Soon after the Z-5 development project was completed, China began efforts to develop an indigenous helicopter independently. Based on the military Services' conversion requirement and to make up Z-5's deficiency, e.g. insufficient power, poor performance at high temperature and high altitude and low payload, the Harbin Aircraft Factory began to develop the first indigenous Z-6 helicopter in 1966.
In August 1966, the designer of the Harbin Aircraft Manufacturing Plant proposed the use of a 792 turbine engine Hunan Zhuzhou Aero Engine Design Research Institute and Harbin Engine Plant developed and produced the Zhi-5 improved design plan. The modified Zhi-5 was later called Zhi-6. During the demonstration of the scheme, some feasibility tests were carried out. Immediately after the plan was proposed, a coordinated prototype was produced, and it was determined that the Zhi-6 was a multi-purpose medium-sized helicopter mainly based on airborne modification and design and engine replacement on the basis of the Zhi-5. This coordinated prototype used the rear of the Zhi-5. Body, combined with a hand-made improved front fuselage, assembled in March 1967.
Compared to the piston-powered Z-5/Mi-4, the Z-6 helicopter had many advanced features, including a 1,618 kW Wozhou-5 turboshaft engine, which provided for a larger payload, and less vibration and noise. The blades and fuselage were re-designed to achieve better performance in highland regions. The Z-6 also borrowed many mature features and technologies from the Z-5's design, including the rear hatch, tail boom and fin.
The Z-6 was primarily intended to carry airborne troops in the frontline, with a fuselage to accommodate 12 soldiers. It is a general purpose helicopter but is mainly used for airborne landing. It can also be converted to adapt different mission requirements. It has a maximum take-off weight of 7,600 kg, a payload of 1,200 kg, a maximum speed of 192 km/h and a ferry range of 650 km.
The Z-6 helicopter is powered by a WZ5 turboshaft engine which is installed at the top of the fuselage. The engine power is 1618 kilowatts (2200 horsepower), which is a great improvement over the maximum power of the 1,250 kilowatts of the Zhi-5 engine. In terms of layout, the aircraft also uses the traditional layout in which the power compartment is placed on the upper fuselage, which overcomes the shortcomings of the Zhi-5 that is not suitable for high temperature and plateau use. The use is much wider than that of the Zhi-5, and it can adapt to four types. Meteorological conditions for flight. Compared with the Zhi-5 equipped with a piston engine, the Zhi-6 starts quickly, has a large take-off power, and has a smooth appearance design. It also has the advantages of the straight-5 in terms of maneuverability and flexibility. The test flight proved that its noise and vibration are obvious - less than Zhi-5.
The first prototype (No.6001) of the Z-6 was completed in 1967 for static tests. In 1968, the Z-6 project was officially authorized by the PLA and Chinese Government. The development work was transfered to a newly founded Helicopter Design and Research Institute in 1968. In 1968, the research and development plan for the Zhi-6 was approved by the higher authorities and formally included in the national project, designed by Helicopter Design Institute and manufactured by Harbin Aircraft Factory. After more than one year of trial production, the 6001 test machine completed the test of 60 states in 10 projects. The test results show that the strength performance of the structural parts such as the fuselage, control system, engine mount, landing gear, and reducer of the Zhi-6 were in line with static conditions and the requirements of the force test program.
On December 15, 1969, pilot Wang Peimin/Peiming piloted this helicopter for a successful first flight. Prior to the first flight he simulated the sudden shutdown of the engine and the autorotation for three times to ensure the successful first flight. The simulation not only tempered the pilot but also further verified the theoretical analysis. In order to make the first flight successful, Wang Peimin had previously made three simulated airborne helicopters on the Zhi-5 helicopter. On 25 December 1969 the second Z-6 prototype No.6002 made its first flight. The assembly of No. 6002 was completed in early December 1969. The Harbin Aircraft Manufacturing Plant manufactured a total of 4 Z-6. The performance index was fully qualified after the test flights.
In 1970 many provinces made great efforts to develop their own aviation industry. In 1970, the original third aircraft department decided that the Changhe Aircraft Manufacturing Plant would continue to produce the Z-6. In 1970, under the influence of the rise of the "big office aviation" in the local area, the development and production of the Zhi-6 was transferred to Jiangsu, and Jiangsu continued to undertake the tasks of development and finalization. The development and the production of the Z-6 were thus transfered to Jiangsu province and Jiangxi province.
From 1970, the Z-6 program was relocated to the newly founded Changhe Aircraft Factory (now Changhe/Jingdezhen Aircraft Industry Corporation ) in Jiangdezhen, Jiangxi, which later became the second largest helicopter manufacturer in China. A situation was formed in which three provinces with a common syllable "jiang" (i.e. Heilongjiang, Jiangsu and Jiangxi) were involved in the Z-6 program. Jiangsu province organized 7 cities, 6 prefectures and more than 470 factories to coordinately work on the Z-6 program. At the end of the same year, the plant assembled 1 Z-6 using bulk parts provided by the Harbin Aircraft Manufacturing Plant. The Hongzhuang Machinery Factory in Changzhou was responsible for final assembly and a total of 11 Z-6s were successively constructed.
On the morning of August 7, 1972, two Zhi-6s (Nos. 02 and 03) took off from Harbin. After meeting with a Zhi-6 produced by Changzhou, they went to take part in a test flight in a high-temperature plateau area. One Z-6 crashed near Gongzhuling, Jilin province and all 6 people onboard including pilot Fu Guifa died in the accident. After analysis, the design unit concluded that the accident was caused by the stuck shaft of the reducer in the engine. The disastrous and bloody lessons were learnt from the accident and 11 design improvements to the helicopter and the engine were made afterwards. Several technical problems, e.g. severe vibration, overtemperature of the oil, over high idle engine power, jam between the rotor and the oil separator and insufficient tail rotor thrust were tackled by the technical people one after another in the development process.
By 1976, a total of 11 Zhi-6 helicopters and 18 turbo 5 engines were trial-produced. The Z-6 helicopter had accumulated 362 hours of test flights and 5000 hours of test flights on the bench. In 1977 the State Council and the Military Commission of CCCPC formally issued a design certificate to the Z-6 helicopter.
The Z-6 helicopter was type classified in 1977, by which time 15 helicopters had already built. However, the final flight and use tests showed that the engine power of the aircraft was still insufficient, especially the single-engine layout greatly reduced the helicopter's flight safety, and the army eventually abandoned the plan of replacing the Zhi-5 with the Zhi-6. In 1978, Zhi-6 won the National Science and Technology Achievement Award, but production ceased in 1979.
Despite being a technologically sophisticaed design, the Z-6 program was cancelled due to various reasons, including unsatisfying performance and poor reliability. The development of the Zhi-6 took a key step in the Chinese helicopter's transition from piston type to turbo. However, due to improper engine selection and unsafe single engine, the Zhi-6 was not officially put into production, and the design layout of the single engine was eventually buried.
The failure of the Z-6 program resulted in a serious setback in the development of the Chinese helicopter industry. From 1978 to 1989, the Chinese helicopter industry took part in a series of international co-operations with Western partners. One significant step from the piston-engined helicopter to the tuboshaft-engined helicopter was taken in the Z-6 program, but unfortunately it was not able to be put into serial production because the improper engine selection and the less safety inherent in a single engine helicopter.
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