System identification studies with the stiff wing mini MUTT Fenrir – Flight 20

Abstract

A successful flight test with the stiff wing mini MUTT, named Fenrir, was conducted on 27 May 2015. The purpose of this flight was to gather preliminary data for system identification focused on low frequency rigid body dynamics. No augmentation was used during the 1st flight on this day, which is formally flight 20. This working paper analyzes flight 20 only. 3-2-1-1 pitch excitations were sent to individual symmetric surface pairs coincident with normal pilot inputs. For reference, a preliminary model of the stiff wing Fenrir (developed by D. K. Schmidt) at a flight condition of 65 ft/s (19.8 m/s) indicates a short period mode at 9.02 rad/s with a damping ratio of 0.658 and a phugoid mode at 0.569 rad/s with a damping ratio of -0.0251. It is expected that the actual aircraft dynamics will differ but these dynamic parameters provide a good baseline for ballpark values for comparison to the flight test data. Analysis of these data were performed in both the frequency and time domains. Short period system parameters were identified using two approaches: 1) frequency domain equation error, and 2) subspace system identification in the time domain.