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An-71 Madcap - Development

In the late 1970's several generations of DRLO aircraft were introduced in the West. The United States Air Force and NATO] had the strategic E-3A Sentry AWACS, and the US Navy had the E-2C Hawkeye. Israel operated the E-2C Hawkeye as a tactical aircraft, and in many respects obtained significant advantages in the war with the Arabs in 1982 because of this aircraft.

At this time the Soviet arsenal consisted of only the strategic Tu-126, but there were no aircraft of operational-tactical designation for the direct control of military operations. In 1982 the Soviet government, according to the idea of the Ministries of Defense, Aviation, Radioelectronics industry, made a decision about performing research work on an operational-tactical DRLO aircraft. The main enterprise for this project as a whole was determined to be the Kiev Machinery Plant ([KMZ] - now ANTK im. O.K. Antonov, and on the radio-electronic complex - Moscow NPO Vega.

Requirements for the aircraft were very high, and periods were compressed. It was proposed to create a ground-based machine which was not inferior to the E-2C. The application of this aircraft would make it possible to considerably increase the combat effectiveness of Soviet attack aviation. In parallel the An-72[P] (the first with this name) was created, which carried out electronic reconnaissance and interference with the enemy, and at the Ilyushen OKB aircraft the RLDN aircraft A-50 and jammer Il-76[PP]. The requirements, formed in 1982-83 by VVS [Air Force] and PVO (Air Defense) with the participation of Research Institutes and enterprises of industry, provided for: duration of flight 4.5-5 h; the possibility of detection at long range low observable targets; simultaneous tracking is not less than 120 targets; the detection over a wide range of frequencies, classification and the determination of bearing, mapping the corresponding information on the working operator's positions; the joint operation of aircraft with the fighter-interceptors both consisting in arsenal, and developed; the transmission of information simultaneously to the control centers and in ASU VVS, PVO, of Navy and ground forces; operation in different natural regions in the simple and adverse weather conditions, in the daytime and at night, at temperatures of surrounding air of +50C; the guarantee of independence of basing in the prolonged period.

By the special feature of the development, the aircraft later received the designation An-71. This was intended to provide operational resolution of the conceptual questions: the determination of layout, composition and technical level of equipment, order and periods of creation, and also tactics of application. As a result, the 4th quarter of 1982 the project tactical-technical requirements [TTZ] and technical proposal for the radio-technical complex [RTK] aircraft in two versions of construction were established. The 1st version which worked in the decimeter wavelength range, had the antenna systems in a fairing above the fuselage of aircraft. The 2nd version, which worked in the centimeter band, had the arrangement of antenna systems in the nose and aft fuselage sections. The development program also studied a version of the aircraft with conformal antennas.

The technical proposals examined several RTK carriers, including: An-32, An-12, An-72 and a specially constructed aircraft. The aerodynamic and assembly special features of the airframe and equipment, energy possibilities and the potential for reaching the assumed TTT were all evaluated. Aerodynamic investigations were conducted on models of two versions of aircraft. The position of antenna fairing (AO) taking into account interference with the fuselage, the wing and the tail assembly, its influence on the stability, the controllability, and the like were evaluated. Unless the aircraft is designed from the outset to carry a large radome, its very difficult to modify an existing aircraft as the radome cannot simply be attached above the fuselage.

By March 1983 the customer accepted the version with the arrangement of the antenna above the fuselage, which became the basis for developing this complex, was on the basis of their comprehensive analysis. The aerodynamic layout An-71 was selected, on the basis of the need for operational provisions of the RTK antenna without shadow regions from the construction of aircraft. Two arrangement diagrams were studied: one on a special pylon and the other on the ending of vertical tail assembly (V).

The designers came up with a novel and unique solution; the An-72 was completely re-designed and swept forward, rather than backward, and the radome housing the Kvant early warning radar was attached on top of the tailfin. The analysis showed the advantages of the latter, though in this case it was necessary to re-develop the tail assembly. It had to sweep forward, with a large chord and thickness. The wingspan of the aircraft was also increased by about six meters. In comparison with the initial An-72 there was almost a 4 meter decrease in length, which negatively affected the controllability of machine. The horizontal tail assembly fell into the zone of the action of exhaust jets from the engines, and experienced high vibration loads. The D-436 engines from Zaporozh'ye enterprise "Progress" were substituted, with considerably increased thrust.

The installation of a significant quantity of radio-electronic equipment, systems of conditioning and cooling, the equipment of the working operator's positions led to a significant increase in the mass of the aircraft. In this case one of the basic requirements remained the possibility of basing on the front airfields and the high rate of climb, caused by the small time of reaction on the anxiety.

To guarantee the possibility of takeoff with the failure of one engine, the tail section An-71 was modified to accept an additional turbojet starting engine, the single-shaft RD-38A, whose air duct was located above the fuselage. In cruising fight this was shut by special fold. This engine was developed in Rybinsk as the lift engine of the Yak-38 vertical takeoff aircraft.

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