An-71 - Soviet mini AWACS
Early warning aircraft represent a significant expansion of the Air Force's capabilities, as they are able to detect targets long before ground-based radars. As a result, the Air Force itself has much more time to respond adequately. Deployment can be directly proportional to the threat, which increases the efficiency of managing allocated forces.
Western countries have replaced several generations of early warning aircraft in the late 1970s, from the first TBM-3W Avenger , which was forced by Kamikaze airstrikes in the Pacific, to Fairey AEW.3 Gannet and Grumman E-1 Tracer to Grumman E-2 Hawkeye Navy or Lockheedy EC-121 Warning Star and Boeing E-3 Sentry in the Air Force. Eastern block, resp. The Soviet Union, on the other hand, had only strategic Tu-126 aircraft based on Tu-114 transport.
In 1982, research work began in the Soviet Union to verify the design options and potential benefits of an early warning aircraft for tactical aviation. The result was the formulation of tactical and technical requirements, in which the contracting authorities were based on the capabilities of the American competitor E-2C Hawkeye . The assignment required an endurance of 4.5-5 hours, the ability to search for low-flying targets in the background, simultaneous tracking of at least 120 targets, the ability to detect and identify working enemy radars, including their classification, the ability to cooperate with tactical aircraft, passing information to air command posts ground forces and the possibility of working in the temperature range -50 to +50 ° C.
At the end of 1982, two conceptual solutions for the future machine were selected: one with a decimeter - band radar housed in a disk - shaped housing above the fuselage, and the other with a centimeter - wave radar and antenna systems at the bow and stern (similar to the Nimrod AEW). 3 ). Because the work was entrusted to the Kiev machine plant (Antonov), figured among the considered carriers An-32 , An-12 , An-72 and a specially built aircraft.
In March 1983, after evaluating the influence of the antenna system on the aerodynamics of the airframe, especially on the controllability and stability of the aircraft, the designers proposed to use the An-72 aircraft as a carrier. The antenna was to be placed in a disk-shaped radome either on a pylon or on top of a vertical tail area. The last solution had the most advantages. The radar had a "clear field of view" not obscured by the tail surfaces, so it was chosen as definitive. However, it also brought a number of complications, such as the need to completely rebuild the rear of the aircraft and design and manufacture a new vertical tail area with negative arrowheads. The influence on the centering was also significant, which affected the fall characteristics and the longitudinal stability of the aircraft.
The horizontal tail surfaces would enter the engine exhaust stream after relocation. This meant thermal stress and constant vibrations, which could be the cause of the fatigue fractures of the hinges. The designers raised the rear part of the fuselage about half a meter upwards and the GTC received a positive lift.This partially got out of the flue gas stream, and in addition improved the lateral stability of the aircraft.
The aircraft, marked " An-71 ", received more powerful engines D-346K, with a thrust of 75 kN, against 64 kN engines D-36 original An-72 . From the point of view of safety, the ability to take off was required even when one engine was stopped. However, with the assumed take-off weight and overall aerodynamic drag of the radom, this was not possible, even with more powerful propulsion units. Therefore, a third RD-38A engine with a thrust of 32 kN was placed in the rear of the fuselage. The engine was supplied with air by a tilting intake manifold on the back of the aircraft. The outlet nozzle opened under the fuselage, in place of the original cargo gate.
Prototypes on stage
When the basic drawings were completed, the designers presented them to Oleg Antonov . He nodded and said, "It looks pretty exotic, but if necessary." In early 1983, the concept was approved, and the preparation of detailed drawing documentation could begin. The work schedule assumed the completion of the drawings in the third quarter of 1983, the preparation of production in 1-3. quarter of 1984, the production of the parts themselves in the second half of 1984 and the overall assembly, ground tests and handover of the prototype for flight tests in the first half of 1985.
The order of the Council of Ministers was signed only subsequently, on January 9, 1984, when the work was already in full swing. AI Naumenko was appointed chief designer. The construction of three prototypes was ordered: two flight (No. 1 and 3) and one for static "breaking" tests (No. 2).
The first prototype, with a scheduled completion date in the second quarter of 1985, was rebuilt from the fourth built An-72 . It was a machine that made the first takeoff of the An-72 on August 31, 1977, and was introduced at the Le Bourget air show in June 1979. Because this pre-series piece (No. 004) had a fuselage shorter than the serial machines An-72 , it was first necessary to insert in front of the wing, between the 14th and 15th bulkhead, an extension ring with a length of 990 mm. The second non-flight prototype An-71 was completed in April 1985. It was based on the first kite An-72 (No. 001), also originally designed for static ground tests. The third prototype was to be completed in the last quarter of 1985. One of the serial An-72 was intended for reconstruction.
Simultaneously with the construction of prototypes, work was underway on the construction of the E-700 radio complex (a system for searching and tracking targets) with the Vega-M surveillance radar. However, the individual pieces assembled into both prototypes differed so much that we can speak of two different complexes. In the version mounted on the first prototype An-71 , the designers focused too much on the function of the radar antenna. After the first tests, it was clear that the background noise and interference with the airframe are so great that it will be necessary to completely rework both the on-board computer and data processing algorithms.
The "second generation" radio complex was mounted on the third prototype An-71 during a forced break in flight tests. The whole set now occupied three sections of the fuselage, while the older version was enough with two.Relatively much attention was paid to the system of liquid cooling of electronics blocks, because the original complex quickly overheated.
A closed electronics cooling intake duct can be seen on the right cover of the An-71 chassis
Based on experience with the operation of the Tu-126 , the designers tried not to neglect the protection of the aircraft crew from electromagnetic radiation. The cockpit glass had a special metal protective layer, the operators' workplaces were electromagnetically shielded, the interior equipment was conductively connected and any electric charge was diverted to the dischargers at the ends of the wings and tail surfaces. Nevertheless, it was assumed that the crews would wear a protective layer of fine metal mesh under the pilot's coveralls.
Another large amount of work awaited the designers during the construction of the radome. The challenge was the production of a sufficiently rigid thin-walled housing covering the antenna. Problems were with the axial bearing ensuring the rotation of the radome, because the dimensions of the vertical tail surface were the limit. In critical places, designers had to help themselves with deficient titanium, which is light, strong, but more difficult to process.
At the same time, another potential customer appeared - the Soviet Navy. In 1985, the hull of an aircraft carrier (heavy aircraft cruiser) Project 1143.5 ( Admiral Kuznetsov class , formerly Tbilisi) was launched. In the fleet since 1982, an early warning aircraft was planned, corresponding in performance to the American E-3C Hawkeye.
The navalized version of the An-71 was one of the candidates. After all, the other aircraft were also just naval versions of ground fighters and fighter jets. However, something else is a superjet with a sufficient excess of power, and something else is an overloaded airliner, moreover, relatively bulky. In order for the An-71K (K - Korabelnyj ) to be able to take off from the deck of a ship equipped only with a "jumping bridge" without a catapult, the designers planned to install two more auxiliary take-off engines RD-38A. Due to the large dead weight of the auxiliary engines, it was clear that there would be a total degradation of aircraft performance. In the end, it was quite reasonable to decide that the early warning naval aircraft would be built from scratch, and the winner was the Jak-44 turboprop project. However, after the collapse of the Eastern bloc, this project was canceled.
The first prototype An-71 with civil registration "SSSR-780151" was completed in early June 1985. There was not yet a system for searching and tracking targets, only mass models of individual blocks. On June 23, 1985, a ceremonial roll-out took place and a protocol was signed for handing over the machine for flight tests. On July 5, the prototype began driving tests. Less than a week later, on July 11, approval was signed for the first takeoff, which took place the following day at 2.30 pm local time.
The first prototype An-71 in flight
The crew consisted of Capt. AV Tkachenko, 1st pilot SA Gorbik, flight engineer VA Petrenko and electronics test technician II Radaucan. On the first flight, the machine moved to Gostomel Airport for further tests. By the end of 1985, the first prototype had made 75 takeoffs and did not fly 117 hours. Since May 1986, flight tests have been conducted with complete equipment for searching and tracking targets.
In 1988, an anti-corkscrew parachute was mounted under the tail of the first prototype for tests of minimum speed and behavior in fall mode.In addition, the machine was equipped with a special device to make it easier to leave the aircraft in an emergency. Behind the pilot's seats, there was a rail in the floor, along which a special cart with two handrails moved. There was a switch on one of them that started the whole device.
When viewed from behind, the nozzle of the third engine hidden in the fuselage can be seen
In an emergency, the pilot released the seat belts, grabbed the handrails with both hands and pressed the switch. The hydraulic cylinder ensured the opening of the door and the electric motor transported the truck and the pilot to the door. Then it was enough to leave the plane and jerk the handle of the parachute. Only pilot seats were equipped with the device, because the fall speed tests were performed only by two-member crews, without technicians. Fortunately, it has never been necessary to verify the functionality of this device.
During a demonstration of the An-71 to the then General Secretary of the Communist Party, Mikhail Gorbachev, one of the journalists photographed a plate at the top of the SOP An-71 . Censorship fell asleep and in 1987 the photo appeared in a publication about Aeroflot, in a chapter devoted to special works. This, of course, did not escape Western reporters, who assigned it the code name " Madcap ".
The third prototype with civil registration "SSSR-780361" was ceremoniously demonstrated on February 19, 1986. The first takeoff with this machine was made by the crew: Capt. VG Lysenko, 1st pilot of AV Tkachenko, flight technician JA Dmitrijev and electronics test technician MN Berzyuk.
The third prototype An-71 has long fallen into disrepair at Kiev airport
Both aircraft first went through factory tests aimed at verifying flight parameters. Subsequently, electronics specialists took part in the flights, the aim of which was to test the function of the radar and the possibilities of the An-71 in searching for and tracking air targets.
Test flights did not take place only in Kiev . An-71 aircraft visited a number of airports, including the regions of Central Asia, Crimea and the Transcaucasus. Based on the evaluation of measurements by research institutes of the Ministry of Defense and the Ministry of the Aeronautical Industry, the deployment of the An-71 aircraft increased the efficiency of the deployment of tactical aviation 2-3 times, depending on the simulated conditions.
In addition to exercises aimed at cooperation with aircraft and air force command posts, air traffic control tests were also performed in areas outside the coverage of the normal ground radar network. It has been practically verified that such an deployment of the An-71 significantly increases the possibilities, for example, during rescue operations and in the search for lost aircraft or crews in emergency.
However positive the results of the An-71 tests were, there was no interest in their further development and there were no funds for it. By the end of the tests at the end of 1990, the first prototype had 387 takeoffs with a total flight time of 650 hours. The third prototype performed 362 takeoffs with a total duration of 380 hours. Several crews took turns on both.
Both prototypes have been standing at Kiev airport since the early 1990s. In 2010, the An-71 with the matriculation "SSSR-780361" was transported to the Ukrainian Museum of Aviation.The Soviet Air Force had to do without the support of early warning aircraft, because the heavy A-50 belongs to the subordination of the air defense of the state and do not cooperate with the tactical air force.
The third prototype during the reconstruction of the Ukrainian Aviation Museum
Photo: VVS archive, www.valka.cz , Ministry of Defense of Ukraine, author
Published with the kind permission of the author.
Published in Military revue 3/2015 by Naše Vojsko.
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