The aviation engine is the "heart" of the aircraft. The engines of civil passenger aircraft focus on safety and reliability, while military engines also pursue greater thrust on this basis, as well as the maximum thrust when afterburner is turned on. It can be seen that the strongest player in the field of aviation engines must be military aviation engines, and military engines are considered the pinnacle of human technology. Countries that are capable of R&D, manufacturing and production of aerospace engines generally do not easily export their own technology. They only export finished engines, and some even need to be sent back to the country of origin for maintenance. How difficult is it to build an aircraft engine? The difficulty in its manufacturing lies in its complex structure and high-precision requirements, which involve many aspects such as material selection, design, manufacturing, control system and rigorous testing. Let's take a look at it together.
Difficult to copy and disassemble
The difficulty of manufacturing aeroengines is first reflected in the difficulty of copying and dismantling. The appearance of a car or aircraft can be copied through reverse mapping. Needless to say, cars are also easy to copy. There are also aircraft appearance copies, such as the Tu-160 and B-1B bombers, but engine copying is simply impossible without the intervention of drawings. For example, the CFM-56 series engine, the mainstream engine currently used on the Boeing 737 passenger aircraft, has produced more than 20,000 units from its first operation in 1974 to today. It is used in almost all single-aisle passenger aircraft mainly produced by Boeing and Airbus.
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When dismantling CFM-56, you will find that the engine blades are covered with many small air holes about the size of a fingernail. Without positioning drawings, it is impossible to copy them. Once the air holes are punched in the wrong position, it will directly affect the heat dissipation of the blades, and the overall performance of the replica will be reduced. Relying on the technical foundation of the CFM-56, GE has developed engines that can be used on various aircraft models, directly competing with Pratt & Whitney.
Materials are difficult to manufacture
The aviation engine is actually very simple. Take the classic CFM-56 engine as an example, including a low-pressure compressor, a nine-stage high-pressure compressor, a first-stage high-pressure turbine, a four-stage low-pressure turbine, and an annular combustion chamber in the middle. However, these structures have different working temperature and pressure environments, which means that the materials used are different. Take turbine blades as an example. The working environment is thousands of degrees Celsius, tens of thousands of revolutions per minute, and they are made of a mixture of multiple metals with different proportions.
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Because the blades near the combustion chamber are subject to higher temperatures and the materials are used to withstand high temperatures, the proportions of rare metal elements are different. If all the same high-temperature-resistant materials are used, the unit price will be high and the economy will be poor. For commercially operated civil passenger aircraft engines, it is best to be cheap and easy to use.
In the same way, in addition to turbine blades, the materials used in each engine component are also different. The CFM-56 engine turbine used by the Boeing 737 is made of high-temperature alloy, and some other parts use composite materials. Currently more popular is resin-based composite material. Pratt & Whitney's F-119 external ducted receiver uses this material, which can withstand temperatures of 400 degrees Celsius, and the cost can also be controlled.
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High processing precision
If you have advanced materials and drawings, it does not mean that you can create an excellent aero engine, because the processing technology is the final obstacle. The fan of a CFM-56 engine aeroengine is only 1.55 meters in diameter and 2.5 meters in length. It has to produce 86 kN of thrust in such a small space. You can imagine how complicated the processing technology is.
From a small perspective, taking the current mainstream single crystal turbine blades as an example, the precision casting process requires an error of 0.1 mm, so as to ensure that each blade can work normally. In order to process various alloy materials together, you need to master the processing skills and welding techniques of high-temperature alloys. At the same time, the engine rotor and blades are running at high speed during operation. Insufficient craftsmanship means that the engine wears out quickly and has a short service life, which directly affects the economy.
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The high requirements of technology also promote the efficiency of aero-engine operation. Taking blades as an example, GE has developed a seamless butt-jointed blade. There is a software made of special material at the outer end of the engine blade, which can be used when the blade is working. Seamlessly connects with the outer ring structure to improve engine efficiency. Such soft materials have very high requirements for processing technology. They must not only maintain stability, but also be economical and require little maintenance. Otherwise, while improving the engine efficiency, it will also increase the burden on the ground staff, and the economic performance will not be obvious enough.
To sum up, from the perspective of reverse surveying, materials and processing technology, aero engines should be said to be the crown of the industrial engineering field and a symbol of a country's scientific and technological strength.
Based on the WS-10 "Taihang" engine, my country has independently developed the WS-20 high-bypass-ratio, high-thrust turbofan engine for both military and civilian use, which is equipped with the Y-20 strategic transport aircraft. Our country is also developing the Yangtze-1000A high-bypass ratio turbofan engine for installation on the C-919 civil aircraft, and plans to assemble and produce the world-class LEAP-X "Safran" engine domestically. At the same time, the next generation of advanced large bypass ratio engines with a thrust of 200 to 400 kN is also being developed. These projects all indicate that the "blowout" era of China's large bypass ratio engines is coming.
