VS744
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Wingtips - What Do They Actually Do?

Wed Oct 24, 2001 5:46 pm

What do wingtips do for an aircraft?
.........other than give them another opportunity to display some livery.
Forgive me if I am ignorant here, but Boeing has opted for big tips on the top of the wing, and Airbus has gone for smaller tips which site on the top and the bottom of the wing. McDonnell Douglas also has them on the top and bottom of the wing edge on the MD11.

Why hasn't the 777 got them? why have them?

 
Timborara
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RE: Wingtips - What Do They Actually Do?

Wed Oct 24, 2001 6:03 pm

Now I might be being a bit ignorant here, but generally what they do is improve the airflow around the end of the wing.
A large amount of air turbulence builds up in these areas which can manifest itself as added drag (be it a small amount). The wingtips' job is to smooth out the airflow around the end of the wing, reducing drag. I know on the 744, the wingtips give an added 3-5% efficiency advantage.

Hope that clears things up for you!

Tim
 
TAA_Airbus
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RE: Wingtips - What Do They Actually Do?

Wed Oct 24, 2001 6:27 pm

Wings tips just are the end of the wing, you cant have a wing that goes forever. However, if you are talking about winglets, then there job is to limit wing vorticies.


The high pressure air under the wing (whats holding the a/c in the air) naturally wants to flow to the lower pressure, so at the wing tips, it flows out then up onto the top, this is what creates the spiralling which we know as vortices. The idea of the wing tip is to break the spiralling into just erratic turbulent air. Despite still beipng turbulent, the induced drag is some what less that before thus increasing efficiency.
The strongest vortices occur when the most lift is being produced. ie. take off
 
VS744
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RE: Wingtips - What Do They Actually Do?

Wed Oct 24, 2001 6:43 pm

So the reason they left them off the 777 was.........?
 
azeem
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RE: Wingtips - What Do They Actually Do?

Wed Oct 24, 2001 6:49 pm

they reduce drag....
 
TAA_Airbus
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RE: Wingtips - What Do They Actually Do?

Wed Oct 24, 2001 6:52 pm

because on some particular aerofoils its not viable as the difference would be minimal.
 
Lucifer
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RE: Wingtips - What Do They Actually Do?

Wed Oct 24, 2001 11:01 pm

They stop the airflow from separating early from the wing and going off the end horizontally, thus forcing it to go over the back of the wing, increasing efficiency. It is one of many ways to get the airflow to 'stick' to the wing rather than slide down it, other examples of which you can see as little teeth-like attachments to the upper surface near the leading edge, or simply jutting out rounded plates of metal on older aircraft such as the Comet or the Hawk basic trainer.

The 777 does not need them as its wings are already so efficient that the aerodynamic benefits if fitted would outweigh the weight penalty of carrying them. Indeed they are only really useful on longer range aircraft if in the bigger Boeing style, since they cause more fuel to be consumed in the climb as they are optimised for cruise conditions. Therefore retrofitted winglets may not suit all operators of the 737.
 
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TS-IOR
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RE: Wingtips - What Do They Actually Do?

Fri Oct 26, 2001 9:31 pm


Hy VS744,

You know,being ignorant is not a shame at all.
The shame is that you keep being ignorant while you
have different sources of information.

Wing tip fences or winglets were considered as a
strange evolution in the aviation field,as it was the
first time to see an aircraft fitted with three tails!!!

Air flow in the wing tip is not as efficient as in the
rest of the wing...this causes an increase in the drag
and therefore in the fuel consumption.
Winglets came to improve this perturbated air flow
by reducing the verocity.(I do not confirm it).
Air flow is at its highest degree of efficiency.
This reduces drag and therefore fuel consumption.

Concerning the 777,i think that the wings performance
are at the top,and installing such metal panels does not
contribute in improving its operational costs.

I hope i've been clear and right in my answer.
Of course any additional information or correction
is greatly appreciated.

Sorry,VS is the IATA code of which airline?
I may have forgotten it...thank you!!!
 
Staffan
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RE: Wingtips - What Do They Actually Do?

Sat Oct 27, 2001 2:14 am

There was a thread about this a couple of months back, and it was claimed that the winglet created "thrust", and not only reduced drag...hmmm...

I got curious to find out where this "thrust" came from, and yep I found it! Basically the winglet works the same way as a normal wing, but it is adjusted so that the "lift force" created by the winglet is pointed slightly forward, and this equals to added thrust.


Regards,

Staffan
 
buckfifty
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RE: Wingtips - What Do They Actually Do?

Sat Oct 27, 2001 5:11 am

It's funny, but TAA_Airbus already explained it correctly the first time. I'll just add a bit to it.

The winglets do not add "thrust", they are merely there to reduce induced drag (drag from the creation of lift) by 'fencing' off the wingtip vortices (HP to LP flow of air from the bottom to the top of the wing.) Thrust and drag equations, in that sense, are mutually exclusive.

LIke Lucifer said, there probably wasn't a need for it on the 777, because of the efficiency of the wing design itself. Much like the 764, which have the 'extended' wingtip instead of a winglet. Though, in essence, the extended tips on the 764 work on the same principle as winglets do in reducing wingtip vortice generation.

Lucifer, your description is for vortex generators, not winglets. They are used to increase laminar flow over the surface of the wing to increase lift. Newer higher aspect ratio wings have deleted this feature (i.e. on the 777) because they themselves have different camber designs to better the laminar flow, without increasing induced drag.
 
Staffan
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RE: Wingtips - What Do They Actually Do?

Sat Oct 27, 2001 6:39 am

Buckfifty, the winglet indeed creates a force that is pointing slightly forward (instead of stright up) because of it's very unique shape and angle of attack.

This forward pointing force is the same thing as thrust, you could say negative drag, but that would equal to thrust in the end.

Staffan
 
jmhLUV2fly
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RE: Wingtips - What Do They Actually Do?

Sat Oct 27, 2001 8:42 am

Here is a question regarding the wing and airflow:
Found on all DC-9 series and MD-80/90/95 (717) models there is a "bar" that sticks out a bit on the wing, a reference book of mine calls it the "Ventral wing fence"
what benifits does this bar have, is it simply to hold the leading edge slats in the extended position, any airflow benefits? I hope you know what bar I am talking about, it is distinctive to all DC-9 aircraft.
JMH
 
VonRichtofen
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RE: Wingtips - What Do They Actually Do?

Sat Oct 27, 2001 3:11 pm

TAA_Airbus has it dead on.

I couldn't have said it better myself  Smile/happy/getting dizzy

 
Staffan
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RE: Wingtips - What Do They Actually Do?

Sun Oct 28, 2001 3:18 am

If you doubt the thrust theory on winglets, please have a look at the following pages.

"Winglets are small, nearly vertical fins installed on an airplane's wing tips to help produce a forward thrust in the vortices that typically swirl off the end of the wing, thereby reducing drag."
http://www.dfrc.nasa.gov/gallery/photo/KC-135/HTML/


"The winglet reduces drag and produces thrust"
http://technology.nasa.gov/scripts/nls_ax.dll/w3SuccItem(4000413)


"Winglets harness this upward flow of air by acting like the sails on a sailboat. This produces a forward thrust that helps to counteract the drag acting upon the aircraft."
http://www.visionengineer.com/aero/winglet.shtml


Regards,

Staffan
 
Klaus
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We´ve Got Both Kinds, Country And Western... 8-)

Sun Oct 28, 2001 11:05 am

I´m not an expert on the topic, but I´m gettin pretty certain that both views ("thrust" and "vortex reduction") are just different wordings of the exact same effect.

If you´re thinking on the basis of an ideal wing, the real wing´s "basic" tip "steals" some of your thrust and lift through the wingtip vortices (which take energy away from the plane). Reducing the vortices through winglets just salvages some of this "stolen" thrust and lift.

If you´re starting from the real, "basic" wing, however, winglets will "donate additional" thrust and lift basically "out of nowhere" (which is why I don´t like that view that much Wink/being sarcastic).

Both explanations are identical. They just view the differencial vector from opposite ends.

Peace?  Wink/being sarcastic
 
seagull
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RE: Wingtips - What Do They Actually Do?

Sun Oct 28, 2001 11:31 am

Klaus figured it out, just different ways of looking at the same thing. Does the reduction in vorticies decrease drag or should be view it by the fact that the winglet redirects flow that creates a forward lift vector, and in the process the flow downstream of the winglet reduces vorticy? Is the improved performance due to the reduction in vorticy itself, or is that really just a by-product of the real action? The truth is that Aerodynamicists are still debating this issue, with leading Aerodynamicists taking opposing points of view!

In the end, it doesn't matter, but it is instructive to understand either theory. Note that these do not "complement" each other, but are just different ways of looking at the same problem, similar to the Newton vs. Bernoulli debates, just two sides of the same coin in the end.

As to the B-777, winglets would work for it as well, but the 777 was designed for both short and long haul, and the winglet cannot be efficient all phases of flight. For this it is better to use the "sail" analogy, where only one "sail" AoA will be ideal for any particular phase of flight, so there is no way to make a winglet optimum for both cruise and climb/descent phases unless you made it adjustable, in which case the costs and weight would negate any advantage.
 
Staffan
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RE: Wingtips - What Do They Actually Do?

Sun Oct 28, 2001 11:53 am

Klaus, I understand what you mean. But there is more to it.
It doesn't only reduce the drag by breaking up the vortices, it uses the vortice to create lift as the air coming from the underside of the wing flows across the surface of the winglet. By positioning the winglet in a certain angle and giving it the right shape, this liftforce can be pointed forward, creating thrust.

If you just placed a vertical fin on the wingtip, this would break up the vortice and reduce drag to a certain extent, but the energy from the vortice would be lost. What the winglet does is that it uses the energy that is gained when the vortice is broken and transforms it into lift.

I'm not sure if this is what you meant, but saying that the winglet only brakes up the vortice would not be the whole truth.

Regards,

Staffan  Smile
 
Guest

RE: Wingtips - What Do They Actually Do?

Sun Oct 28, 2001 12:00 pm

I heard that on the 744, it extends the 744 wing like 6 feet, without making it go out exactly like 180 degrees so it doesn't go out too far at gates.
 
Staffan
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RE: Wingtips - What Do They Actually Do?

Sun Oct 28, 2001 12:11 pm

Seagull,
I think it's a combination of both, the reduction of vortices definately reduces the energy lost when high-pressured air otherwise would reach the top of the wing, but instead of simply "shielding" this air off, why not use it to create a lift force that could improve the performance even more?
Think about it, when slowing air down, you get drag, drag creates lift, why not use this lift?

Regards,

Staffan  Smile
 
travellin'man
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RE: Wingtips - What Do They Actually Do?

Sun Oct 28, 2001 12:29 pm

Seagull has it right on for the 777 question.
On short hauls the added weight decreases fuel efficiency. This is why the 744 domestic you see for ANA and JAL doesn't have any either.
It is not enough to be rude; one must also be incorrect.
 
Staffan
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RE: Wingtips - What Do They Actually Do?

Sun Oct 28, 2001 12:34 pm

Travellin'man, Agree on that! Also, the 777 wing is so advanced that the small gains from winglets wouldn't justify the added weight and cost for fitting them.

Regards,

Staffan
 
lehpron
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RE: Wingtips - What Do They Actually Do?

Sun Oct 28, 2001 5:21 pm

I think you are refering to the vertical pieces at the ends of wings, they are called "winglets."

I found this book called "Aerodynamics for Engineering Students", 4th ed. by E.L. Houghton and P.W. Carpenter. On page 459, they talk about winglets, I'll quote them and let's see if it makes sence:

..on all subsonic wings there is a tendency for a secondary flow to develop from the high pressure region below the wing round the tip into the relatively lower-pressure region on the upper surface, this process forms the trailing vortices. If a winglet of appropriate design and orientation is fitted to the wing-tip, the secondary flow causes the winglet to be at an effective angle of incidence, giving rise to lift and drag components. Both components counter the aircrafts drag as a whole. For a well-designed winglet the contribution of lift predonminates, resulting in a net reduction of overall drag, or a thrust.

In otherwords, these winglets are bent away from the plane at a very small angle so that they experience a force from both the plane's movement and the airflow that creates the swirls at the wing's tip which is known as the secondary flow. All force directions cancel away and we are just left with a very small lift force in the direction of flight; these winglets act like sails on a boat getting what looks like free thrust.

Hope this helps.  Big thumbs up

The meaning of life is curiosity; we were put on this planet to explore opportunities.
 
Staffan
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RE: Wingtips - What Do They Actually Do?

Sun Oct 28, 2001 9:56 pm

Thanks, Lehpron!

Staffan Big grin
 
seagull
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RE: Wingtips - What Do They Actually Do?

Mon Oct 29, 2001 12:23 am

Staffan,

No, it is not a "combination", they are just two approaches to the same problem. As I said before, there are current aerodynamic debates on this issue, but I view it as a "chicken or egg" situation. However, it is defnitely NOT a case of being a "bit of this and a bit of that"! You can use one explanation or the other. I understand completely the argument for the wing tip "sails" that you are using, and have used that in explaining it to others many times. That is used in many current textbooks. However, the physicists seem to prefer the vorticy argument, and aerodynamics is just an area of applied physics, afterall!

Look here for some interesting reading:

http://adg.stanford.edu/aa241/AircraftDesign.html

http://aerodyn.org/

http://www.rz.uni-frankfurt.de/~weltner/Mis6/mis6.html


 
Staffan
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RE: Wingtips - What Do They Actually Do?

Mon Oct 29, 2001 2:39 am

I'm having difficulty in understanding that these two explainations are looking at the same thing.

Reduction in vortices reduces drag, since high pressured air is stopped from flowing across the wing tip. But taking this process one step further and actually using this air that is redirected to create a lift force, is IMO something totally different than just blocking of the airflow.

If I'm totally wrong on it please explain, because I want to know.

Regards,

Staffan
 
seagull
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RE: Wingtips - What Do They Actually Do?

Mon Oct 29, 2001 3:13 am

You are missing where the air is being used. The air is already curling around and inboard due to the pressure differential. The higher pressure air under the wing wants to "escape" and it does so out the sides, where it naturally moves first outboard from under the wing then upwards. This creates a relative airflow at the wingtip that is aft and inboard slightly. It is this inboard flow that is utilized to create the forward thrust, however, there is another way to look at it. The "lift" off the winglet creates its own "downwash" that moves outward from the wing, which opposes the inboard rotation from the original vorticy, thus reducing the amount of rotation in the air.

Now, that means that less energy is imparted to the air so there is less energy wasted in the production of useless vorticy. The fact that the inboard lift is created is the reason the vorticies are less. The vorticies are less because the inboard lift is created. The aircraft gains efficiency from the lift vector, or because there is less vorticy created, and you can calculate it using either model, but you can't really use both at the same time because you don't get one without the other.

This is like Bernoulli vs. Newton for lift creation. Bernoullis laws are derived from Newton's, so you don't use both at the same time to get a value for total lift. Bernoulli is a useful way for estimating the total lift force that is actually a result of Newtonion principles.
 
delta-flyer
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RE: Wingtips - What Do They Actually Do?

Mon Oct 29, 2001 3:16 am

I agree with Seagull's explanation.

Many problems in physics can be explained using different theories, but ultimately they all tie back "to the basics" - Newton's laws. One example is looking at motion using the conservation of energy approach, or the mass-force-acceleration approach. The answers come out the same.

Now, on to vortices. Whenever lift is produced, there must be "circulation" component around the wing. This is more mathematical than physical, but the if you want to imagine it physically, assume that superimposed on your streamlines around the wing is another component of circular streamlines. The resultant streamlines are obtained by adding the two together. This is accomplished by adding the stream functions of each set together, point by point, and joining points of equal stream function together to get the streamlines. The strength of this circular component is adjusted (mathematically) to skew the resultant streamilines so that the stagnation points fall at the leading and trailing edges in the actual (physical) locations. This circulation, mathematically, is equivalent to lift.

However, there is a physical manifestation of circulation, and that is vortices. These are generated whenever there is lift. Vortex shedding has been a challenge from the early days. There are many schemes for controlling it, and I would assume from the posts above that the winglets may be another tool for this.

Regardless of how you explain it, ALL equations and principles of physics apply to winglets, be it Bernouli, Newton, etc.

I know this sounds complicated in words, maybe one day I will make some sketches and post them on a website.

Cheers
Pete

"In God we trust, everyone else bring data"
 
Staffan
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RE: Wingtips - What Do They Actually Do?

Mon Oct 29, 2001 3:57 am

Ok, I think I misunderstood your first post. I understand the difference.

Staffan
 
Staffan
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RE: Wingtips - What Do They Actually Do?

Mon Oct 29, 2001 4:51 am

Thanks alot for the explainations!

Staffan
 
lehpron
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RE: Wingtips - What Do They Actually Do?

Mon Oct 29, 2001 3:34 pm

Your welcome Staffan.  Wink/being sarcastic

However, I believe winglets reduce the induced drag by 5%, according to NASA. Last month I came up with an innovation that can replace the winglet and provide upwards of 20% reduction in the induced drag. I am currently looking through US patents to see if I can get one.:D
The meaning of life is curiosity; we were put on this planet to explore opportunities.

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