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Dalnaya Radio-Lokacyonnovo Obnaruzhyeniya [DRLO]
Long-range Radio-Location and Control [DRLO]
Airborne Early Warning [AEW]
Airborne Warning and Control Systems (AWACS)

The primary way in which the Soviet Union sought to remedy the shortcomings of its ground-based air defense radars was to deploy large radars on aircraft. These aircraft, known as Airborne Early Warning [AEW] or Airborne Warning and Control Systems (AWACS), monitor enemy penetrators - AEW - and coordinate air defenses over a large area - AWACS. One of the factors in the radar horizon formula is antenna height. The same aircraft operating at 3000 feet against an antenna height of 25,000 feet (in an Airborne Warning and Control, AWACs, type system) would have a radar detection horizon of over 250 miles. The range of an AWACS is much greater than that of ground-based radars - over 200 miles to the horizon and over 400 miles to another aircraft at a high altitude. A line-of-sight radar standing 50 feet above the ground theoretically can detect at about 30 miles abomber flying at 300 feet above the ground. At greater distances, the bomber is hidden by theearth's curvature. The actual detection range might be less than the theoretical range because ofthe disruption or blocking of radar pulses by terrain features such as hills. The actual detectionrange might be greater than the theoretical range if the radar is located on a hill.

Countries possessing airborne look-down, shoot-down radars have a definite advantage in detecting low altitude attacks. These radars are usually pulsed doppler radars and capable of detecting moving targets in ground clutter. When airborne, the AWACS cannot be targeted in advance since its precise location is unknown. AEW aircraft can make a decisive contribution to air operations, detecting hostile aircraft as soon as they take off, and managing air defense and counter-air operations. While one side vainly gropes in the dark, the side with AEW capability knows exactly where the enemy is -- and isn't -- can most efficiently direct friendly forces against the enemy's weak points, and maximize surprise. Well known American airborne early warning radar systems for manned aircraft are the AWACS and HAWKEYE, both of which employ specially designed airframes and are relatively expensive.

  1. The first indication of a Soviet AEW program was the 1968 release of a documentary film showing a transport-type aircraft which appeared to be carrying a radar dome. This first Soviet AWACS, the Moss, was relatively ineffective in tracking low-flying bombers and cruise missiles.
  2. The more recent Soviet AWACS, the Mainstay, is considered to be much more capable. The MAINSTAY airborne warning and control system (AWACS), deployed in the late 1980s, provided the Soviet Air Forces with a battle management capability for their new FLANKER and FULCRUM aircraft. An effective AWACS capability was essential for the Soviet drive for theater air superiority over NATO. Mainstay can detect remote threats and vector an interceptor such as the Flanker. Its mission is to detect low-flying aircraft and missiles and to help direct fighter operations. The Mainstays might patrol near the Soviet borders to track approaching U.S. bombers, providing the greatest possible reaction time.
  3. Two Naval AEW aircraft were developed but cancelled. The first was an AEW version of the Antonov An-72 twin-turbofan STOL transport, codenamed "Madcap" by NATO; this interesting design (the radar disc was mounted atop a forward-swept, V-shaped set of tail fins) was cancelled. Systems evidently affected by cutbacks included the Madcap airborne warning and control aircraft, which probably had been canceled by 1991. The official reason given was that a turboprop was more efficient for the AEW role than a jet The fact that Yakovlev is a Russian company while Antonov is Ukrainian probably had something to do with this.
  4. The second was Yakovlev's Yak-44, a twin turboprop rather similar to the Grumman E-2 Hawkeye. The Yak-44 was also in turn cancelled (although a revival has been considered).
  5. The Ka-31 Helix-B AEW version of the Kamov Ka-32 helicopter was developed on the basis of Ka-27 ship-borne coaxial helicopter.

The design of aircraft to carry radar equipment suitable for carrying out an airborne early warning (AEW) mission poses significant problems. One requirement for such a mission is provision of azimuthal radar coverage. This creates the need to install, in the aircraft, radar antenna arrays having substantial physical space requirements. One solution to this problem is to mount additional structures on a standard aircraft to accommodate the required radar equipment. The well-known addition of an external rotodome onto an aircraft is an exemplary implementation of such a solution. Use of a dorsal fin mounted on an aircraft to house antenna arrays is another known example of such a solution. The addition of such structures typically requires structural modification to the aircraft to accommodate the additional structure.

One obvious adverse affect of such additional structures is that the aircraft suffers aerodynamic drag penalties. As a result, the overall performance of the aircraft is limited. The drag penalties also serve to limit the flying range of the aircraft. This result is contrary to the AEW mission of the aircraft since it is desirable for the aircraft to travel significant distances from its base of operation and/or remain airborne for extended periods in order to scan over a large area. A further adverse effect of additional structures is that the aircraft becomes mission dedicated. That is, the aircraft serves no useful function other than to fly the AEW mission.

The utilization of integral radome-antenna structures, and particularly such types of structures which are rotatably mounted on aircraft and employed as so-called airborne early warning systems (AEW) is well-known in the technology, and has successfully found widespread applications in conjunction with military surveillance aircraft,, especially aircraft adapted to be launched from naval carriers. In various instances, as currently utilized in military aircraft, such radome-antenna structures are mounted positions so as to be superimposed above the fuselage of the aircraft, although conceivably also being suspendable from below the fuselage, and incorporate a depending shaft structure, generally hollow in nature, extending downwardly from the radome into the fuselage of the aircraft, and wherein the shaft is operatively connected to a suitable drive arrangement for simultaneously rotating the shaft about the longitudinal axis thereof and the radome-antenna structure at specified speeds of rotation.

Suitable couplings and slip ring assemblies may be provided in order to connect the antenna array contained in the radome to suitable stationary sources of electrical energy while, concurrently, enabling the pick-up of signals received by the antenna array and to transmit the signals to stationary signal processing component and/or display consoles which are located in the cabin of the aircraft. Moreover, a suitable cooling fluid may also be transmitted to the antenna components contained in the radome through the intermediary of the hollow shaft mounting and supporting the radome-antenna installation for rotation.

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