Do winglets produce thrust?

Anyone?

That's against the laws of thermodynamics. If you can make a passive device produce thrust you should rule the world with your new perpetual motion machine! At best it reduces losses.

Winglets produce lift, with a vector. The vector direction can be perpendicular to the winglet surface, fwd or aft. That is dependant on how it is shaped and mounted. A lift vector facing the nose (fwd) being called thrust might be a mishmash of terms, but it happens. I usually think of thrust as a motive force acting on the vehicle. Winglet vectors are recovery of lost energy by reshaping flow to our advantage. Good idea, yes, thrust...... probably not a really good description of what is happening........

Yes

No.

Provided the thrust of the winglets is not higher than the drag of the other part of the glider, that's not (and of course the winglet thrust is only a few % of the glider drag)

Not thrust in the same way as a propulsion system, but winglets generally do produce a lift vector that has a spanwise and a chordwise component. Since the flowfield at the wingtip is angled inward, the winglet has an incidence angle that is slightly outward-facing

Look at it from another point of view. If all forces are balanced and winglets are added, drag is reduced. Then velocity increases until the thrust/drag forces are equalized. The result of increased velocity is additional lift. The horizontal component of the lift vector is thrust, which increases as lift increases. Ergo, winglets produce thrust. ;>

LittleJohn Madison, AL

This has to be winter RAS debate bait, right Bob?

For those of you responding in the affirmative, park the nearest winglet-equipped glider on the runway on a still day and measure the 'thrust' being produced by those puppies. Be careful not to stand in front of the wing when you do it. <wink>

Winglets reduce induced drag by effectively making the wingspan longer.

I've never seen anyone argue convincingly that a half a meter of vertical wingspan does anything that couldn't be done equally well with an extra half meter of normal wingspan. On the other hand winglets are worse than span in that they don't produce lift in a useful direction, and they are harder to make strong and rigid than ordinary span is.

If it wasn't for class rules limiting winspan I don't think anyone would have winglets.

But the spar does not have to deal with the extra lift on a *long* moment arm. Well not all of it anyway.

I wonder what class rules the 744 design has in mind

The winglet holder in my Cobra trailer comes with a bungee cord to keep the winglets in place. I have noted that whenever I leave the bungee off, the winglets wind up in all imaginable places inside the trailer. Thus, I would conclude, that they do indeed produce thrust.

Yes.
The winglet produces a net aerodynamic vector which is inclined slightly forward, producing a slight forward thrust, thus reducing the net drag of the wing. This is possible because on top of the wing at the wing tip the air is flowing slightly inboard, so a carefully placed airfoil can thrust slightly forward. See B. McCormick, "Aerodynamics, A, & FD".
The root wing bending moment is influenced by the winglet just as if were an extension of the wing (more span). Bending moment relief is not a reason for using a winglet.

I know an aircraft designer, Martin Hollman, AircraftDesigns.com, who considers winglets only functional excuse is a place to put vents for fuel tanks.