I would like to share this design made by a group of undergraduate students in the course called "Aerospace Systems Design Project".
Tilt rotor aircraft - The Flying Battenberg
The iMechE set out a competition for undergraduate students across the UK to develop an autonomous UAS (Unmanned Aircraft System) to deliver aid to remote coastal locations. This presented the opportunity to investigate innovative methods of aerospace design for micro systems.
A difficulty in autonomous control of fixed wing aircraft is take off and landing, however they benefit from reduced power consumption, increased range and increased speed over multi rotor designs. As multi-rotors are capable of VTOL (Vertical take-off and landing).
The design pursued was to gain the benefits of VTOL and accurate payload delivery of multi rotors and attempted to also incorporate a fixed wing to increase range and additional forward propulsion for higher speeds.
The UAS constructed featured a meter long body with wings spanning 1.5 m and a chord of 300 mm. The wings hold pylons of 700 mm long on either side of the aircraft with three phase pancake style motors spinning 12" x 6.5" carbon fibre propellers at either end of the pylons. With four motors in total the UAS can operate as a quad rotor.
To take advantage of the large wing the motors are held on mounts that allow them to tilt forward. Once in sufficiently high forward speed the wing will generate lift for the UAS, leaving the propellers responsible for forward thrust only. During forward flight the four motors can no longer compensate for disturbances especially in pitch, as the mathematical model shows. This required the addition of aerodynamic actuators to be used in forward flight - aileron, elevator and rudder. In this flight regime the propellers act as a single thrust unit.
During forward flight the UAS back motors operate as pusher propellers as opposed to puller propellers as a multi rotor would commonly do. As the back motors were pusher they had to be mounted asymmetrically from the front two puller motors, and thus point downwards in multi-rotor flight regime.
The structure of the UAS was composed of rolled carbon fibre tubes, held together with 3D printed PLA clamps. The 3D printed clamps featured inserts for rubber O-rings, intended for plumbing application but research discovered they increased the friction coefficient of the clamps significantly, allowed additional force to be applied as they could be compressed more without fracturing like PLA alone and provided damping to reduce vibrations caused by the propellers.
3D printing was implemented not only for rapid prototyping of design components, but as a means of low cost high quality manufacturing that was very effective for low scale production.
The wing and tail-plane were constructed out of foam used in model aircraft. For the tail-plane a series of ribs were 3D printed and coated in film. The body of the aircraft is composed of a series of foam ribs, again coated in film.
Limited time, skills and budget constraints has resulted in the target of making the proposed aircraft autonomous unreasonable. A few solutions have been theorised but they either require intensive adaptations to readily available flight controllers or multiple flight controllers and a mixer as a work around.
Extensive testing has yet to take place, but initial performance analysis has suggested the UAS will operate at reduced performance in both quad-rotor regime and fixed wing. This is primarily due to the additional weight the UAS must carry. As the UAS essentially has a payload of a fixed wing aircraft in multi-rotor mode and a payload of a multi-rotor in fixed wing mode.
Further development of these concepts would require further work on possible structures of hybrid aircraft that do not suffer from the added weight incurred in this design.
Note: Is not fully autonomous (yet...)
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