Originally Posted by glekichi
Nobody has tackled the original question of thrust vs lift...
...So.. how much work is required to keep an aircraft in flight?
Every airplane has a lift/drag characteristic (l/d ratio). It's actually a curve, with a maximum value perhaps slightly below cruising speed, but falling off at higher or lower speeds.
It can be determined experimentally by setting the engines to zero thrust and measuring the glide ratio, which is the same thing as l/d.
The work done by the engines is simply F x V (i.e. lbf x ft/sec), where F = drag for stable flight.
Are we getting there?
