A Sample Feature From Aviation News

NIMROD MRA.4 – The Advanced Hunter

Following last month’s article on the Nimrod MR.2, Aviation News’s Dino Carrara looks at the next generation Nimrod MRA.4 which will be the most advanced aircraft in the RAF, and require three times more lines of computer code than the Northrop Grumman B-2.

THE Staff Requirement (Air) 420, to replace the Nimrod MR.2 gave the RAF the chance to assess the latest maritime patrol aircraft (MPA). Competing for the order was the Dassault Atlantique 3, Lockheed Martin Orion 2000, Loral/Marshall Valkyrie and BAe Nimrod 2000. One benefit the Nimrod 2000 had over the other types was that it was jet-powered, which creates significantly less noise when compared with a turboprop. While a jet can be far noisier during take-off, on patrol it is a great deal quieter and this is where it counts as it will reduce the likelihood of a submarine hearing it. The US is reportedly interested in this form of propulsion for their next generation MPA for this very reason. Currently, Nimrod is unique in being the only land-based jet-powered MPA in the world. The faster transit times to an area of operations as well as the higher ceiling level, giving better radar and sensor coverage, also had a part in the decision to proceed with the significantly upgraded Nimrod 2000, later MRA.4, which was deemed overall to provide the best value for money and capability. As a result, a £2bn contract was awarded in July 1996 to BAE Systems to convert 21 Nimrod MR.2s to MRA.4s.

The change in the Nimrod’s designation belies the fact it will virtually be a new aircraft with only the main fuselage being retained and even this will be re-lifed to give a further 25 years of service. The wings, centrebox, bomb-bay and undercarriage will all be of new design, while the rest of the main components will be either upgraded or re-lifed. The new undercarriage is to allow for an increased maximum take-off weight. The wings will have a 23% larger surface area and redesigned intakes and mountings will house the four Rolls-Royce Germany BR710s, which have been adapted to better withstand the harsh and corrosive environment of operating regularly low over the sea. The engine will give enhanced reliability, greater thrust (15,500lb) and lower fuel consumption. This latter point tied to a 30% larger fuel load will permit sortie duration in excess of 15 hours without air-to-air refuelling, though it will retain the capability. Crew fatigue on long sorties, which is the norm for MPA aircraft, is also an important factor and this is helped on the MRA.4 by lower internal noise due to the engines being quieter, less vibration and better sound proofing.

A company artist’s impression of the Nimrod MRA.4. External differences compared with the MR.2 is the turret under the nose, which is the Night Giant electro-optical search and detection system, larger nacelles for the new engines and an extra two weapons hardpoints. (Illus, BAE Systems). Below: A stripped down Nimrod MR.2 at Woodford undergoing the changes to produce an MRA.4. Reduced to the basic airframe and Nimrod radome removed, the design of the Comet fuselage, which Nimrod is based on, is revealed. (Photo, BAE Systems).

It will also have new hydraulic systems, environmental control system, crew oxygen system, automated fuel system, electrical generators and wiring, a new auxiliary power unit plus an improved flight control system. The cockpit will be re-configured for two-pilot operation – it is three at present with the inclusion of the Air Engineer – and a ‘glass cockpit’ design with most of the same systems, displays and architecture of the Airbus family of airliners. A Routine Navigator will not be carried, the two pilots undertaking this function. The amount of changes taking place to the MR.2 is illustrated by the fact that the MRA.4s will be given new serials, from ZJ514 to ZJ534. They will also wear a medium sea grey paint scheme in place of the hemp colour worn by the MR.2s, although a number of the latter have been seen in this type of scheme.

Systems and weapons

It is not only the airframe that will undergo a radical change, the mission systems are also being extensively revamped with Boeing developing the Nimrod MRA.4 Tactical Command System (TCS) and the integration of the sensors and systems that will feed into it. Its main tasks will be to control and provide data for self-defence, communications and armament systems. The information generated by the TCS will be on seven workstations, each with large high resolution multi-function colour displays. This will allow flexibility and multiple redundancy, with BAE Systems claiming that no single fault will cause a mission abort.

An artist’s impression of the Rolls-Royce Germany BR710 engines which replace the Rolls-Royce RB168-20 Spey 250s. Larger nacelles have had to be designed to accommodate the new powerplants. (Illus, Rolls-Royce Germany).

The package of equipment that will be incorporated is extensive with upgrades to current equipment, such as in the case of the Magnetic Anomaly Detector, though in many cases it will be completely new. An example of this is the CDC UYS503/AQS 970 acoustics suite, which is a development of that used on the Royal Australian Air Force (RAAF) AP-3C Orion upgrade. A new radar in the form of Racal Searchwater 2000MR will improve the ability to identify ships, be it at sea or in ports, from a greater distance. Another new piece of equipment that will aid identification of vessels is the Northrop Grumman Night Giant electro-optical search and detection system, which will be mounted in a retractable turret under the fuselage and operate in two bands of infra-red as well as in the visual spectrum.

The first four aircraft in the programme, XV247, XV234, XV242 and XV251, pictured undergoing conversion at Woodford. (Photo, BAE Systems).

The ELTA EL/L-8300UK ESM suite, again a development from the AP-3C, will be capable of detecting and classifying all types of modern radars and be an improvement over the MR.2 system by being able to gather more detailed information on emitters on the ships and aircraft in which Nimrod will be interested.

An extensive communications capability will include Link 11, Link 16, for the first time satellite communications (SATCOM) in super high frequency (SHF) and ultra high frequency (UHF) modes, as well as the usual UHF, VHF and HF radios. It will also be able to encrypt both voice and data communications.

The aircraft will have extensive self-protection equipment integrated and slaved to the Defensive Aids Subsystem (DAS), which will be the standard for many large RAF aircraft such as the C-130J, ASTOR and soon the E-3D. The DAS, feeding into the TCS, will control a radar warning receiver (RWR), a missile approach warning system (MAWS), towed radar decoy (TRD), plus chaff and flares. It will also have the contingency to carry Sidewinders and ASRAAMs, though currently no tests are planned to trial these weapons on the aircraft.

The ‘A’ in the designation of the aircraft stands for ‘attack’ and is well justified as the MRA.4 will be able to carry Stingray torpedoes, the same number as the MR.2 despite a smaller bomb-bay, more Harpoon anti-shipping missiles, with the capability of firing ALARM, Maverick and Stormshadow missiles as well as dropping mines, though again no trials are planned. The ability to carry more munitions is partly due to the addition of two more hardpoints under the wings, making a total of four. The size of the aircraft’s bomb-bay is illustrated by the fact that it will see no reduction in weapons carriage capability, yet be divided up into two smaller bays separated by an area between them which will incorporate a sonobuoy tracking sensor. There will also be two more sonobuoy launchers, over the four on the MR.2.

All these new systems and equipment and their integration into one aircraft will make the new Nimrod the most advanced aircraft in the RAF. It will have 5.4 billion lines of computer code, which is four times that of Eurofighter and, impressively, three times that required for the USAF B-2 Spirit. All this new equipment comes with a weight penalty and the MRA.4 will be 30% heavier than the MR.2, though the powerful new engines will negate this, while the advancements with computing power means the tactical crew is able to be reduced from ten to eight.

Programme progress

Work on the aircraft was initially contracted out to FRA/Serco at Bournemouth Hurn airport. Three aircraft that were in store at Kinloss, XV234, XV242 and XV247, were flown south in Antonov An-124s over 14-16 February 1997 for work to begin. When it became clear that the initial timetable and costing was over-ambitious BAE Systems moved the project in-house to its Woodford factory. With the amount of work being undertaken inside and out to produce what is virtually a new aircraft, it is perhaps not surprising that the programme has not quite gone to plan. As a result BAE Systems and the MoD re-negotiated the contract. The programme overall has slipped 23 months, though when compared with other new military aircraft projects, which can take well over a decade to enter service, the timetable for the MRA.4 compares favourably.

The production line at the Manchester factory is currently working on four aircraft, XV247 Production Aircraft (PA) 1, XV234 (PA2), XV242 (PA3) and XV251 (PA4), while there is the provision to work on seven at a time should it be required. The lead airframe, PA1, XV247 is expected to conduct its first flight towards the end of 2002 and be delivered to the RAF in the third quarter of 2004. The in-service date (ISD), which to the RAF equates to when it will have seven aircraft or one squadron’s worth, is expected to be in the second quarter of 2005. After the initial crews from the operational conversion unit, No 42(R) Sqn, are trained, the first unit to transfer to the MRA.4 will be No 120 Sqn which is expected to be operational mid-2005.

The new technology being installed will allow for a better availability rate, quicker turnround times and therefore a greater number of sorties will be able to be flown. The aircraft will perform the military tasks of anti-submarine warfare (ASW), anti-surface unit warfare (ASUW), maritime reconnaissance and SAR, and as now, assist in civilian emergencies. The versatility of the aircraft is evident by BAE Systems stating it could assist non-military authorities in anti-drug smuggling, anti-gun running, counter-terrorism and fisheries protection.

The banks of cockpit dials of the Nimrod MR.2 are replaced by colour multi-function displays. Some of the design for the MRA.4 cockpit, a mock-up is pictured here, is taken from the Airbus family of airliners. (Photo, BAE Systems). Left: A company cut-away of the Nimrod MRA.4. The two banks of racks for carrying sonobuoys can be seen towards the rear of the aircraft next, to the six white coloured launchers. (Illus, BAE Systems).

It is not only the aircraft that are being upgraded, RAF Kinloss is having considerable work take place to accommodate the MRA.4. Due to its 8ft wider main landing gear and 12ft longer wing, the taxiways and aircraft parking bays are having to be widened. A new building is also being constructed to house an MRA.4 simulator, while new maintenance bays are also being built.

Though the Nimrod MR.2 and MRA.4 may look fundamentally the same, it is clear that the RAF will receive a formidable MPA which will continue to live up to its name of Nimrod – the Mighty Hunter – in the 21st century.

A diagram illustrating the amount of work being undertaken on different parts of the airframe. The proliferation of orange, which is either new design or new build, demonstrates the major changes taking place to convert the Nimrod MR.2 to MRA.4. (Illus, BAE Systems).

A three-view of the Nimrod MRA.4, note the weapons pylons which can carry three missiles each. (Illus, BAE Systems).

Acknowledgements

Aviation News wishes to thank Andrew McKerney at BAE Systems, Dale Donovan at HQ Strike Command, Wg Cdr Simon Ruddock-West, and Dawn McNiven, Corporate Communications Officer at RAF Kinloss for their assistance with this article.