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Aviation History
1976
1976 - 2700.PDF
1504 FLIGHT International, 20 November 197 AEW Nimrod gets into top gear AFTER several years of low-key development, a recent increase in Government funding has accelerated work on the airborne early-warning (AEW) version of Hawker Siddeley's Nimrod anti-submarine aircraft (see artist's impression below). The British equivalent of the US Awacs, AEW Nimrod was first mooted over six years ago. A prototype AEW radar was built by Marconi-Elliott Avionics in 1970 and delivered to the Royal Radar Establishment in the spring of the following year. Although it performed satisfactorily in ground trials the system was never flown. For the Marconi-Elliott radar team at Borehamwood this represented their first AEW design venture. Over the frame/radar options were considered once last year's design go-ahead had been received. The design team even tually chose to use a fore-and-aft arrangement in preference to a roto- dome, seeking to avoid the radar "shadow" which the airframe causes in the latter layout. The obvious carrier airframe for the system was the already heavily modified Nimrod, though the addition of bulbous nose and tail radomes did nothing to enhance the aircraft's appearance. Even so, it is claimed that no signifi cant drag penalty will result from the modification. The scanner design is based on a cassegrain principle unique to Marconi-Elliott radars. This type of previous 20 years the company had provided technical support for APS-20 AEW radars in Gannets and Shackel- tons, and it continues to support and steadily update this equipment. Out standing amongst a succession of re finements to the APS-20 is the digital airborne moving target indicator <AMTI) system fitted to the AEW Shackleton's APS-20F(I) radar to re ject reflections from weather and re duce radarscope clutter. The range of the APS-20 has also been increased. But despite a promising start AEW Nimrod lay in limbo between 1971 and early 1975. According to Mr. R. Aytoun, special projects marketing manager at Borehamwood, six air- scanner produces a beam with low sidelobe characteristics, transmitting a pulse-Doppler signal format to separate moving targets and ground returns, and to give a measure of target relative speeds. Airborne de tection and ship-surveillance modes are interleaved, a valuable capability for overwater AEW operations. Pulse- transmission rate can be varied to suit different terrain conditions or sea states. Maximum radar range is claimed to be 250 n.m. An IFF inter rogator is mounted with each primary scanner. Each scanner is stabilised in roll and pitch and covers a 180° sector. Their operations are integrated to provide Nasa uses SLAR for ice-mapping A sideway-looking airborne radar (SLAR) has been used by Nasa to provide high-quality ice information for shipping in Alaskan waters. In a joint Nasa US Coast Guard/National Weather Service/USN exercise just completed, a radar-equipped C-130 flew along the coast to obtain daily ice-formation pictures. The' SLAR was able to penetrate cloud cover and could operate in almost all weathers. The resulting data were con verted aboard the aircraft for trans mission via satellite to a receiver at Wallops Island, Va, where black-and- white pictures were put together. The pictures were examined by US Navy ice interpreters, who compared them with long-term ice movements before recommending route changes to shipping. Ice forecasts were also pre pared. It is estimated that this tech nique could lead to annual savings of over $30 million. The technique has been used over the Great Lakes for the last two winters to make shipping movements possible throughout the year. Formerly, ship movements had to stop on December 15 each year. CJ U 4 ••• wBKmKm !•• viomcs 360° coverage, with the "quiet" scanner being repositioned at a speed greater than scan rate after each sweep. AEW Nimrod processing capacity is likely to be about 300-400 simultaneous targets, a figure under stood to be the minimum required for operations in Europe and con siderably in excess of that achieved by the current Boeing E-3A Awacs. Comparison of the AEW Nimrod and E-3A shows many differences. The Nimrod radar has a maximum range about 50 n.m. less than that of the E-3A system. But as it can auto matically designate and track targets the overall disadvantage is only slight, according to Marconi-Elliott engineers. Carrier-aircraft endurance and cruis ing speeds are comparable, and it is claimed that similar numbers of air craft would be needed for any given task. The E-3A can be refuelled in the air for extended missions, but re fuelling equipment is understood to be only optional AEW Nimrod. AEW Nimrod is believed to be cheaper than the E-3A as offered to Nato, but uncertainties about final equipment standards and production quantities make it nearly impossible to estimate prices. AEW Nimrod unit cost would probably be about 25 per cent less than the Awacs figure, how ever, and it is claimed that the British type would be considerably cheaper for a given production run. AEW Nimrod should take a signifi cant step forward when the develop ment aircraft takes to the air in May next year. This heavily modified Comet is currently being worked on by Hawker Siddeley at Woodford. A nose scanner and radome will be installed, and two operator's consoles and comprehensive instrumentation are being fitted in the cabin. At the moment AEW Nimrod and the Boeing Awacs are not in com petition for a Nato order. Nato still has no definite requirement, but the E-3A is seen as the only candidate if an airborne control aircraft is even tually needed. If Nato does not buy Awacs, Britain will have a home-grown product with which to equip a national AEW force, but it is not intended to ask Nato to evaluate AEW Nimrod. If Nato defers its December dead line it is possible that the E-3A's only Western equivalent will be airborne before the European Awacs decision is made. Some of the AEW Nimrod development team believe that the longer Nato puts off an Awacs move, the more attractive the British type will become.
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