Thrust-specific fuel consumption: Difference between revisions

m (LordOfPens moved page Thrust specific fuel consumption to Thrust-specific fuel consumption: Missing hyphen in compound modifier)
SFC varies with throttle setting,altitude and climate. For jet engines, flight speed also has a significant effect upon SFC; SFC is roughly proportional to air speed (actually exhaust velocity), but speed along the ground is also proportional to air speed. Since work done is force times distance, mechanical power is force times speed. Thus, although the nominal SFC is a useful measure of fuel efficiency, it should be divided by speed to get a way to compare engines that fly at different speeds.
For example, [[Concorde]] cruised at 1354&nbsp;mph, or 7.15 million feet per hour, with its engines giving an SFC of 1.195&nbsp;lb/(lbf·h) (see below); this means the engines transferred 5.98 million [[foot pound]]s per pound of fuel (17.9 MJ/kg), equivalent to an SFC of 0.50&nbsp;lb/(lbf·h) for a subsonic aircraft flying at 570&nbsp;mph, which would be better than even modern engines; the [[Rolls-Royce/Snecma_Olympus_593|Olympus 593]] used in the Concorde was the world's most efficient jet engine.<ref>[ Supersonic Dream]</ref><ref>"[ The turbofan engine]", page 5. ''[[SRM UniversityInstitute of Science and Technology]], Department of aerospace engineering''</ref> However, Concorde ultimately has a heavier airframe and, due to being supersonic, is less aerodynamically efficient, i.e., the [[lift to drag ratio]] is far lower. In general, the total fuel burn of a complete aircraft is of far more importance to the customer.