J-8I (Jian-8 Fighter aircraft 8)
The initial J-8 model was limited in that it could not operate at night and in did not have all weather capabilities. Development for a second, all-weather version of the J-8 (designated as the J-8I) began in 1976. For improvements, 11 additional avionics upgrades were added, one of which was an all‑weather radar. The J-8I also features a newly designed canopy, seat, oxygen system, and integrated instruments. In regards to armaments, the J-8I was given a new cannon and had the capability to carry up to 4 air-to-air missiles and 4 rocket pods.
Design for the J-8I was completed in early 1978, thus allowing the Shenyang Aircraft Factory to commence trial production. In May 1980, the first production aircraft was rolled out, however it unfortunately was destroyed in a fire caused by the aircraft’s faulty hydraulic pump. The unproven hydraulic system was replaced with a new pump designed by Institute 601 improved the design in accordance with the lessons learned and replaced the hydraulic pump with a different type pump. In April 1981, a new J-8I was produced. Testing finally resumed, which took an additional 3 years to produce.
An important feature of the J-8 was the addition of a fire control system, which was a paired with a Type 204 monopulse radar developed by both the Ministry of Aviation Industry and the Ministry of Electronics Industry. The Type SM-8 aeronautical optical gunsight was the first Chinese system that utilized a rate gyroscope, which resulted in higher performance and firing accuracy. The J-8I paired with the system was tested in 1982.
The J-8I was an all-weather fighter. Compared with the day fighter J-8, it was mainly improved in three areas, i.e. the addition of eleven items in the avionics including the fire control radar, the redesigns of the canopy, pilot seat, oxygen system and combined instrument and the installation of 23-M aerial gun, 4 " Pili" (it means thunderbolt in Chinese) -2B air-to-air missiles and 4 rocket packs.
Soon after all the production drawings of the J-8I were released by the Shenyang Aircraft Design Institute in February 1978, the Shenyang Aircraft Company (formerly the Shenyang Aircraft Factory) started the prototype production. The final assembly of the first prototype was completed by May 1980.
A major accident happened on 25 June 1978 when the prototype aircraft was carrying out its first engine ground run. The running had barely lasted for twenty minutes, when the engine suddenly broke out into fire. The aircraft was completely burnt. A significant loss and a delay of the development program were caused. The later analysis, investigations and tests on the accident showed that the fire was caused by hydraulic fluid which was sprayed on to the engine through a rupture of hydraulic pipe.
In the J-8I design the hydraulic pump was changed to YB-20B. The manufacturer of the pump thought the pump was qualified in view of the fact that its dynamic pressure at the outlet was not higher than the specified value. But it had not been tested with a complete hydraulic system according to the actual aircraft condition. The test carried out after the accident showed that the resonance occurred when the pressure pulse frequency of the pump coincided with the natural frequency of the pipe at 0.8 engine rated speed. The resonance caused rapid increase of the pulse pressure inside the pipe and, therefore, the rupture of the pipe.
The lessons given by the accident are profound. It explains once more that science should be taken seriously. In the development of a new aircraft, a complete test specification must be set up, tests must be fully carried out, and the simulations of the systems in ground tests must be as true as possible, otherwise something serious could unexpectedly happen. In order to remove the design deficiencies which had caused accidents, the Shenyang Aircraft Design Institute decided to replace the pump with ZB-34. The Shenyang Aircraft Company organized its all staff and workers to assemble another J-8I aircraft to the best quality and in the shortest time. The finished aircraft was flown into air by pilot Lu Mingdong on April 24, 1981. In October second J-8I was flown. The static destructive test of a full size airframe was conducted in July 1983 and it proved that the design was in conformity with the design criteria.
The J-8I had been flown in three and half years for the tests of performance, avionics including radar and armament system, as well as for the solutions of some difficult technical problems. The flight test program was completed in November 1984. The 204 radar installed in the aircraft was jointly developed by relevant institutes and factories of the Ministry of Electronics Industry and the MAI. Ninety flight tests carried out after the radar had been installed showed that the main performances of the radar were in conformity with the original requirements, or even better.
On July 27, 1985 the Aero Products Certification Commission formally awarded the design certificate to the J-8I. The development period from the beginning of the design to the design 'certification was only a little more than eight years, far less than that of the basic J-8. This was because the development of the J-8I was carried out in one of the best political and economical periods in China. In addition the technical team had obtained more experience in the past J-8 program; the leadership of the J-8I flight test was powerful and actions taken by the leaders were effective and a total of four prototypes were used for the flight test. Among the aforementioned reasons the last one was considered as a valuable experience to speed up the development of a new aircraft.
The successful developments of the J-8 and the J-8I marked a new level the Chinese ever reached in developing their own fighters. In October 1985, these two programs were awarded a Special Class Merit of National Science and Technology Progress Prize by the National Evaluation Committee of the Science and Technology Progress. The main awardees were Gu Songfen, Wang Nanshou, Ye Zhengda, Luo Shida, Zhao Peilin, Fang Wenfu, Lu Mingdong and Zhu Kexin.
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