Hawker Siddeley Nimrod

AEW3

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In the mid-1970s a modified Nimrod was proposed for the [Vous devez être inscrit et connecté pour voir ce lien] (AEW) mission – again as a replacement for the [Vous devez être inscrit et connecté pour voir ce lien]-derived, piston-engined [Vous devez être inscrit et connecté pour voir ce lien].

Eleven existing Nimrod airframes were to be converted by [Vous devez être inscrit et connecté pour voir ce lien] at the former Avro plant at [Vous devez être inscrit et connecté pour voir ce lien] to house the [Vous devez être inscrit et connecté pour voir ce lien] radars in a bulbous nose and tail.

The Nimrod AEW3 project was plagued by cost over-runs and problems with the [Vous devez être inscrit et connecté pour voir ce lien] computer used.

Eventually, the MoD recognised that the cost of developing the radar system to achieve the required level of performance was prohibitive and the probability of success very uncertain, and in December 1986 the project was cancelled.

The RAF eventually received seven [Vous devez être inscrit et connecté pour voir ce lien] aircraft instead.

MRA4


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The Nimrod MRA4 was intended to replace the capability provided by the MR2.

It was essentially a new aircraft, with current-generation [Vous devez être inscrit et connecté pour voir ce lien] turbofan engines, a new larger wing, and fully refurbished fuselage.

However the project was subject to delays, cost over-runs, and contract re-negotiations.

It was cancelled in 2010 as a result of the Strategic Defence and Security Review at which point it was £789 million
over-budget and nine years late.

The prototype aircraft, produced at a cost of over £1bn each, have been scrapped.

Design

The Nimrod is the first jet-powered Maritime Patrol Aircraft (MPA).

Earlier MPA designs used [Vous devez être inscrit et connecté pour voir ce lien] or [Vous devez être inscrit et connecté pour voir ce lien] engines to improve fuel economy and to allow for lengthy patrols at low altitudes, as with the [Vous devez être inscrit et connecté pour voir ce lien].

Jet engines are most economical at high altitudes and less economical at low altitudes; the aircraft can travel to the operational area at high altitude which is economical on fuel and fast compared to earlier piston aircraft.

On reaching the patrol area the Nimrod descends to its working altitude.

On patrol at high weight all four engines are used, but as fuel is consumed and weight is reduced first one and then a second engine is shut down, allowing the remaining engines to be run at an efficient RPM rather than running all engines at less efficient RPM.

A "rapid start" system is fitted should the closed-down engines need to be restarted quickly; instead of relying only on ram air for restarting an engine, compressor air from a live engine is used in a starter turbine which rapidly accelerates the engine being started.

All engines are used for travel back to base at high altitude.