The WP7A engine is the powerplant of the Chinese-designed high altitude high speed fighter J-8. It was developed from the WP7 engine by using some advanced achievements and a successful engine version. In May 1964, the Chinese Aeronautical Establishment (CAE) held the first evaluation meet¬ing on the design concept feasibility of the new fighter. In order to meet the aircraft's requirements of good performance at high altitude and high speed, good climb rate and long range, high thrust and low s.f.c. were required for the engine. There were two options: one was to adopt a single newly designed 12 ton (120 kN) thrust class big engine, another was to use two modified WP7 engines. On the second evaluation meeting held in October the same year, selection would be made between the two alternatives. As the lead time for a brand new designed large engine was too long, the single engine design could not meet the schedule requirement.
The twice-modified WP7 (i.e.the WP7A) design, with the increased thrust had difficulties in increasing TET by 100 C . The increase of TET could raise the useful energy of the gas, which in turn increased the thrust. However, the increase of the gas temperature would require new high temperature alloys, structure design and machining processes for the turbine blades; it gave the meeting a difficult decision to make. Rong Ke, deputy director of BAMI and a casting expert made a proposition. He proposed to modify the 'solid turbine blade to a hollow one, and induce cooling air to cool the blade. He advised that he had great confidence in developing the hollow blades with the materials and work processes already available. Despite the fact that this was still a relatively unadvanced technique, little-used abroad, and a major task to undertake, Rong Ke decisively expressed a wish to accept a "life or death order" to develop the hollow blades in approximately twelve months. Based on his many years of study in high temperature and work processes, the factory shared his confidence. Thus, his strong confidence at this critical moment made the twin-engined J-8 aircraft.
In May 1965, the leading organization formally approved the design targets of the J-8 aircraft and the development programme for the WP7A. It decided that the engine design and prototype manufacture would be carried out by SARI and SEF respectively, and that the hollow turbine blades would be jointly developed by SEF, SARI, the Shenyang Metal Research Institute (SMRI) of CAS, BAMI, BAMTRI, and the Steel Research Establishment (SRE) of the Ministry of Metallurgical Industry (MMI).
SARI specially set up a WP7A design office and deputy chief engineer Chen Jiheng was appointed program manager and director of the design office. Zhang Hong, Chen Dafa, and Fang Wenfu were assigned to be responsible for this programme. Some 20 people of the design office, closely supported by other departments of SARI, worked hard on solid ground, and explored carefully. They carried out design and calculation work, issued drawings when urgently required and timely solved the problems occurred in the development. The technical problem associated with hollow blades was the critical point for the success of WP7A. It was arranged that the casting and forging hollow blades were simultaneously developed.
On the casting blade side, SMRI had already developed a high property nickle-based cast¬ing high temperature alloy - the M17 - and the precision casting technology in SEF had also reached a certain level; thus the conditions were capable of fulfiling the task. However, to combine new materials and new work processes into an advanced component of the engine was still a task requiring advanced R&D and a prolonged period of time. The time limit was only one year, and the risks were great. With the full support from Director Li Xun of SMRI and Chief Engineer Chen Huaming of SEF, plus the involvement and guidance of Rong Ke, all worked hard to solve the problem. SARI was given responsibility to design the blade, SMRI endeavoured to make the 9 holed-hollow blade in the laboratory, and SEF made the industrial trial production. SMRI solved many technical problems such as the selection of core material, broken cores, core drawings, casting porosity, and blade straightening at room temperature. Work proceeded gradually.
BAMTRI, XEF, SRE, Fushun Steel Plant (FSP) and BAMI worked together in great tension to develop the 3-holed air-cooled forged blades. At that time the high temperature forging alloy was not available, the special machine for machining the blade was only a demonstrator and the advanced R& D in the hole shape and passage was just started. It was 'extremely pressing and demanding work, and for this all departments concerned gave their best efforts and kept close links with each other. After repeated tests, they solved the. difficulties which had arisen in the new forging alloys, deep hole electrical spark machines, profile hole electrodes, wall thickness measurement of the deep holes etc, one by one. After some seven months, in January 1966, they presented their first set of forged hollow blades. This happy news promoted the whole development work for the new engine. Two months later, SEF assembled the first WP7A engine with forged hollow turbine blades. The bench test was conducted on April 12th, and all present felt tension in the air in anticipation of success. Following the order for starting, a loud rumble came, and the starting proved successful. The complete test procedures went on smoothly, and the engine performance reached its design goals for the very first time. Compared with the original version, the WP7A gained an increase of 12.8% in maximum dry thrust and a reduction of 13% in specific fuel consumption.
In September of the same year, the casting hollow turbine blade was also developed in the laboratory. In November, SEF precision casting production line cast one set of blades, and in December, the engine with casting hollow turbine blades was on the ground test bed. The result was most successful.
As the cast 9 holes blades Shad better cooling efficiency, higher residual strength, more simple manufacturing requirements and a lower rejected rate than the 3 big holes forged blades, it was finally approved that the cast hollow turbine blades would be the type certification blades for the WP7A engine. This achievement in hollow turbine blades brought the birth of the WP7A engine. This hollow air-cooled blade technique was later applied to several other engines.
In July 1969, the J-8 aircraft with the WP7A engine made its first flight and it was successful. In 1970, the design task was transferred from SARI to SEF. Because of the interference of the "great cultural revolution", the work was semi-stopped. In 1974, the original design team of SARI was assigned to SEF for continuous development. The test run up of the engine on the sea-level test bed, the tests in simulated altitude test facility and the all round flight tests for performance were carried out individually. In June 1982, the WP7A engine was certified.
The development of the WP7A engine covered the complete process of design, trial production, rig tests, engine ground test, engine simulated altitude test, flight test and design certification. It also promoted the construction of test facilities and provided training for personnel. The success of the air-cooled hollow turbine blading proved that the-creation and break through of the critical technique on the existing basis was the correct technical path. It also proved that only with the availability of new high temperature alloy and new work processes (i.e.technical base) such as forged and cast hollow blades, a breakthrough could be made in a relatively short period. The WP7A was a profound achievement in the development. It received 6 awards for achievements in science and technology beyond the provincial level. In 1985, together with the J-8 aircraft, it was awarded a special class national prize for science and technology progress.
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