Editing Frank Whittle (section)

===Continued impact===
[[File:GE J-31 Turbojet Engine.jpg|thumb|A cutaway [[General Electric J31]] (I-16) turbojet engine based on the [[Power Jets W.1|W.1]]/[[Power Jets W.2|W.2B]]]]

Whittle wanted to improve the efficiency of the jet engine at lower speeds.  According to Whittle, "I wanted to 'gear down the jet', ie to convert a low-mass high-velocity jet into a high-mass low-velocity jet. The obvious way to do this was to use an additional turbine to extract energy from the jet and use this energy to drive a low-pressure compressor or fan capable of 'breathing' far more air than the jet engine itself and forcing this additional air rearwards as a 'cold jet'. The complete system is known as a '[[turbofan]]'."  The first embodiment was referred to as a No 1 Thrust Augmentor, which consisted of an "aft fan", or additional turbine, in the exhaust of the main engine. In 1942, No 2 Augmentor, a conventional two-stage system with the fan blades external to the turbine blades, was used by GE in the [[Convair 990 Coronado]]. A No 3 Augmentor, known as the "tip turbine", had the turbine blades outside the fan. A No 4 Augmentor, in combination with the W2/700, included an [[afterburner]] and was the design powerplant for the [[Miles M.52]] project.  According to Whittle, "The first attempt at the turbofan proper, ie having the fan ahead of and supercharging the core engine, was the LR1 intended as the power plant of a four-engined bomber for operations in the Pacific. The mass flow through the fan of the LR1 was to have been 3–4 times that through the core engine, ie the '[[bypass ratio]]' was 2–3."  Filed in March 1936, Whittle's main turbofan patent 471368, expired in 1962.{{sfn|Golley|1987|pp=262–264}}

Whittle's work had caused a minor revolution within the British engine manufacturing industry and, even before the E.28/39 flew, most companies had set up their own research efforts. In 1939, [[Metropolitan-Vickers]] set up a project to develop an axial-flow design as a [[turboprop]] but later re-engineered the design as a pure jet known as the [[Metrovick F.2]].{{sfn|Golley|1987|p=180}} Rolls-Royce had already copied the W.1 to produce the low-rated WR.1 but later stopped work on this project after taking over Rover's efforts.{{sfn|Golley|1987|p=187}} In 1941, de Havilland started a jet fighter project, the Spider Crab&nbsp;– later called [[de Havilland Vampire|Vampire]]&nbsp;– along with their own engine to power it,{{sfn|Golley|1987|p=179}} [[Frank Halford]]'s [[de Havilland Goblin|Goblin]] (Halford H.1). [[Armstrong Siddeley]] also developed a more complex axial-flow design with an engineer called Heppner,{{sfn|Golley|1987|p=180}} the [[Armstrong Siddeley ASX|ASX]] but reversed Vickers' thinking and later modified it into a turboprop instead, the [[Armstrong Siddeley Python|Python]]. The [[Bristol Aeroplane Company]] proposed to combine jet and piston engines but dropped the idea and concentrated on propeller turbines instead.{{sfn|Golley|1987|p=180}}