Z-7 Heavy Helicopter Zhishengji-7

In the mid-1960s medium helicopters had been put into mass production and light helicopters were being developed in the Chinese helicopter field. But the heavy helicopters still did not exist. Based on the needs of war preparation and training, the military Services requested to develop a heavy helicopter which could carry a reinforced platoon of troops.

China Zhi-7 helicopter is a single-rotor large-scale transport helicopter developed by Harbin Aircraft Manufactory (Hafei) and Helicopter Design Institute. 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 developing light and medium helicopter products, China began to consider the development of adapting large helicopters capable of loading platoon unitsto the high temperature in South China and the conditions of the Southwest Plateau.

In the fall of 1966, the sixth research institute (sixth academy) of the Ministry of National Defense gave Hafei the task of developing a large transport helicopter. In May 1967, Hafei established the Zhi-7 helicopter program demonstration group. In April 1968, Hafei transferred the Zhi-7 development program to the helicopter design institute. The design proposed by the helicopter using two 792A engines, six rotors, and a takeoff weight of 14,400 kg was approved in March 1970. The plan clarified that apart from redesigning the propeller hub and reducer, other straight-to--5 and straight-to--6 components should be used as far as possible. After the design plan was approved, the development of the Zhi-7 helicopter was fully launched.

In 1969 the CAE decided that the design task of the heavy helicopter designated as Z-7 would be undertaken by the newly founded Helicopter Design and Research Institute and CAE owned factories and institutes would perform the main development activities. The Helicopter Design and Research Institute was assigned the design effort on the Z-7 Heavy Helicopter (HH) shortly after it was established in 1969. By early 1970, Vice President Marshal Ye Jianying indicated that the target of the heavy helicopter development project in China was clear, requiring this helicopter to carry a platoon of soldiers. But at that time the Cultural Revolution was in full swing, and various conditions were poor.

At the end of 1970, the main design work was basically completed and a fuselage wind tunnel test was conducted. In 1971, the Zhi-7 helicopter development project was listed as a national key project, and the Zhi-7 was intended to be used as a test aircraft for shipborne helicopters. In 1974, the Sixth Academy transferred the prototype and assembly work of the Zhi-7 helicopter body from the Test Flight Academy to Jingdezhen Helicopter Factory.

In 1975, the static test of the Zhi-7 helicopter was undertaken by the helicopter handed over by the Institute of Intensity. In March 1976, the State Council and the Central Military Commission's Standing Equipment Development Leading Group requested that the Zhi-7 helicopter be produced and equipped for the army around 1980. In the same year, the development focus of the Zhi-7 helicopter was transferred from the test flight institute and other units to the helicopter institute and Jingdezhen helicopter factory.

In May 1975, 97% of the parts of the Zhi-7 were processed, and they have been assembled into two bodies. The supporting products have reached 90%. In 1979, the Zhi-7 helicopter completed the whole machine static test and conducted more than a dozen other tests.

The Z-7 design concept was to use two WZ5A turboshaft engines driving a six-blade rotor, and new designs of rotor hub and gear box. The WZ5 was developed from the WJ5 (i.e. modification of the mechanical transmission and free turbine governor) by the Zhuzhou Aero-Engine Research Institute and the Harbin Aero-Engine Factory, and was produced in Jiangsu Province since 1976 for the Z-6 helicopter. The remaining parts and components should be as common as possible with the ones in the Z-5 and Z-6. The design targets were as follows: maximum takeoff weight 14,400 kg, payload 3,500 kg, maximum speed 240 km / h, maximum range 350 km and service ceiling 6,000 m.

Whether a fixed-wing aircraft or a helicopter, the control torque required to control surfaces is large, and human effort alone is difficult to achieve this without using a booster. When guiding the helicopter, all levers and the rocker arm are moving in space. Of course, the regularity of movement, can be precisely calculated by computer, but the result is not intuitive, and it is difficult to conduct an overall coordination. A slight negligence will cause the trolley or rocker arm to come across other part. Thus, a leading technical problem in the design was is the accurate measurement of individual trajectory of the levers of the rocker arm. In this way, systems design engineer from the map at a glance to see whether the movement control system will affect the work of other systems.

In a helicopter there are many moving parts, such as engine, rotor, tail rotor, the automatic orientation, and so on. Helicopters have vibration problems, particularly in these parts. Therefore, every lever of the control system, with its natural vibration frequency, had to avoid integer times of the speed of the moving parts, so as to avoid resonance. Because resonance will directly affect the functions of control system and its operating efficiency. To this end, dozens of levers of control systems in the Z-7 were subjected to natural frequency calculations.

China was ready to develop intercontinental ballistic missile, which is a major policy decisions that concern national prestige, and military prowess. In the summer of 1971, the central issue of the "718 Project" was the development of three main models of ships: "Yuanwang Hao " (the main measurement ship used for tracking and comprehensive measurement), "Xiangyanghong No.10" (an ocean survey boat) and "J121 Hao" (an ocean salvage lifesaving boat). However, the escort and salvage ships needed helicopters. At that time the situation was that missile development progress was assured and the ships were no problem, just waiting for the helicopter.

By May 1975 the manufacturing of 97 per cent of Z-7 parts and sub-assemblies had been completed, two airframes assembled and 90 per cent of vendor-furnished-equipment and components supplied. The WZ5A began 50-hour bench tests in 1978 and showed good results, meeting the performance target. The full size static test was completed in 1979. But the Z-7 was in the right place at the wrong time. But the limited national resource could not support at one time both the Z-7 and Z-8, two heavy helicopter development programs.

On June 28, 1979, because it was clear that the Zhi-7 helicopter was no longer equipped with troops, it was decided that the development of the Zhi-7 was stopped and the development work for more than 10 years ended. The Z-7 was dropped in favor of the Z-8, which was a copy of the French SA-321G Super Frelon.

The development of the Zhi-7 helicopter was carried out under the condition that domestic helicopters emphasized specifications, flight quality specifications had not been perfected, and helicopter design theory and calculation methods had not yet passed verification. In order to explore the way of designing helicopters by itself, in the overall layout, aerodynamics, and strength design of the Zhi-7 helicopter, it mainly adopted the layout of similar foreign helicopters, selected conservative parameters in the calculation of strength such as aerodynamic strength, and tried to follow the straight -5 Zhi-6's mature technology and other measures ensure the smooth development of research and development. However, the above measures also seriously affected the advanced and practicality of the Zhi-7 helicopter, resulting in excessive strength of the Zhi-7 structure, serious overweight structure, and reduced aircraft performance.

The reason why the state decided to stop the development of the Zhi-7 large-scale helicopter is that due to the limited financial resources of the Zhi-8 project after the launch of the Zhi-8 project, it is impossible to invest in the development of two large helicopters at the same time. In order to fully ensure that the development of the Zhi-8 helicopter is undertaken by Jiangxi Jingdezhen Helicopter Factory For the project, the Zhi-7 helicopter had to make way for the Zhi-8, thus announcing the death of the Zhi-7 large helicopter.

Chronology

1. 1962 - Vice President Marshal Ye Jianying demanded a large helicopter
2. Autum 1966 - the Aviation Institute assigned the large helicopter development task to Harbin Aircraft Factory
3. May 1967 - Harbin Aircraft Factory formed a development group and issued technical target of 4500kg cargo, 600km range, hover at 3000m and 30 degrees celsius, and the task was transfered to the Helicopter Design Institute
4. March 1969 - The Air Force required development of a large helicopter, and later in the year the Aviation Institute decided to found the Helicopter Institute, engaged in the large helicopter development task, project code Z-7
5. September 1969 - Helicopter Institute (not formally established until December) issued a proposal with maximum takeoff weight 22,600kg, but due to the unavailability of a powerplant, this was changed to a interim proposal equiped with 2 Wozhou-5jia engines
6. 20 March 1970 - proposal was approved and full-scall development was initiated, with design by the Helicopter Institute, engine / deduction / transmission by Zhuzhou Engine Institute, and manufacture / assembly / test by the Flight Test Institute.
7. 28 June 1979 task terminated after two airframes had been built and full-scale static test completed