1: Civil passenger aircraft: high duct ratio, large power, saving fuel, but the engine diameter is large, and the positive force is large.
Military aircraft: low culvert ratio. Although it consumes fuel, it is small in size and flexible. The fighter aircraft has a limited body. The engine with high duct ratio is too thick, which is not conducive to the pneumatic design of fighter jets. The high culvert ratio engine is more fuel-efficient and more efficient. However, fighter jets are used for war, and the fuel consumption is not excessive compared with performance. Consider. Passenger planes are relatively large, and do not require mobility. Safety and economy are the core of the design, so use a high wine ratio.
2: The power of the aircraft to start:
The start of the aircraft engine. The structure and cycle process of the aviation gas turbine engine determine that it cannot start spontaneously like a car engine. Because the direct injection of oil in the stationary engine ignites, because the compressor does not rotate and the air in front does not have pressure, the gas cannot flow backwards, and the turbine cannot be rotated, which will burn the combustion chamber and turbine guide blades. Therefore, the starting characteristics of the gas turbine engine are: first, the air flow flows, and then ignites and burns, that is, the engine center must rotate and then start. This is the contradiction. The engine has not started yet, and it has not been started yet, but it has to turn first. According to this starting characteristic, the engine must be driven by other energy sources before ignition and combustion. In the previous small-power engines, the power required to drive the engine to a certain speed was small, so the starting motor was used to drive the engine to rotate, such as the vortex-dy-dyed 5 and vortex-dyed 6 engines of the Yun-8 aircraft. However, with the emergence of high-thrust engines, electric motors can no longer provide such a large amount of energy to drive the engine and reach the speed of ignition and combustion, so more energy is needed to drive the engine. At this time, APU is used to generate compressed air, and the gas source is used instead of power supply to start the engine. There is a high duct ratio engine starting mode.
