British Aerospace Nimrod AEW3
- Garth Calitz
- 49 minutes ago
- 6 min read
By Rob Russell
It was ugly to start with and got uglier as the British tried to put more stuff onto it. It reminded people of the Australian platypus with its monstrous, ugly nose! It was in the tradition of all British aircraft - build a good aircraft and then add on and on - remember the Canberra, with the cockpit on the side, almost as an afterthought and the original Hs25 series, where it looked like the cockpits were stuck on the front?
The British Aerospace Nimrod AEW3 was a proposed airborne early warning (AEW) aircraft which was to provide airborne radar cover for the air defence of the United Kingdom by the Royal Air Force (RAF). The project was designed to use the existing Nimrod airframe, then in use with the RAF as a maritime patrol aircraft, combined with a new radar system and avionics package developed by Marconi Avionics.
In the mid 1960s, following the development of the Grumman E-2 Hawkeye carrier-borne AEW aircraft and its associated systems, which was used extensively by the US Navy, the British government began looking for an aircraft and radar system that could provide airborne early warning for the United Kingdom. At the time, the only recognised AEW aircraft in British service was the Fairey Gannet aircraft used by the Fleet Air Arm on board Royal Navy aircraft carriers. These were fitted with the AN/APS-20 Radar, which had been developed during World War II and was rapidly becoming obsolete.
In the early 1960s, efforts began to develop a new AEW platform for the Royal Navy to succeed the Gannet, featuring a novel radar system on a new aircraft, the P.139. Although the P.139 was cancelled due to mid-1960s defence budget reductions, development of a British-designed radar system persisted. Concurrently, it was determined that the RAF required an AEW aircraft to support the national air defence strategy.
To fulfil the planned requirements for a new AEW aircraft, the government had several factors to consider:
The Frequency Modulated Interrupted Continuous Wave (FMICW) radar initially proposed for the P.139 and intended for the RAF's new aircraft would not operate effectively near propellers, meaning a jet aircraft would be needed.
The size of antennas needed for the required scanning range, together with the fairly large mission crew, meant that a large aircraft was required.
Designers at Hawker Siddeley Aviation came up with a proposal that would see the FMICW radar system installed using a Fore Aft Scanner System in the new Nimrod aircraft. This proposal was rejected as being too expensive, with instead, a proposal to convert surplus Andover transport aircraft. This was also rejected due to the potential cost of development, as well as the Andover being a propeller aircraft coming to the end of its life, never mind being too small!
In the interim, to provide a land-based AEW aircraft, radar systems from withdrawn Royal Navy Gannets were installed in similarly surplus Avro Shackleton maritime patrol aircraft and entered service from 1972. Around the same time, it was decided not to proceed with FMICW technology as the basis of an AEW system, as research from the United States Air Force (USAF) had shown that pulse-Doppler radar was superior and would be used in the Boeing E-3 Sentry then under development.
As a consequence, the idea of a new land-based AEW aircraft for the RAF was re-examined and again it was decided that the Nimrod met the requirements
The decision was taken to procure the aircraft fitted with a pulse-Doppler radar system, which then proceeded to a range of options:
Purchase the AN/APS-125 pulse-Doppler radar system and its associated avionics, as fitted to the E-2 Hawkeye, and fit them into the Nimrod.
Purchase the rotodome and antenna from the E-2 and combine with a British radar transmitter, receiver and avionics package.
Develop a wholly British radar system and avionics package using a Fore Aft Scanner System (FASS) rather than the E-2 radome.
The third option would maintain both employment and Britain's position at the forefront of radar technology and development; however, it was also riskier than purchasing an "off the shelf" product or spreading the risk across multiple partners. In 1977, the US had made an offer to NATO for purchasing several of the new E-3 Sentry aircraft, which were being delivered to the USAF; this was intended to provide airborne early warning cover for Europe's NATO nations without having to rely on the United States, and eventually came into being as the NATO E-3A Component, which was planned to be stationed in the United Kingdom, these aircraft subsequently being based at bases in the Netherlands. However, the complex multi-lateral negotiations eventually led the United Kingdom to pursue the all-British development.
The complexity of the AEW requirement proved too much for British industry to overcome by itself. A major project management issue was the appointment of British Aerospace (BAe) and GEC Marconi as joint programme leaders. This meant in practice that as development issues arose, the companies had a distressing tendency to blame each other for the problem rather than try to resolve it. Whilst BAe was able to fulfil its part of the contract by delivering the aircraft on time (the first was due to be delivered in 1982, with full delivery by 1984), GEC was unable to solve the difficulties in developing the avionics.
In 1977, an RAF Comet 4 was modified for flight testing with the nose radome and conducted a series of trials, the results of which proved promising enough for an order for three prototype Nimrods to be built using redundant MR1 airframes. The first of these was rolled out in March 1980 and flew for the first time in July, and was intended to test the flight characteristics, with the second airframe planned to carry out trials of the Mission Systems Avionics (MSA) package.
Despite the problems, the project continued and 8 production aircraft were ordered (which would also come from spare MR1 airframes). The first of these flew in March 1982. Even while the technical problems were being worked on, the aircraft was delivered to the RAF's No 8 Squadron to begin crew training. It was at this time that the British and Argentinians were having a good battle over the ownership of the Falkland Islands. The technical problems proved insurmountable for the Nimrod AEW to be deployed in the Falklands arena. The idea was to base the aircraft at Ascension Island and operate them from there. To provide some degree of cover, several Nimrod MR.2 were quickly modified to undertake the airborne surveillance role for the task force, however.
The choice of the Nimrod airframe proved to be the wrong one, as it was too small to accommodate the radar, electronics, power generation and cooling systems needed for a system as complex as the one required – at just over 38.5 m, the Nimrod was close to 8 m shorter than the Boeing 707 aircraft that formed the basis of the E-3 Sentry, with the planned all-up weight around half that of the American aircraft, but was expected to accommodate sufficient crew and equipment to perform a similar function.
The Nimrod was designed to have a total of six operator consoles (4 for the radar, one for ESM and one for communications), which was less than the nine stations fitted aboard the E-3A. The size of the Sentry also meant there was room to increase the number of operators, as the need arose and the role of the Sentry evolved. Having the Sentry's radar in the rotodome above the aircraft allowed for cooling to be undertaken directly by the airflow, with cooling doors mounted in the installation, while the transmitter had a separate liquid cooling system, and the avionics in the main section were sufficiently cooled by a conventional air cycle environmental system. This was in contrast to Nimrod's "heat sink" design that dispersed the heat through the fuel system, and which needed the fuel tanks to be at least half-full to work efficiently when the aircraft's system operated at full power.
At the time that the first production Nimrods were being delivered to the RAF, the MoD decided to conduct a complete review of the AEW programme. The result of this was the start of a bid process to supply AEW aircraft for the RAF that began in 1986, with a number of different options put forward, including the E-2C Hawkeye, E-3 Sentry, P-3 Orion, a proposal from Airship Industries, and the Nimrod. Eventually, the selection came down to two aircraft: the Nimrod with the GEC Marconi package and Boeing with its Sentry. In December 1986, the Sentry was finally chosen and the Nimrod AEW programme was cancelled.
In spite of the project's difficulties, India expressed interest in procuring the Nimrod AEW3; these investigations continued well after the British government's eventual cancellation of the project. The Indians eventually chose the Ilyushin IL76, with a rotodome and the Israeli Phalcon radar system on it.
