Different types of winglets?
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Different types of winglets?
Just want to know are there any differences between each types of winglets? eg: A319/20 comapre to the A346? or even the B738 and B744! Also the new 787's?
Thanks.
Thanks.
Different size, different weight, different shape, different part number, different materials, different colour. But all intended to do the same thing - save money. Whether or not they do, depends.
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Most assuredly
Winglets convert Drag associated with tip vortices to a small amount of lift. The aerodynamics are complicated and the fixture is expensive, but in directing some of the turbulence to the outboard portion of the winglet, a small amount of otherwise wasted burble "pushes up" the canted underside and can save as much as three percent in Fuel costs. For you Nascar fans, it is similar to "drafting" only it is drafting itself instead of another vehicle.
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I have often wondered - the winglet has the effect of moving the spanwise center of lift outboard on the wing, and thus increases the bending stresses in the centersection/wingbox area.
Surely this is accounted for in the max ZFW calculation - ??
Surely this is accounted for in the max ZFW calculation - ??
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No
The Span is not effectively increased, that increase in Aspect Ratio would harm the performance of the wing itself, increasing drag. That is why the Winglet is canted steeply, the newly captured lift is not based on chord, but the pounding it takes from the displaced Vortex. Think Vortex Generator in reverse. Picture a VG, then picture the flow going backwards, "collecting" on the VG and providing lift. Zero Fuel Weight of course is increased, but the net is a positive product from the Dynamics of Flight.
(Plus, they look marvelous)
Airfoilmod
(Plus, they look marvelous)
Airfoilmod
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Wing
The fact that it is called a Winglet instead of a wing tip, is instructive. Everything about aviation is expensive, and margins are tight in construction as well as at the Gate. Even the selection of a new word costs money. So though it is attached at the end of the wing, it isn't invested with the same purpose, exactly. Is it useful? Does Bill Boeing spin in his grave at the cost sheet? Of course they work. Different aircraft, different wings, different Winglets. They save Fuel because they convert some useless Drag into Lift, producing a well considered cost benefit.
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The aerodynamics are complicated but lets not simplify it so much as to get the explanations wrong.
Winglets do increase the aspect ratio by increasing the effective span while not increasing the physical span of the wing. They have the same effect as raked wing tips which aren't canted and are what Boeing has opted for in the 747-8. Ideally aircraft would have very long thin wings but this causes nightmares for the structural engineers and makes for bigger hangers/ground handling problems etc.
By increasing the span you reduced the spanwise flow of air which flows from the bottom surface to the top around the wingtips. This flow of air causes tip vortices which while pretty, increase the induced drag. Winglets reduced that flow by increasing the aspect ratio, reducing the size/strength of the tip vortices and thus reducing the induced drag.
They don't capture lift or produce lift in the vertical sense themselves, however due to the decreased downwash behind the wing there is small increase in lift produced by the wing - which in reality then increases the lift induced drag again!. They also increase the parasitic drag and they do produce a small amount of apparent thrust. These factors along with the structural/weight implications offsets some the gains and makes it a bit of a balancing act to give the best improvements.
And with that in mind..back to the original question: Winglets/Wingtip fences/raked wingtips while structurally different are all various solutions to the same problem of wing tip vortices and induced drag.
Winglets do increase the aspect ratio by increasing the effective span while not increasing the physical span of the wing. They have the same effect as raked wing tips which aren't canted and are what Boeing has opted for in the 747-8. Ideally aircraft would have very long thin wings but this causes nightmares for the structural engineers and makes for bigger hangers/ground handling problems etc.
By increasing the span you reduced the spanwise flow of air which flows from the bottom surface to the top around the wingtips. This flow of air causes tip vortices which while pretty, increase the induced drag. Winglets reduced that flow by increasing the aspect ratio, reducing the size/strength of the tip vortices and thus reducing the induced drag.
They don't capture lift or produce lift in the vertical sense themselves, however due to the decreased downwash behind the wing there is small increase in lift produced by the wing - which in reality then increases the lift induced drag again!. They also increase the parasitic drag and they do produce a small amount of apparent thrust. These factors along with the structural/weight implications offsets some the gains and makes it a bit of a balancing act to give the best improvements.
And with that in mind..back to the original question: Winglets/Wingtip fences/raked wingtips while structurally different are all various solutions to the same problem of wing tip vortices and induced drag.
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The Reason
I used words like "effectively increased" and "increasing drag" to purposely avoid a word parsing contest. Nothing you write contravenes my description; your excellent journey is a different path to the conclusion at which you arrive, virtually verbatim of mine. You left out a great deal as I did; I did so purposely. An even simpler result is to say that winglets aren't about "wing" lifting, but "drag" reduction.
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Apologies if I've missed the gist of your posts and started word picking, its tempting to start picking holes with wording when you're dealing with technical subjects.
But I did take issue with Post #6 where you mentioned the span not effectively being increased and an increase in aspect ratio harming the performance of the wing and increasing drag. In fact the reality is quite the opposite! The description that followed regarding the effect of the canted surface and it capturing lift I also felt was wrong..not least because you get get the same effect of a winglet without canting it and instead extending the wing and raking the wingtip.
Maybe I am not reading your description in the right way. This is an open forum and I'm sure others will correct if I'm wrong. I do agree our conclusions are much the same and any where else I probably wouldn't have taken issue, but this being Tech Log I thought I would make an attempt at a technical answer if possible!
But I did take issue with Post #6 where you mentioned the span not effectively being increased and an increase in aspect ratio harming the performance of the wing and increasing drag. In fact the reality is quite the opposite! The description that followed regarding the effect of the canted surface and it capturing lift I also felt was wrong..not least because you get get the same effect of a winglet without canting it and instead extending the wing and raking the wingtip.
Maybe I am not reading your description in the right way. This is an open forum and I'm sure others will correct if I'm wrong. I do agree our conclusions are much the same and any where else I probably wouldn't have taken issue, but this being Tech Log I thought I would make an attempt at a technical answer if possible!
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Wazzoo
I also took exception to your comment that winglets don't produce lift by themselves; though that isn't their intention or purpose they certainly do produce lift. In a way that will explain why it isn't helpful to say wingspan is increased with their installation. If a wing is 30 meters in span to the point of winglet attachment and the winglet is 1 meter in length and canted at 77 Degrees, is the span 31 meters? Yes. And No. In plan view, the span is 30.17 meters, the dihedral of the wing with winglet is two separate values, and this assembly will derive lift from both wing and winglet. Likewise Aspect Ratio. It is increased, but because the winglet cants, it is less than what it would be had the wing simply been increased in length by the length of the winglet without the cant. I think we see the same thing in mildly differing perspective. I may have been cautious unnecessarily, if I have offended anyone, I apologize. Regards, Bill
