How does the domestic large aircraft "evolve"?

â–  Organizing this reporter Xu Wei

Yesterday, the Chinese large-scale commercial aircraft C919, which was developed by the Chinese and had independent intellectual property rights, successfully completed the second test flight.

What kind of difficult journey has it gone through in the sky? In the "Shanghai Association for Science and Technology Forum and Frontiers of Science and Technology Masters" held recently, C919 executive deputy chief designer Chen Yingchun, engine expert Liu Dasheng and material science expert Cao Chunxiao told the evolution of domestic large aircraft. history".

The business card of a big country, the patent of a rich country, the symbol of a strong country

â– Chen Yingchun

Why is the big plane called C919? C is the abbreviation of China China, indicating that this aircraft is the Chinese own aircraft. We used to call McDonnell Douglas when we assembled McDonnell Douglas in Shanghai. We had 320 in Tianjin to assemble 320. In so many cars in China, Shanghai Volkswagen and Beijing Mercedes have to add other people’s brands, and our own children can surname their own surnames. , so C is the Chinese own aircraft. 919, the meaning of the first "9" is forever. "19" stands for China's first medium-sized passenger aircraft with a maximum capacity of 190 passengers. The middle "1" also represents the first large-scale development of China Commercial Aircraft. Passenger aircraft, the future research and development will be called 929, 939...

After more than 100 years of development, aircraft has become the main means of transportation for human society. China is currently the second largest civil aviation market in the world. More than 3 million people fly in the air every day. In the next 20 years, China needs to increase six or seven thousand aircraft.

Commercial aircraft, also known as large aircraft, is the pinnacle of technology. The world's current large commercial aircraft (more than 150 seats), only the United States Boeing company and Europe's Airbus company, it is a big country's business card, rich country's patent, a symbol of a strong country. Like the US President’s attendance at all over the world, they are all taking the Boeing 747 made by their own country. The European leaders are all visiting the Airbus aircraft they made in Europe. In the future, our country’s leaders will go abroad and have to take their own planes. .

The development of commercial aircraft in China is roughly divided into the following four stages.

The first stage was before the reform and opening up in the 1950s and 1978, mainly to map and imitate the Soviet aircraft. The second stage was from 1978 to 2002, which was the stage of international cooperation in bowing down to the West. But we learn from others, people are not willing to teach, and key technologies are not willing to teach you; the third stage is from 2002 to 2015, the central government decided to independently develop commercial aircraft, the Chinese themselves, from the 2002 ARJ21 regional passenger aircraft project In 2008, China Commercial Aircraft was established in Shanghai. The fourth stage is from 2015 to the present, we began to work hard to engage in international cooperation, such as the Sino-Russian cooperation C929, the Sino-US cooperation B737 completion center, are all equal and foreign cooperation.

In history, we have wanted to engage in commercial aircraft many times, but it was limited to the country’s economic strength, and the industrial base did not have the conditions, so there was no success at that time. After the 21st century, all aspects of the country have developed, and we finally have the strength and ability to develop large aircraft.

On May 11, 2008, COMAC was established in Shanghai. On May 23, 2014, General Secretary Xi Jinping came to Shangfei Company to inspect. He said that if we want to become a strong country, we must carry out the equipment manufacturing industry, get the big planes up, play the role, and play a symbolic role.

The C919 large passenger aircraft started in 2008 and made its first flight on May 5, 2017. It took a full nine years. It is a 150-seat aircraft with a range of 5,550 kilometers. The C919 is currently the most advanced single-aisle aircraft in the world.

After the first flight of the C919, the Party Central Committee and the State Council sent a congratulatory message, stating that "it is necessary to strive to build a large-scale passenger aircraft project into a landmark project for reform and opening up in the new era, and to build an innovative country and a landmark project for manufacturing a powerful country." Since the 18th National Congress of the Communist Party of China, the State Council and the State Council have sent a total of 8 scientific and technological achievements, indicating that the first flight of a large aircraft has epoch-making significance in the history of our country, especially in the history of aviation.

At present, COMAC has launched the C929 project of 300-seat dual-aisle aircraft, which was jointly developed by us and Russia, with a range of 12,000 kilometers. The development of the C929 wide-body aircraft will realize four major leapfrogs in our country's large aircraft field: one is narrow-body single-channel to wide-body dual-channel crossing, the second is short-range inland flight to long-distance transoceanic flight, and the third is metal material. The main thing is composite materials, and the fourth is to leap from the rising star to the international commercial aircraft powerhouse.

In the future, the trend of commercial aircraft in technology development is “four sexes and four reductions”. “Four sexes” are safety, economy, comfort and environmental protection; “four reductions” means reducing drag, reducing weight, reducing noise and reducing emissions. We will also develop a new generation of supersonic commercial aircraft that can achieve horizontal and low takeoff at conventional airports, achieving low noise and zero emissions. It takes only three to four hours to fly from China to the United States. This is our dream.

Building the Chinese people's own big planes is a national dream, a people's expectation, and a historical responsibility. We will certainly shoulder this responsibility and do this well.

The "heart" of the plane, why is it called the country's heavy weapon?

â–  Liu Daxiang

The aero engine is the "heart" of the aircraft, the "jewel in the crown", and the heavy weapon of the country. It is an important strategic emerging industry of the country.

Since the late 1940s, the world's fighter jet engines have been developed for four generations, and the US F22 uses the fourth-generation engine. Civilian engines have also been developed for four generations. At present, the domestically produced large aircraft C919 uses the latest generation of engines produced by the United States and France. We are stepping up research on the domestically produced advanced large bypass ratio turbofan engine in Shanghai. It may take some time to complete, and eventually it will be used to replace the engine developed by the United States and France.

The development of the engine is more difficult. According to foreign statistics, the development cycle of general engines is twice or even twice as long as airplanes. The C919's engine and aircraft are simultaneously established, so it is impossible for our domestic engines to catch up with the development of the aircraft.

Although the commercial engine company was established more than two years later than the Chinese commercial aircraft company, we firmly believe that if you want to build a large aircraft, you must build your own engine. If you don't have your own "heart", it is impossible for a large aircraft to be successfully developed independently.

The civil aviation engine is a very complicated thermal machine that needs to work reliably under extreme conditions such as high temperature, high pressure, high speed and alternating load, and meets large thrust, low fuel consumption, light weight, long life and low noise. Many demanding and contradictory requirements such as low emissions, high reliability, good safety, and low development and maintenance costs.

Let me talk about the characteristics and difficulties of engine development.

First, it must have high security and high reliability. The Airworthiness Regulations stipulate that the air parking rate per 1000 hours of the engine is only allowed to be 0.002-0.005 times. In order to make the engine not in the air, we must do a lot of ground experiments to eliminate the problem and eliminate hidden dangers. Second, the pressure ratio is very high. The thin internal casing of the civil engine is subjected to 50 to 60 atmospheres, which is equivalent to the pressure of the two and a half Yangtze River Three Gorges Dam, and cannot be deformed or damaged. Third, the speed is very high. The high-speed rotor speed of the large bypass ratio turbofan engine generally reaches 15000-20000 rpm. The small blade is subjected to a centrifugal load of about 20,000 times its own weight without cracking or breaking. Fourth, the temperature is very high. The gas temperature in front of the modern engine turbine is 2100K for military engines and 1900K for civilian engines. At this high temperature, all the metals melt. We must take many steps to overcome these difficulties from design, materials, processes and testing. Fifth, the flow rate in the engine is very high, equivalent to 8 to 10 winds. The combustion chamber must be reliably ignited under these conditions and the flame must be stable.

Because of this, a large amount of experimental research work must be done before the aeroengine is finalized and installed. According to statistics, foreign countries generally have to do nearly 200,000 hours of parts testing, 20,000 to 30,000 hours of ground machine testing, 3,000 to 6,000 hours of high-altitude test, 5000 to 10,000 hours of flight test. Why is the engine development cycle so long? This is one of the important reasons.

For a long time, a few developed countries such as the United States, Russia, Britain, and France have always prioritized the development of aero-engines as a basic national policy, and developed the aero-engine industry into a high-value-added national high-tech strategic industry, which lists aviation power technology as a tightly sealed lock. The key technologies for export transfer are strictly prohibited, and a monopoly position on aerodynamic technology and the global market is gradually formed.

At the Fifth Plenary Session of the 18th CPC Central Committee, General Secretary Xi Jinping proposed that on the basis of the original 16 major scientific and technological projects, we must select a number of major scientific and technological projects that reflect the country's strategic will, and strive to make breakthroughs. Among them, aviation engines and gas turbines were clearly listed as one of the major national science and technology projects, and on August 28, 2016, China Aviation Engine Group Corporation was established. This is a major strategic decision made by the Party Central Committee and the State Council in the new era!

We hope that through the implementation of major scientific and technological projects for aero-engines and gas turbines, we will unswervingly follow the path of independent development, further consolidate the foundation, break through and master key technologies, comprehensively enhance our independent innovation capabilities, and realize the third and fourth-generation main battle aircraft and The self-protection of the power of the C919 trunk airliner has completed the strategic transformation from tracking to independent development, thus becoming one of the world's aerodynamic powerhouses.

We firmly believe that China's self-developed high-performance aerospace engine will be installed on its own aircraft in the near future, soaring in the blue sky, an aerodynamic power will surely stand in the east of the world!

Generation of materials, a generation of aircraft

■曹春晓

"One generation of materials, one generation of aircraft", this is a true portrayal of the history of world aviation development. For more than 100 years, materials and aircraft have continued to evolve under mutual dependence and mutual promotion.

Aviation structural materials are usually at the forefront of the material field, and their high technical content and technical difficulty are worthy of the “world pride” of the material world.

Aviation structural materials have undergone five stages of development over the years. The first phase began in 1903 when the American Wright brothers invented the aircraft until the 1910s. The structure on the aircraft body is mainly wood and cloth structure. At that time, the aircraft did not fly fast and barely stood up. The second stage was from the 1920s to the 1940s. The structural materials of the aircraft were mainly aluminum and steel. The third stage was in the 1950s and 1960s. Titanium alloys appeared as new metal materials. The trinity of aluminum, titanium and steel formed the main structural materials of the aircraft. The fourth stage was the emergence of composite materials from the 1970s to the beginning of the 21st century and was gradually added to aircraft structural materials. The fifth stage is the beginning of the century and has entered the era of composite materials.

Why do these changes occur in the structural materials of the aircraft? A very important reason is that the specific strength requirements of the materials are constantly increasing. The so-called specific strength refers to the strength of the unit density, that is, the ratio of the tensile strength of the material to the density of the material. In general, the higher the specific strength, the lighter the material used to achieve the corresponding strength; and the specific strength of the different materials varies with temperature. When the temperature reaches about 350 to 600 degrees Celsius, the specific strength of the titanium alloy is the highest, so in places where the temperature is high, titanium alloy must be used.

In recent years, whether it is a large transport aircraft or a civilian passenger aircraft, the use of titanium alloy in aviation structures is increasing, and it is constantly innovating. The titanium alloy of our large aircraft C919 has reached 7.3% to 9.3%, which is comparable to the Boeing 777. It is relatively advanced; however, there is still a gap compared with the Boeing 787 and the Airbus A350. Their usage has reached 14% to 15%. %. The current record of titanium alloy usage was created by the Russian MS21, which reached 25%.

The biggest disadvantage of titanium alloys is that they are expensive, so on civil aircraft, it is impossible to use too much for economic reasons, and it should be used on the knife edge.

So which aircraft parts are titanium alloys used for? There are many, I am talking about a typical part today - the landing gear. There is a bogie under the landing gear, 6 wheels plus a beam, this beam has to bear a lot of power, so on the Boeing 777 in the United States, this beam is made of titanium alloy, which is a large forging. It was forged on a 45,000-ton forging hydraulic press in the United States. As the aircraft gets bigger and bigger, the parts of the landing gear are getting bigger and bigger. For example, the beam on the Airbus A380 has a forging weight of 3210 kg, which is by far the heaviest titanium alloy aerospace forging. In order to forge this forging, Russia had to be commissioned because Russia had 75,000 tons of hydraulic presses.

And we have a 80,000-ton hydraulic press in Deyang, Sichuan, which can independently develop and produce large forgings. The 80,000-ton hydraulic press is the largest hydraulic press in the world today. Before that, the world's largest forging hydraulic press with a capacity of 40,000 tons or more was only in the United States, Russia and France.

Let me talk about the composite material below.

Composite materials have developed very rapidly in recent years and are increasingly used on large aircraft. The composite material on the Boeing 787 is 50%, and the original composite of the Airbus A350 is only 40%. But the Boeing 787 uses so many composite materials to reduce fuel and is more popular, so the A350 has improved the design and used it. The composite material reached 53%.

Why is there a new pattern dominated by composite materials in the material structure of the body? Because of the use of composite materials, first, the price is cheaper than in the past, and second, the performance is better than in the past. There are hundreds of thousands of parts on the plane, and millions of designers, of course, the designer wants fewer parts as possible, which can save a lot of structural weight. Composite materials are not only high in strength, but also particularly easy to integrate, and dozens of small parts can be turned into one large part to solve the problem.

The current use of composite materials in our country also needs to be continuously developed. The military transport aircraft Y20 currently uses 8% composite materials, commercial aircraft ARJ21 is 1%, C919 is still improving, and strive to reach 12%.

Finally talk about aluminum alloy and steel. Aluminum alloys and steels are still indispensable. At least for a long time, aircraft materials are still inseparable from aluminum alloys and steels. Because they are cheaper and their performance is constantly improving, they have to be used in many places. For example, the landing gear of the C919 uses 300M steel.

I am 83 years old and have been in the aviation and materials fields for 61 years. What is the biggest sentiment in my life? The world of materials is really exciting, the aviation world is really exciting, and the entire technology world is really exciting.

Of course, there are many things in this world that make us very helpless. There are many problems that make us really tricky, but this does not stop us from pursuing the world. If a person can't offer anything for the wonderful world, there is no wonderful life to say.