kaddyuk
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Do Winglets Work?

Mon Feb 23, 2004 7:28 pm

I have heard a few oppinions from several techs and other apprentices. I known that in theory winglets should work but do they work in practice?

As there is obviously a difference between theory and practice.
Whoever said "laughter is the best medicine" never had Gonorrhea
 
Rick767
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RE: Do Winglets Work?

Mon Feb 23, 2004 7:40 pm

They must work otherwise they wouldn't be there I suppose!

A 747-400 has about a 4% fuel penalty with a single winglet missing I believe, as BA had one flying around for a few weeks with only one.
I used to love the smell of Jet-A in the morning...
 
Ikarus
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RE: Do Winglets Work?

Mon Feb 23, 2004 8:25 pm

What do you mean by "work"?

The winglets have two effects: They usually increase lateral stability (i.e. the plane without winglets behaves slightly different from the one with winglets), and secondly they reduce drag during cruise. If they did not achieve the latter, they would not be installed: The planes are not produced based purely on theory (I presume you mean CFD), but practical tests (wind tunnels). So there should be no difference between design performance and operational performance.

Regards

Ikarus
 
flyingbronco05
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RE: Do Winglets Work?

Tue Feb 24, 2004 3:02 am

Nope, they don't work.

That's why the:
747-400 has them.
737's can be equipped with them.
Lear Jet's have them.
Bombardier Challenger have them.
Global Express have them.
Gulfstreams have them.
MD-11 has them
CRJ-700 have them
 Yeah sure  Yeah sure  Yeah sure  Yeah sure  Yeah sure  Yeah sure
Never Trust Your Fuel Gauge
 
A/c train
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RE: Do Winglets Work?

Tue Feb 24, 2004 3:14 am

Kevin, have you done module 8 of your licence course yet ?, they will teach you about induced drag spanwise flow of air and wing tip losses, I cant believe a licenced Aircraft Technician working for VS would be silly enough to say they are pointless!! just believe some guy who gets paid more than us has done the numbers and we just fit and certify em.
You have too think about your topics before you put them on here, you seem a clever guy, use the common.  Wink/being sarcastic it will get you through a lot of tough and tricky situations in this job mate !!
regards a/c
 
lehpron
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RE: Do Winglets Work?

Tue Feb 24, 2004 4:34 am

Nothing is perfect but if it does the job to a certain degree of certainty then it is worth the cause I guess.
The meaning of life is curiosity; we were put on this planet to explore opportunities.
 
FredT
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RE: Do Winglets Work?

Tue Feb 24, 2004 5:43 am

Yes, they provide a very nice visible area for the corporate logo.  Insane

Cheers,
Fred
I thought I was doing good trying to avoid those airport hotels... and look at me now.
 
Guest

RE: Do Winglets Work?

Tue Feb 24, 2004 6:30 am

This topic come up all of the time. To answer your question, yes, they work, but...

They are definitely not the latest aeronautical fashion accessory that every well dressed aircraft must have. They are not appropriate or worthwhile for all wing designs. Marcel Dassault, the famous French aircraft designer, said that properly designed wings don't need winglets. It seems to me that few, if any, new aircraft with "clean sheet" wing designs, such as the Boeing 777, incorporate them, while airframe manufacturers will incorporate them on "old technology" designs (i.e. B747-400, B737, etc.) that they're trying to improve aerodynamically. Winglets are much cheaper to incorporate on older airfoil designs because they have minimal redesign and recertification costs.

I'm not an aeronautical engineer by any means, but I've flown thousands of hours in turbojet aircraft that were essencially identical except some had winglets and some didn't. My personal observation is that whatever small performance gains they provide often is usurped by the handling penalties they impose. Additionally, from what I've heard and read, their design is still somewhat of a "black art" and claims for increased efficiencies can often be tenuous at best.

Just for grins, I went to the Aviation Partners Boeing website, (They're the folks that do the winglets for the Boeing 737.) they list as one of the benefits of winglets:

"MODERN DRAMATIC APPEARANCE...Blended Winglets bring a modern look and feel to aircraft, and improve customers' perceptions of the reliability and modernity of the airline.

One of the problems associated with winglets is that they happen to be the current aeronautical fad much like "T-Tails" were 25 or 30 years ago. Remember, that was when you saw T-Tails introduced on several single-engine Pipers, the Beech King Air F90 and several other designs where the advantages of a T-Tail were (are) extremely hard to see. Unfortunately, IMHO, winglets fall into the same category.

Do winglets have their place? Of course, but they need to be thought of as "Aerodynamic Band-Aides".

Jetguy
 
MITaero
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RE: Do Winglets Work?

Tue Feb 24, 2004 12:26 pm

Winglets lead to (proven) fuel savings by reducing induced drag at the expense of a bit more weight. Going to have to disagree  Smile

Aviation Partners are appealing to businesspeople with those claims. They're not band-aides, and I think we'll see some further develompent.
 
Guest

RE: Do Winglets Work?

Tue Feb 24, 2004 2:00 pm

MIT...
Absolutely no question about it, they do work. My point was, that there are few "fully optimized clean sheet" wing designs that really need them. Where they are most effective is in optimizing older wing designs. You need to understand that even if we are discussing a new model aircraft that doesn't necessarily mean that the manufacturer designed from scratch the wing or, for that matter, any other componet (or system) of the aircraft. Certification costs being what they are, designers frequently try to graft preexisting designs into the new models when and where ever possible. It's much cheaper to certify preexisting designs.

Unfortunately, winglets are probably best described as the latest aeronautical fad - I've seen winglets on homebuilt singles, light twins, turboprops, and even gliders! Do they have their place? Of course, but they need to be thought of as "Aerodynamic Band-Aides", not the latest fashion accessory that every well dressed aircraft must have.

Jetguy

 
MITaero
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RE: Do Winglets Work?

Tue Feb 24, 2004 2:02 pm

I misunderstood your point. Well explained  Smile
 
Klaus
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RE: Do Winglets Work?

Tue Feb 24, 2004 8:10 pm

As far as I´ve understood it, it´s got nothing to do with the age of the design per se... Otherwise, I seriously doubt that Airbus would sacrifice performance - of all things! - in the A380 design where the performance difference would be most pronounced and which is definitely a clean-sheet design with wingtip fences.

As far as I´ve learned in the frequent discussions about the topic there are basically two ways to reduce the wing-tip-vortex-induced drag:

- shaping the wing tips so that the pressure differential is reduced, reducing vortices and drag, but this comes at increased wingspan and weight without the increased lift that this would normally get you

- using wingtip fences / winglets to reduce vortices, which will keep the wing span lower but will also increase weight

Both solutions would come at a cost, and it´s basically down to manufacturing techniques which one would be lighter or more efficient...

Or, if I´m mistaken, where´s the mistake?
 
AVANTI
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RE: Do Winglets Work?

Tue Feb 24, 2004 10:18 pm

Its an interesting topic. And with aircraft coming fresh off the design board or still on it (such as the ERJ 170/190 family and the A380 respectively) it certainly isn't an issue to do with updating 'old' designs.

But it still doesn't answer questions floating in my head like why Boeing doesn't have to use them on its 777, or why the winglets on the proposed 7E7 design are so subtle and integrated whereas the 737 NGs winglets are so radical (check out www.boeing.com they have a photo of Luxair's 737 with massive winglets today).

I asked my uncle who is an aeronautical engineer but he wasn't able to add anything new to what I already knew about vortex reduction etc... It would be nice to get a comprehensive and reliable article on this subject sometime.
 
FredT
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RE: Do Winglets Work?

Wed Feb 25, 2004 1:41 am

Should be in the FAQ...

You can add winglets without changing the wing design much, as they will not increase the forces acting upon the wing significantly. The main issue in certification is what they'll do in a sideslip, if I'm not misinformed on the matter.

If you design a new wing, the same weight is better spent in extending the wing span. A winglet giving the same increase in performance as the longer wing would weigh more.

If you end up in the situation where the aircraft will not fit the airports if you extend the wing span more, winglets provide a way around the problem.

Cheers,
Fred
I thought I was doing good trying to avoid those airport hotels... and look at me now.
 
Klaus
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FredT

Wed Feb 25, 2004 2:21 am

FredT: If you design a new wing, the same weight is better spent in extending the wing span. A winglet giving the same increase in performance as the longer wing would weigh more.

And you´re sure that all the specifics of different design and manufacturing methods would always be superseded by such a general rule?
 
MITaero
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RE: Do Winglets Work?

Wed Feb 25, 2004 2:52 am

FredT -

I'm not 100% sure, but wouldn't extending the wing be a poorer option in some cases? Induced drag would improve because of AR, but more lift would lead to more induced drag, and the lift coefficient is squared. A winglet whose induced drag benefit saves more fuel than is spent on its extra weight might be a better option sometimes.

Again, not sure.
 
QantasA332
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RE: Do Winglets Work?

Wed Feb 25, 2004 5:09 am

And here again we come to the problem I discussed with FredT before. For the added weight, etc., is increasing AR or adding winglets more effective? I had read that the latter was true, but FredT said otherwise........

Cheers,
QantasA332
 
lehpron
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RE: Do Winglets Work?

Wed Feb 25, 2004 5:24 am

A winglet is a very cost effective way to tweek increased efficiency from the traditional wing design; I vote to change the whole wingspace completely for more dramatic effects.  Smile/happy/getting dizzy Ever watch a bird's wings during thier landing sequence? Swept forward with outer wingtips down.

Why do you suppose their doing that? **hint hint**
The meaning of life is curiosity; we were put on this planet to explore opportunities.
 
FredT
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RE: Do Winglets Work?

Wed Feb 25, 2004 5:37 am

MIT,
if you add n kg of weight as a longer wing, the lift generated only increases by n * g N.

Add the same weight as a winglet, and you again increase the lift by n * g N.

You're not generating more lift on a longer wing. So, what it comes down to is which wing generates the same amount of lift the most efficiently. And the answer to that is typically the longer wing. The increased efficiency will be more beneficial than the drag reduction (or increased efficiency) caused by the same weight winglet.

QA332,
got the book now. It was a bit of misinterpretation there as I suspected. I'll find the quote again when I find time and remember. Sorry about it taking me a while, been busy with lots of other things so it slipped my mind. I do maintain that it is a poor book for aerodynamical knowledge. The erroneous lift explanation did arrive at Newton's law eventually, but in a half-arsed way which seemed like an afterthought added on the morning before the book went to printing.

Cheers,
Fred

I thought I was doing good trying to avoid those airport hotels... and look at me now.
 
QantasA332
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RE: Do Winglets Work?

Wed Feb 25, 2004 5:46 am

Don't get me wrong FredT, that is just one of many books on the subject that I have studied from. I do understand that it's a bit poor and thin, but with a statistic like the one I quoted, you'd hope that it'd be correct. Just have a look.

Cheers,
QantasA332
 
MITaero
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RE: Do Winglets Work?

Wed Feb 25, 2004 6:36 am

sorry, I messed up on this post and want it removed  Smile

[Edited 2004-02-24 22:37:34]
 
MITaero
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RE: Do Winglets Work?

Wed Feb 25, 2004 6:41 am

>You're not generating more lift on a longer wing.

Are we talking about just increasing the span of a current wing, or designing a new wing with the same approximate area (lift) with higher AR? I now think you mean the latter, whereas I thought you meant the first one before.
 
FredT
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RE: Do Winglets Work?

Wed Feb 25, 2004 7:51 pm

MIT,
that's the point. You wouldn't increase the span of an existing wing, as it would require mind-boggingly complex modifications of the wing structure to cope with the added loads.

Hence, winglets.

And you will not add winglets to a new wing, as it is better to simply increase the span (AR).

Cheers,
Fred
I thought I was doing good trying to avoid those airport hotels... and look at me now.
 
Klaus
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FredT

Thu Feb 26, 2004 5:36 am

A wing which produces the same amount of lift with a longer span would be heavier, would it not? You´d need a stronger structure to withstand the bending moment near the root while by necessity having a thinner wing at the same time; You´d have more total surface per wing area...

I´m certainly not disputing that it´s a valid option, but you´re not getting anything for free either way - for the weight saved by discarding winglets you´re paying with weight and inefficiencies elsewhere...

All I´ve heard before was that it´s a complex system of compromises. Has this changed in the meantime and the winglet-less design become the perfect option for all cases all of a sudden? I´d really like to know where this is coming from...
 
FredT
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RE: Do Winglets Work?

Thu Feb 26, 2004 6:01 am

Klaus,
think of it this way:

Design a new wing which will generate the right amount of lift without a winglet, including all the normal design compromises.

If you then shorten the span of this design, redesigning it as you go, so it will not simply be a truncated wing. The weight saved through shortening it will be less than the weight of the winglet required to bring it back to the same efficiency.

Clear as mud?  Big grin

Cheers,
Fred
I thought I was doing good trying to avoid those airport hotels... and look at me now.
 
Klaus
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FredT

Thu Feb 26, 2004 6:29 am

Nobody would design a wing like that - even I can see that.

A clean-sheet wing design would always be a complete package where the "body" structure is designed to complement the specific wingtip design selected to deal with vortex reduction. You don´t design an optimized wing and then simply "saw the tip off and slap a winglet on instead"! That would just be silly and nobody´s doing that. If they did, you would probably be right.

If your statement is just based on that, I´ll still have to wait for some Boeing / Airbus / Embraer / ... design engineer to pop up and "officially" shed some light on the latest state of the matter...

I can´t claim to have a deep knowledge about aerodynamics, but I know that it´s not that simple. At least when sub-percent fine tuning of airliner wings is concerned.

[Edited 2004-02-25 22:33:08]
 
MITaero
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RE: Do Winglets Work?

Thu Feb 26, 2004 7:16 am

I'm a Boeing engineer (although not working on aerodynamics until the summer) and I think FredT's logic is sound, as is yours.

The aspect ratio makes a big difference in induced drag. You're right about the tradeoffs, Klaus, and it's really not simple. I think that the added structural weight for high aspect ratio wings complicates things. But for already-existing wings, like 737NG, winglets are the easier efficiency upgrade, for obvious reasons.

Hopefully I'll learn more about the theory of designing wings for practical use, as I'm not really sure right now about all the factors.
 
QantasA332
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RE: Do Winglets Work?

Thu Feb 26, 2004 7:31 am

A wing which produces the same amount of lift with a longer span would be heavier, would it not?

It wouldn't necessarily. If you're talking about choosing an airfoil with a lower Cl and then increasing span until the lift is the same as your "control" wing, then it would definitely be heavier. But if the same airfoil is used, it wouldn't be heavier. For the added area due to extending its span, you would have to correspondingly decrease chord until the lift of your new wing equals that of the "control" wing, such that weight remains pretty much the same. Again, that's only the case if you're talking about having the two airfoils being compared equal in lift, as, if I'm correct, you were supposing.

Again, as you guessed, designing an aircraft is a whole string of compromises, really. You have this, you don't have that. What needs to be done is chose the compromises best suited to the intended use of the plane.

Cheers,
QantasA332
 
MITaero
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RE: Do Winglets Work?

Thu Feb 26, 2004 11:01 am

I think he meant that higher aspect ratio wings need more strucural reinforcement, but I don't know that this is true for small changes in AR.
 
Klaus
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MITaero

Thu Feb 26, 2004 9:27 pm

MITaero: I think he meant that higher aspect ratio wings need more strucural reinforcement,

Yes, exactly.

MITaero: but I don't know that this is true for small changes in AR.

You would be cutting into your safety margins in that case, wouldn´t you?
 
MITaero
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RE: Do Winglets Work?

Fri Feb 27, 2004 1:49 am

I suppose so  Smile

But who knows - there are improvements being made in wing skin material, etc., so changes like this might become possible. Just a thought.
 
backfire
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RE: Do Winglets Work?

Tue Mar 02, 2004 2:10 am

I known that in theory winglets should work but do they work in practice?

Everything that works in theory also works in practice.

If it doesn't, then your theory is either incomplete or flawed.
 
airplay
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RE: Do Winglets Work?

Tue Mar 02, 2004 3:05 am

Everything that works in theory also works in practice.

What kind of nonsense is that? Anything that works in theory, may be yet to be proven in practice.

Theoretically, if you travel close to the speed of light, your mass increases rather dramatically. But nobody knows for sure....
 
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Starlionblue
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RE: Do Winglets Work?

Tue Mar 02, 2004 4:15 am

Airlay: Yu know what Backfire meant... If the theory is correct, the practice will work.

MITAero: Now that you will start designing wings, maybe you could take on some suggestions from a.net members then?  Big grin We want T-tails and rear-mounted engines!
"There are no stupid questions, but there are a lot of inquisitive idiots." - John Ringo

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