Design and Implementation of a VTOL UAV with Flight Transition Optimisation
A tilt-rotor UAV designed around the hardest part of the flight envelope: the transition itself
Two aircraft in one airframe
A multirotor can take off from anywhere and hover, and pays for it with terrible cruise efficiency — it holds itself up entirely on thrust. A fixed-wing aircraft cruises efficiently on a wing and needs a runway. A tilt-rotor tries to be both: rotors pointing up for takeoff and hover, then rotated forward so the wing takes over the lift and the rotors become propellers.
The design work covered the whole aircraft — structure, propulsion and aerodynamics, modelled in CATIA — but the configuration only makes sense if one specific manoeuvre works, and that manoeuvre is where the project's attention went.
The few seconds where the aircraft is neither one thing nor the other
Transition is the interesting engineering problem. Partway through the tilt the rotors are no longer holding the aircraft up and the wing is not yet flying — the aircraft is at low airspeed with a wing near its stall, control authority shifting from differential thrust to aerodynamic surfaces, and every degree of tilt changing the balance between the two.
Optimising that means choosing how fast to rotate the nacelles and how to schedule the transition against airspeed: tilt too quickly and the wing has no speed to generate lift when the rotors stop supporting the aircraft; tilt too slowly and the aircraft spends longer than necessary in the regime where neither system has full authority.
That coupling — the tilt schedule, the airspeed build-up and the control handover all constraining each other — was the core of the design study, and it drove the mechanism, the wing sizing and the propulsion layout alike.