Y-10 civil passenger jet - Design
The Shanghai Y-10 was a four engined civil passenger jet aircraft developed in the 1970s by Shanghai Aircraft Manufacture Factory (now known as Shanghai Aviation Industrial Company, or SAIC). The Y-10 designation stands for Yunshuji ("transport") model 10. After a thaw in relations with the West in 1972, China had acquired a Boeing 707 fleet but decided to forge ahead with its own jetliner that was free of dependence on foreign parts, except for the American engine. The cabin of the Y-10 can be configured into three classes: tourist class (149 seats), mixed class (124 seats) and economic class (178 seats). The flight deck was designed for five—man layout: pilot, co-pilot, flight engineer, navigator, and radio operator. The maximum takeoff weight of the aircraft was 102,000 kg. The aircraft used Pratt & Whitney JT3D-7 turbofan engines, which were spares belonging to CAAC's small fleet of Boeing 707 aircraft. Shanghai had intended to use a Chinese-built Shanghai WS8 turbofan, but the Pratt & Whitney engine was selected before the WS8 could reach certification.
The original intention of developing Project 708 was very simple, just to provide the leaders with a "special plane for visits" that could take off from Xinjiang, fly directly to the European country of Albania without landing for refueling. Therefore, the range of Project 708 must be guaranteed to be more than 5,000 kilometers. At that time, the "H-6A" had a range of 6,000 kilometers under extreme flight conditions, so Project 708 was initially intended to make minor changes based on the "H-6A".
The designers wanted to transform the H-6A into a passenger plane powered by 3-4 engines, while keeping the general layout of the fuselage and wings unchanged, and only make major changes to its interior decoration to provide a comfortable environment for passengers. However, there was a fatal flaw in the H-6A conversion into a passenger plane, that is, its fuselage layout greatly affects the comfort of the passengers. This makes it certainly not a feasible solution as a special aircraft.
The flight time of "Yun-10" was designed to be mostly in the high subsonic area, and at that time only the Soviet Union's "Tu-104", the European and British "Trident" and the American Boeing aircraft could reach this speed. Deputy Chief Designer Cheng Bushi recalled the development work at that time and said: "This is a process full of innovative consciousness. Everyone put all three design plans on the table, discussed with each other, compared and analyzed, and learned from others' strengths for our own use."
For example, in the installation method of the engine, the designers first rejected the Soviet wing root layout, then made a 1:1 full-size wooden prototype by hand, conducted wind tunnel tests according to the British tail hanging style and the American wing hanging style, and finally selected the wing hanging style. Practice has proved that this layout later became the mainstream layout in the world, and the newly developed aircraft in the 21st century still adopts this layout. For another example, the wing shape of the aircraft, everyone put all the Soviet, European and American wing shapes available at that time into the wind tunnel for testing, and finally compared the test data to select the most suitable wing shape for the "Yun 10".
There persistent suggestions are rumors that the Y-10 was a reverse-engineered design of the Boeing 707 Model 120 with some minor differences, while other sources, the designers and the personnel of Boeing denied that the Y-10 was the copy of its Boeing 707, and claim it was an indigenous design. Often dismissed as a Chinese 707 copy, in reality, this aircraft looks about as much like a 707 as a DC-8 does. The aircraft was entirely designed by Chinese engineers; only the engines are spares from the CAAC 707-3J6 fleet. In dimensions, the aircraft was actually closer to the Boeing 720. The Shanghai Y-10 looked generally like the B-707-320C, except for a few minor issues. For example, the Y-10 did not have the famous Boeing style "eye brow" windows, or the "stinger" style HF radio antenna atop the fin.
The external shape was similar, but so was the IL-62 compared to VC-10, as aircraft design during the 60's period came from the same aerodyamic principles. However, internally the Y-10 was quite different than the B707. Every systems onboard were not the same as that of the B707, and the structure was vastly different. That was why both Boeing and China refer the Y-10 as a different aircraft to the B707.
"Yun-10" was the first time that China's aircraft design had sprinted from 10 tons to 100 tons. This enlargement and jump in magnitude had a "scale effect" and a new solution needs to be found. Many structures and systems, even concepts and methods, have posed many new challenges.
There were eight breakthroughs in the Y-10 design:
- The American Federal Air Regulation was used as a standard and the Soviet regulation only as a reference so that the past traditional way in which only the soviet regulation was used was changed.
- A peaky airfoil profile was used in the wing design so that the aircraft had better high speed behavior and the maximum cruise aerodynamic efficiency reached 15.4.
- The aircraft structure was designed according to the fail—safe and safe—life concepts and the rules and regulations for the detailed design to prevent the structure from fatigue were made according to the aircraft total life of 130,000 hours or of ten years.
- The largest integral wing fuel tank and pressurized cabin were designed and the problems of fuel leakage and air tightness were solved.
- A unique control method for control surfaces, in which the control surfaces were brought into motion by tabs, and a general configuration with underwing mounted engine pods were adopted.
- The largest full scale simulation tests of control system, hydraulic system, fuel system and electrical network were carried out.
- A great number of new materials, new vendor—furnished—equipment and components and new standards were used. A total of 76 new materials were used, which was 18 per cent of all the materials used. 305 new vendor—furnished—equipment and components were 70 per cent of the total and 164 new standards were 17 per cent of the total.
- The computer was widely used in the analysis of the general configuration, aerodynamics, stress, structure and system design. More than 50 big application programs were prepared and among them was an optimization program for the general configuration parameters.
The localization rate of the fuselage was 100%, and the localization rate of avionics and mechanical systems exceeds 96%, except for the engine purchased from abroad. Its development broke through the design specifications of Soviet aircraft and was the first time that China developed it in accordance with the FAR-25 standard of the US airworthiness regulations. Moreover, the entire development process did not rely on any foreigners. It was a large aircraft with completely independent intellectual property rights in China.
At the same time, the Y-10 extensively adopted advanced foreign technologies and was not a "product of isolation." The implementation of "Project 708" brought a qualitative leap in China's aviation research and design. The Ministry of Aerospace Industry at that time commented that it "filled the gap in China's civil aviation industry in this regard." The major problem with the Y-10 was its weight, plus with a very small CG shift limit, making it not safe for civil application. It was extremely heavy compared to the Boeing 707, with high fuel consumption and a very limited range. The test models were, reportedly, only able to fly for around half an hour at a time.
The overall design was based on the most advanced Boeing 707 at the time, but it was indeed quite different. The Air Force attaché of the US Embassy in China personally boarded the plane to observe. He was once a Boeing 707 pilot and had thousands of hours of experience flying the Boeing 707. As soon as the attaché boarded the gangway and looked back at the cabin door, he asserted that "this plane is completely different from the Boeing 707 because I am too familiar with the Boeing 707."
As it concerns intellectual property rights and technological competition, Boeing's vice president also attached great importance to the Y-10 and personally boarded the plane to observe it. After a careful inspection of the Y-10, he concluded that "this is a completely independent practice of the Chinese in this field."
According to the logic of the mockers, because the light bulb invented by Edison was round, China must make it square; Ford's car has four wheels, so China can only be national if it makes five wheels. In fact, throughout the 20th century, the wing profiles used by all Chinese aircraft have never used the "Li Shizhen wing profile" or "Zu Chongzhi wing profile" and other purely national brand wing profiles.
To sum up all the differences, there are only two ideas: one was the "imitation theory", which identifies an ideology, disregards technical analysis and test data, and advocates copying Soviet aircraft without thinking to copy China's "Tu-104".
The development of the "Yun-10" took another route: putting aside the interference of ideology, speaking with experiments and data, and using the most advanced technical means required in the design. This was the method that Xu Shunshou, the founder of China's aircraft design, has always advocated, "Reading 300 Tang poems, not only foreign models", that is, according to the mission needs and objective data of the aircraft, selecting appropriate means from the world's aviation technology library, and independently conducting new "engineering synthesis" to form its own design. Also known as the "comprehensive design method", it integrates the strengths of hundreds of schools, integrates innovation, and forms its own overall plan.
