When mention the C919, a large civil airliner made in China, we have to connect to three percentages – 10%, 60% and 100%. This is the “localization rate” of large aircraft.
At the beginning of the C919 project, considering that the Chinese people have never touched the “big plane” after the domestic ten planes, the internal conservative estimation of COMAC is that the localization rate of C919 is more than 10%; after the delivery, the Chinese big plane, which can be compared with Boeing and Airbus, has achieved nearly 60% localization rate and achieved 57% 0 orders.
The C919 will eventually achieve 100% localization. During the manufacturing of C919 aircraft, for some parts that are temporarily unable to realize domestic production, two ways are selected: first, foreign original factories, domestic joint ventures; second, original import, to a certain extent, to achieve partial domestic production, and finally all domestic production.
“Final localization” is the “threshold” set by COMAC when buying original imported products, that is to say, once a product is purchased by COMAC, it will eventually be gradually localized. This is the basic agreement between the product manufacturer and COMAC.
"It's hard to make control laws for C919. This is the first time."
If an airplane is compared to a person, the engine is the heart, the hydraulic system is the blood, and the control law is the soul. When ARJ21-700, a medium and short range regional airliner developed by COMAC, is undergoing various flight tests, the design of C919, a large domestic aircraft, is also racing against time.
“The control law is actually an algorithm.” Zheng Xiaohui, deputy director of the operation stability characteristics and control law office of Shanghai Aircraft Design and Research Institute, introduced that according to the professional explanation, the fly by wire control law is the control law for the operation of the fly by wire control system. The control law shows the relationship between the pilot’s control and the aircraft’s motion response.
Taking the automatic parking technology as an example, the current automatic parking technology can make the operator press the key to “set the goal”, and the car can park itself in the designated position. In this process, the algorithm plays an important role. “It looks like the car is backing in by itself, but it’s actually the sensor on the car that measures the distance, angle and other factors, and controls the wheels to complete it through data calculation.”
The algorithm of flight control law also plays the same role. The more complex the control law algorithm is, the lighter the pilot’s burden is, and the easier it is to control the aircraft. “Through algorithm design, the aircraft will be more intelligent and the possibility of human error will be reduced.”
In 2012, COMAC set up a research team mainly composed of designers from the operation stability characteristics and control law room of Shanghai Aircraft Design and Research Institute to design the fly by wire control law for C919. Four years later, this team, mainly composed of the post-80s, completed the preliminary design.
COMAC has developed its own algorithm for C919 flight control law. ARJ21-700 regional aircraft uses relatively simple open-loop control law, and many operations need to be completed manually by the pilot; C919 uses a much more complex closed-loop control law, and the content of the pilot’s manual operation is much less.
Honeywell is the supplier of C919 flight control system. Subject to the laws of the United States, it cannot provide the C919 project with the technology of flight control law algorithm, which can only be independently developed by COMAC. In the R & D process, Honeywell is only responsible for the functional realization of the algorithm and scheme designed by COMAC. Honeywell only answers “yes” or “no” to the question of whether the program design is appropriate, and COMAC will locate and remove the fault by itself.
“For the first time, it’s hard to make a control law for the C919.” Zheng Xiaohui said that compared with foreign countries, China’s experience in flight control law algorithm is seriously insufficient. Once the first design is completed, it will be much easier to design subsequent models. For example, the Airbus A320 is also the first time to engage in telex. At 330 and 340, as long as it is adjusted on the basis of 320, a new algorithm can be made soon.
COMAC has set up a special bus for the algorithm research team to leave for the subway station at 10 o’clock every night. There are several folding beds in the office. If it’s too late for work, young people will sleep in the office directly. There is an unwritten “rule” in this office. Each person has to work at least three days from Monday to Friday, and one day on Saturday. The normal off-duty time from Monday to Friday is 21 o’clock. All people are treated equally and stick to it for at least two years.
Each time, the team designs the algorithm, and forms the system technical specifications, which are translated into English and sent to the supplier, who then writes the software code. Zhao Jinghui, a team member, said that the control law they designed for the C919 had more than 4100 English requirements, and they held more than 200 English conference calls with suppliers.
Crazy materials that can't be bought In C919
Advanced materials have been applied on a large scale for the first time.
On its “skin”, the consumption of the third generation aluminum lithium alloy materials and advanced composite materials reached 8.8% and 12% respectively, compared with the previous application of only 1% in ARJ airliner. ARJ’s new materials are used for non load bearing structures, while C919 is used for load bearing parts such as the rear section of the fuselage and the flat tail. Compared with the “competitors” of Boeing 737 and Airbus A320, more advanced composite materials are used in C919.
Therefore, C919 is considered as “a milestone in the field of materials in China”. According to the public information, the new material reduces the weight of the larger C919 by more than 7%.