A Sample Feature From Aviation News

A New Nimrod

Post first flight, David Willis reviews the troubled MRA.4 programme.

Above: The Nimrod MRA.Mk 4 programme has been subject to numerous delays, cost-overruns and production cuts since it was signed for in late 1996. A victim of the UK government’s competitive fixed-price culture and the contractors ‘under-bid and hope more money follows’ mentality, is the real loser the future of the RAF’s maritime patrol capability? (Photo, BAE Systems).

One of the surprises of the recent defence review was that the delayed BAE Systems Nimrod MRA.Mk 4 was not cancelled. The programme, running seven years behind its initial schedule and suffering from cost-overruns and production cuts, was the subject of much speculation about its future at the recent Farnborough airshow. What was not expected was a reduction in the number to be purchased from 18 to just 12. The programme had already been reduced from 21 aircraft.

Genesis

The Nimrod MRA.Mk 4 arose from a requirement to replace the Nimrod MR.Mk 2 as the RAF’s primary maritime patrol aircraft. Staff Requirement (Air) 420 called for between 12 and 25 low-risk/non (or minimum) developmental Replacement Maritime Patrol Aircraft (RMPA) for delivery by a single prime contractor. Fitted with a two-man cockpit, the aircraft would be in service by 2001 – 2002, have endurance of 13+hr with a time on station of between 8 and 10hr at 2,980 miles (1,850km) from base. Equipped with a MIL-STD-1760 databus, sensor data fusion technology, an electro-optical/infra-red (EO/IR) sensor, synthetic aperture radar/inverse synthetic aperture radar (SAR/ISAR), a defensive-aids system, electronic support measures (ESM), multiple datalinks and advanced communications (including satellite), the RMPA would have a service life of 25 years. Finally, the industrial teams were to offer 100% offsets on the contract.

The requirement for the RMPA pitted the British Aerospace (BAe) Nimrod 2000, Lockheed Martin Orion 2000 and Lockheed Tactical Systems UK (formerly Loral) Valkyrie upgrade of the P-3 Orion against each other. When the request for information was initially released in 1993 the Dassault Breguet Atlantic 3 was also in the running, but it was withdrawn in 1996 as the RAF’s preference for a four-engined maritime patrol aircraft became clear.

Mission systems

Above: When this stripped Nimrod MR.Mk 2 fuselage was being loaded inside the An-124, a total of 21 MRA.Mk 4s were to be produced. FR Aviation was due to fit the aircraft with new wings, engines, undercarriages and internal systems, but delays resulted in this part of the programme being taken in-house by BAE Systems. (Photo, BAE Systems).

In late June 1996 the UK Ministry of Defence’s Equipment Approvals Committee recommended that the BAe Nimrod 2000 be selected for the RMPA programme. In December 1996 a fixed-price contract worth £2.2bn for 21 Nimrod 2000s, training systems and initial support was signed. In early 1998 the Nimrod 2000 was renamed the Nimrod MRA.Mk 4, with MRA standing for Maritime Reconnaissance Attack, to highlight the aircraft’s offensive capabilities.

A total of 95% of the components used on the MRA.Mk 4 are new. The only MR.Mk 2 parts re-used are the fuselage pressure shell and empennage. It was initially planned to re-use the outer wings, but this plan was abandoned.

The Nimrod MRA.Mk 4 is powered by BMW Rolls-Royce BR710 turbofans in place of the Rolls-Royce Speys. The BR710 consumes 30% less fuel than the Speys while providing 25% more thrust. Fitting the new engines into the wing bays required a considerable re-design of the bays, with enlarged intakes to deal with the increased airflow of the larger diameter powerplant. At one point BAe evaluated a ‘Nimrod specific’ version of the General Electric CF34-8C – the – 34N - as an alternative powerplant. It offered the advantage of requiring less redesign of the engine-bay area, but BAe decided to retain the BR710.

Other external differences between the MR.Mk 2 and MRA.Mk 4 are apparent. A teardrop shape fairing on the port side of the forward fuselage houses a ram-air turbine. On the base of the fin, is a single inlet for the environmental control system, replacing two inlets on the rear fuselage on the MR.Mk 2. Maximum take-off weight has grown to 230,200lb (104,420kg) from 190,000lb (86,260kg).

The Nimrod MRA.Mk 4 cockpit is based on that of the Airbus A330/340 family, but with seven large multifunctional displays instead of the airliner’s six. The cockpit crew has been reduced from four to two, the flight engineer and en-route navigator having been removed.

The new generation Nimrod has a comprehensive mission suite. The Tactical Command Systems were contracted from Boeing, which used the experience it gained on the US Navy’s cancelled P-3C Update IV suite and the Indonesian Boeing 737 Surveiller programme. It incorporates seven reconfigurable workstations and the pilots’ tactical display, linked by six MIL-STD-1553s and a –1760 databus to each other and systems in the aircraft. The cabin crew stations are for the Radar, Comms, TACCO (tactical co-ordinator) 1, TACCO 2, Acoustic and ESM operators, while an optional eighth workstation can be provided.

The radar is the Thales Sensors Searchwater 2000, used primarily for ocean search tasks although it does have air-to-air, weather and spot synthetic aperture modes. Searchwater 2000 also has the potential for further overland modes of operation, a growth area for once exclusively ‘blue water’ maritime patrol aircraft. The radar was selected by the UK government instead of the ELTA EL/2020 originally offered by BAE Systems, the change being made on political grounds.

Located in a retractable turret under the nose, the Northrop Grumman Nighthunter Electro-Optical Surveillance and Detection System uses a medium-wave and long-wave infrared sensor in combination with a visible and near visible infrared sensor. Images from any two wave-lengths can be fused into a single false-colour image picture for display on the monitors in the cabin. To counter the yaw predicted to occur when the turret is deployed, 59in (1.5m) composite finlets have been built on to the horizontal tailplanes.

Above: The first prototype Nimrod MRA.Mk 4 (ZJ516) is seen approaching Warton on August 26, at the conclusion of its first flight. The new nose radome area stands out well against the yellow primer.

Below: ZJ516 making its first landing; note the big ‘barn door’ flaps. The undercarriage has been strengthened to accommodate the heavier all-up weight of the aircraft. All three development machines will be based at Warton during the test programme. (Photos, Neville Beckett).

Overland and littoral surveillance roles will increase the Nimrod’s exposure to anti-aircraft defences, so the aircraft will be fitted with a Defensive Aids Sub-System (DASS) produced by BAE North America. The DASS comprises an ALR-56M(v) radar warning receiver, an AAR-57 missile approach warner, an ALE-50 towed radar decoy and Thales Vinten Vicon 78 chaff and flare dispensers. The upgraded ELTA EL/L-8300UK ESM system also adds to the situational awareness of the aircraft’s crew, even though its primary role will be detection of radio frequency emitters for classification.

The communication equipment is provided by Telephonics. It consists of five V/UHF and two HF radios, Link 11 and Link 16 datalinks, and a satellite communication facility. A fibreoptic intercom network links the communications systems within the aircraft. The Nimrod will have one of the best communications suites in the RAF, allowing it to undertake a secondary role of battlefield command and control and act as a communications relay station.

Smiths provide an Armament Control System (ACS) that allows the control of stores released from the weapons bay and the four underwing hardpoints. The MIL-STD-1760 databus will also allow the Nimrod to ‘communicate’ with weapons currently in the planning stage (many associated with overland roles) such as stand-off missiles. ACS also manages the release of the sonobuoys. The Smiths system is derived from that used on the Boeing F/A-18 Hornet.

The acoustic systems, data recorders and mission support system comes from Ultra. Capable of handling up to 64 sonobuoys at a time, the Ultra AQS970 acoustic system is a development the earlier CDC UYS503 system and is capable of using the full range of buoys – analogue, digital, passive and active. The magnetic anomaly detector, located in the MAD-boom, is a CAE product.

Above: PA01 at Woodford before its first flight. The larger intakes, inlet on the base of the fin and finlets are some of the features distinguishing the Nimrod MRA.Mk 4 from earlier versions of the aircraft. (Photo, BAE Systems).

For the rest of this article please see the November 2004 issue.