Winglets - Benefit?
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Grapes,
I've heard figures of 10% being quoted for well designed winglets - whether they actually work is another thing! During my degree, however, the principle has been explained to me and it seems fesable. Only of real benefit to an a/c in the cruise, and thus, better fitted to aircraft with long ranges.
As for the 777, I don't really know why winglets are not used - this is something I have thought about myself. However, it must be appreciated that the 747 wing design is 1960's technology, whilst te 777 is very much later - prehaps thats the key?? Anyone know?
Cheers,
Cuban_8
I've heard figures of 10% being quoted for well designed winglets - whether they actually work is another thing! During my degree, however, the principle has been explained to me and it seems fesable. Only of real benefit to an a/c in the cruise, and thus, better fitted to aircraft with long ranges.
As for the 777, I don't really know why winglets are not used - this is something I have thought about myself. However, it must be appreciated that the 747 wing design is 1960's technology, whilst te 777 is very much later - prehaps thats the key?? Anyone know?
Cheers,
Cuban_8
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Currently having winglets installed on the BBJ I fly. Boeing is claiming approx 7% improvement in range. I'm looking forward to making some direct comparisons myself and to see whether this is all hype. Mind you for a mod costing $1.5m thats a lot of fuel to burn before your benefit kicks in!
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While I do not know for sure, I suspect the reason they didn't put winglets on the 777 had to do with the fact that it was designed to be efficient in short-haul markets as well as long haul. They increased the span instead, which nets benefits in both short and long haul, as opposed to the long haul benefits of winglets. There has been talk of adding winglets to the 777 for future aircraft designed exclusively for ultra-long haul.
As to the new super-critical wing, the 777 has it, but then, so do the A-330/340, etc., and they do have winglets as well.
As to the new super-critical wing, the 777 has it, but then, so do the A-330/340, etc., and they do have winglets as well.
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GJB,
Agree totally with your point. The fact is that winglets are an experimental development by the manufacturers. Thus, the likelyhood of obtaining any conclusive information on their performance from them is slim!!
I remember reading an article some months ago (in Airliner World or something) that showed a BA 744 operating with one winglet! From that, I imagine that the effect of the winglet could not be very significant!
Cheers,
Cuban_8
Agree totally with your point. The fact is that winglets are an experimental development by the manufacturers. Thus, the likelyhood of obtaining any conclusive information on their performance from them is slim!!
I remember reading an article some months ago (in Airliner World or something) that showed a BA 744 operating with one winglet! From that, I imagine that the effect of the winglet could not be very significant!
Cheers,
Cuban_8
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I don't have the numbers handy, but for the MD-11 the lack of even a lower winglet adds a fair amount. Sure, you can operate that way, but you must take into account the increased fuel burn. The numbers are well known and contained in the configuration deviation list (CDL) which is FAA approved in the U.S. by the FSB and FOEB process. The MMEL is also created in this way, and these docs are adopted by most operators around the world.
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From memory the MEL permits removal of winglet(s) off the B744 for dispatch with a minimal fuel penalty. And the marketing of the component has always been that it stops spanwise flow and spillage of air from the airfoil to reduce wing tip vortices, but perhaps the biggest driver for thier use is keeping up with the competitor (airbus) and that their use is more for cosmetic rather than truely performance reasons - ie manufacturer seen to be updating a design?
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Its life Jim, but not as we know it!!
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Its life Jim, but not as we know it!!
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Winglets are only useful in the long range cruise. But what about the approach? Do they actually reduce wingtip vortices at all? Interesting to note that the 747-400SR(short range) does not have these winglets fitted- so i'm guessing the cruise length would be the determining factor.
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JL,
Winglets (or wingtip sails) do not actually reduce the strength of the trailing vorticies. The vortex strength related to the wing lifting vortex, which in turn is related to the lift generated by the wing. There is nothing that can be done to reduce the trailing vortex strength - bar changing the shape of the wing planform.
Winglets take advantage of the local flow induced at the wingtips by the trailing vortex and use it to both create extra lift and create thrust (believe it or not!). This is how the extra efficiency is achieved. Further, they operate best in steady flow conditions, and thus, are best installed onto aircraft that cruise for long periods of time. For short range aircraft, I can't really see a point in installing them.
Although I have no doubt that they do work to a degree, I'm inclined to agree with tagaroo in that they are probably there for show as much as function - especially when you consider the fact that SOP allows individual sails to be removed. However, I am not an airline pilot, and I may very well be totally wrong!
Cheers
Cuban_8
Winglets (or wingtip sails) do not actually reduce the strength of the trailing vorticies. The vortex strength related to the wing lifting vortex, which in turn is related to the lift generated by the wing. There is nothing that can be done to reduce the trailing vortex strength - bar changing the shape of the wing planform.
Winglets take advantage of the local flow induced at the wingtips by the trailing vortex and use it to both create extra lift and create thrust (believe it or not!). This is how the extra efficiency is achieved. Further, they operate best in steady flow conditions, and thus, are best installed onto aircraft that cruise for long periods of time. For short range aircraft, I can't really see a point in installing them.
Although I have no doubt that they do work to a degree, I'm inclined to agree with tagaroo in that they are probably there for show as much as function - especially when you consider the fact that SOP allows individual sails to be removed. However, I am not an airline pilot, and I may very well be totally wrong!
Cheers
Cuban_8
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Cuban_8 - good post. I have been wondering about the benefits of winglets for a while (being a PP with less than 100 hours, I still want to learn everything! 
)
I was wondering - how do the winglets improve thrust? For that matter, can anyone explain the physics behind the winglet? What the advantage is, why it works to increase lift (I have an idea) and thrust (lost on that one)?
Thanks! =)
)I was wondering - how do the winglets improve thrust? For that matter, can anyone explain the physics behind the winglet? What the advantage is, why it works to increase lift (I have an idea) and thrust (lost on that one)?
Thanks! =)
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Plap;
At the wing tip the pressure difference between the upper and lower surface MUST be equal to zero, this means that there is a varying pressure distribution along the wing span, hence the formation of the trailing vorticies. Consequently, the flow has a velocity component along the spanwise direction (towards the fuselage on the upper surface) therefore the local flow direction at the wing tip is NOT perpendicular to the mean free stream flow but acutally flows inboard. Winglets, or wingtip sails, attempt to take advantage of the fact that the local flow direction at the wingtip is not perpendicular to the free stream flow. Acting as small aerofoils, there is an effective angle of attack between the local flow direction and the winglet. This leads to a resultant aerodynamic force with a component in the direction of motion - hence the 'thrust' or reduction in drag.
Hope this helps,
Regards
ASI
[This message has been edited by ASI (edited 08 March 2001).]
At the wing tip the pressure difference between the upper and lower surface MUST be equal to zero, this means that there is a varying pressure distribution along the wing span, hence the formation of the trailing vorticies. Consequently, the flow has a velocity component along the spanwise direction (towards the fuselage on the upper surface) therefore the local flow direction at the wing tip is NOT perpendicular to the mean free stream flow but acutally flows inboard. Winglets, or wingtip sails, attempt to take advantage of the fact that the local flow direction at the wingtip is not perpendicular to the free stream flow. Acting as small aerofoils, there is an effective angle of attack between the local flow direction and the winglet. This leads to a resultant aerodynamic force with a component in the direction of motion - hence the 'thrust' or reduction in drag.
Hope this helps,
Regards
ASI
[This message has been edited by ASI (edited 08 March 2001).]
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To: Togaroo
I quote: “but perhaps the biggest driver for their use is keeping up with the competitor (Airbus) and that their use is more for cosmetic rather than truly performance reasons - i.e. manufacturer seen to be updating a design”.
Boeing designed the winglets used on Airbus aircraft under a NASA contract. The design was offered to Airbus at no cost but if Boeing or anyone else wanted to use them they would have to pay a stiff licensing fee to offset the cost of development. That is why only Airbus uses the design. I can only assume that wing tip sails were installed on Boeing aircraft because there would be some operational benefit and not for cosmetic purposes.
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The Cat
I quote: “but perhaps the biggest driver for their use is keeping up with the competitor (Airbus) and that their use is more for cosmetic rather than truly performance reasons - i.e. manufacturer seen to be updating a design”.
Boeing designed the winglets used on Airbus aircraft under a NASA contract. The design was offered to Airbus at no cost but if Boeing or anyone else wanted to use them they would have to pay a stiff licensing fee to offset the cost of development. That is why only Airbus uses the design. I can only assume that wing tip sails were installed on Boeing aircraft because there would be some operational benefit and not for cosmetic purposes.
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The Cat
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Lu
My response was not to generate a Boeing / Airbus slanging match - I was brought up on the seattle metal and prefer the product, my comment was to illustrate why things are sometimes done for marketing rather than pure technical reasons. So if the fences designed by Boeing and used by Airbus were to improve performance greatly then everyone would be using them now. However Airbus is quite clever at exploiting new technology as a part of thier sales pitch, whereas Boeing prefer the tried and tested method.
However the thrust of my post was aimed at the B747-400, essentially a tried and tested product, but with a few enhancements. How to distinguish this product on the jet way as a good marketing strategy (from the 'classics') - add winglets. The reduction in drag 'in cruise' performance another justification for inclusion on the airframe, especially since the MTOW had increased through the use of horizontal stab fuel tanks.
I was not aware of the history of the design of the winglets, but wanted to point out that around the time of their imergence on the A321 (could be wrong that this was the first commercial jet airliner to use them) other manufacturers may have used wing fences or winglets to update the image of the product ie B747-400 and the conglomeration that is the MD-11 (I apologise if I offend anyone about the MD-11)
As my friend Cuban has stated the wing fence or sail has proved its performance in cruise are worth while for certain designs, but as the new wing of the B777 doesnt include them then why werent they included?
Like most things in life an aircraft design is a compromise of many factors - to include or omit certain components are not always dictated by common sense!!
I quite like the look of a winglet - but the BBJ is taking a bit far!!!
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Its life Jim, but not as we know it!!
My response was not to generate a Boeing / Airbus slanging match - I was brought up on the seattle metal and prefer the product, my comment was to illustrate why things are sometimes done for marketing rather than pure technical reasons. So if the fences designed by Boeing and used by Airbus were to improve performance greatly then everyone would be using them now. However Airbus is quite clever at exploiting new technology as a part of thier sales pitch, whereas Boeing prefer the tried and tested method.
However the thrust of my post was aimed at the B747-400, essentially a tried and tested product, but with a few enhancements. How to distinguish this product on the jet way as a good marketing strategy (from the 'classics') - add winglets. The reduction in drag 'in cruise' performance another justification for inclusion on the airframe, especially since the MTOW had increased through the use of horizontal stab fuel tanks.
I was not aware of the history of the design of the winglets, but wanted to point out that around the time of their imergence on the A321 (could be wrong that this was the first commercial jet airliner to use them) other manufacturers may have used wing fences or winglets to update the image of the product ie B747-400 and the conglomeration that is the MD-11 (I apologise if I offend anyone about the MD-11)
As my friend Cuban has stated the wing fence or sail has proved its performance in cruise are worth while for certain designs, but as the new wing of the B777 doesnt include them then why werent they included?
Like most things in life an aircraft design is a compromise of many factors - to include or omit certain components are not always dictated by common sense!!
I quite like the look of a winglet - but the BBJ is taking a bit far!!!
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Its life Jim, but not as we know it!!
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Speaking to a techie in the hangar at Boeing field he told me that the new 767-400 wing tip is the state of the art as far as drag reduction goes. Forget your winglets especially the 747-400, they are not very beneficial. 3-6% on the BBJ unless its very heavy then it tends to twist the inboard root of the wing negating any benefit. They are working on it though! But next time you see a 767-400 check out the last two or three meters of the wing, it's very different.
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Wingtips prevent the large downwash (created by the vortices induced at the wingtips) immediately behind the wings from forming thus keeping a low effective angle of attack.
They might not prove beneficial on the 777 because although they reduce induced drag, they increase parasite drag. It might not be worth it.
I don't understand why boeing would introduce winglets on a very long haul 777. Induced drag decreases with speed and in cruise, the aeroplane is moving at it's quickest. Go figure
They might not prove beneficial on the 777 because although they reduce induced drag, they increase parasite drag. It might not be worth it.
I don't understand why boeing would introduce winglets on a very long haul 777. Induced drag decreases with speed and in cruise, the aeroplane is moving at it's quickest. Go figure
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Cuban is correct about how winglet work, the other posts are not. They are designed to be specifically optimized for the cruise configuration. On the MD-11 they reduce fuel consuption 3-6%. Not sure on the 747-400, but I doubt very much they are just marketing.
Although a super-critical wing does not need them as much, they still would help for long haul. They aren't that useful for short haul because you have to choose one flight regime for them to work, and they will actually add drag in other regimes (unless you designed adjustable winglets!).
Consequently, aircraft that are designed to do well in short haul markets have to find other solutions. The 777 used longer wings as well as super-critical airfoil shapes.
Historical footnote is that the MD-11 was originally conceived to have super-critical wings also, but MD chose not to allocate the funding that would have been required. That turned out to be a good thing for the 777, because an MD-11 with super-critical wings would likely burn less fuel for a given sector than a 777 and not be ETOPS restricted. Couple that with the higher payload capability of the MD-11 and we might be in a different world today.
Although a super-critical wing does not need them as much, they still would help for long haul. They aren't that useful for short haul because you have to choose one flight regime for them to work, and they will actually add drag in other regimes (unless you designed adjustable winglets!).
Consequently, aircraft that are designed to do well in short haul markets have to find other solutions. The 777 used longer wings as well as super-critical airfoil shapes.
Historical footnote is that the MD-11 was originally conceived to have super-critical wings also, but MD chose not to allocate the funding that would have been required. That turned out to be a good thing for the 777, because an MD-11 with super-critical wings would likely burn less fuel for a given sector than a 777 and not be ETOPS restricted. Couple that with the higher payload capability of the MD-11 and we might be in a different world today.
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Ceppo,
I'm afraid that there is not much one can do to reduce the strength of trialing vorticies behind an aircraft - and you certianly cannot do it through the use of winglets! Winglets use the vortex pattern shed off the wing to increase airframe efficiency. Further, the downwash angle induced by the aircraft is directly related to the lift produced by the wing - reduce the downwash, reduce the lift produced!
My own thinking with regards to the 777 situation is that due to the increased wing efficiency over that of the 747 or 767, the company has calculated that the net benefit of winglets would be marginal or negetive.
I have been meaning to ask my departments Prof. about this for a while - he's an international authorty on wing design and might be able to sort out our problems!!!
Regards,
Cuban_8
I'm afraid that there is not much one can do to reduce the strength of trialing vorticies behind an aircraft - and you certianly cannot do it through the use of winglets! Winglets use the vortex pattern shed off the wing to increase airframe efficiency. Further, the downwash angle induced by the aircraft is directly related to the lift produced by the wing - reduce the downwash, reduce the lift produced!
My own thinking with regards to the 777 situation is that due to the increased wing efficiency over that of the 747 or 767, the company has calculated that the net benefit of winglets would be marginal or negetive.
I have been meaning to ask my departments Prof. about this for a while - he's an international authorty on wing design and might be able to sort out our problems!!!
Regards,
Cuban_8
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Prof2MDA;
While I agree with the comments made by Cuban, as an aerospace engineering student - 3rd year university -, before making my previous post I referenced current course materials from a once NASA Ames Research Centre associate, so as to describe the physics of winglets.
Without meaning to be funny, I would therefore be grateful if you could explain to me the mistakes made in my previous post.
Regards,
ASI
While I agree with the comments made by Cuban, as an aerospace engineering student - 3rd year university -, before making my previous post I referenced current course materials from a once NASA Ames Research Centre associate, so as to describe the physics of winglets.
Without meaning to be funny, I would therefore be grateful if you could explain to me the mistakes made in my previous post.
Regards,
ASI
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The current winglets on the 747-400 are more for show than anything else. Call them the golden rivet that allowed for changing the way that Boeing certified performance for the bird. The BBJ actually only gets about 4.5% to 5.5% depending on CG and other conditions. Low speed aero performance is enhanced on most aircraft so MTOW can be greater out of runway limited airports. They also have some noise benefits. The new raked ones are the "tweak of the week" at Boeing. They are no more efficient than a winglet, in fact they do the same thing: increase wing span loading further out from the plane. In rear engined planes at heavy aft CG they can cause problems in stall recovery. If they could design them to last and not fall off the most effiecient wing design known to man would look like the outer part of a turkey wing when inflight. You will find that trim drag has a far greater affect on cruise performance than those winglets.