WP6 - China's First Engine for Supersonic Fighters

The WP6 engine was produced according to RD-9B engine's technical documentation supplied by the Soviet Union, and was for the application to J-6 fighter. Compared with WP5, the performance of the engine developed from subsonic to supersonic and the compressor from centrifugal flow to axial flow. Its maximum dry thrust is 25.5 kN (2,600 kgf) and the thrust with reheat is 31.9 kN (3,250 kgf), which are the same level as WP5. But the engine weight and maximum diameter were 30% and 48% less than those of the WP5. Thus the engine front area was great reduced, making the engine suitable for supersonic flight.

The trial production and the follow-on mass production were carried out by SEF. The Soviet documents arrived in the Factory consecutively in the first half of 1958. The factory selected the experienced technicians and workers for the trial production. The engine had 2,521 . parts and components, which was 46% more than WP5 engine. Especially, the axial engine had more blades, pipes and the original WP5 production line could not meet the requirement. Thus a necessary technical reformation and expansion were undertaken and the production capability of blade forging and machining, pipe producing, magnesium parts machining and precision cast¬ing were strengthened. The technical lay-out of manufacture and assembly of parts was rearranged.

In the Summer and Autumn of 1958, under the influence of the "Great Leap Forward" in the entire country, the policy was to " Speed up trial production" which caused great problems, namely poor translation of technical documents, copying was incomplete through lack of thorough study, vast cuts in tooling and equipment, poor quality of toolings and equipment and cancellation of technical management systems, particularly in control and inspection. Thus, when the first engine was tested at the end of 1958, the main performance goals were not reached. Then with new parts and components made in a hurry, the engine failed the second test again. In 1959, the engine passed, the acceptance test after continuously troubleshooting. By the end of that year, the first batch of 60 engines had been built. Due to the poor quality, up to the end of 1960, the factory could not deliver a single qualified engine.

From November 1960, the factory rectified the quality, and started again on the trial production of the WP6 engine. The directors of the factory, Yu Xiaping and Li Mingshi led the cadres, from the top management down to carry out a deep education on "Quality First" . They reorganized the technical management, strengthened the chief engineer system, restored the original rules and regulations, formulated product quality standards, and mobilized the enthusiasm of the massive staff members and workers. The trial production was sped up on the basis of ensured quality. In October 1961, the newly-made engine smoothly passed the endurance test and the quality was high. The State reorganized the appraisal and acceptance, and approval was granted for series production. That year 72 were delivered. In September 1963, the WP6 engine was installed into the quality approved J-6 aircraft and passed the flight test. The Military Commission of CCCPC issued a letter of congratulation to SEF and SAF. The engine was awarded the national first-class prize for new industrial products in May 1964. The tortuosity and reversal of the WP6 trial production was a deep lesson on quality and scientific management to the employees in the aeroengine industry. It had also been good practice for solving key technical problems in design and testing. We accumulated experiences which were very useful for the promoting of engine development and production.

The WP6 engine was the powerplant of both the J-6 and Q-5 aircraft, and therefore there was a great demand for the engine. Later it was concurrently manufactured in SEF and the Chengdu Aeroengine Factory (CEF).

The construction of CEF began in October 1958, which was completely put in charge of SEOF. 60% of the manpower and other resources of SEOF were transferred to Chengdu with Yang Cheng and Cui Guangwei as the heads. Thus the production capabilities were soon formed in CEF. In the first half of 1959, trial production of the RD-500K engine for a coast defense missiles started. In July the following year the engine passed the acceptance test. The trial production of the WP6 engine began in the Spring of 1962. Great attention was paid to the training of new workers. By way of "Sending students out and inviting teachers in" CEF learned a lot from SEF. During the trial production mare than 100 key manufacturing technologies were learned and mastered, such as abrasive belt dressing of blades, adjustment of complicated tracers, broaching of turbine disc firtree grooves, machining of precise holes in engine casings, refining of high temperature alloys, casting of magnesium casings and spraying of heat resistance ceramics. The engine passed the endurance test on September 15, 1964 and it was put into series production on October 11 after the State's appraisal.

SEF and CEF produced a large number of WP6 engines, which satisfied the requirement for J-6 and Q-5 aircraft. Some of them were also for foreign aid and export. In the process of mass production of WP6 engines, the life extension program and modifications were also carried out.

The overhaul life of the aeroengine means the operational hours between the delivery and the first overhaul or between two overhauls. The first overhaul life of WP6 was very short, only 100 hours, causing concern to both the manufacturer and the operator. At the beginning of 1965, the life extension program was executed. After repeated tests and studies, 41 technical improvements were, adopted. When the modified engine, passed the acceptance test, the first overhaul life of 200 hours was approved at the end of 1965. As there was no thorough understanding of the original design' s weak points, by the end of 1969, the engine's turbine discs and combustion liners had major failures in operation and the overhaul life was reduced to 100 hours again.

In 1970, SEF reorganized the life extension work with emphasis on turbine discs and combustion liners. This took the fine adjustment of pitch and 3 other measurements, and the cracks on the firtree groove were cleared. They also made reference to the modified combustion liners of CEF, completely gave up the original design, used all air-film cooled combustion liners and solved the cracking problem on the liners: In addition, floating heat shield and other 20 technical improvements were adopted. In 1973, all these improvements were incorporated into the mass production engines and, as a result, the technical achievement of doubling the life (200 hours) of WP6 engine in 1965 was actually re-aligned.

CEF started to solve the problem of cracks and flakes of the combustion liners in 1968. They designed a complete new structure with all air-film cooling. After more than 300 single flame tube tests and nearly 100 engine bench tests and through more than 500 hours endurance test and 5 major flight tests under various operating conditions such as high speed at low altitude, high altitude with reheat-on and medium altitude acrobatic it was approved for series production in 1971 and designated as 4-71 type all air filmed combustion liner. That played an important role in the life extension of the WP6 engines.

Afterward, it was found that 4-71 type liners were difficult to start in very cold area. It was the disturbance period of the "great cultural revolution" and the factory stopped the production activities. But Qin Xueqi and other engineers, technicians and old workers were worried about what the operators were worried about and formed a special team covering all specialities. They adhered to carrying out further tests and, finally in October 1976, developed a new 4-76 type all air filmed liner. They then modified the manufacturing processes. In 1978, they produced a vastly improved 4-78 type all air filmed liner. Compared with the original liner, the new one had stable combustion under all flight conditions and good starting characteristics both on the ground and in the air. The engine thrust was increased and s.f.c. reduced. This liner won the national silver medal in 1982.

Their achievements in combustion liners also gained them a good reputation among the related manufacturers in the World. In 1983, they signed a contract with American Pratt Whitney company for making combustion liners for JT-8D series engines. The first two types of liners were produced by the end of 1984. After inspection by the American side, it was agreed to commence formal production in 1985.

When the life extension program of the WP6 engines was being undertaken, the work to increase the strength of the turbine shaft was carried out. In the early 1970s, fractures of turbine shafts during operation occurred on the WP6 engines made by both CEF and SEF. In 1977, the MAI held a special meeting to analyse the failure. It appeared that the main season for the failure was insufficient residual strength in the original design, particularly during spin. During the meeting, it was decided that CEF would be given responsibility to develop a new turbine shaft in order to meet the requirement of spin flight training. In 1978, MAI assigned to the factory the mission of "Study on the Structure Integrity Technology of the Aeroengine Shafts." This program was headed by Gao Lianshen, Liu Dunhui, and Wang Changyuan. They carried out three major cycles of shaft modification design, test-piece production and fatigue tests; substantial progress was made in each cycle.

The tests achieved satisfactory results by the end of 1979. The strength of the new shaft was greatly increased. It was reliable for long time operation under the spinning load for training purposes and able to sustain certain amounts of spin during normal flight operations. In 1981, the new shaft passed the flight test. In 1982, it was jointly reviewed by MAI and the Engineering Department of the Air Force and pronounced " suitable for practical operations." They also advised " it provides precious experiences for future design, test and study of other types of turbine shafts." It was approved for series production immediately.

Many modifications on the WP6 engine made its quality improved and life extended and the engine gained high appraisal from both domestic and foreign end users.

WP6A Engine

The WP6A engine was modified and developed from the WP6 engine and used for Q-5I attack aircraft. The mission profile of attack aircraft generally consists of penetration and ground attack at low altitudes and breakaway from the target area and return home at medium and high altitudes. It carries a heavy load of weapons and bombs, thus requiring the engine to have a high thrust, good acceleration rate at take-off and climbing, and minimum stable thrust when attacking the target. Therefore, the original WP6 for Q-5 aircraft needed to be modified.

SEF started the program of increasing the thrust of the WP6 by the end of 1964. The major requirements were to increase the turbine entry temperature (TET) and redesign the first stage compressor blades. The new engine was named WP6A. In 1966, it passed the endurance and flight tests. The thrust with reheat increased by 4.9 kN (500 kgf) and there was an obvious improvement in climbing characteristics. However, when the bleed valve was operated (in order to prevent engine surge, the bleed valve had to be opened to release some air at certain r.p.m.), there was a sudden change of thrust; and the r.p.m. of the upper surge limit moved up, which made the bleed valve open earlier. This phenomenon greatly reduced the engine's stable operation range and severely affected the aircraft performance.

CEF and SEF seperately studied the variable geometry compressor vane to solve this problem. They gained good results. Yan Chengxiang and Shen Zhongming of SEF added a zero stage variable vane before the first stage compressor blade, which, together with the bleed valve, formed a " zero stage adjustable surge-preventing system". After tests, it effectively increased the engine stable working range, and could obtain the minimum stable thrust required by the attack aircraft. That was beneficial for the flight performance during fleet formation, penetrating clouds, aiming and shooting. In October 1979, it was formally decided that the WP6A engine would be the power-plant for Q-5I aircraft. After the appraisal by the State, the engine was certified in August 1983 and released for production and delivery.

At the end of 1984, Zhao Guangwu, Zhu Yuanhu, Zhou Zhiying and their colleages at Shenyang Aeroengine Company (SAC) (merged from SEF and SARI in 1979) supported by the company's leader Cheng Huaming worked together with Gao Ge a post-graduate of BIAA. They successfully applied the "stability theory on barchan dune" invented by Gao Ge to the flame holder of WP6A afterburner. They achieved reliable engagement of reheat and stable flaming both at poor and rich fuel conditions and cleared the problem of oscillatory burning which was most damaging to the flight. It also increased the engine thrust by 1.5% - 2%, and reduced the specific fuel consumption by 1 - 1.5%. The test acceptance rate was improved at the same time.

CEF made two improvements to the WP6 engine. One was the WP6A engine developed in 1969 for the application in Q-5 torpedo type and its thrust was 5.9 kN (600 kgf) more than that of WP6. The other one was the WP6B developed in 1970 for the J-12 fighter and its thrust was 7.8 kN (800 kgf) more than that of WP6. The two versions were all flight tested. As the developments of the aircraft were given up, the engine programs were also cancelled.