Winglet effect on wing lift and drag? 4

[TurboTag]

OK, anyone want to take a stab at the effect on wing lift and drag with the addition of winglets. I am looking for an equation or rule of thumb. I have read Kroo's papers and others. I had seen something at one time that said the winglet could be considered to add half its height to the wing span (or something similar). Any and all help appreciated. If you know of a particular NACA or NASA report please cite it.

Thanks, Tim

 

[TheGreatWaldoPepper]

Regarding up and down winglets - the IAI Arava has pretty large winglets both above and below the wing, and this is quite an old design.

 

[Minifloresta]

Winglets are rather interesting. However there is no simple rule to determine if the winglet is beneficial or not.
Our experience with winglets showed that there are many factors involved. At high subsonic speeds care must be taken to avoid local shock waves; the twist, camber and tickness distribution must be carefully designed for maximum efficiency. And it must be optimum at the condition where the performance improvement is needed. If the intention is to increase range, then the optimum condition should be the long range speed; if the intention is to improve takeoff climbout, then the target speed must be something not far from V2.
The most effective and time-saving way of dimensioning winglets is by using a good CFD tool.
And last but not least: winglets do generate a lot of bending moment, not much different from the extra bending moment due to increasing the wingspan by about the same dimension.
We suspect that:
1 - The 747-400 winglet is just cosmetic;
2 - The A330/340 winglets have very little effect;
3 - The A318/319/320/321 winglets are slightly more effective;
4 - The MD-11 has classical winglets that are fairly effective;
5 - The blended winglets on the 737BBJ are the most effective.

 

[TJMF]

Charsat, Don't quite agree that birds don't have winglets. If you look at some birds of prey their wings definitely curve upwards at the ends during soaring - A kind of winglet I would suggest. Blended obviously!