Identification of Lateral/Directional Model for a UAV Helicopter in Forward Flight

A lateral/directional state-space model of the Raptor 50 helicopter is identified in forward flight condition. A frequency sweep test is properly designed and executed to collect a well-suited time-history database. The measured accelerometers are transferred from the sensor location to the gravity, then, a complete set of non-parametric input-to-output frequency responses that fully characterizes the coupled helicopter dynamics are extracted from the frequency sweep test data. With the help of small perturbation theory, a linearized dynamic model for the stability and control derivative is extracted from linearization of a nonlinear mathematical model. A nonlinear search based on secant method is conducted for the linear lateral/directional state-space model that matches the frequency-response data set. The identified model is verified in the time domain, which indicates that the model matches the flight data well.