soylentgreen
Topic Author
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### How Do Winglets Work?

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

legacy135
Posts: 966
Joined: Sat May 14, 2005 11:06 pm

### RE: How Do Winglets Work?

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

airportugal310
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### RE: How Do Winglets Work?

That was a well written explanation. Damn.
I sell airplanes and airplane accessories

Starlionblue
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### RE: How Do Winglets Work?

"There are no stupid questions, but there are a lot of inquisitive idiots." - John Ringo

aeroweanie
Posts: 1576
Joined: Fri Dec 03, 2004 9:33 pm

### RE: How Do Winglets Work?

 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]

Tg 747-300
Posts: 1282
Joined: Fri Nov 26, 1999 6:08 am

### RE: How Do Winglets Work?

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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AR1300
Posts: 1686
Joined: Mon Feb 07, 2005 1:22 pm

### RE: How Do Winglets Work?

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
You are now free to move about the cabin

Tg 747-300
Posts: 1282
Joined: Fri Nov 26, 1999 6:08 am

### RE: How Do Winglets Work?

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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HAWK21M
Posts: 30014
Joined: Fri Jan 05, 2001 10:05 pm

### RE: How Do Winglets Work?

Thats it.Thanks.
Another good Explanation.
http://www.airspacemag.com/ASM/Mag/Index/2001/AS/htww.html
regds
MEL
I may not win often, but I damn well never lose!!!

Sinlock
Posts: 1631
Joined: Fri Dec 22, 2000 12:55 am

### RE: How Do Winglets Work?

 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.

AR1300
Posts: 1686
Joined: Mon Feb 07, 2005 1:22 pm

### RE: How Do Winglets Work?

those are the ones I meant.Thx!!!

Mike
You are now free to move about the cabin

aeroweanie
Posts: 1576
Joined: Fri Dec 03, 2004 9:33 pm

### RE: How Do Winglets Work?

 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.

FredT
Posts: 2166
Joined: Thu Feb 07, 2002 9:51 pm

### RE: How Do Winglets Work?

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.

aeroweanie
Posts: 1576
Joined: Fri Dec 03, 2004 9:33 pm

### RE: How Do Winglets Work?

 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.

AirIndiaOne
Posts: 139
Joined: Sat Mar 05, 2005 2:10 pm

### RE: How Do Winglets Work?

 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

Tg 747-300
Posts: 1282
Joined: Fri Nov 26, 1999 6:08 am

### RE: How Do Winglets Work?

 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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HAWK21M
Posts: 30014
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### RE: How Do Winglets Work?

 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
I may not win often, but I damn well never lose!!!

Starlionblue
Posts: 17961
Joined: Fri Feb 27, 2004 9:54 pm

### RE: How Do Winglets Work?

 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." - John Ringo

Sinlock
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Joined: Fri Dec 22, 2000 12:55 am

### RE: How Do Winglets Work?

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.

Starlionblue
Posts: 17961
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### RE: How Do Winglets Work?

 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." - John Ringo

2H4
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### RE: How Do Winglets Work?

 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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Starlionblue
Posts: 17961
Joined: Fri Feb 27, 2004 9:54 pm

### RE: How Do Winglets Work?

 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." - John Ringo

2H4
Posts: 7960
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### RE: How Do Winglets Work?

 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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aeroweanie
Posts: 1576
Joined: Fri Dec 03, 2004 9:33 pm

### RE: How Do Winglets Work?

 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.

2H4
Posts: 7960
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### RE: How Do Winglets Work?

 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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FredT
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Joined: Thu Feb 07, 2002 9:51 pm

### RE: How Do Winglets Work?

 Quoting AeroWeanie (Reply 13):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.

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 a bit? Acceleration loads in turbulence due to the added weight? Load changes due to the changed lift distribution?
I thought I was doing good trying to avoid those airport hotels... and look at me now.

2H4
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### RE: How Do Winglets Work?

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 a dive.

Correct me if I'm wrong, though.

2H4

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FredT
Posts: 2166
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### RE: How Do Winglets Work?

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 way, it does not put a vertical load on the wing but rather a bending moment, which is pretty much the problem with winglets as far as structural strength goes.
I thought I was doing good trying to avoid those airport hotels... and look at me now.

2H4
Posts: 7960
Joined: Tue Oct 19, 2004 11:11 pm

### RE: How Do Winglets Work?

 Quoting FredT (Reply 27):that's not a pitch load tough as it is acting in a lateral direction.

Oh, ok. I interpreted it as a load induced by a change in pitch.

2H4

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Jetlagged
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### RE: How Do Winglets Work?

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 irrelevant, it's still attached to the wingtip. The sketch of the 737NG with and without winglets, shows a smaller vortex with the winglet. That's the reason.

Extended wingtips don't work be moving the vortices either. They increase aspect ratio, which reduces induced drag.
The glass isn't half empty, or half full, it's twice as big as it needs to be.

Sinlock
Posts: 1631
Joined: Fri Dec 22, 2000 12:55 am

### RE: How Do Winglets Work?

 Quoting Starlionblue (Reply 19):Well it's not only the weight of the winglet, but the increased wing loading it entails, which is also "weight".

The point I was getting at was that people make statements about winglets adding weight as if we were talking about 1000s of pounds.

aeroweanie
Posts: 1576
Joined: Fri Dec 03, 2004 9:33 pm

### RE: How Do Winglets Work?

 Quoting 2H4 (Reply 26):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 a dive. Correct me if I'm wrong, though.

You got it right.

 Quoting Jetlagged (Reply 29):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 irrelevant, it's still attached to the wingtip. The sketch of the 737NG with and without winglets, shows a smaller vortex with the winglet. That's the reason. Extended wingtips don't work be moving the vortices either. They increase aspect ratio, which reduces induced drag.

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 dissapears and only span is left. Where the tip vortices are is everything!

Starlionblue
Posts: 17961
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### RE: How Do Winglets Work?

 Quoting Sinlock (Reply 30): The point I was getting at was that people make statements about winglets adding weight as if we were talking about 1000s of pounds.

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 "the winglet guy". He could easily do the work himself. Mounting including using a sledgehammer!
"There are no stupid questions, but there are a lot of inquisitive idiots." - John Ringo

FredT
Posts: 2166
Joined: Thu Feb 07, 2002 9:51 pm

### RE: How Do Winglets Work?

 Quoting Jetlagged (Reply 29):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 irrelevant, it's still attached to the wingtip. The sketch of the 737NG with and without winglets, shows a smaller vortex with the winglet. That's the reason.

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 move the vortices out to any significant degree, but reduce the strength of the vortices, putting the energy to better use. That's your winglets.

Yet other devices put the vortices over the top of the wing, utilizing the low pressure in the vortices to create lift, e g raked wingtips.

All these devices have one thing in common: They make the wing appear to have a larger span than it physically does, from an aerodynamics point of view. Thus, we talk about the effective span of the wing. Smoke and mirrors, but it is good enough to fool the aerodynamic gremlins so we are happy.

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

aeroweanie
Posts: 1576
Joined: Fri Dec 03, 2004 9:33 pm

### RE: How Do Winglets Work?

 Quoting FredT (Reply 33):Other devices don't move the vortices out to any significant degree, but reduce the strength of the vortices, putting the energy to better use. That's your winglets.

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 further away from one another, as measured along the bound vortex.

 Quoting FredT (Reply 33):Yet other devices put the vortices over the top of the wing, utilizing the low pressure in the vortices to create lift, e g raked wingtips.

Again, not true. Raked tips also move the vortices apart. Raked tips are just span extensions that are tapered, to increase local lift coefficients, and swept.

 Quoting FredT (Reply 33):All these devices have one thing in common: They make the wing appear to have a larger span than it physically does, from an aerodynamics point of view. Thus, we talk about the effective span of the wing. Smoke and mirrors, but it is good enough to fool the aerodynamic gremlins so we are happy.

Very true!

2H4
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### RE: How Do Winglets Work?

Do forward-swept wings have comparitively more or less induced drag than their straight or rearward-swept counterparts? Or is it impossible to say without more specific information?

2H4

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Starlionblue
Posts: 17961
Joined: Fri Feb 27, 2004 9:54 pm

### RE: How Do Winglets Work?

 Quoting 2H4 (Reply 35):Do forward-swept wings have comparitively more or less induced drag than their straight or rearward-swept counterparts? Or is it impossible to say without more specific information?

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 tips. So you get more lift with the same wing and less drag.

Also it looks way cool.

The main problem is that the wing will try to bend upwards, so it needs to be pretty strong. This is why we didn't see any WWII era German forward sweep fighters actually flying. There were plenty of paper studies at the time though, including the Heinkel P.1076 (piston), a couple of unnamed early jet proposals from Focke-Wulf, the Focke-Wulf P.1073 (precursor to the He-162) and Blohm und Voss P209/02 (single engine jet).

Also there are some stability issues. In a fighter, the planes are unstable anyway so it's just a matter of programming the FBW correctly. But the FAA would probably be a bit leery of certifying an unstable airliner.

I bet Aeroweanie et al can explain it better, and tell me where I went wrong.

[Edited 2006-02-04 01:22:35]
"There are no stupid questions, but there are a lot of inquisitive idiots." - John Ringo

2H4
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### RE: How Do Winglets Work?

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 tendencies?

2H4

Edit - added the word "tendencies".

[Edited 2006-02-04 01:24:15]
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Starlionblue
Posts: 17961
Joined: Fri Feb 27, 2004 9:54 pm

### RE: How Do Winglets Work?

 Quoting 2H4 (Reply 37): So is it safe to say winglets would definitely not reduce drag on a forward-swept wing?

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 for air to go from the lower surface of the wing to the upper surface at the wingtip.
"There are no stupid questions, but there are a lot of inquisitive idiots." - John Ringo

Starlionblue
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Joined: Fri Feb 27, 2004 9:54 pm

### RE: How Do Winglets Work?

 Quoting Starlionblue (Reply 38):Quoting 2H4 (Reply 37): So is it safe to say winglets would definitely not reduce drag on a forward-swept wing? 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 for air to go from the lower surface of the wing to the upper surface at the wingtip.

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 Germans played with this too during WWII, except it was with backward sweep.
"There are no stupid questions, but there are a lot of inquisitive idiots." - John Ringo

2H4
Posts: 7960
Joined: Tue Oct 19, 2004 11:11 pm

### RE: How Do Winglets Work?

Woah....check this patent application out:

...employs a variable forward swept wing configuration which has a mechanism that makes it possible to vary the forward sweep angle as the main wing configuration.

Since the supersonic aircraft entire airplane shape of the present invention employs a variable forward swept wing configuration equipped with a mechanism that makes it possible to vary the forward sweep angle as the main wing configuration, the forward sweep angle can be reduced to optimize performance during takeoff and landing, and during subsonic flight.

Furthermore, the optimal forward sweep angle for sonic boom reduction can be set by adjusting the forward sweep angle in order to obtain the optimal lift equivalent cross-sectional area distribution in the axial direction of the aircraft body during supersonic flight. As a result, both a suppression of sonic booms and a reduction of wave-drag can be achieved.

2H4

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Starlionblue
Posts: 17961
Joined: Fri Feb 27, 2004 9:54 pm

### RE: How Do Winglets Work?

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's from this book. Besides being porn for aircraft lovers, it does show that most of what is flying today started as the brainchild of some German aerodynamics genius or other: http://www.amazon.com/gp/product/185...-4017743?s=books&v=glance&n=283155

This one is also great: http://www.amazon.com/gp/product/185...-4017743?s=books&v=glance&n=283155
"There are no stupid questions, but there are a lot of inquisitive idiots." - John Ringo

2H4
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### RE: How Do Winglets Work?

 Quoting Starlionblue (Reply 41):You have waaaay too much time on your hands 2H4.

Heh heh....day off + weather too cold (for me) to be on the bike or motorcycle = A.net day.

2H4

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Jetlagged
Posts: 2564
Joined: Sun Jan 23, 2005 3:00 pm

### RE: How Do Winglets Work?

 Quoting AeroWeanie (Reply 31):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 dissapears and only span is left. Where the tip vortices are is everything!

Mathematically you are correct. I was thinking purely of the non-dimensional equation. Actually what you are left with is span squared. However, for a given wing, if you extend span, you inevitably increase aspect ratio. You can't change one without the other.

For the extended span wing, you could argue it was the position of the vortex which was important. However in the case of the classical winglet, although you are increasing the effective span, the actual span remains pretty much as it is. So the vortices just move upward relative to the non-winglet case.

The tip vortices are no further apart, yet the induced drag is less. So it is really the effective wingspan which is important, not the actual span, nor the distance of the vortex from the centreline.
The glass isn't half empty, or half full, it's twice as big as it needs to be.

aeroweanie
Posts: 1576
Joined: Fri Dec 03, 2004 9:33 pm

### RE: How Do Winglets Work?

 Quoting Starlionblue (Reply 36):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 tips. So you get more lift with the same wing and less drag.

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 swept wings.

 Quoting Starlionblue (Reply 36):The main problem is that the wing will try to bend upwards, so it needs to be pretty strong. This is why we didn't see any WWII era German forward sweep fighters actually flying. There were plenty of paper studies at the time though, including the Heinkel P.1076 (piston), a couple of unnamed early jet proposals from Focke-Wulf, the Focke-Wulf P.1073 (precursor to the He-162) and Blohm und Voss P209/02 (single engine jet).

Every wing tries to bend upwards with load. As the bending is normal to the elastic axis, on aft swept wings the bending induces a nose down twist on the wing. On a forward swept wing, a nose up twist is induced. This increases the lift at the tip, which causes more bending and more twist, the process being divergent. It was Norris Krone who thought up the idea of using composites to counter this tendency. This was used on the X-29.

 Quoting Starlionblue (Reply 36):Also there are some stability issues. In a fighter, the planes are unstable anyway so it's just a matter of programming the FBW correctly. But the FAA would probably be a bit leery of certifying an unstable airliner.

A forward swept wing aircraft doesn't have to be longitudinally unstable. The X-29 was designed this way to increase its maneouverablility, just like the F-16. A FBW system then makes the aircraft controllable.

 Quoting Jetlagged (Reply 43):For the extended span wing, you could argue it was the position of the vortex which was important. However in the case of the classical winglet, although you are increasing the effective span, the actual span remains pretty much as it is. So the vortices just move upward relative to the non-winglet case. The tip vortices are no further apart, yet the induced drag is less. So it is really the effective wingspan which is important, not the actual span, nor the distance of the vortex from the centreline.

Ah, you missed the subtle part of the argument. The important part is how far the tip vortices are apart, as measured along the bound vortex of the wing. If the bound vortex is bent up (to follow the winglet), this still counts for distance. I suppose you might say this is really the measure of effective span.

HAWK21M
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Joined: Fri Jan 05, 2001 10:05 pm

### RE: How Do Winglets Work?

 Quoting 2H4 (Reply 20):Winglets are beneficial in more ways than just long-range cruise. They also improve climb performance and have been known to reduce approach speeds

True.In that post I was referring to Weight penalty & how cruise time beng longer would be more Economical
regds
MEL
I may not win often, but I damn well never lose!!!

Starlionblue
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### RE: How Do Winglets Work?

See, told ya AeroWeanie would tell me where I went wrong
"There are no stupid questions, but there are a lot of inquisitive idiots." - John Ringo

Jetlagged
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### RE: How Do Winglets Work?

 Quoting AeroWeanie (Reply 44):Ah, you missed the subtle part of the argument. The important part is how far the tip vortices are apart, as measured along the bound vortex of the wing. If the bound vortex is bent up (to follow the winglet), this still counts for distance. I suppose you might say this is really the measure of effective span.

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
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lehpron
Posts: 6846
Joined: Tue Jul 10, 2001 3:42 am

### RE: How Do Winglets Work?

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 overall drag. This results in increased performance such as rate of clamb, range, fuel efficiency, etc. Increase may be small, but its better than getting a new plane or new engines or lightening the load.

Long version:

First we must look at the situation of the wing tip itself. When an aft-swept wing lifts, it not only bends up but curls forward a bit. The resulting wing tip:

• from the side view, is angled downwards and

• from the front view, the back of the wingtip bends more upwards.

• Make a fake wing out of some paperboard and 'lift' it, you'll have to exaggerate to see what I mean. (Since the boosts in efficiency are small, you are not going to notice anything if you bend it like real-life airplanes).

Winglets end up somewhat facing away from the plane when fixed on the wingtip. The fin itself is not symetrical, and the air flowing around it is not moving straight through. There are two components of airflow: 1) from the direction of flight and 2) from the air flowing around the tip. The air flow in the vicinity of the wing tip is moving inwards and back. A winglet then lifts inwards along the wing's bend. This lift direction is more inwards but there is a tiny bit going forwards.

Raked wingtip devices do about the same thing, except their lift force is directed mostly upwards (they take some of the wing's load) and a bit of force goes forwards.

While I am aware I may upset members here when I say that the wingtip device 'pulls' at a plane's wingtip forward like a kite using the flow moving there -- we get a smaller value for drag with a wingtip device than without. Hence: They call it a drag reduction. And like above:

 Quoting Lehpron (Reply 48):This results in increased performance such as rate of clamb, range, fuel efficiency, etc. Increase may be small, but its better than getting a new plane or new engines or lightening the load.

[Edited 2006-02-05 07:41:42]
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keta
Posts: 405
Joined: Thu Mar 24, 2005 7:14 am

### RE: How Do Winglets Work?

 Quoting AeroWeanie (Reply 34):a properly designed winglet has the same tip vortex strength, as the bound vortex has the same circulation. Its just that the vortices are further away from one another, as measured along the bound vortex.

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 are the same, wouldn't that be the same energy, no matter where they are?
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