Rapid ascent maneuver of a dual propulsion VTOL drone from high-speed cruise flight

The maneuverability of a dual propulsion VTOL drone may be enhanced by the two types of rotors mounted on it, one for rotary-wing mode and the other for fixed-wing mode, when they are used simultaneously. This paper investigates how much altitude gain can be achieved within a specified time from a high-speed cruise flight by using the two types of rotors together, and discusses the flight states and the forces applied to the aircraft during the ascent. A dynamic model of the drone is developed by modeling the aerodynamic and thrust forces. Using this model, numerical optimization is performed to obtain a rapid ascent maneuver that maximizes the altitude gain at a specified end time, with the rotor battery voltages and the elevator angles during the maneuver as the optimization variables. The altitude increase achieved by the rapid ascent maneuver is much larger than that obtained in the conventional fixed-wing mode flight. In the early stages of ascent, both aerodynamic lift and rotor thrust forces are used together to accelerate the drone upward. In the later stages, the drone continues its ascent using the rotor thrust forces while suppressing large pitch angles caused by aerodynamic pitch-up moments due to a negative angle of attack. These results demonstrate the enhanced maneuverability of a dual propulsion VTOL drone in achieving rapid ascent by simultaneously utilizing both types of rotors.