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Nimrod MRA4 for the RAF
By Karl Schwarz
“We should never have accepted this contract,” sighs Allan Cantwell, head of development for the Nimrod MRA4 at BAE Systems in Warton. The original order dating from January 1997 was based on a fixed price which had been negotiated down to a rock-bottom £2.81 billion. But in view of a number of technical difficulties, this turned out to be far too low, so that BAE has twice had to post significant losses, causing its share price to nosedive. Again, the schedule, which anticipated that this multi-purpose naval aircraft based on the existing Nimrod MR2 would be in service in April 2003, proved totally unrealistic.
However, according to BAE Chief Executive Mike Turner, the crisis between the company and the Ministry of Defence is finally over. According to Defence Minister Des Browne, the programme, which for a long time was viewed as the archetypal example of a procurement which had been completely botched up, has finally advanced to the point at which it is possible to place a production order. The order was announced during the recent Farnborough Air Show and, as expected, was for 12 aircraft rather than the 21 originally planned.
In the view of the BAE Systems, however, the “world-class” quality makes up for the smaller quantity. As Turner explains, “The Nimrod MRA4 will play an important strategic role as a versatile and adaptable platform for the Royal Air Force.” For example, compared to the Nimrod MR2, the data processing capacity has been increased by a factor of 20. Also, the range has been extended to over 11,000 kilometres.
Originally, the MRA4 was marketed as a simple derivative of the MR2. But less than 5 percent of the original airframe is being reused or, to be precise, the fuselage hull and the empennage. The wings are now completely new, and at the same time the opportunity has been taken to enlarge them slightly and to use modern construction methods such as milled spars and an external skin with integral stiffeners. Above all, extensive changes were necessary in the root area to accommodate the new BR710 turbofans from Rolls-Royce Deutschland. Their diameter is 50% greater than that of the old Spey engines. They deliver 69kN of thrust each, an increase of one quarter, while at the same time consuming 30 percent less fuel.
Naturally the upgraded aircraft have also been given new electrical systems and hydraulics. The reinforced undercarriage has carbon brakes. Moreover, the oxygen is generated directly on board, and the auxiliary power unit works completely autonomously. The air conditioning system has also been improved.
However, the one change which is critical to the capability of the Nimrod MRA4 is the integrated Tactical Command and Sensor System (TCSS) supplied by Boeing as subcontractor. This offers an open architecture with UNIX software and networks the extensive sensor equipment over several standard 1553B data buses and ethernet links. The weapon stations are integrated via a special 1760 bus.
At the heart of the TCSS are the seven operator consoles situated in the forward area of the cabin in an U-pattern. These are manned by two Tactical Coordinators (TACCOs), two sonar operators for the anti-submarine warfare (ASW) role, one communications manager, one radar operator and one electronic reconnaissance specialist. A further member of the crew in the aft cabin area looks after the sonobuoy launchers and can also be deployed as an observer. Two pilots in the cockpit complete the crew. The pilots' equipment is based on experience gained with the civil Airbus types and comprises seven LCD screens, one of which is used as a tactical display.
For the classic ASW, anti-surface unit warfare and search & rescue missions, and also for the increasingly important overland reconnaissance role, the Nimrod MRA4 has a huge array of sensors:
- Situated in the nose is the Thales Searchwater 2000MR radar, which in addition to its search mode for maritime targets also has air-to-air operating modes and can generate radar maps.
- The Electro-Optical Surveillance and Detection System (EOSDS) from Northrop Grumman is accommodated in a retractable sensor head behind the nose gear. Its three sensors operate in parallel in the medium and long-wave infrared spectra and also in the visible range.
- The acoustic system from Ultra Electronics is capable of processing the data from up to 64 sonobuoys simultaneously. For this purpose two 32-channel receivers are mounted on the weapon bay doors.
- The Magnetic Anomaly Detector (MAD), which detects localised changes in the Earth's magnetic field caused by submarines, is accommodated, as normal, in the tail “sting”. It has been taken over with minor modifications from the Nimrod MR2 and is built by CAE.
- Elta is supplying the EL/L8300UK electronic support measures system.
To enable integration into network centric operations, as is essential these days, there are five VHF/UHF radio sets and two HF radio sets, plus Link 11 and Link 16. On top of this there is a satellite communication system.
Given the likely requirement for more overland missions, the Nimrod MRA4 is equipped with a comprehensive electronic self-defence system. This includes the Lockheed Martin ALR-56M radar warning receiver and AAR-57 Common Missile Warning System (CMWS), chaff/flare dispensers (Vicon 78) and an active towed target (Raytheon ALE-50). One possible later upgrade will be a laser for engaging approaching missiles.
The Nimrod MRA4 is naturally armed with torpedoes, depth charges and sea mines. On top of this there are anti-ship guided missiles (probably Harpoons) and Mavericks. On search and rescue missions, lifeboats and dinghies can be released. Recently consideration has been given to the question of whether the MRA4 could also be used as a platform for precision weapons such as Paveway IV or the Storm Shadow stand-off cruise missile.
Integration of these weapons would further enhance the flexibility of the Nimrod MRA4. This is bound to be required, since once the aircraft are finally operationally ready at the RAF airbase of Kinloss, Scotland at the beginning of the next decade, they are to remain in service for at least 30 years.
From page 36 of FLUG REVUE 12/2006
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