  This paper presents a novel model of large-size tilt-rotor aircraft, which
can operate as a helicopter as well as being capable of transition to
fixed-wing flight. Aerodynamics of the dynamic large-size tilt-rotors based on
blade element method is analyzed during mode transition. For the large-size
aircraft with turboshaft engines, the blade pitch angles of the rotors are
regulated to vary according to the desired level of thrust, and the following
expressions are formulated explicitly: rotor thrust and blade pitch angle, drag
torque and blade pitch angle. A finite-time convergent observer based on
Lyapunov function is developed to reconstruct the unknown variables and
uncertainties during mode transitions. The merits of this design include the
modeling of dynamic large-size tilt-rotor, ease of the uncertainties estimation
during the tilting and the widely applications. Moreover, a switched logic
controller based on the finite-time convergent observer is proposed to drive
the aircraft to implement the mode transition with invariant flying height.
