straight-7 (codename: Z-7, English: HAMC Z-7) helicopter is a single-rotor, large-scale transport helicopter with tail rotor independently developed by China's Harbin Aircraft Manufacturing Factory (abbreviation: Harbin Aircraft Manufacturing Company) and the Helicopter Design Institute of China Aviation Research Institute (abbreviation: 602 Institute). 20th century In the 1960s, many countries in the world developed and produced medium and large transport helicopters with a take-off weight of more than 10 tons. While China was developing light and medium helicopter products, it also began to develop products that could adapt to the high temperatures in southern China and the use conditions of the southwest plateau. A large helicopter carrying platoon-level units.
The Z-7 helicopter was seriously overweight during the design process, and the project was eventually scrapped and replaced by the Z-8.
Historical background
As early as the mid-1960s, while China was developing light Z-5 and medium Z-6 helicopters, it also began to consider the development of large helicopters. Because the Z-5 helicopter that has been successfully trial-produced cannot meet the country's needs in all aspects. In 1962, Vice Chairman of the Central Military Commission Ye Jianying proposed the development of a large helicopter capable of carrying a reinforced platoon of armed soldiers. In the autumn of 1966, the China Aviation Research Institute (abbreviation: Sixth Academy) officially issued a document to the Harbin Aircraft Manufacturing Factory (abbreviation: Hafei, code name: 122 Factory) to develop the Z-7 large helicopter, requiring that this helicopter can adapt to the high temperature and humidity in southern China. Conditions of use on the Southwest Plateau [2-4]. Z-7 is a twin-turboshaft engine, mechanically driven single-rotor helicopter with tail rotor . It adopts a short-wing layout to fix the landing gear and store fuel. The tail rotor blades and flat tail are respectively placed on the inclined beam. Upper sides. The rear section of the fuselage has a retractable springboard-type tailgate.
In the summer of 1971, the Central Committee of the Communist Party of China issued a plan for Project 718, which meant that China was preparing to develop and launch intercontinental ballistic missiles. However, the intercontinental missile launch test requires observation and salvage in the sea area where the warhead lands. Therefore, escort, salvage ships and helicopters are required to be built by China itself. The situation at that time was "missile waiting for ship, ship waiting for aircraft", that is, if the progress of missile development was guaranteed, we would wait for the ship, and if there was no problem with the ship, we would wait for the large ship-based salvage helicopter. As a candidate model, the Z-7 has been put on the agenda to accelerate its development.
In May 1967, Factory 122 formed a Z-7 aircraft plan demonstration team. Through research, it was proposed that the Z-7 tactical and technical indicators are: load capacity 4,500,000 Gram, with a range of 600 kilometers, and can effectively hover at a plateau of 3,000 meters and a temperature of 30°C. In April 1968, Factory 122 transferred the plan to develop the Z-7 to the 604th Institute of the Sixth Academy (602) established in Harbin. predecessor). After that, the 604th Institute further demonstrated the Z-7 plan with the assistance of the 120th Factory and the 331st Factory, and proposed a plan with a total take-off weight of 22,600 kilograms in September 1969. In view of the fact that the new engine development or modification cycle is too long, it was decided that the Z-7 engine would adopt a transitional plan of two 792A (turboshaft-5A) engines and use 6 rotors; in addition to redesigning the propeller hub and reducer , Other parts of the Z-5 and Z-6 are used as much as possible, and the total take-off weight is reduced to 14,400 kilograms. According to this plan, the Z-7 aircraft is mainly responsible for transportation. It can carry 35 passengers or 3,500 kilograms of cargo. It can lift 2,000 kilograms of weight in a hovering state. The cargo compartment can drive a Beijing jeep; the maximum speed is 240 kilometers. / hour, the maximum range is 350 kilometers, and the practical ceiling is 6,000 meters. The plan was approved on March 20, 1970.
Z-7 wind tunnel test
After the engine transition plan was approved, the development work was fully launched. The 602 Institute was responsible for the full engine design and provided a complete set of drawings and corresponding technical documents. Institute 608 is responsible for the design and testing of engines, reducers and transmission systems. Institute 630 is responsible for the production, final assembly and flight testing of airframe structures and system parts. Factory 573 is responsible for the production of main and tail rotor hubs and automatic tilters. Factory 574 and 621 are responsible for the production of engines and main reducers.
At the end of 1970, the Z-7 development task was listed as one of the national key projects. In order to accelerate the development of the Z-7, large-scale diffusion and large-scale collaboration of parts will be carried out. It was planned to use the Z-7 aircraft as a test machine for carrier-based helicopters, and a water tank hydrodynamic model test was conducted. By September 1971, the work of converting the Z-7 into a carrier-based helicopter was stopped.
In May 1975, 97% of the Z-7 parts were processed and assembled into two airframes. 90% of the supporting finished products had arrived.In 1979, the Z-7 helicopter completed the static test of the entire aircraft and conducted more than ten other tests.
In 1976, the Central Military Commission's Conventional Equipment Development Leading Group issued another document, clearly requiring the Z-7 to be finalized and produced around 1980 and equipped with troops. Starting from February 1976, the focus of developing the Z-7 was transferred from the China Flight Test Institute (namely 630 Institute) and Factory 573 to the China Helicopter Design Institute (named 602 Institute) in Jingdezhen and Jingdezhen Helicopter Factory (codename : Factory 372, Changhe Aircraft Manufacturing Factory).
Starting in March 1977, the 602 Institute conducted a major review of the design and process documents of all Z-7 components. In 1979, the 602 Institute completed the static test of the whole machine and also conducted other tests, mainly including main reducer and transmission system cycle power test, lubricating oil system simulation test, hydraulic system simulation test, whole machine power grid principle test, and all Aircraft antenna layout simulation test, fuselage blowing, rotor blade fatigue test, tail rotor resonance test, automatic tilter applicability test, landing gear drop shock and stiffness damping test, etc. The 792A engine has also completed various component tests and long-term test runs of the entire machine.
Zhi-7 static loading test
On June 28, 1979, the General Staff Headquarters and the National Defense Industry Office of the State Council issued a document and decided to cancel the development tasks of Zhi-7 and other models. The Third Machinery Department then dealt with the components, materials, finished products, process equipment, etc. that had been terminated from development of the Z-7. The reason is that due to the limited financial resources of the country, it is impossible to invest in the development of two heavy-duty helicopters at the same time. In order to fully ensure the project of replicating the French "Super Hornet" helicopter (i.e. Z-8) undertaken by the 372 Factory, the Z-7 helicopter had to make way for the Z-8. , announced the demise of the Z-7 heavy-lift helicopter. At this point, the Z-7 development that lasted for more than 10 years only produced two prototypes and was discontinued.
Overall evaluation
The Z-7 helicopter was developed according to China's helicopter strength standards and flight quality standards.
has not yet been perfected, and the helicopter design theory and calculation methods have not yet been verified. In order to explore the way of self-designed helicopters, the Z-7 helicopter mainly adopted the layout of similar international helicopters in the overall layout, aerodynamic and strength design, selected conservative parameters in terms of aerodynamic strength and other force calculations, and tried to use the Z-5 and Z-7 helicopters. Z-6’s mature technology and other measures ensure the smooth development of the aircraft. However, the above measures have also seriously affected the advancement and practicality of the Z-7 helicopter, resulting in the excessive structural strength and serious overweight of the Z-7 helicopter, which has reduced the performance of the aircraft.
Although the Z-7 project was cancelled, many achievements in the development of the Z-7 laid the foundation for the later successful development of the Z-8 heavy-duty helicopter, and also filled the gap that China has not developed a heavy-duty helicopter (10-ton class).
