The basic design of the Rolls-Royce Military Spey Mk202 engine originates from the commercial Spey Mk5l1 and Mk512 engines. These commercial engines were fitted in the BAC 1-11, Gulfstream 2 and 3 and Trident aircraft and were fitted with a 5 stage low pressure (LP) compressor and a larger turbine relative to the earlier lower thrust Mk505 (Trident), Mk506 (BAC1-1l) and Military Mk101 (Buccaneer) engines fitted with 4 stage LP compressors.
The original Spey Mk202 engine was developed from these improved Mk511 and Mk512 engines for the RAF and Royal Navy McDonnell Douglas Phantom aircraft, the most obvious change being the addition of reheat to produce 20,500 lbs thrust.
The Spey Mk203 had the same basic engine configuration as the Spey Mk202 but had a modified reheat control system designed to give faster reheat light-up time. A common misconception is that this facility was to assist the Navy Phantoms in which the engine was fitted, to take off from aircraft carriers. This is not the case as the maximum thrust rating of the Mk205 is identical to that of the Mk202. The Spey Mk203 reheat system provided a quicker reheat light-up to cover the event of aborted landings on aircraft carriers.
Further development of the Spey Mk202 concentrated primarily on reliability and life improvement modifications to the standard engine. Production engines fitted with a package of these modifications would eventually have been introduced into service as the Spey Mk205, however no engines were ever produced which carried a Spey Mk205 nameplate. Some existing Spey Mk202s were fitted with some of these reliability and life improvement modifications on a "special order only" basis. "Spey Mk205" has become a convenient label to describe those Spey Mk202 engines which were built with these modifications incorporated.
The most significant life improvement introduced by these modifications was in the turbine area of the engine by the use of more advanced materials. This improvement in material properties means that some of the life of the material can be traded off for more thrust if required. This additional thrust is achieved by allowing the engine to run at a higher turbine temperature, enabling more fuel to be added to the engine by the fuel control system and thus more power to be produced by the engine. A significant point to note however is that, even with improved materials, a small increase in the permitted running temperature within the turbine results in a drastic reduction in component life. Fortunately the life required from the engines in Thrust SSC will only be a small fraction of the 1000 hour life required for RAF service for the Phantom.
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