winglets

bLizZuE

bLizZuE

Calling for engine starts en français
So I've got this ground school instructor who claims that winglets create forward lift (thrust) due to the way they're installed. Claiming they are airfoils, and thus are capable of creating lift.

I've always seen them just as ways of reducing wing-tip vortices.

Comments?
 
Just because they're attached to the wing doesnt mean they "reduce" wingtip vortices. They just use them to their advantage to reduce drag.

Usually the vortex increases drag by the downwash it produces. By placing the winglet on the tip, it combines with the free airstream which results in somewhat of an angled flow.

By doing this there is a lift vector provided which acts perpindicular to the local airstream therefore producing a vector that is pointed forward.

Just remember that the winglets still produce a parasite drag penalty and added weight to the wing.

So, I'd say your instructor was right!

(how'd I do tgrayson?)
 
heh, I researched a little and found this

"Winglets, which are airfoils operating just like a sailboat tacking upwind, produce a forward thrust inside the circulation field of the vortices and reduce their strength. Weaker vortices mean less drag at the wingtips and lift is restored. Improved wing efficiency translates to more payload, reduced fuel consumption, and a longer cruising range that can allow an air carrier to expand routes and destinations."

from: http://www.nasa.gov/centers/dryden/about/Organizations/Technology/Facts/TF-2004-15-DFRC.html
 
meritflyer said:
(how'd I do tgrayson?)
Click to expand...

Flawless. :)

bLizZuE is probably thinking they function as end plates. An effective end plate would have to be much larger than a winglet and would produce a lot more weight and drag penalty than a winglet, rendering them useless.

The end plate effect is only useful when the "plate" must be there regardless. For instance, twin vertical stabilizers on many aircraft will function as end plates on the horizontal stabilizer.
 
Nah see, I've never heard of end plates. Your description makes sense, but have never heard the term.
 
Exactly!

The reduction of vorticy does happen, but it is a result of the rest, and not the cause of the increased efficiency.

Incidentally, the MD11 winglets are 9' from the top of the upper to the bottom of the lower.
 
bLizZuE said:
Winglets, which are airfoils operating just like a sailboat tacking upwind, produce a forward thrust inside the circulation field of the vortices and reduce their strength. Weaker vortices mean less drag at the wingtips and lift is restored.
Click to expand...

The description offered by MeritFlyer is accurate and in all the aerodynamic books that discuss the subject. The NASA page is concurring when it says
Winglets, which are airfoils operating just like a sailboat tacking upwind, produce a forward thrust inside the circulation field of the vortices
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but creates what I consider to be an "attractive nuisance" when it follows with what appears to be a non sequitur
and reduce their strength
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Are these two opposing views?

I don't think so. Take a look at what Richard T. Whitcomb, the inventor of the winglet said in NASA Technical Note D8264.
Induced drag is, of course, directly related to the total energy of the crossflow circulation. Thus, the induced drag reduction caused by the addition of the winglets must result from a diminishing of this energy. (See ref. 10.) This energy reduction is associated primarily with the marked reduction of the measured high crossflow velocities near the vortex center for the configuration with the basic tip. Analyses indicate that the primary mechanism by which the reduction of the drag force on the model is accomplished is the forward inclination of the side-force vectors on the winglets resulting from the local crossflows. The reduction is also conjectured to be caused by a small decrease in the downwash of the flow approaching the wing. Link: http://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/19760019076_1976019076.pdf


​
So what appears to be the case is that the vortex velocities are reduced in proportion to the lift being generated by the winglet. What this says to me is that the two explanations are essentially the same; however, the forward pointing vector has the advantage that it demonstrates how the reduction occurs.
 
So what about wingtip fences like on Airbus planes are they less effective then winglets? And are raked wingtip extension more effective then the classic winglet design?

Enquiring minds would like to know!
 
Maximillian_Jenius said:
So what about wingtip fences like on Airbus planes are they less effective then winglets?
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Yes, they are less effective. Airbus wanted to add winglets to an updated A320, but has since claimed that they would have to strengthen the wings and this will add enough weight that the winglets would not add any efficiency. There is speculation that with the A380 and A400 eating Airbuses lunch, they probably don't have the engineering capacity to spare and just made the weight problem up as an excuse not to introduce winglets in the near future.
 
ananoman said:
Yes, they are less effective. Airbus wanted to add winglets to an updated A320, but has since claimed that they would have to strengthen the wings and this will add enough weight that the winglets would not add any efficiency. There is speculation that with the A380 and A400 eating Airbuses lunch, they probably don't have the engineering capacity to spare and just made the weight problem up as an excuse not to introduce winglets in the near future.
Click to expand...

Well, not sure, but winglets DO add a lot of wing bending moment. We have speed limitations with the tips tanks less tha full due to that issue. I would not be surprised at all that a retrofit might not add enough over the current tips to make up for what it would take to compensate for the bending moment.
 
Re: Winglet Thread #2

I like Boeing's thoughts on winglets however, I feel like they dont touch on a few key points about a winglets funtion.
 
Re: Winglet Thread #2

My dad always asks me what the winglets do and I just tell him that it reduces drag.

I don't understand it in depth yet but I see if at stoping the over flow of low pressure seeking high pressure.
 
Re: Winglet Thread #2

Champcar said:
My dad always asks me what the winglets do and I just tell him that it reduces drag.

I don't understand it in depth yet but I see if at stoping the over flow of low pressure seeking high pressure.
Click to expand...
On a normal wing the wingtip vortices accumulate at the tip of the wing, causing induced drag on a portion of the wing causing that part of the wing not to produce any net lift.
Winglets move the vortices to the very tip of the winglet, allowing the entire surface of the wing to produce lift. It's like getting extra wing without any additional weight (except for what the winglet weighs) and without redesigning the entire wing. Winglets also change the patterns of the wingtip vorticies, spreading them out and reducing the kinetic energy the vortices have and that also reduces drag.
 
Re: Winglet Thread #2

I'm a dumbass. I thought the original winglet thread was in CFI corner, but it's in Technical Talk. Can a mod merge this thread to the other one?
 
Re: Winglet Thread #2

SpiraMirabilis said:
On a normal wing the wingtip vortices accumulate at the tip of the wing, causing induced drag on a portion of the wing causing that part of the wing not to produce any net lift.
Winglets move the vortices to the very tip of the winglet, allowing the entire surface of the wing to produce lift. It's like getting extra wing without any additional weight (except for what the winglet weighs) and without redesigning the entire wing. Winglets also change the patterns of the wingtip vorticies, spreading them out and reducing the kinetic energy the vortices have and that also reduces drag.
Click to expand...

???

I will respond to this once I have some more time.

I immediately see a few "misconceptions" with this idea.

Stay tuned.
 
I saw some winglets on a NWA 757 here in LAS the other day. :) They look pretty effing sweet on the 75s .
 
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