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The relevance for gas turbine-powered aircraft is the use of a secondary jet of air with a propeller or, for jet engine performance, the introduction of the bypass engine. The overall efficiency of the jet engine is thermal efficiency multiplied by propulsive efficiency ( η o = η t h η p r {\displaystyle \eta _{o}=\eta _{th}\eta _{pr}} ).
Jet airliners became 70% more fuel efficient between 1967 and 2007, [49] 40% due to improvements in engine efficiency and 30% from airframes. [50] Efficiency gains were larger early in the jet age than later, with a 55-67% gain from 1960 to 1980 and a 20-26% gain from 1980 to 2000. [45]
Aircraft engine performance refers to factors including thrust or shaft power for fuel consumed, weight, cost, outside dimensions and life. It includes meeting regulated environmental limits which apply to emissions of noise and chemical pollutants, and regulated safety aspects which require a design that can safely tolerate environmental hazards such as birds, rain, hail and icing conditions.
Thrust-specific fuel consumption (TSFC) is the fuel efficiency of an engine design with respect to thrust output. TSFC may also be thought of as fuel consumption (grams/second) per unit of thrust (newtons, or N), hence thrust-specific.
The efficiency of turbojet engines was still rather worse than piston engines, but by the 1970s, with the advent of high-bypass turbofan jet engines (an innovation not foreseen by the early commentators such as Edgar Buckingham, at high speeds and high altitudes that seemed absurd to them), fuel efficiency was about the same as the best piston ...
A corollary of this is that, particularly in air breathing engines, it is more energy efficient to accelerate a large amount of air by a small amount, than it is to accelerate a small amount of air by a large amount, even though the thrust is the same. This is why turbofan engines are more efficient than simple jet engines at subsonic speeds.
A CFM56-3 series engine mounted on a Boeing 737-400 airliner showing flattening of the nacelle at the bottom of the inlet lip. The first derivative of the CFM56 series, the CFM56-3 was designed for Boeing 737 Classic series (737-300/-400/-500), with static thrust ratings from 18,500 to 23,500 lbf (82.3 to 105 kN). A "cropped fan" derivative of ...
The Pratt & Whitney JT8D is a low-bypass (0.96 to 1) turbofan engine introduced by Pratt & Whitney in February 1963 with the inaugural flight of the Boeing 727.It was a modification of the Pratt & Whitney J52 turbojet engine which powered the US Navy A-6 Intruder and A-4 Skyhawk attack aircraft.