Aerodynamics and Propulsive Modeling of a Bi-Rotor Convertible Aircraft for the Identification of Trim Conditions in Longitudinal Flight

Increasing attention is being paid recently to eVTOL (electric Vertical Take-Off and Landing) vehicles for different applications, such as Search and Rescue. Convertible aircraft such as tilt-rotors seem to be one of the most promising concepts. The dynamics modeling and simulation of these vehicles is very challenging due to their wide flight envelope (from hovering to horizontal flight) and to the reduced amount of available data. This paper presents a model for the dynamics of a Bi-Rotor Convertible Aircraft, the ProVANT-EMERGENTIa, with a general formulation of the forces and moments acting over it. The equations are simplified to determine longitudinal flight trim conditions using wind tunnel identified aerodynamic and propulsive models. Trimmable flight envelope maps were successfully calculated considering the aircraft state variables (flight path angle, airspeed, and angle of attack) and the longitudinal control inputs (control surfaces deflection, propeller orientation, and throttle lever position). The flight envelope was found to be limited either by the saturation of the control surfaces deflection when the pitch moments were too large, or by the throttle lever when the propeller air incidence angle was too low. The size and shape of the envelope was impacted by the flight path angle: more limited for climb conditions due to the excess of Thrust demanded and of the greater pitch moments involved; less restricted for descents because of the opposite reasons.