The KongJing-1 (KJ-1) Airborne Early Warning [AEW] system placed a rotating radar on a Chinese copy of the Russian Tupolev Tu-4, itself a copy of the Boeing B-29 bomber. In the 1960s the difficulty of night air defense combat was manifest in ground-based radar command structure many problems. Especially the southeast coast province's mountainous area created a massive radar shadow, allowing Taiwan's airplanes to repeatedly frustrate night interception. The Continental air command needed to be able to cover the airspace with an early radar warning system.
In the autumn of 1969 the Great Cultural Revolution had stopped. On 26 September 1968 the Central Military Committee issued the instruction for the development of an AEW aircraft. Following the development trend of world air force equipment construction at that time, the Air Force proposed the development of an airborne early warning aircraft. According to the time when the development work was approved, the AWACS aircraft under development was replaced by the "926 Aircraft". Looking around the world at that time, only the United States, the former Soviet Union, and the United Kingdom had air-warning aircraft. The first E-2 "Eagle Eye" specially designed by the United States is a turboprop passenger aircraft; the former Soviet Tu-126 "Moss" airborne early-warning aircraft, which began to equip troops in 1969; the Royal Air Force of the same year received the MK1 electronic reconnaissance aircraft converted from the "Comet" 4C jet airliner.
On 25 November 1969, the Air force headquarters issued a notice that reassigned personnel to carry on the AEW aircraft development. At the same time, the air force party committee decided that re-equipping a Tu-4 airplane was the basis for an AEW aircraft, under project code number 926. The re-equipping work was to be carried on west of the Shanxi Xianyang's Wugong, at the 5702 Factory, which had related large-scale processing and the maintenance equipment.
At that time the Tu-4 was a good foundation for re-equipping, as for practical purposes there were at that time few other large aircraft available to the mainland. The choices were the Il-18, Tridents, Boeing 707, Viscount, Tu-104, Tu-4 and so on. These airplanes were British, Soviet or American products, and at that time Sino-Soviet and the Sino-US relations were in a nervous state, with spare parts guaranteed with difficulty. The British domestic product "Viscount" had already suspended production. But the mechanical condition was quite good to process the spares part for Tu-4, and therefore the use of the Tu-4 to make an early-warning aircraft platform was reasonable.
At the end of 1969, Xian Aircraft Design Institute (603 Institute) handled jointly with others to send out the personnel to set up the design staff. Lou Guo Yao was the technical person in charge, though in a later period Zhou Guangyao held the post. At that time requested national various units to need the material processing materialto give the green light completely allows to pass, only could lean coordinates not to with all one's strength inquire about.
Early warning aircraft carried a 7 meters diameter radar dome on the fuselage. Installing an early warning radar antenna on a carrier aircraft was not a simple matter and requires major technical modifications to the aircraft as a whole. After the modified aircraft installing the huge radome and bracket system on the back, the total resistance of the aircraft increased by about 30%. In order to ensure the flight performance and safety of the aircraft, they replaced the original piston engine of the Tu-4 aircraft, which increased the power of the whole aircraft power unit by 67%. It was decided re-equipp the plane with domestically manufacture turboprop engines. Because the forced-air cooling piston engine nacelle is small, it was not possible to install the turboprop in the piston engine compartment. The installation was done with precision, and only one month was needed to smoothly complete the work. In addition, from December 1969 to August 1970, the technicians modified the aerodynamic shape and structure of the carrier, and the air blowing test during the entire development process exceeded 2,000 times.
Although the engine compartment was re-equipped, the lengthened engine stretched out forward amounting to 2.3 meters, which affected airplane's stability and the maneuverability. Engineers solves this problem with enlarged stabilizer area, and in the stabilizer both sides addition terminal plate, simultaneously increasing the ventral fin and enlarging the dorsal fin to guarantee the stability. The stabilizer area was lengthened 2 meters, the chord direction lengthened 400 millimeters.
In order to install the radar and onboard systems, the airplane's original "Cobalt" radar and all turrets were demolished. The dome carried on the back of the plane was 7 meters in diameter with a thickness of 1.2 meters, made of glass fiber reinforced plastic. Because the prototype organism corresponding load-carrying structure has not been able to use in installing the radar to cover the support, the ordinary frame could not withstand the radar cover inflight stress, the the Tu-4 fuselages received a strengthed frame, and installed the radar bracket on this load-carrying structures.
The Tu-4 center-section's bomb bay and several sections were re-equipped with an airtight cabin for the radar operator and control personnel. An early warning aircraft main subsystem including electronic warning system, data processing system, data demonstration and control system, friend-or-foe identification, correspondence and data transmission system, guidance and homing system, electronic countermeasure system. The data transmitting equipment used a wireless teleprinter, air zone air situation display was mainly by chart board mapping. The performance of this early-warning aircraft was by no means a modern early-warning aircraft in the true sense. According to material which then already publicized, the early warning aircraft to low target's survey area is equal to 40 P-3 radar stations, this has the use value regarding the mainland air defense then.
In early-warning aircraft's manufacture history, Chinese's re-equipping was the fastest in the world. Started from December 1969, only one year and seven month elapsed until 10 June 1971, when the early warning aircraft started the initial test flight, and afterward entered the flight-test stage. In the tests, it was discovered that with the engine power enlarged, the propeller sidewash hit the vertical stabilizer. In the Tu-4 original installation the piston engines were dextro-rotating, but the turboprop were laevo-rotatories. The original design was accomodated completely to the dextrorotary aerodynamic moment, creating the airplane's right deviation. But China's technical personnel solved what looked like a very thorny question, and adjusted the accelerators to cause the thrust force to come together to compensate for this yawing moment.
Another the question which appeared in the test flight was actually not so simple. Because the radar dome's thickness is located in frontof the vertical stabilizer, the air flow has a separation which causes turbulent flow and produces vibration on the vertical stabilizer. This not only causes the flying crews to feel weary, it also causes the structure to be weary. Starting from September 1972, the design team began to remove the sources of vibration. The method adopted was to install hull shape cowling on the antenna frame, and install power on the vertical stabilizer to offset the vibration. Repeated tests proved that these methods were effective.
The "926 Aircraft" made its first successful test flight on June 10, 1971, and was named "Air Police One". The first test flight with a radome, Air Police One experienced a severe vibration in the air. In the cockpit, the pilot's pedal board felt intermittent tapping and rattled; in the middle cabin, all three shooters could see the obvious periodic swing of the vertical tail; in the cockpit, people could not shake to write. After analysis, researchers proposed 17 kinds of vibration elimination schemes. After more than two years of difficult research, the tail chatter caused by the turbulence at the rear of the radome was finally eliminated.
After the early warning aircraft re-equipment was completed, it carried on several hundred hour flight test. Beginning in the second half of 1976, the Air Force organized research to improve radar resistance to ground objects and sea clutter. From November 20, 1978 to January 18, 1979, Air Police One organized a sea test flight, and the effect was not obvious. In the end, because the performance of the early warning radar could not meet the needs, the development of Air Police One ceased in 1979.
The high-altitude simulation goal is the H-6 bomber aircraft and marine low altitude targets by transport aircraft. Early warning aircraft can track the H-6 target to a range of 300~350 kilometers, and wavehopping transport aircraft at a range of 250 kilometers. Early warning aircraft also aimed at the marine ships to carry on the experiment, a survey large-scale submarine chaser was detected at a distance of 300 kilometers. Although at that time early warning aircraft used electron tube systems, including the command computer, but these ranges compared favorably with on the ranges of advanced early-warning aircraft in other countries. The backwardness in the radar-data processing and the information transmission link of the Chinese early warning aircraft, which lacked practical man-machine interfaces, compromised the manual plotting and the voice communication notification of air intelligence.
Before 1980, the Chinese Air Force mainly continued to use Soviet Union's equipment systems and the operational control patterns, with short-range ground radar control primarily. China's land area is very big, and so this needed many ground-based radars, the fighter aircraft and the airport, and divides the respective anti-aircraft air zone, this is also caused China ultimately to produce nearly 6000 J-5 and J-6 fighter aircraft. It was a great challenge to coordinate and dispatch so huge a quantity of fighter aircraft and distribute them to Air force bases. In addition there were nearly 100,000 anti-aircraft guns and several thousand anti-aircraft missile launchers, so the Continental air command was not an easy matter.
The Soviet Union's early-warning aircraft generally deployed 150 kilometers behind the security perimeter, nearby friendly fighter aircraft and ground defenses. This procedure can not only monitor the air zone effectively, it can also cause the early-warning aircraft to be under the protection of one's own anti-aircraft network. The early-warning aircraft warning range is far, and when the enemy fighter aircraft attempt to attack early-warning aircraft, they may retrocede promptly, and guide friendly fighter aircraft and the air defense ground environment to carriy on the interception.
In 1981 Syria attempted to use high speed Mig-25 fighters when attacked by Israel. The Israeli early-warning aircraft promptly guided fighter aircraft to the successful interception of Syria's Mig-25. The early-warning aircraft's superiority in detection range is considerable, and can be separated from the enemy'y ground-based radar by a considerable distance. The Syrian Mig-25 fighter aircraft needed ground control, and were unable to be under the ground panoramic air intelligence guidance. They therefore fell into the Israeli fighter aircraft's snare.
The China Air Force's early-warning aircraft also very possibly adopted this kind of tactic, but China's actual situation was different from that of Soviet Union and the US, lacking the long range fighter planes. China needed to guide large quantities of J-5 and J-6 fighters in combat. Even with the air defense ground environment coordination, the early-warning aircraft's command control would be complex. After 1970, mainland China's air defense would be as though it were "covered with thorn's hedgehog" - an invading enemy's airplane would encounter airborne and ground interception on unprecedentedly crowded scale.
After the early warning aircraft was developed successfully, it did not enter air force service. Since the 1970s, Taiwan Kuomintang airplane harassing attacks gradually subsided. The mainland's electronic net gradually improved, and covered the majority national territory. When Air Police No. 1 was dismounted that year, the early warning equipment was dismantled and restored to a bomber. Today, the "Air Police One" exhibited at the China Aviation Museum is reassembled with the same type of aircraft.
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