The Extended/Unscented Kalman Filter of DLR's ACT/FHS

Abstract

DLR’s active control technology/flying helicopter simulator (ACT/FHS) research rotorcraft supports research in a variety of fields like automatic flight control, active sidestick technology for pilot assistance, and external sling load stabilization. For the online estimation of variables relevant for the automatic control system as well as for pilot feedback, an Extended Kalman Filter / Unscented Kalman Filter combination was implemented. The filter fuses measurements taken by multiple sensors and estimates relevant rotary and translatory variables. Additionally, it performs an online wind estimation. Multiple output variables are computed for further processing in flight control systems and/or displays for the pilot. The filter also accounts for delayed sensor measurements which typically occur in GPS-measurements and supports the user-defined override of the internal wind estimation. Accounting for the unreliability of aerodynamic measurements of helicopters during hover, this filter neglects wind measurements below a certain speed threshold.