Originally Posted by
Farjer
Probably a silly question, but is it possible to save fuel on a long-haul flight by slowing down a bit? You can do this in a car on a motorway, but I'm not sure how this works up in the air... obviously you have to avoid the falling-out-of-the-sky problem.
thanks,
Farjer.
Yes, slowing down does help save gas. Increasing cruise speed increases the drag associated with higher Mach numbers.
757 and 767-200 most efficient cruise is .78. 767-300 is .78-.79. Most airliners fly the 757 at .79-.80 and the 767's at .80 in my experience.
Slowing the .01 Mach only saves about 100-200 pounds per hour. Increasing above .81 becomes more and more inefficient.
757 wing is very speed critical for optimum cruise altitude. 767-200 is less so(above .82) and 767-300 not at all(until above .845 Mach when OPT ALT starts to change).