01
China's large aircraft is not limited to the C919
Not long ago, the Commercial Aircraft Corporation of China (hereinafter referred to as "COMAC"), which is responsible for the manufacture of domestic large aircraft, jointly carried out a one-week seminar with six special groups, including overall aerodynamics, composite structure, mechanical system and propulsion system, and the main topic was the joint research of the C929 project. This means that the first intercontinental passenger aircraft independently developed by China, the C929, is steadily advancing to the detailed design stage, and is getting closer and closer to the final stage of the research and development of the two large civil aircraft, "manufacturing and assembly" and "flight test and certification".
As we mentioned in previous articles, the ARJ21 regional airliner, which officially began commercial operation in June 2016, and the large passenger aircraft C919, which achieved its commercial maiden flight in May 2023, can be regarded as the "prelude" to the C929. At the beginning of 2022, the State Council issued the "14th Five-Year Plan for the Development of a Modern Comprehensive Transportation System", which mentioned a "three-step" plan for the development of China's civil aviation industry: from regional aircraft to single-aisle aircraft, and then to dual-aisle large trunk aircraft. Together, the three will form a relatively complete product system for domestic commercial aircraft.
Industry insiders have said that ARJ21 has laid out more than 200 domestic routes, if it is said that it has made a domestic commercial aircraft technical route for C919, then the technical research and commercial operation results of C919 will greatly affect the development of the future dual-aisle large trunk aircraft C929.
Why? Let's start with a brief introduction to the C929. In 2016, when the large-scale long-range wide-body passenger aircraft R&D and manufacturing project was officially established, it was actually called CR929, C stands for China, and R stands for Russia. But in 2022, due to changes in the international situation, Russia withdrew from the project research and development at the preliminary design stage, and "CR929" became "C929".
From the outside, the C929 is as its name suggests, much like an "enlarged version" of the C919, and it can even be said to be a real "big plane". The width of the fuselage of C919 is 3.96 meters, while the C929 can reach 5.92 meters, and the difference between the two is nearly 14 meters in length, which leads to the passenger and cargo capacity of C929 is much higher than that of C919.
In addition, according to COMAC's information, the CR929 is divided into three types: shortened, basic and extended, named CR929-500, CR929-600 and CR929-700 respectively. Among them, the basic CR929-600 has a design range of 12,000 kilometers and 280 seats, far exceeding the C919's 4,000-kilometer range and 168-seat carrying capacity.
In the civil aviation industry, the manufacture of trunk aircraft with more than 150 seats has been monopolized by the two giants of Boeing and Airbus, and C919 is officially going to squeeze into this field; The C929 control group is the 250-seat Boeing B787 and Airbus A350. Judging from the R&D experience of C919, R&D and manufacturing of a large aircraft can indeed drive the ultra-long industrial chain and show the level of the national aviation industry, but this is not easy to say, C919 took 8 years from the project to the final assembly line, not to mention the cultivation and game in the core technology arena of "aerospace engine".
02
The "Chinese Heart" of Widebody Aircraft
Larger aircraft means stronger power, the C919 with a take-off weight of 75 tons now uses the LEAP-1C engine jointly developed by General Motors and Safran of France, but in fact, in the original planning of China Aero Engine Group, C919 should be equipped with the Yangtze River-1000 (CJ1000) engine, C929 equipped with the Yangtze River-2000 (CJ2000), and the improved version of the ARJ21 regional airliner uses the Yangtze River-500 (CJ-500).
However, due to the fact that the engine development process lagged behind the commercialization schedule of the C919, considering the safety of civil aircraft, this "Chinese heart" was not used in the first aircraft. And when it comes to the C929, the CJ2000 may be one of the candidates for the engine.
According to the available information, the take-off weight of the C929 can be close to 248 tons, which is similar to the technical specifications of passenger aircraft such as the Boeing B787-9 and Airbus A350-800 - both have a take-off weight of about 250 tons and a thrust-to-weight ratio of about 0.25. "Thrust-to-weight ratio" is one of the important indicators to measure engine performance, which refers to the ratio of engine thrust to the weight of the engine itself, which is used to express the thrust that can be generated by the unit weight of the engine.
These two passenger aircraft take into account the issues of economy, fuel consumption, environmental protection, etc., and finally adopt the "twin-engine" design, that is, an aircraft is equipped with two engines, and each engine has a take-off thrust of about 31.5 tons, which is as good as the C929.
Rolls-Royce's Trent XWB engine
In general, the engines used by Boeing and Airbus are General Motors (GE) GEnx, Rolls-Royce Trent 1000 and Trent XWB.
The first is to meet the above thrust standards, the second is the large diameter fan, and the third is the bypass ratio, that is, the bypass ratio, which is higher than 10:1. "Bypass ratio" is the ratio of air flow between the outer duct and the inner channel of the turbofan engine, also known as the flow ratio, which is an important design parameter of the turbofan engine, which has a great impact on the fuel consumption rate and thrust-to-weight ratio of the engine.
The design of CJ2000 is quite consistent with these points. A few years ago, AECC showed a 1:2 scale CJ2000 (i.e., AEF3500 verification machine), from the naming standard can be seen that its thrust is about 35 tons, the fan diameter can reach 3 meters, and the bypass ratio is likely to reach 11:1, which is larger than the bypass ratio of GEnx and Trent 1000 engines.
The CJ2000 engine has entered the test stage
There is also a point that may reduce the difficulty of the research and development of CJ2000, for example, his core machine, can be based on the core machine of CJ1000, using the international similar amplification and local optimization to develop the core machine of CJ2000, which is much stronger than the original Continental completely in the field of large thrust and large duct than turbofan engine.
Of course, the CJ2000 has its shortcomings compared to Rolls-Royce's Trent series. The CJ2000 is a twin-rotor or twin-shaft design, while Rolls-Royce's engine in its class uses a three-rotor design, and "rotor" here refers to several shafts that can rotate independently.
The three-rotor structure generally means that there are three sets of compressors and turbines: the inner shaft is a low-pressure turbine that drives the fan at the lowest speed; The central shaft is a medium-pressure turbine driving a low-pressure compressor with a higher speed; The outer shaft is a high-pressure turbine driving a high-pressure compressor with the highest speed. All three rotors can work at the optimal speed, with high efficiency, small size and light weight. However, this kind of research and development difficulty and cost is too high, and it is understandable that the Yangtze River series engine starts with a twin rotor.
After all, the most reliable and commercialized technology is often not the most advanced, not to mention, in the field of civil aviation, when weighing advanced and reliable, it must be on the basis of ensuring safety and then pursuing advanced.