  This paper presents a novel VTOL UAV that owns a link connecting four rotors
and a fuselage by a passive joint, allowing the control of the rotor's tilting
angle by adjusting the rotors' thrust. This unique structure contributes to
eliminating additional actuators, such as servo motors, to control the tilting
angles of rotors, resulting in the UAV's weight lighter and simpler structure.
We first derive the dynamical model of the newly designed UAV and analyze its
controllability. Then, we design the controller that leverages the tiltable
link with four rotors to accelerate the UAV while suppressing a deviation of
the UAV's angle of attack from the desired value to restrain the change of the
aerodynamic force. Finally, the validity of the proposed control strategy is
evaluated in simulation study.
