# Design of a Hand-Launched Solar-Powered Unmanned Aerial Vehicle (UAV) System for Plateau
## 3 Detailed Design
### Structure and Avionics  
The structure of MP Solar UAV was a traditional beam-rib structure made of carbon, KEVLAR, and balsa wood. The beam of the main wing was a rectangular hollow section beam consisting of rectangular carbon tubes arranged up and down and walls with lightening holes. The rectangular beam had better bending resistance than the circular carbon tube beam, which was harder to deform under overload caused by sudden wind, ensuring the safety of solar cells. The wing ribs, trusses, and the solar cells laid on the upper surface of the wing formed a shell structure, ensuring good torsional stiffness of the wing (Figure 9b).  
To prevent the propeller from interfering with the optical payload, the fuselage was of a tail-pushed configuration, in which the propulsion system is located at the rear of the fuselage. The hard landing adopted by MP Solar UAV required the fuselage to have enough strength, so the fuselage structure (Figure 9a) adopted a shell structure composed of transverse mediastinum frame, truss, and skin.  
The power generation and storage system consisted of solar cells, MPPT, and lithium-ion batteries, which were the core of the MP Solar UAV's perpetual flight. The energy was generated by 42 monocrystalline silicon solar cells laid on the surface of the main wing and stored in two high-energy density batteries located via MPPT. The packaged lithium-ion battery was connected in a 3S (11.1v) layout, which can provide 354 Wh energy. Solar cells had an energy conversion efficiency of about 23%.  
It is important to note that low temperatures can seriously affect battery discharge performance and thus threaten flight endurance. Thus, the use of low thermal insulation material turned the fuselage into a closed cabin, and the self-heating from the batteries and avionics kept the cabin at the suitable temperature.  
Avionics systems (See Figure 9a for avionics system arrangement) of MP Solar UAV included autopilot [14], digital radio, remote control (RC) receiver, sensors, propulsion systems, etc. In order to obtain necessary information of position velocity and altitude for flight controller, many low-cost and highly robust MEMS (micro-electro-mechanical systems) sensors were equipped on this UAV, including accelerometer gyroscope, magnetometer, barometer, and GPS. The actuation system was driven by two brushless servos to drive the rudder and all-moving elevator, which had high sensitivity and reliability. The propulsion system used a brushless motor direct drive 10- \(\times\) 7-inch propeller, with  
Figure 8: Computational Fluid Dynamics (CFD) result of cruise at 5000-m altitude of the UAV: (**a**) Lift coefficient, angle of attack data; (**b**) drag coefficient, angle of attack data; (**c**) pitching moment coefficient, angle of attack data; (**d**) lift–drag ratio data.  
a maximum power output of about 430 W at takeoff. The UAV offered a fully manual mode to deal with a severe case of autopilot failure [15].  
MP Solar UAV was designed to have a maximum payload capacity of 450 g. Different functional payloads mean different payload weights, and the aircraft can be fitted with different loads to suit different missions. The aircraft had a designed payload capacity of 50 g for perpetual flight, which is enough to carry a small fixed-focus camera with video recording capability. The UAV can also carry a 450 g optical-infrared optoelectronic pod for complex missions at the expense of perpetual flight capability. The whole energy route of payload and avionics instruments are shown in Figure 10.  
Figure 10: Topological system overview over the MP Solar UAV.  
Figure 9: (a)The fuselage structure and arrangement of instruments, (b) wing structure.