between aerodynamics, propulsion, and control subsystems characteristic of aircraft with distributed electric propulsion systems.