By Zhou Mingyang
At the Airshow China 2016 concluded days before, UAV (unmanned aerial vehicle) came to be the hotspot. The journalist from Economic Daily found at the show that the exhibits are mainly related components and professional-level UAV including industrial and military UAVs. At present, China's consumer UAV has reached the world leading level, while the professional UAV has failed to see more satisfactory achievements mainly constrained by power system.
Aircraft operation is driven by propeller, while the thrust generated by propeller lies in power system. Power technology is the key to UAV. As the backbone of UAV system development, the development of UAV power system directly determines the flying length and time of it.
Power driven to fuel driven
Different types of UAV platforms raise different demands for power devices, which determines the flying time and load weight and also restrains the operating capacity of UAV in turn. At present, the power system of UAV falls into electric motor and engine, or "power driven" and "fuel driven".
Electric motor, also known as electro-motor and motor, is generally applied in MUAV and most commercial UAVs on the market are driven by motor. Such a power unit features simple structure, light weight and convenient use and thus is suitable for providing power for low-altitude, low-speed UAV and MUAV. "Fuel driven" motor is mostly applied in such military aircraft as unmanned helicopters. Currently, most UAVs are designed with reciprocating motor, rotary piston engine or gas turbine engine including turbojet, turbofan, turboprop and turboshaft. The carrying capacity of SUAV driven by motor is 3-5kg roughly and such UAVs can fly for 15-20min continuously. However, the carrying capacity of those driven by gasoline engine is as high as 15kg at least and such UAVs can fly for 2h continuously.
Professional UAV has seen stably increased application in electricity, security, agriculture, forest fire prevention, police and other different niche fields. Compared with consumer UAVs, UAVs applied in industry are raised with higher demands for load capacity and flight duration. Most power-driven multi-rotor UAVs available on the market can fly for 40min at most while carrying the load of 5kg because of the limitation of lithium battery. The absence of heavy-load multi-rotor UAV for long flight length has become a "dead spot" of China's UAV market.
Many domestic manufacturers have made efforts to integrate the advantages of electricity-driven multi-rotor and fuel-driven UAVs to prolong the flight duration, increase the aircraft flight stability and improve the comprehensive performance of aircraft. EWATT is a leading civil UAV system manufacturer in China and such products as fixed wing UAV, multi-rotor UAV, heavy-load unmanned helicopter developed by the company have been extensively applied in more than 10 fields, such as film and television, logistics, agriculture, forestry and plant protection. During the show, EWATT unveiled its new product UAV, i.e. EWZ110 fuel-driven bending moment multi-rotor UAV. This multi-rotor UAV is developed with the maximum effective load of 20kg, maximum take-off weight of 40kg and the longest flight duration of 120min, achieving a breakthrough in limitation of most commercial power-driven UAV power system and greatly improving the performances of UAV in every aspect.
According To Zhao Guocheng, president of EWATT, this efficient multi-rotor UAV and power system rendering longer flight duration are derived from the independently developed forced cooling reciprocating aeroengine for fuel-driven bending moment multi-rotor UAV. The energy density of gasoline and lithium battery is 11.8kWh/KG and 0.25kWh/KG separately. As a result, the flight duration of aircraft designed with gasoline engine can be greatly prolonged under the condition that gasoline and lithium battery is of the same weight. In addition, the frame of this UAV is mainly made of aerial aluminum alloy and carbon fiber materials, significantly reducing the frame weight while maintaining the strength of the frame structure.
Stability performance of power system is of vital importance for professional UAVs, given the motor or engine in UAV would bring stronger vibration in general and produce large acceleration during flight in case of poor vibration damping control, leading to angle change, unstable UAV flight and greater vibration of the fuel engine than the electric motor. To address this problem, EWATT has independently developed dual-output shaft and dual-cylinder forced cooling power system with the two cylinder body arranged in opposite horizontally, making the vibration generated by operating crank piston mechanism balanced out mutually. In addition, its vibration value is 1/10 of that of common aircraft piston, thus greatly improving aircraft stability.
Military UAV: Better match between power and platform
UCAV (Unmanned Combat Air Vehicle) has grown to be the main force for future air battles owing to its advantages as "zero casualty", "no contact", "no blood", super maneuverability and large load capacity. At this show, such high-end aircrafts as mid-high altitude long-endurance UAV and UCAV came to be the focus. Such air vehicles are mainly used for executing strategic and operational reconnaissance tasks and can search complete intelligence information of the targeted area and execute various strike missions, thus being the highest-end one among various UAVs. At the show, "Changhong-5" (CH-5) medium altitude long-endurance UAV driven by astatki engine made its debut. This vehicle is mounted with 16 guided missiles and can last for consecutive 60h at most.
At present, much focus has been put on turbofan engine to provide power for high-end UAVs in China. Given the lower fuel consumption and matched quality and thrust level with UAV, turbofan engine is a perfect match to mid-high altitude long-endurance UAVs and UCAVs. In addition, China has also intensified efforts in layout, research and development of engine. Aero Engine (Group) Corporation of China (AECC) founded in August this year and bearing the mission of creating "China Heart", made its first presence at the show. The independently developed "Taihang", "Yulong" and "Jinsha" turbofan engines designed with high performance, large thrust and torque as well as proprietary intellectual property rights was all exhibited at the show, presenting the advanced research and development outcomes of China.