Winglets?

[PETIGRAM]

Great article in this months AERO about winglets.

It appears from the runway length limit diagram that winglets will not provide any increase in runway length take off performance on the 737 until lenghts above 6000'. I would think that the slow flight regime would be an area that you would expect performance to benefit.

Any winglet experts out there care to comment?

[Keith.Williams.]

Grew,

Winglets reduce the (apparent) induced drag by producing a small amount of thrust. They do this by reacting with the wing tip vortex flow, such that their total reaction is angled slightly forwards.

Because their angle is fixed they can be most efficient in only one, fairly narrow part of the speed range. So to get the best from them they are tuned to the cruise, where the aircraft spends most of its time.

I'm surprised to hear that they do much at all during the take-off run, but then designers contiue to improve things.

Today's conventional wisdom soon becomes tomorrows old wives tales (I hope that's not being too sexist)