Tupolev Tu-126 – In 1958, eleven years before the USAF began to work on its AWACS counterpart, the Soviet Union tested prototypes of its first large DRLO, (long-range airborne surveillance radar). At this time OKB-156, headed by Tupolev, was instructed to study aircraft to carry what became the AK-RLDN (aviation complex for radar for patrol and air control) – the Tupolev Tu-126. The requirement was to keep watch on all airspace surrounding the USSR.
The Tupolev Tu-126 radar, named Liana, was being developed by what became NP Vega. The main antenna was distributed across a beam 10.5m (34ft 5in) long. To give the necessary 360 deg coverage in azimuth, this antenna, bigger than any previously designed for airspace surveillance, either had to rotate inside a radome or to have D-shaped fairings added in front and behind so that it formed the central diameter of a rotodome. The latter consistently proved to be the superior solution. Complete engineering design of the Liana installation took place in 1959, still ten years before the AWACS radar was designed by Westinghouse.
Work began at OKB-156 on studying how to fit this installation into a Tupolev Tu-95M, but it was soon obvious that, even with a redesigned fully- pressurised fuselage, there was inadequate internal volume. In 1960 the decision was taken to base the carrier aircraft on the Tupolev Tu-114, and this made the task at first seem straightforward. There was room for a total operating crew of twenty-four, of whom twelve would be resting off-duty at any one time.
Aft of the flight-crew cockpit in the nose the enormous pressurised volume above the floor was divided into six compartments. Compartment 1 housed the Tupolev Tu-126 aircraft commander and eight operator stations, with a mass of underfloor equipment including liquid oxygen flasks, gaseous-nitrogen cylinders and the complete Roza (rose) station. No. 2, shown blank in the drawing, housed most of the main radar racking and an engineering workshop for repairs and servicing. No. 3 was for controlling the images sent to the operator stations, with a telescopic sight in the roof for viewing the antennas. No. 4 was a dining area. No. 5 housed the rotodome drive and cooling, with an air radiator under the fuselage. No. 6 housed beds for the off- duty crew, with the Krystall electronic complex at the extreme rear.
Each crew of Tupolev Tu-126 comprised two pilots, two navigators, a control officer for interceptors, three Liana operators, an operator for other sensors, an operator for air/ground radio, an engineer for equipment and an engineer to rectify faults. The main radar, an extremely powerful pulse-doppler equipment, used electronic scanning in elevation, while the antenna rotated at a normal operating speed of 10 rotations per minute. One of the principal additional sensing systems was called Lira (Lyre), served by antennas in streamlined containers on the tips of the tailplane as in the Tupolev Tu-95RTs. ECM receivers and jammers were distributed around the rear fuselage, and though the original intention was to have a Tupolev Tu-95 tail turret, with twin AM-23 cannon, this was replaced in series aircraft by an SPS tailcone. Other antennas were mounted on a ventral underfin.
The primary Tupolev Tu-126 mission was long-range reconnaissance for the IA-PVO force of manned interceptors, working normally with the Tu-128S-4 complex to intercept all bombers at a distance of 1,000km (621 miles). The intention was to place the radar at an assigned patrol point 2,000km (1,242 miles) from its base, in emergency within three hours. Provided the Tupolev Tu-126 was at a height between 2,000m (6,560ft) and its operating ceiling of 10,700m (35,100ft, compared with 29,000ft for the Boeing E-3), it was designed to detect fighters head-on at any height above ‘treetop level’ at a range of 100km (62 miles) or bombers at 200-300km (124-186 miles) or a warship at 400knm (248 miles).
Development of the Tupolev Tu-126 was assigned to a special brigade at GAZ No. 18 at Kuibyshev headed by veteran aircraft designer A I Putilov. By far the greatest problem to be overcome was EM (electro-magnetic) interference. EM effects extended throughout the aircraft, interactions between the numerous emitters and approximately twenty-five receivers proving difficult to eliminate. The problem was especially acute when everything was operative in the prototype aircraft, No. 6860, first flown in 1962. After three years of meticulous research and development it was possible to complete eight series aircraft, built at Kuibyshev in 1965-67.
After such difficulties it was a relief to find that initial integration into PVO with the first series aircraft in 1965 went without a hitch. The first operating base was Shyaulyai in Lithuania. The Tupolev Tu-126 soon proved its ability to meet PVO requirements, no matter what the weather. Operating from this base, one of the first in service flew to the Kolski peninsula and thence round the entire Arctic shore of the USSR to land at Vladivostok 10 hours later. Soon flight- refuelling probes were added, the fuel pipe running externally along the right of the fuselage to the wing, extending normal patrols to 20 hours. For the first time the PVO had radar coverage of the entire Arctic, and ability quickly to respond to changed dispositions of NATO aircraft.
After 1970 the Liana radar was becoming inadequate to meet new threats. From 1969 development had been in progress on a replacement, Shmel (bumblebee), and in 1974 this flew in the Tupolev Tu-126 prototype. Reluctantly, Tupolev agreed that a completely new carrier aircraft was needed, and this was projected as the Tu-156. The ASCC reporting name for the Tupolev Tu-126 was ‘Moss’.