Most efficient wing...

[south coast]

I have been having a debate with a friend about the most efficient wing...and by that I mean the best lidt to drag ratio.

I was under the impression, the most effective and efficient wing is a clean wing.

The lift created by a clean wing also generates x amount of drag.
Now, when trainling edge flaps are deployed, I understand that lift is increased, and that drag is also increased.

Question: Is the increase in lift and drag giving the wing with flaps down a better lift to drag ratio, better efficieny , than that of a clean wing.

P of F buffs needed on this one....

Thanks

[Penworth]

I'm far from being an expert on PoF, but surely if the lift to drag ratio was greater with the trailing edge flaps extended, then there would be no incentive to have them retracted in cruise flight (structural limitations notwithstanding)?

As far as I understand it, the lift does increase with flaps extended (hence the reason for extending them) but the drag increases more.

PW

[Cabotage Kid]

Clean wing is best. Induced Drag is increased with an increase in Coeff of Lift. CL increases with increased camber and wing area - e.g. flaps deployed. If you extend flaps then both lines (induced and profile) on the drag curve move up and left. So Vimd (best lift/drag speed) reduces but more power is required to maintain Vimd as the overall drag has increased.