Abstract The Vertical Take-Off and Landing (VTOL) aircraft exhibit complex and rapidly varying dynamics during the transition flight phase, which poses significant challenges for accurate modeling and aerodynamic parameter estimation. This paper presents a parameter estimation framework to identify unknown aerodynamic coefficients governing the transition flight, leveraging experimental flight data of a tilt-rotor VTOL UAV in outdoor experiments. The VTOL UAV has a hybrid configuration with two tilting rotors, two static rotors, and fixed wings. A nonlinear dynamic model describing the longitudinal motion is developed and reformulated into a regression structure suitable for parameter estimation. A projection-based constrained Recursive Least Squares (RLS) algorithm is then applied to estimate critical aerodynamic parameters, including lift, drag, and thrust coefficients, under physical constraints. The convergence and accuracy of estimation algorithm for time-varying coefficients is firstly verified by simulation. The parameter estimation is further validated by six experimental flight tests with different tilting rates of 12 deg/s and 14 deg/s. Experimental results demonstrate the accurate estimation by accurate predictions of the aircraft states υx, υz, ωy with RMSEs of 0.7230 m/s, 0.0990 m/s, and 0.0508 rad/s, respectively.
He et al. (Tue,) studied this question.