The engine is the "heart" of the aircraft, which is no exception for military UAVs. At present, the power devices widely used in military UAVs include reciprocating or rotary piston engines, turboshaft engines, turbojet engines, turbofan engines, Pulse detonation motors, solid rocket motors and scramjets, etc., as well as battery-driven motors commonly used in micro-UAVs. The power units of these military UAVs can be applied to high-altitude and high-speed UAVs, reconnaissance UAVs, and attack UAVs, respectively. Due to the different requirements of military UAVs, the power required by the UAV power unit is also different, but in general it is still a small and medium-sized engine.

The selection of military UAV engines is not only related to the technical and tactical index requirements of UAVs, but also to the development level of the engines and the economic capabilities of users." From the perspective of existing military UAV power units, piston engines are suitable for Reconnaissance and surveillance drones for low-speed, medium-low altitude. Due to the limitation of the power system, the take-off weight of the aircraft is small, generally several hundred kilograms, and a few can reach 1200Kg. The take-off weight of the drones that can reach 1020Kg is still relatively small. ;The turbojet engine is suitable for medium and high altitude, high-speed unmanned reconnaissance aircraft, target drones, unmanned attack aircraft, etc. with short flight time, and its take-off weight is larger than that of piston drones. The turboshaft engine is suitable for medium and low altitude, low speed and short speed. Distance/vertical take-off and landing UAV cargo rotary-wing UAV; turboprop engine is suitable for mid-to-high-altitude long-endurance UAV, the take-off weight is larger than turbojet UAV. Turbofan engine is suitable for high-altitude long-endurance UAV The take-off weight of man-machine and unmanned attack aircraft is very large. Micro-power such as micro-motor is suitable for micro-UAV, and the take-off weight is very small, generally less than 0.1Kg.

At present, most UAVs use piston engines. However, due to the limitations of some factors of the piston engine itself, the piston engine is only suitable for low-speed and small UAVs, and the limitations are relatively large; The turbofan engine with low fuel rate and good high-altitude performance will occupy a very important position in the UAV power plant. So far, there are not many small turbofan engines for UAVs developed and researched abroad, and these engines are developed on the basis of the power of existing civil regional aircraft or business jets. At present, the development of turbofan engines for UAVs in foreign countries basically follows the approach of using existing engines as much as possible, making improvements and series development according to mission requirements, which reduces the initial cost of the aircraft platform and shortens the development time. and reduced risk.

UAVs with different uses have different requirements for power devices, but they all hope that the selected devices are small in size, reliable in operation, low in cost and good in maintainability. For one-time-use power devices such as target drones, it is required to have large thrust and strong anti-overload ability, but the service life can be short; Long-endurance drones require low fuel consumption, long service life, and good high-altitude performance; due to the small power of the power system of the small unmanned reconnaissance aircraft, the power system is required to reduce the weight as much as possible on the premise of satisfying the power, and Reduce processing costs.

From the perspective of economy, safety and reliability, the development of UAV engines will be carried out in two ways. One is to use advanced technology to further modify and develop on the basis of existing engines, and the other way is to develop a brand-new engine. engine. Unmanned aerial vehicles currently under development use off-the-shelf propulsion units. Doing so reduces the initial cost of the aircraft platform. However, with current propulsion systems, the range of the aircraft will be limited due to the extensive maintenance requirements. When the current engine cannot meet the needs of the aircraft, it becomes inevitable to develop a new type of engine. Some advanced small turbofan engine concepts for future UAVs have been proposed abroad, and although they cannot achieve the full performance capabilities of traditional twin-rotor turbofan engines, they may still bring economic benefits.

Due to some limitations of piston engines, piston engines are only suitable for low-altitude, low-speed and low take-off weight UAVs. For larger range drones, gas turbine engines should be the first choice. Due to the different structures and performance characteristics of gas turbine engines such as turboshaft, turbojet, and turbofan engines, the choice of UAVs in power devices has greatly increased. For example, turboshaft engines are suitable for unmanned helicopters, and turbojet and turbofan engines are suitable for fixed-wing drones. Among these types of engines, medium-thrust turbofan engines are more suitable for drones because of their low fuel consumption, thrust and weight, so these types of engines are more suitable for high-altitude long-duration unmanned reconnaissance aircraft and unmanned attack aircraft.

Future drones will require more power than manned aircraft, and future drones will also require engines to be service-free for extended storage periods, so a multi-electric engine that does not require lubrication and greatly reduces maintenance work will be A development direction of future UAV power. Future advanced small UAVs have higher requirements for durability and stealth, and have a wider range of tasks, so small turbofan engines with higher thermal efficiency and power density are required. In addition, for single-use UAVs, short-life, low-cost engines are required. Therefore, reducing the number of engine components and simplifying the flow path is an important development direction for future UAV power technology.
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