"I’m not sure they produce no bending moment. They add to the mass of the wing so I would think the bending moment is increased to some degree. The bending moment does not occur at the wing tip, but at the wing root."

This would give relief to the wing bending moment.!!

winglets
 

hello all,
just some more info,

1) winglets are angled so that they have a forward resultant (b737ng), opposed to wingfences(A320) that are not.

2) there are models (i don't recall which ones) that have both, upwards winglets and smaller downward winglets mounted just aft of the upwards ones, on the same wingtips.

3)winglets by their additional weight & momentarm, should give some bending relief at the wingroot, same as fuel in wingtanks & underslung pod engines do.
(b737, A320, A330,etc.)

4)fuel savings btw. 2 & 4%, depending on aircraft utilisation.

5) expressed in formulae: winglets artificially increase the AR( aspect ratio)

AR= b/cm = b2/S : b.b=b2 & cmxb= S
b= wingspan in m(meters) & cm = wingchord in m(meters), S= wingarea in square meters.

also cdi(induced drag coefficient)= cl square /pi. AR. e

cl= liftcoefficient, pi = 3.14, e= efficiency factor(real wing is not identical to a prandtl wing, which has an optimal elliptical winglift distribution à la spitfire). remember adolf galland,famous ace & chiefpilot of luftwaffe,(wwar 2), asked by goering(infamous nazi luftwaffe airmarshal), what he needed to beat the RAF(Royal Air Force):" herr goering, give me a spirfire!" goering went krimp & almost swallowed his marshalbaton.

AR being below the fraction line we can see that if AR increases, then cdi or induced drag decreases.

Average total 4,5% on 737NG and 5,0 % on B757

M

The MD-11 springs to mind, though in its case the small downward winglet seems just slight forward of the large upward one for leading edge, so trailing edge is far forward.
see:
http://www.airlinercafe.com/Walkarou...let%20Stbd.JPG

Agreed that the effective AR increases, which is akin to saying the spanwise centre of lift has moved outboard, isn't it?

In that case the centresection bending moment has increased, hasn't it?

:confused:

Thanks for all great answers & i appreciated your corporation

757 with winglets!
 

i have only seen them in shannon.

that is the ultimate beauty of an airplane!!!

the 737-800 with winglets is great but the 57 is the top of the top.