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How Do Winglets Work?  
User currently offlineSoylentgreen From United States of America, joined Jul 2005, 244 posts, RR: 2
Posted (8 years 5 months 3 weeks 3 days 4 hours ago) and read 27198 times:

WOuld someone explain winglet technology? When was it developed? Does it work on all aircraft? Cost as an add on feature? Thank you.

55 replies: All unread, showing first 25:
 
User currently offlineLegacy135 From Switzerland, joined May 2005, 1052 posts, RR: 26
Reply 1, posted (8 years 5 months 3 weeks 3 days 3 hours ago) and read 27493 times:

The thing is this: The wing of an aircraft has basically an elliptic shape. This makes the air, that flows on the upper half flowing faster than the air, flowing on the lower. When you remember back to highschool physics classes, you may remember, that the faster you make air flow, the lower the pressure is. We are talking here about the "Venturi Effect".
This basics, we got now together, you need to make an aircraft fly. By producing a lower pressure on the upper side of the wing and a pressure on the lower one, we generate lift, or in other words, we make the aircraft fly. The relativity between those two forces is about

2/3 of lift on the upper half, generated by low pressure (soaking up) and
1/3 of lift produced on the lower half, produced by higher pressure (pushing up)

Now you can imagine, we have two different pressure situations pretty close to each other. Whenever you have a difference, nature wants to bring that into the equilibrate. For this reason, the air on the wing has a tendency to flow outwards, towards the wingtips, where high- and lowpressure meet. This generates vortexes, the so called "weak turbulence". This is induced drag.

Every drag on a plane is a penalty for performance and economics. This induced drag can be eliminated for a good part by installing winglets.

A number of aircrafts can by retrofitted but don't ask me the price. As everything in aviation, it's for sure quite expensive.

Cheers
Legacy135 Wink


User currently offlineAirPortugal310 From Palau, joined Apr 2004, 3575 posts, RR: 2
Reply 2, posted (8 years 5 months 3 weeks 3 days 3 hours ago) and read 27206 times:

That was a well written explanation. Damn.


I sell airplanes and airplane accessories
User currently offlineStarlionblue From Greenland, joined Feb 2004, 16991 posts, RR: 67
Reply 3, posted (8 years 5 months 3 weeks 3 days 2 hours ago) and read 27179 times:

And I thought they were cosmetic Big grin

http://www.airliners.net/discussions...h_ops/read.main/141444/6/#ID141444 Note Reply 3



"There are no stupid questions, but there are a lot of inquisitive idiots."
User currently offlineAeroWeanie From United States of America, joined Dec 2004, 1607 posts, RR: 52
Reply 4, posted (8 years 5 months 3 weeks 2 days 23 hours ago) and read 27195 times:
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Quoting AirPortugal310 (Reply 2):
That was a well written explanation. Damn.

But not completely right - the venturi effect argument is just the Bernoulli argument repackaged, and it is not correct. You are right that the pressure on the top of the wing is generally lower than on the bottom. However, induced drag comes from the circulation of the wing, which is not explained by the venturi or Bernoulli arguments.

Winglets are just non-planar span extensions. By moving the tip vortices further away from one another (as measured along the trailing edge), induced drag is reduced.

[Edited 2006-02-02 03:10:13]

User currently offlineTg 747-300 From Norway, joined Nov 1999, 1318 posts, RR: 0
Reply 5, posted (8 years 5 months 3 weeks 2 days 23 hours ago) and read 27159 times:

just to add a little to the discussion:

Every time a wing generates lift, there will be a pressure difference between the upper and lower surface of a wing, thus creating tip vortices. ( as well as root vortices, which is neglectable in this discussion).

These vortices will alter the downwash (flow of air) behind the wing, so that it is inclined more downward. Since the relative wind is a part of this downwash, and the lift acts perpendicular to relative wind, the total component of lift will be inclined somewhat more rearwards.

Before we continue on, lets analyse the total component of lift. Drag is the vector that acts along the longitudial axis of an airplane, and lift is the vector that acts perpendicular to that axis.

When the total lift component is altered towards the rear, the drag vector will increase and lift vector decrease.

How much the downwash, and thus the total component lift is altered will depend on the strenght of the tip vortices. the stronger the vortex, the more rearwards its altered.

A Winglet will more or less prevent vortices from forming and thus eliminating this alteration of airflow behind the wing = less drag.

Hope this helps, and plaese, please correct me if i got anything wrong here. I'm still a novice in aerodynamics.

tg 747-300



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User currently offlineAR1300 From Argentina, joined Feb 2005, 1740 posts, RR: 3
Reply 6, posted (8 years 5 months 3 weeks 2 days 22 hours ago) and read 27139 times:

Mel once posted a pic showing the vortexes on a winglet/wingfence ac and a conventional one.The thing basically was that it ''moves'' the vortex further up or so, clearing this turbulence and drag away from the wing.
Where is that pic, Mel??

mike



They don't call us Continental for nothing.
User currently offlineTg 747-300 From Norway, joined Nov 1999, 1318 posts, RR: 0
Reply 7, posted (8 years 5 months 3 weeks 2 days 21 hours ago) and read 27132 times:

Here: http://www.b737.org.uk/winglets.htm upper right corner is a picture of how the vortex is altered with winglets.

tg 747-300



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User currently offlineHAWK21M From India, joined Jan 2001, 31667 posts, RR: 56
Reply 8, posted (8 years 5 months 3 weeks 2 days 14 hours ago) and read 27023 times:

Quoting Tg 747-300 (Reply 7):

Thats it.Thanks.
Another good Explanation.
http://www.airspacemag.com/ASM/Mag/Index/2001/AS/htww.html
regds
MEL



Think of the brighter side!
User currently offlineSinlock From United States of America, joined Dec 2000, 1637 posts, RR: 2
Reply 9, posted (8 years 5 months 3 weeks 2 days 12 hours ago) and read 26980 times:

Quoting Tg 747-300 (Reply 7):
Here: http://www.b737.org.uk/winglets.htm upper right corner is a picture of how the vortex is altered with winglets.

Thanks for the link TG747!!! If it wern't for you I'd never had known that Quiet Wing Corp had recived a FAA STC for the mini-winglet/Flap package. Must have sliped through the cracks.

As for the question of the topic here is a link that will get you a view of the 737NG winglet in action....

http://www.aviationpartnersboeing.com/main.htm
Click "How winglets work" near the top of the page.



My Country can beat up your Country....
User currently offlineAR1300 From Argentina, joined Feb 2005, 1740 posts, RR: 3
Reply 10, posted (8 years 5 months 3 weeks 2 days 7 hours ago) and read 26917 times:

those are the ones I meant.Thx!!!  Smile


Mike



They don't call us Continental for nothing.
User currently offlineAeroWeanie From United States of America, joined Dec 2004, 1607 posts, RR: 52
Reply 11, posted (8 years 5 months 3 weeks 2 days 5 hours ago) and read 26898 times:
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Quoting Sinlock (Reply 9):
Thanks for the link TG747!!! If it wern't for you I'd never had known that Quiet Wing Corp had recived a FAA STC for the mini-winglet/Flap package. Must have sliped through the cracks.

QuietWing hasn't gotten an STC for the winglets - only the flap droop. The winglets shown are only for display and have never flown.


User currently offlineFredT From United Kingdom, joined Feb 2002, 2185 posts, RR: 26
Reply 12, posted (8 years 5 months 3 weeks 2 days 4 hours ago) and read 26901 times:

What basically happens:

You have low pressure above the wing and high pressure above it.

Air will try to flow around the wingtip, from the bottom to the top. This is what sets up a wingtip vortex.

The net result is that the air flowing over the top side of the tip of the wing will not only flow backwards, but will also flow somewhat inwards toward the fuselage.

The winglet is a small wing sticking up into this slightly inwards airflow. It generates lift at a straight angle to the aiflow and drag in the direction of the airflow, like any wing. When designed right, the resulting total aerodynamic force will point slightly forward, thus producing thrust... or reducing drag, depending on how you look at it.

The same effect can be had from extending the wing. However, extending the wing will generate higher bending moments on the wing and require structural strengthening, whereas a winglet will actually relieve the wing of some of the drag on the wing tip, thus reducing the load on the wing. This is why it is relatively easy to retrofit wings with winglets while extending the wings is tricky. Extending the wing would give more performance per kg of structure, though.

There are problems with winglets though, such as loads when there's a crosswind of when slipping the aircraft.

Cheers,
Fred



I thought I was doing good trying to avoid those airport hotels... and look at me now.
User currently offlineAeroWeanie From United States of America, joined Dec 2004, 1607 posts, RR: 52
Reply 13, posted (8 years 5 months 3 weeks 1 day 23 hours ago) and read 26853 times:
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Quoting FredT (Reply 12):
There are problems with winglets though, such as loads when there's a crosswind of when slipping the aircraft.

Interestingly, yaw or crosswind loads on winglets are less than the max loads in pitch. This is because the winglets provide an extension of the wing bound vortex and load up in pitch in unison with the wing.


User currently offlineAirIndiaOne From India, joined Mar 2005, 146 posts, RR: 0
Reply 14, posted (8 years 5 months 3 weeks 1 day 18 hours ago) and read 26816 times:

Quoting Legacy135 (Reply 1):
Every drag on a plane is a penalty for performance and economics. This induced drag can be eliminated for a good part by installing winglets.

Still many aircrafts dont install winglets ? If doing this would improve their performance and lessen the penalty drag, then why not install them in the entire fleet.
Wouldn't it be beneficial in the long run ?



"You don't have to be crazy to be in aviation, but it helps", JRD Tata
User currently offlineTg 747-300 From Norway, joined Nov 1999, 1318 posts, RR: 0
Reply 15, posted (8 years 5 months 3 weeks 1 day 18 hours ago) and read 26817 times:

Quoting AirIndiaOne (Reply 14):
Still many aircrafts dont install winglets ? If doing this would improve their performance and lessen the penalty drag, then why not install them in the entire fleet.

There is also a weight penalty, and mx issue with instaling winglets on an aircraft. For aircrafts that fly mostly short hops with very litte cruise time, there is actualy not that big of a benefit, because the increased weight etc. will "bite" more during climb on a shorter flight, due to a greater % of the flight beeing climb.

For longhaul the picture is a bit different.



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User currently offlineHAWK21M From India, joined Jan 2001, 31667 posts, RR: 56
Reply 16, posted (8 years 5 months 3 weeks 1 day 18 hours ago) and read 26806 times:

Quoting AirIndiaOne (Reply 14):
Still many aircrafts dont install winglets ? If doing this would improve their performance and lessen the penalty drag, then why not install them in the entire fleet

Its benificial only in Flight sectors of longer cruising time,as the Winglets add a unwelcome Weight penalty.Hence if used over longer cruising time the benifits can be achieved.
regds
MEL



Think of the brighter side!
User currently offlineStarlionblue From Greenland, joined Feb 2004, 16991 posts, RR: 67
Reply 17, posted (8 years 5 months 3 weeks 1 day 12 hours ago) and read 26796 times:

Quoting AirIndiaOne (Reply 14):
Still many aircrafts dont install winglets ? If doing this would improve their performance and lessen the penalty drag, then why not install them in the entire fleet.
Wouldn't it be beneficial in the long run ?

Also, a span extension (raked wingtips) can be more beneficial than winglets. But in many cases (737, 380) there are gate space considerations.



"There are no stupid questions, but there are a lot of inquisitive idiots."
User currently offlineSinlock From United States of America, joined Dec 2000, 1637 posts, RR: 2
Reply 18, posted (8 years 5 months 3 weeks 1 day 11 hours ago) and read 26776 times:

I myself have never bought into the Weight penitly argument. The installed weight of the 737NG winglet kit (iirc) is 142 lbs thats just (0.17%) added to the Operating Empty Weight of the 737-700.

Plus this is not just dead weight as they generate a great amount of lift that easly over comes the added weight.



My Country can beat up your Country....
User currently offlineStarlionblue From Greenland, joined Feb 2004, 16991 posts, RR: 67
Reply 19, posted (8 years 5 months 3 weeks 1 day 10 hours ago) and read 26773 times:

Quoting Sinlock (Reply 18):
I myself have never bought into the Weight penitly argument. The installed weight of the 737NG winglet kit (iirc) is 142 lbs thats just (0.17%) added to the Operating Empty Weight of the 737-700.

Well it's not only the weight of the winglet, but the increased wing loading it entails, which is also "weight".

But I think it's mostly a case of cost.



"There are no stupid questions, but there are a lot of inquisitive idiots."
User currently offline2H4 From United States of America, joined Oct 2004, 8955 posts, RR: 60
Reply 20, posted (8 years 5 months 3 weeks 1 day 10 hours ago) and read 26772 times:
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DATABASE EDITOR




Quoting HAWK21M (Reply 16):
Its benificial only in Flight sectors of longer cruising time,as the Winglets add a unwelcome Weight penalty

Winglets are beneficial in more ways than just long-range cruise. They also improve climb performance and have been known to reduce approach speeds.




2H4





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User currently offlineStarlionblue From Greenland, joined Feb 2004, 16991 posts, RR: 67
Reply 21, posted (8 years 5 months 3 weeks 1 day 9 hours ago) and read 26760 times:

Quoting 2H4 (Reply 20):
They also improve climb performance and have been known to reduce approach speeds.

This is an interesting aspect in that winglets can enable older aircraft to meet noise regs by climbing faster. This includes wingleted 727s.



"There are no stupid questions, but there are a lot of inquisitive idiots."
User currently offline2H4 From United States of America, joined Oct 2004, 8955 posts, RR: 60
Reply 22, posted (8 years 5 months 3 weeks 1 day 9 hours ago) and read 26753 times:
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Quoting Starlionblue (Reply 21):

This is an interesting aspect in that winglets can enable older aircraft to meet noise regs by climbing faster. This includes wingleted 727s.

Yeah, according to Aviation Partners, two engine climb performance on the Gulfstream II improves 5%, and single engine climb improves 10%-12%. Also, stalls more easily recognized and controlled.

Granted, this is just one aircraft model we're talking about, but it certainly illustrates the benefits.




2H4





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User currently offlineAeroWeanie From United States of America, joined Dec 2004, 1607 posts, RR: 52
Reply 23, posted (8 years 5 months 3 weeks 1 day 8 hours ago) and read 26743 times:
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Quoting 2H4 (Reply 22):
Also, stalls more easily recognized and controlled.

This is actually from another part of the mod package. Along with adding the winglets, they remove the G II's wing fences and replace them with vortilons configured like those on the G IV.


User currently offline2H4 From United States of America, joined Oct 2004, 8955 posts, RR: 60
Reply 24, posted (8 years 5 months 3 weeks 1 day 8 hours ago) and read 26735 times:
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DATABASE EDITOR




Quoting AeroWeanie (Reply 23):
This is actually from another part of the mod package.

Ah...thanks for the clarification, AeroWeanie.




2H4





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25 FredT : Now I didn't quite follow you. You say they induce a pitch load in the wing which is more significant than the side loads? Could you please elaborate
26 2H4 : I think AeroWeanie is referring to the significant inward loads placed on the winglets when the wing is loaded up during, for example, recovery from
27 FredT : 2H4, that's not a pitch load tough as it is acting in a lateral direction. In the winglet reference system, it is indeed a pitch load though. Either w
28 2H4 : Oh, ok. I interpreted it as a load induced by a change in pitch. 2H4
29 Jetlagged : A few people have posted about how winglets move the vortices away from the wing, so reducing drag. This doesn't make sense. Where it is moved to is i
30 Sinlock : I'm aware of the issuse of winglets and wingloading, it's the main reason the 767-300 winglet program hasn't made much headway. The point I was getti
31 AeroWeanie : You got it right. Aspect ratio is not what matters, span is. If you take the equation CDi=CL^2/Pi/AR/e and solve for Drag, you will find that area di
32 Starlionblue : Agreed. I saw this 747 docu and there was all of one guy responsible for mounting the 744 winglets. He used to have a name but they now just call him
33 Post contains images FredT : Some wing tip devices move the vortices. Hoerner tips is an example. The vortices end up outside of the actual span of the wing. Other devices don't
34 AeroWeanie : Not true - a properly designed winglet has the same tip vortex strength, as the bound vortex has the same circulation. Its just that the vortices are
35 2H4 : Do forward-swept wings have comparitively more or less induced drag than their straight or rearward-swept counterparts? Or is it impossible to say wi
36 Starlionblue : As I understand it, the basic idea with forward sweep is to eliminate wingtip vortices. Spanwise flow will be towards the fuse instead of towards the
37 2H4 : So is it safe to say winglets would definitely not reduce drag on a forward-swept wing? Also, are forward-swept wings susceptable to dutch roll tende
38 Starlionblue : As I see it (and I may be wrong) winglets on a forward swept wing would be purely something to paint your livery on since there isn't any tendency fo
39 Starlionblue : Hmmm, I thought about this a while. If you want to build a tail-less forward swept wing aircraft you could put small rudders at the wingtips. The Ger
40 Post contains links 2H4 : Woah....check this patent application out: ...employs a variable forward swept wing configuration which has a mechanism that makes it possible to var
41 Post contains links and images Starlionblue : You have waaaay too much time on your hands 2H4. But thanks for sharing. BTW if you want to know where I stole all that WWII German X-plane stuff, it'
42 Post contains images 2H4 : Heh heh....day off + weather too cold (for me) to be on the bike or motorcycle = A.net day. 2H4
43 Jetlagged : Mathematically you are correct. I was thinking purely of the non-dimensional equation. Actually what you are left with is span squared. However, for
44 AeroWeanie : You can't avoid tip vortices. They are how the bound vortex system convects to the far field. Forward swept wings have tip vortices, just like aft sw
45 Post contains images HAWK21M : True.In that post I was referring to Weight penalty & how cruise time beng longer would be more Economical regds MEL
46 Post contains images Starlionblue : See, told ya AeroWeanie would tell me where I went wrong
47 Post contains images Jetlagged : I didn't miss it and I knew that's what you meant. I just couldn't think of the right words to describe it
48 Post contains images Lehpron : While this is the definition I go by, AeroWeanie may tell me off.  Long story short, they use the flow going around the wing tip to reduce the overal
49 Keta : I don't quite understand you. How does more separated vortices mean less drag? Isn't the drag caused by vortices wasted kinetic energy? If vortices a
50 AeroWeanie : I'll buy what you said! I'd use the words "total drag", rather than "overall drag", but thats a tiny quibble. The strength of the tip vortices is dep
51 Starlionblue : Ok I meant that a forward swept wing needed to be strongER.
52 Post contains images Lehpron : Oh sh*t, I didnt even see that! I hope you folks knew what I meant.
53 Keta : I still don't get it. I know that's induced drag, but how do you reduce the inductive effect by moving the tips?
54 Keta : OK, wait, let's see if this works: By moving the tips further apart, that would mean that more air is diverted down (more effective span). Now you nee
55 Post contains links and images Lightsaber : AeroWeanie, while I agree with almost everything else a bound vortex theoretically should have the same circulation if no external force is applied;
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