The Rolls-Royce Spey (company designations RB.163 and RB.168 and RB.183) is a low-bypass turbofan engine originally designed and manufactured by Rolls-Royce that has been in widespread service for over 40 years. Intended for the civilian jet airliner market when it was being designed in the late 1950s, the Spey concept was also used in various military engines, and later as a turboshaft engine for ships known as the Marine Spey, and even as the basis for a new civilian line, the Rolls-Royce Tay. A licensed version built by the XAEC is known as the WS-9 Qin Ling. Aviation versions of the "base model" have accumulated over 50 million hours of flight time. In keeping with Rolls-Royce naming practices, the engine is named after the River Spey.
In 1954 Rolls-Royce introduced the first commercial bypass engine, the Rolls-Royce Conway, with a 21,000 lbf (94 kN) thrust aimed at what was then the "large end" of the market. This was far too large for smaller aircraft such as the Sud Caravelle, BAC One-Eleven or Hawker Siddeley Trident which were then under design. Rolls then started work on a smaller engine otherwise identical in design, the RB.163, using the same two-spool turbine system and a fairly small fan delivering bypass ratios of about 0.64:1. The first versions entered service in 1964, powering both the 1-11 and Trident. Several versions with higher power ratings were delivered through the 1960s, but development was ended nearing the 1970s due to the introduction of engines with much higher bypass ratios, and thus better fuel economy. Spey-powered airliners continued in widespread service until the 1980s, when noise limitations in European airports forced them from service.
In the late 1950s the Soviet Union started the development of a new series of large cruisers that would put the Royal Navy at serious risk. After studying the problem, the RN decided to respond in a "non-linear" fashion, and instead of producing a series of new cruisers themselves, they would introduce a new strike aircraft with the performance needed to guarantee successful attacks on the Soviet fleet. The winning design was the Blackburn Buccaneer, which had an emphasis on low altitude performance (i.e. to evade enemy radar) as opposed to outright speed.
Flying at low altitude, in denser air, requires much more fuel; the air-fuel mixture in a jet engine needs to be kept very close to a constant value to burn properly, and more air requires proportionally more fuel. This presented a serious problem for aircraft such as the Buccaneer, which would have had very short range unless the engines were optimised for low-level flight. The early pre-production versions, powered by the de Havilland Gyron Junior, also proved to be dangerously underpowered.
Rolls-Royce attacked this problem by offering a militarized version of the Spey, which emerged as the RB.168. The resulting Spey-powered Buccaneer S.2 served into the 1990s. The Spey proved so successful in this role that it was produced under license in the United States as the TF41 and F113, and was used in a number of British and US designs.
The British versions of the McDonnell Douglas F-4 Phantom II F-4K (designated Phantom FG.Mk.1) replaced the 16,000 lb thrust J79 turbojets with a pair of 12,250 lb thrust dry and 20,515 lb thrust with afterburning RB.168-15R Spey 201 turbofans. These provided extra thrust for operation from smaller British aircraft carriers, and provided additional bleed air for the boundary layer control system for slower landing speeds. The air intake area was increased by twenty percent, while the aft fuselage under the engines had to be redesigned. Compared to the original turbojets, the afterburning turbofans produced a ten and fifteen percent improvement in combat radius and ferry range, respectively, and improved take-off, initial climb, and acceleration, but at the cost of a reduction in top speed.
During its lifetime the Spey has garnered an impressive safety record. Its relatively low maintenance costs provide one of the major reasons it continued in service even when newer designs were available. With the need for a 10,000 to 15,000 lbf (44 to 67 kN) thrust class engine starting up again with the removal of the Spey from service, Rolls then used the Spey turbomachinery with a much larger fan to produce the Rolls-Royce Tay, a rather modern design even though its ancestors can be traced to the 1950s.