This design by the University of Calgary Schulich UAV club is an elegant merger of two proven designs, a quadcopter and a common high wing plane. The plane has a rectangular straight wing, a twin tail, and a large pusher motor located at the rear of the fuselage. The quadcopter aspects of the aircraft are located around the center of gravity of the plane. The entire design is built on two circular booms that run the length of the aircraft, and provide detachable mounting points for each component, allowing for a modular design. The concept was developed by Schulich UAV in 2015 for the UAV Medical Express Outback Challenge. The original design was about half the size of this cargo design. The design draws heavily on the properties of fiber reinforced composites such carbon fiber for its high stiffness and lightweight properties, and 3D printed parts for their ease of fabrication and low cost. Since the development of our original design, we have created 5 further iterations, tested our software on a scale prototype, and are in the fabrication phase of our second prototype.
Since the primary focus of this vehicle is to transport cargo, we have optimized our design with payload capability as our primary objective. In order to keep the vehicle’s center of gravity (CG) constant — independent of the mass of the the payload — we have placed the cargo’s center of gravity (CG) directly below aircraft’s optimal CG range which is located slightly aft of the leading edge. This is achieved by building the aircraft around a cargo box, which is central to the design. This “box” must always remain in place whether or not the aircraft is carrying a payload and be customized based on the type of payload that the aircraft is carrying. It is held in place using 8 servo actuated pins that extend into the box to secure it. The design does not use flaps on its wings, which in conventional planes reduce stall speed during landing. This aircraft’s vertical takeoff and landing abilities eliminate the need for flaps and therefore reduce the complexity of the wings.
Within the design, each part is simplified for efficiency and effectiveness. The fuselage has a semi-monocoque construction and is composed of a skin, fabricated from a blend of reinforced composites materials that provide stiffness, strength and shock resistance and 3D printed ribs that support the equipment that is needed to control the aircraft. The wing has been optimized to carry 23 kg of total weight, which is the average mass of the aircraft in all configurations. It is also optimized for efficiency at a cruise speed of 116 km/h and can easily be removed from the aircraft for transport. Twin carbon fiber booms support the VTOL capabilities of the aircraft and provide a stiff and lightweight mounting point for each of the UAV’s components. They run from the front of the aircraft where they attach to the front two VTOL motors, through an attachment in the wings, to the tail attachment system. Each boom runs the length of the aircraft to aid the structural stability of the aircraft. This also allows for easier disassembly and replacement of broken parts. The Electronic Speed Controllers (ESC) for the 4 vertical motors are mounted on the booms for simplified wiring and excellent cooling mechanism for the ESC.
The horizontal and vertical stabilizers have been designed around the parameters set by the wing and performance of the overall design, which behaves similar to a cargo or bomber type plane. They will be 3D printed and wrapped with carbon fiber to ensure form, stiffness and lightweight.
Determining the battery capacity of the plane is a cart before the horse situation. Adding battery capacity increases flight time but the additional battery weight decreases flight time. This problem is better solved by simulation rather than analysis. Using expected weight and battery characteristics, it’s possible to find the expected battery weight for each mode of flight. These calculations can be found in the Propulsion Balance section of the data sheet. Using a combination of these calculations, we proposed 7.6kg of batteries with the capacity of 1250 Wh. With these requirements, we chose four PULSE Ultra PLU15-160006 batteries wired with 2 batteries in series for a total of 32 Ah in a 12 cell (44.4V) configuration. We chose to use these instead of the given values as they were calculated from the thrust value that was chosen through aerodynamic design. For the autonomous navigation of the UAV, we have tested with the Pixhawk autonomous flight controller from 3DR with considerable success. For propulsion, we have selected T-Motor brand motors for their high efficiency. Our pusher motor for cruising in fixed wing flight is the T-Motor U12 with a 30x10.5 propeller, while our VTOL lifting motors will be 4 T-Motor U8 motors with 29x9.5 propellers.
The aircraft lands vertically on the belly of the fuselage. There are also four landing legs located under the four corners of the booms to protect the wings and keep the aircraft from tipping if it touches down on uneven ground. These landing legs contain suspension to protect onboard items in the event of a hard landing.
- Flexible gaskets seal all the mating surfaces that could allow water ingress. Drain holes at low points prevent any internal accumulation of water that does get past gaskets.
- Waterproof connectors are used for all electrical connections.
- All motors are brushless 3 phase AC motors that can run submerged in water. After flights in wet conditions, they would need to be dried off to prevent corrosion. Small strategically placed cowlings minimize the ingress of water to the motors.
- For cold weather flights, the batteries are temperature regulated using foam protection sleeves with heating elements.