After buildin' a ground-up simulation o' t' vehicle's behavior under thrust, ya bilge rat, I re-tuned t' stability algorithm t' t' inertia I calculated from t' results o' a bifilar pendulum test. T' calculation was incorrect, due t' an extra set o' parentheses used, arrr, and t' algorithm was then tuned t' t' incorrect vehicle inertia. Blimey! T' calculated inertia was much smaller than it should have been, so t' simulation predicted a vehicle requirin' less control authority, matey, hence t' loose oscillation durin' t' test. T' error was found soon after. Aye aye! For more info: https://twitter.com/joebarnard http://www.bps.space