WP7 - Mach 2 Fighter Engine
The WP7 was made according to the Soviet R11-F-300 engine technical documents, and installed in the J-7 fighter. Its maximum dry thrust was 38 kN (3,900 kgf) and the thrust with reheat was 56 kN (5,750 kgf), which were 50% and 77% respectively more than those of the WP6. This axial flow, two shaft turbojet engine had 6 stages of compressor and 2 stages of. turbine, which formed high pressure (HP) rotor and low pressure (LP) rotor. The LP rotor shaft went through the inner bore of the HP rotor shaft. The combustion liners were air filmed and inner and outside walls were coated with heat resistant ceramics. The improvement in the afterburner solved the problem of unstable reheat ignition of the WP6 engine at high altitude. The exhaust nozzle was variable and automatically controlled. This engine incorporated many new materials such as stainless steel and high temperature alloy on the compressor and turbine blades. The WP7 engine was more advanced than the WP6 engine both in performance and in structure, and the manufacturing processes were more complicated.
The preparation for trial production was formally started in 1963 in SEF. Having learned the lessons from the WP6 engine trial production, the leading organization placed high stress on having a thorough understanding of the technology before starting to cut the metal. Therefore, SEF organized 1 / 3 of its design and production engineers to form a team dedicated to the trial production of the WP7 engine. Shenyang Aeroengine Research Institute (SARI) and other science and research organizations also took the thorough-studying of the engine's techniques as its main task. They made analysis, calculations and rig tests and wrote technical reports.
According to the investigation, they corrected and supplemented 1,097 original documents which had errors or ommissions. Before the 3rd quarter of 1965, aeronautical factories and research institutes, as well as related organizations of the Chinese Academy of Sciences (CAS) and the industries of metallurgy, machinery, and chemistry had finished " tackling the key technical problems" included 26 new materials, 10 aero bearings, 46 new technologies and new production processes. For instance, the properties of the two kinds of high temperature alloy were even better than the Russian specifications. Through several years' hard work, the GH46 HT alloy was successfully produced by the joint efforts of the Ministry of Metallurgical Industry (MMI), CAS, the related factories, research institutes, colleges and universities of MAI. By usČing this alloy, only a small number of the turbine blades were rejected. For the imported blanks, due to hair cracks and the large forging grain size of the raw material, the rejectionrate was over 50%. The deep hole machining of the turbine shaft was a critical process.
The "three-in-one combining team" (consisting of workers, engineers and cadres) in the factory studied the machining experiences of the gun factory and Beijing Aeronautical Manufacturing Technology Research Institute (BAMTRI), and modified a machine tool which adopted the new technology of deep hole boring instead of the deep hole grinding specified in the original documents. That guaranteed the quality and improved the productivity. For turbine blades, they used new process of electrolysis to replace the original cutting. The Soviet Union did not provide the technical documents for the sea level ground test cell with heated inlet air. The factory solved this problem together with design and research institutes. The test cell of the WP7 engine was a complicated non-standard equipment. Normally, it would need 20 months to build. After thoughtful arrangement and continuous hard work, it was completed within only 7 months.
The all-round trial production started at the beginning of 1965. In October the same year, the final assembly of the first WP7 engine was finished. After three endurance tests which lasted more than one year, it was certified by the State and released for series production in December 1966.
The WP7 engine was made of indigenous materials, and the Soviet Union did not supply some of the key documents, thus showing that China's manufacturing technology of jet engines and the raw materials of the basic industries had come to a new and higher level. According to the arrangement of the 3rd line (inland area) construction and as the production and development work in SEF was too heavy, in 1970, WP7 engines were transferČred to the Guizhou Aeroengine Factory (GEF) for production.
The set up of GEF started at the beginning of 1965. The SEF was responsible for the construction. In 1968, some parts of GEF started trial production and others were still under construction. At the end of 1969, the engine was trial tested in the ground test cell. As the factory was located in the Yun Gui plateau, the ambient atmospheric conditions changed greatly, which brought difficulties to the trial test. The engineers, technicians and workers made analyses and tests repeatedly and finally found a solution. In August 1970, the WP7 engine successfully passed the life test, marking the success of the transfer of production. Since that time, jet engines roar frequently among the previously-poor Miao Ling Mountains. Another great achievement in China's industry moving to the inland remote areas.
There were many shortcomings in the original design. During the operation, there were eight major failures including fracture of the first stage compressor blades due to flutter, which threatened flight safety. The manufacturers resolved to initiate the study and improvement. The designer, Cai Yunjin, and his colleagues of SEF designed the new reinforced first stage compressor blades and reduced the number of blades from 31 to 24. After laboratory, ground and flight tests under various conditions, the property of the new blades proved excellent, the structure reliable and the surge margin was enlarged. That effectively eliminated the stall flutter and cracking failure and greatly improved the engine reliability. Designer Jiang Hefu and his colleagues of GEF successfully incorporated the blade mistuning technology in assembly and treated the blades with shot peening. That further improved the new blades.
Additionally, by enlarging the oil nozzle diameter for bearings GEF solved the engine shut-down problem caused by the over-heated intermediate bearing; the factory worked together with the Qiqihar Steel Plant to develop GH 33A heat resistance alloy with micro-elements instead of the original GH33 alloy. That solved the problems associated with the over-expansion of the first stage turbine disc; designer Wen Junfeng modified the structure design of the flaps of the afterburner nozzle, thus clearing the major nozzle failure of being unable to open or close. In 1979, GEF adopted 25 modifications and solved all the 8 major failures. That obviously improved the quality of WP7 engines. The above modifications were also incorporated in new versions of the WP7 family. The production of the original WP7 stopped in 1980 and the production of the WP7B engine began.
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