porterjet wrote:If drag with flaps at low speeds is such a big deal why don't you see 747's starting the takeoff with 0 flaps, then extending them starting at some speed that would give them TO flaps by the time they reach Vr?
Because 747's are not intended to be operating out of short strips
Because 747's have a very large amount of excess thrust
Because 747 crews have too many other things to manage during a takeoff roll
Because 747's don't have propeller blast over the flaps to create extra drag
(there is a gap between the flaps for the engine exhaust and bypass air so it doesn't blow the flaps off the wing)
Unfortunately I'm not an aero engineer, but if there are any trained aero's here perhaps they could calculate the reduction in takeoff distance a 747 would enjoy if it were mechanically possible
to wait until rotation speed and deploy the flaps instantly (like you can do on a Pacer). I'll bet it's several hundred feet.
With all due (and sincere) respect to the professional jet pilots on this group, I think the more relevant question is... why do so many old grizzly bush pilots feel that this technique shortens their takeoff distance?
A significant number of pilots who do not use this flap technique may be making that choice not because it doesn't work, but because of other safety and control factors (visibility, directional control, pilot restraint system)... for which there is now a good solution... ahem