737 Winglets
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From: The Neverlands
737 Winglets
Nosey SLF speaking....
Had the pleasure of paxing on a KL 737 with winglets this afternoon and noticed that the wings seem to flex a lot more on ground and in flight. How much does the winglet weigh and would increased wing flex be looked at as part of the certification process? Is wing flex even increased, or is it just more apparent from the cabin on the wingletted models?
Also wondered if the winglet affects how the aircraft handles in crosswinds, as they must have a fairly substantial surface area...
Had the pleasure of paxing on a KL 737 with winglets this afternoon and noticed that the wings seem to flex a lot more on ground and in flight. How much does the winglet weigh and would increased wing flex be looked at as part of the certification process? Is wing flex even increased, or is it just more apparent from the cabin on the wingletted models?
Also wondered if the winglet affects how the aircraft handles in crosswinds, as they must have a fairly substantial surface area...
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From: Manchester, England
Evening,
i have to agree with you, ive flown on alot of 737/w over the last year and ive noticed the exact same thing.
Its quite obvious that when weight added to the end of the wing surfaces then it will fluctuate more than without winglets, would like to see some technical data on this.
G-STAW
i have to agree with you, ive flown on alot of 737/w over the last year and ive noticed the exact same thing.
Its quite obvious that when weight added to the end of the wing surfaces then it will fluctuate more than without winglets, would like to see some technical data on this.
G-STAW
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From: No one's home...
[quote] How much does the winglet weigh and would increased wing flex be looked at as part of the certification process? Is wing flex even increased, or is it just more apparent from the cabin on the wingletted models? [/quote}
When putting winglets on a wing, it is not merely a matter of pasting the winglets on. LOTS of structure testing has to be done because you are adding wing at the weakest point of the formerly created wing AND you are re-distributing the loads. So it is not just figuring out a way to bolt on some end plates.
Remember, there are a number of wings on the airplane. The first is the aero wing which is the wing as it is designed but not attached to a fuselage. Then you attach the wing and that changes the wing due to loading and then there is the wing that flies.. subject to lift, twist etc. Lots of studies to see how the wing handles each environment
FWIW, winglets or 'endplates' were studied before the Wright brothers flew because the problems with vortex drag were already understood. The problem was that 'endplates' created more drag than they reduced so they were not adopted. You can find 'endplates' on the airfoils of race cars today.
When putting winglets on a wing, it is not merely a matter of pasting the winglets on. LOTS of structure testing has to be done because you are adding wing at the weakest point of the formerly created wing AND you are re-distributing the loads. So it is not just figuring out a way to bolt on some end plates.
Remember, there are a number of wings on the airplane. The first is the aero wing which is the wing as it is designed but not attached to a fuselage. Then you attach the wing and that changes the wing due to loading and then there is the wing that flies.. subject to lift, twist etc. Lots of studies to see how the wing handles each environment
FWIW, winglets or 'endplates' were studied before the Wright brothers flew because the problems with vortex drag were already understood. The problem was that 'endplates' created more drag than they reduced so they were not adopted. You can find 'endplates' on the airfoils of race cars today.
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From: Omicron Persei 8
You will find a lot of information and the answers to some of your questions from this website....
http://www.b737.org.uk/winglets.htm
http://www.b737.org.uk/winglets.htm
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From: Northampton
FWIW, winglets or 'endplates' were studied before the Wright brothers flew because the problems with vortex drag were already understood. The problem was that 'endplates' created more drag than they reduced so they were not adopted. You can find 'endplates' on the airfoils of race cars today.
Maybe Beg Tibs is right.
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From: New Zealand
The end plates may very well have reduced the induced drag, but there's other sorts of drag too. I'm thinking of form drag and skin friction drag. Maybe the overall drag increased, despite having less induced drag.
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From: N/A
would increased wing flex be looked at as part of the certification process? Is wing flex even increased, or is it just more apparent from the cabin on the wingletted models?
First, the primary reason for adding the winglets, overall drag reduction, has to be evaluated by aero, and the results incorporated into the performance models. The aero guys will want to account for wing flexibility in their models, and there would probably be wind tunnel testing as well. Aircraft handling and stability also has to be re-evaluated.
The loads models would then need to be updated, not only to account for added weight at the wingtip, but also to account for the changed loads distribution on the rest of the wing... you may end up actually increasing your wing root bending moment for design maneuvers.
And that's just the "static" loads. Even more importantly, the dynamic effect of the winglet has to be analyzed. Changing the mass of the wing in that way, and the aerodynamics of the wingtip as well for that matter, will have an impact on flutter. The added mass will change the fundamental structural modes of the wing. Probably, you will have to do a partial ground vibration test with the added winglet to tune your flutter model. Once you have a tuned structural model, you have to evaluate your "dynamic" loads, such as landings and gusts, as these have a tendancy to shake the wingtip around, and the results of the analysis depend on knowing well the structural modes of the aircraft.
Of course changes to loads mean stress analysis. The objective would be to make sure that with any loads changes, you're not reducing your safety margins to the point where you have to introduce structural changes to the wing. If your wing is built by a partner or a supplier, you definitely don't want to worry about design changes, because then contract considerations come into play.
More than you probably wanted to know about the subject, but adding a winglet is far from a simple undertaking.
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From: UTC +8
Captain Planet . . ."Well if they don't reduce wing tip vortices, why do most modern day aircraft manufacturers use them??? For the laugh???? CP.
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From: Cloud Cookoo Land
X-Winds
Someone mentioned crosswind handling in relation to an aircraft with winglets (ie the 737-800). From what I believe the crosswind limit is reduced? Unsure of the reason though...Am I being silly?
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From: north
Someone mentioned crosswind handling in relation to an aircraft with winglets (ie the 737-800). From what I believe the crosswind limit is reduced? Unsure of the reason though...Am I being silly?
which again requires more rudder input.
M
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From: FL 410
no winglet retrofits have yet been suggested for the popular "modern day" B777
Made sense to me.
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From: La Belle Province
From what I believe the crosswind limit is reduced? Unsure of the reason though...Am I being silly?
Think thats correct. Adding winglets increases longitudal stability
which again requires more rudder input.
which again requires more rudder input.
And the most likely reason for a xwind "limit" change is that no larger value was demonstrated - in many cases so-called crosswind "limits" do not represent actual limits but rather the largest value demonstrated by the OEM, which may well be annotated as "not limiting" or similar words by the OEM; nevertheless, many people do treat the demonstrated maxima as operational limits (and that's a reasonable thing to do, IMHO).
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From: La Belle Province
the length of time that a test plane must be out of service, i.e. approaching a year or more.
If the winglet mod takes anything like a year to apply to the airframe, then no-one would buy one - it'd take a lot of savings per flight to make up for a year out-of-service.
And there's no way a test programme to clear a winglet should take anything like a year of flying - that's getting close to the time to certify a new design from scratch.
I'd have thought you could install and test a new winglet in a month or less (depending on the type); which is still a bunch of time out-of-service, but by no means prohibitive.
I'd have thought that a more credible reason is that the benefit of a winglet retrofit can't be shown to be worthwhile, because the existing tip design is sufficiently good as-is.
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From: eire
If you take a look at the wing tips on a 777, you will notice that they are 'raked' , thus eliminating the need for a conventional 'winglet'. Its all to do with how the air spills off the end of the wing, it does'nt always need a winglet to make the wing more efficient.
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From: No one's home...
The early endplates used materials of that era on wings of that era. The end plates had to be braced and the overall effect or sum of the reduced induced drag and the increased parasite drag was a negative effect.
Winglets came alive again when Dr. Whitcomb, the same NASA scientist that came up with the area ruled fuselages, began study of bird wings and how some were better fliers than others. Whitcomb then found early studies and did wind tunnel testing and later attached winglets to a KC-135 for actual flight tests. The results were very good but given the choice of new engines or winglets, the USAF opted for the engines.
Some of what you see today are 'pretendlets' which are on the wing as a result of marketing and do not actually reduce the vortex that much. Others are very effective but they are point designs.. ie, where does the airplane spend the most time and so you design the winglet for that regime of flight. This means in other flight regimes, the winglets may actually have only a modest effect if any.
As for the 'endplates' look at the formula 1 racers which have an inverted wing held in place by braces on the end. These winglets create a down-force to nail the racer to the course. Those are the modern endplates.
More here... http://oea.larc.nasa.gov/PAIS/Concep.../winglets.html
And here you can see the Phillips "Multiplane" which used very high aspect ratio airfoils with 'endplates'. http://www.aerospaceweb.org/question...ry/q0232.shtml
As you can see, it took a while to get the concept to a working tool.
Winglets came alive again when Dr. Whitcomb, the same NASA scientist that came up with the area ruled fuselages, began study of bird wings and how some were better fliers than others. Whitcomb then found early studies and did wind tunnel testing and later attached winglets to a KC-135 for actual flight tests. The results were very good but given the choice of new engines or winglets, the USAF opted for the engines.
Some of what you see today are 'pretendlets' which are on the wing as a result of marketing and do not actually reduce the vortex that much. Others are very effective but they are point designs.. ie, where does the airplane spend the most time and so you design the winglet for that regime of flight. This means in other flight regimes, the winglets may actually have only a modest effect if any.
As for the 'endplates' look at the formula 1 racers which have an inverted wing held in place by braces on the end. These winglets create a down-force to nail the racer to the course. Those are the modern endplates.
More here... http://oea.larc.nasa.gov/PAIS/Concep.../winglets.html
And here you can see the Phillips "Multiplane" which used very high aspect ratio airfoils with 'endplates'. http://www.aerospaceweb.org/question...ry/q0232.shtml
As you can see, it took a while to get the concept to a working tool.
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From: No one's home...
Glueball
Remember the Triple 7 originally was to come with the option for a folding wingtip but no one wanted it.. added weight and complexity.
And Boeing has joined with Aviation Partners to put winglets on the other machines.. because it is not there now does not mean it won't be there later.
Curiously, [not laughing now] . . . no winglet retrofits have yet been suggested for the popular "modern day" B777, nor for its latest factory fresh ER and LR versions.
And Boeing has joined with Aviation Partners to put winglets on the other machines.. because it is not there now does not mean it won't be there later.