Originally Posted by
taupo
A jet pilot is welcome to correct me if I'm wrong, but once you go over a certain power setting, the amount of extra power and fuel burn required to go a little faster is significant. I know through personal experience that this is the case in piston engine planes. Drag increases with speed. In my own plane the speed gain from say 60% power to 75% power is not worth the minimal extra speed gained. The 25% increase in power setting equals a speed increase of about 5%, fuel burn increases by about 20%, engine wear increases.
Yes -- drag is proportionate to the
cube of the airspeed. On an aircraft where rolling resistance is not a factor (as it is in a car), that makes rough calculations easy. Slowing down by 10% means that you have reduced energy lost to drag (and thus fuel consumption, as the engine efficiency doesn't that vary much) by 1 - 0.9x0.9x0.9 or 27%.