Experimental development of an UAV nonlinear dynamic model

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Experimental development of an UAV nonlinear dynamic model

Chumalee, Sunan / Whidborne, James F.

Wind tunnel tests for developing aircraft nonlinear mathematical models are expensive in terms of schedule and budget for UAV (Unmanned Aerial Vehicle) applications. System identification techniques are an alternative approach that can be used to estimate stability and control derivatives or aerodynamic coefficients from flight data. However, to obtain accurate results from system identification techniques, an aircraft is typically required to fly at trim condition and to manoeuvre with a suitable amplitude (not too low and not too high) of a particular 3-2-1-1 waveform of each control surfaces deflections at a time. In practice, these requirements could be difficult and time-consuming to perform for fast, large and heavy UAVs. In this paper, an ordinary piloted manoeuvre and off-trim condition (racetrack pattern) flight data, of an aerial target of Royal Thai Air Force (RTAF) is considered, for which an equation-error parameter identification technique is proposed that is based on the principle of least squares fitting in order to estimate the aerodynamic coefficients. Experimentally, a reliable nonlinear model of RTAF aerial target was obtained. Moreover, based on this nonlinear model, the gains in each loop of a proportional, integral and derivative (PID) flight controller has been successfully determined and validated through hardware-in-the-loop (HIL) simulation. Furthermore, this PID flight controller has also been validated through flight test at one particular flight envelope. As a result of the flight test, this PID flight controller successfully performed its functions without any need to adjust the controller gains.