Identification of powered parafoil-vehicle dynamics from modelling and flight test data

Abstract

During the final approach and landing phase of the X-38/Crew Return Vehicle, a steerable parafoil is used to maneuver and land at a targeted ground base under autonomous control. To simulate and verify performance of the onboard Parafoil Guidance, Navigation and Control system (PGNC), a commercial powered parafoil- vehicle, called the Buckeye consisting of a parafoil and vehicle two-body system like the X-38/CRV was modified to accommodate the avionics and scale-downed parafoil for aerodynamic similarity and a series of flight tests were conducted. Dynamic modelling and system identification results for the Buckeye are de- scribed in this dissertation. The vehicle dynamics are modelled as all 8 degrees-of- freedom system comprising 6 states for the parafoil and 2 states for the relative pitch and yaw motion of the vehicle with respect to the parafoil. Modal analysis for the linearized model from the nonlinear model shows the number and order of dynamic modes as well as the system is controllable and observable. For system identifica- tion, the overparameterized Observer/Kalman Filter Identification (OKID) method is applied to identify a linear model of the Buckeye two-body system from the flight data assuming that disturbances at a calm day are represented as periodic distur- bances. The identification results show that the overparameterized OKID works well for powered parafoil-vehicle two-body system identification under calm day condi- tions using flight data. For the data with possible discrete gusts the OKID shows limitation to identify a linearized model properly. Several sensor packages including airdata and Inertial Measurement Unit are designed and installed for the parameters for identification. The sensor packages successfully supply data of the parameters for identification and suggest a feasible, low cost method for the parafoil-vehicle two-body dynamic parameters.