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Starlionblue
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Kink On Trailing Edge In Airbus Vs Boeing Wings

Fri Jul 09, 2010 8:04 am

Before we start, I don't want to start an A vs. B thing. I'm just interested in what factors influenced the different designs.

If we take a "typical" Boeing wing, it widens from wing tip to root at an "even" rate, that is trailing and leading edges are both straight, up to a point about one quarter of the span from the fuselage, at which point the trailing edge "turns" towards the rear, giving a bigger "chord change" close to the root. In fact, at this point the trailing edge is perpendicular to the fuselage.


If we look instead at a "typical" Airbus widebody wing, the taper has no kink, or less kink, with the trailing edge straight, especially on the 380. There is definitely no point at which the trailing edge is perpendicular to the fuselage.


On the narrowbodies, however, we see the "Boeing" type both for 737 and 320, with a long section perpendicular to the fuselage.



So here's my question: What is the difference between a wing that is evenly tapered, and one that has a kink in the trailing edge? Is there any relation to the pronounced gulling in Airbus widebodies?
"There are no stupid questions, but there are a lot of inquisitive idiots." - John Ringo
 
Pihero
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RE: Kink On Trailing Edge In Airbus Vs Boeing Wings

Fri Jul 09, 2010 11:50 am

Would you believe, that "kink", which is obtained by inserting a triangular section at the trailing edge is called a yehudi.
The subject is vast, but it could be resumed in a few positive results ;
- it provides a more efficient high speed aileron
- a stiffening of the total wing
- a bigger / wider space for retracted landing gear
- an increase of the wing surface at a low cost
- a relative thinner thickness ratio, condusive to a delayed sonic wave on a large part of the wing and a more natural stall characteristics as it would see an onset before the wingtip....

You should have included in your list the A300 and A310, the initial 'Buses which displayed a very prominent yehudi, à la Boeing.

The inconvenients of the design are mainly about low speed, flaps extended aerodynamics : the high lift devices either become too heavy or not very efficient ( they talk about Fowler ratio as a measure of the flap efficiency, given by the ratio of the flap-retracted chord to the flap-extended one ).

The two above concerns in fact give you the reason why there are differences : Airbus generally use a thicker foil, which, by being stiffer can do away with the need of a high-speed aileron, but is optimised for lower Mach numbers (the case for the 330 / 340) than the Boeings of the same generation.
At the same time, the A wing being smaller has a higher wing loading...but due to a continuous trailing edge allows an uninterrupted set of both leading-edge and trailing-edge flaps, which in turn gives the 'Bus family an incredibly efficient, though very simple high-lift devices.
So, again, this is all a matter of compromises.
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tdscanuck
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RE: Kink On Trailing Edge In Airbus Vs Boeing Wings

Fri Jul 09, 2010 1:21 pm

Quoting Starlionblue (Thread starter):
What is the difference between a wing that is evenly tapered, and one that has a kink in the trailing edge?

As Pihero very correctly posted, it's all about how the yehudi is implemented. Structurally, there's not really any difference in the main wing box and, given that both those designs use a landing gear beam to "flesh out" the yehudi, there isn't much difference there either. The major difference to whether the kind is there or not is in how the fixed and moveable trailing edges are implemented.

Quoting Starlionblue (Thread starter):
Is there any relation to the pronounced gulling in Airbus widebodies?

Not that I'm aware of...making the different trailing edges work with different degrees of gulling is just a kinematics problem to be solved.

Quoting Pihero (Reply 1):
Would you believe, that "kink", which is obtained by inserting a triangular section at the trailing edge is called a yehudi.

Both Boeing and Airbus use yehudi's exensively...that's just the "filler" triangle that goes between the rear spar and the trailing edge, not specifically the kink. I think Starlionblue is asking specifically about whether the trailing edge is a smooth curve (a la A380) or whether it's straight with a pronounced kink...in either case, you've still go at yehudi.

Quoting Pihero (Reply 1):
- it provides a more efficient high speed aileron

Can you elaborate on this a little more? I hadn't heard about this benefit and I'm intrigued how it works.

Tom.
 
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Starlionblue
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RE: Kink On Trailing Edge In Airbus Vs Boeing Wings

Fri Jul 09, 2010 2:19 pm

Wow, thanks for the great replies so far. Any ideas why it is called a yehudi? Jewish inventor? And where did it originate exactly, as in what design?

Quoting tdscanuck (Reply 2):
I think Starlionblue is asking specifically about whether the trailing edge is a smooth curve (a la A380) or whether it's straight with a pronounced kink...in either case, you've still go at yehudi.

Well, it's been informative so far, but I am indeed also interested in why one would make an actual "corner" with a perpendicular section (767, 777) as opposed to a smooth curve and no perpendicular section (380) . And are there no flow issues with a sharp corner?
"There are no stupid questions, but there are a lot of inquisitive idiots." - John Ringo
 
aeroweanie
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RE: Kink On Trailing Edge In Airbus Vs Boeing Wings

Fri Jul 09, 2010 3:48 pm

Quoting Starlionblue (Reply 3):
Wow, thanks for the great replies so far. Any ideas why it is called a yehudi? Jewish inventor? And where did it originate exactly, as in what design?

It originated when Boeing developed the 707-300 wing from the 707-120 wing. The name came from them "fiddling" around. (Yehudi Menuhin is a famous violinist).
 
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bikerthai
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RE: Kink On Trailing Edge In Airbus Vs Boeing Wings

Fri Jul 09, 2010 4:05 pm

It's a nice little trivia when you get to name something.
I hope someday someone would ask about the "tower of power" on the AEW&C aircraft  .

Tower of Power: 70's Funk Band

bikerthai

[Edited 2010-07-09 09:07:30]
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RE: Kink On Trailing Edge In Airbus Vs Boeing Wings

Fri Jul 09, 2010 5:14 pm

Quoting Aeroweanie (Reply 4):
It originated when Boeing developed the 707-300 wing from the 707-120 wing. The name came from them "fiddling" around. (Yehudi Menuhin is a famous violinist).

Thats interesting, I wonder what caused North Americam Aviation to add the "yehudi" to the wing of the F-100D over two years before Boeing added it to the 707-300?

In addition to what "Pihero" pointed out in Reply 1: The inboard portion of the wing creates the majority of the wings lift.
 
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RE: Kink On Trailing Edge In Airbus Vs Boeing Wings

Fri Jul 09, 2010 6:11 pm

Quoting Aeroweanie (Reply 4):
Quoting Starlionblue (Reply 3):
Wow, thanks for the great replies so far. Any ideas why it is called a yehudi? Jewish inventor? And where did it originate exactly, as in what design?

It originated when Boeing developed the 707-300 wing from the 707-120 wing. The name came from them "fiddling" around. (Yehudi Menuhin is a famous violinist).

Summary of 707 wing design differences on the various models. (Sidenote: Yehudi Menuhin WAS a famous violinist. He died in 1999.)

 
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RE: Kink On Trailing Edge In Airbus Vs Boeing Wings

Fri Jul 09, 2010 9:24 pm

Quoting Pihero (Reply 1):
Would you believe, that "kink", which is obtained by inserting a triangular section at the trailing edge is called a yehudi.

OK, Pihero, I have always read your posts intently and have learned much from you, but this is something I had never even thought about the nomenclature of. That is a great vocabulary word, and my hat's off to you for the excellent explanation.
 
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RE: Kink On Trailing Edge In Airbus Vs Boeing Wings

Fri Jul 09, 2010 11:34 pm

Quoting Viscount724 (Reply 7):

Great picture!
Any particular reasoning behind the dogtooth? (last diagram)
"There is an art, or rather a knack to flying. The knack lies in learning how to throw yourself at the ground and miss."
 
njxc500
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RE: Kink On Trailing Edge In Airbus Vs Boeing Wings

Sat Jul 10, 2010 12:10 am

I believe the dogtooth is a device that aims to reduce the stall speed of the outer wing areas, therefore maintaining control from the ailerons during a stall. Please correct me if I'm wrong, but I believe there is a vortex generated by this in a high AOA situation, which helps stick the flow to the wing. I believe this is a feature on newer learjets.
 
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RE: Kink On Trailing Edge In Airbus Vs Boeing Wings

Sat Jul 10, 2010 12:30 am

Quoting Starlionblue (Reply 3):
but I am indeed also interested in why one would make an actual "corner" with a perpendicular section (767, 777) as opposed to a smooth curve

On the 787 the corners have been rounded. The trailing edge at the outboard end of the inboard flap and the inboard end of the outboard flap is curved and blends into the trailing edge of the flaperon.
 
tdscanuck
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RE: Kink On Trailing Edge In Airbus Vs Boeing Wings

Sat Jul 10, 2010 2:45 am

Quoting Starlionblue (Reply 3):
I am indeed also interested in why one would make an actual "corner" with a perpendicular section (767, 777) as opposed to a smooth curve and no perpendicular section (380) . And are there no flow issues with a sharp corner?

Sharp corners across the flow like that aren't really an issue...the flow can't really "see" a corner in that plane.

All other things being equal, straight lines are easier to design, analyze, and build. Like the A380, the 787 has switched to a smooth curve. I suspect either the emphasis on efficiency tipped the trade towards curved trailing edges, or technology (for design, analysis, and manufacturing) progressed to the point that the straight construction didn't pay its way anymore.

Tom.
 
Viscount724
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RE: Kink On Trailing Edge In Airbus Vs Boeing Wings

Sat Jul 10, 2010 2:58 am

Quoting GAIsweetGAI (Reply 9):
Quoting Viscount724 (Reply 7):


Great picture!
Any particular reasoning behind the dogtooth? (last diagram)
Quoting njxc500 (Reply 10):
I believe the dogtooth is a device that aims to reduce the stall speed of the outer wing areas, therefore maintaining control from the ailerons during a stall. Please correct me if I'm wrong, but I believe there is a vortex generated by this in a high AOA situation, which helps stick the flow to the wing. I believe this is a feature on newer learjets.

Photo showing the "dogtooth" leading edge on the 707-320B/C.

http://upload.wikimedia.org/wikipedia/en/thumb/c/c1/Boeing_707_engineviewedit.jpg/800px-Boeing_707_engineviewedit.jpg

Another aircraft with a much more prominent dogtooth was the Ilyushin 62.


View Large View Medium
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Photo © Anton Bannikov

 
UAL747
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RE: Kink On Trailing Edge In Airbus Vs Boeing Wings

Sat Jul 10, 2010 3:25 am

To stir the pot a bit, the 747 has another quirk with it's wing. It's difficult to show on diagrams because I know of none that point it out, so I will resort to my own picture:

http://hphotos-snc3.fbcdn.net/hs316.snc3/28484_821210066377_9609877_44492153_3400484_n.jpg

The 747 has a definite wing sweep, that is until you get passed the outer engine pylon. The sweep changes to a lesser degree than the rest of the wing.

Another interesting thing I noted is where the winglet attaches to the wing:

http://hphotos-snc3.fbcdn.net/hs296.snc3/28484_821209672167_9609877_44492109_7234186_n.jpg

There is a definite downward curvature to the wing around the winglet. It's more pronounced from behind since the wing looks thinner. Can anyone explain this to me? I've asked this question before, but people have said that it's fuel, but this occurs too far out toward the winglet to be impacted by fuel, ie, the structure is too thick and short by that time for the weigh of fuel to have that dramatic of a "drooping" affect in that particular area.

UAL
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RE: Kink On Trailing Edge In Airbus Vs Boeing Wings

Sat Jul 10, 2010 3:26 am

Quoting njxc500 (Reply 10):

Now that you mention it - we have a Mirage III on campus, which has some sort of "tooth" in the wing leading edge. One of our teachers (I forget if it was the aerodynamics or the flight dynamics teacher) told us that that dent was added during testing to improve stall characteristics.
"There is an art, or rather a knack to flying. The knack lies in learning how to throw yourself at the ground and miss."
 
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RE: Kink On Trailing Edge In Airbus Vs Boeing Wings

Sat Jul 10, 2010 3:42 am

Quoting tdscanuck (Reply 12):
I suspect either the emphasis on efficiency tipped the trade towards curved trailing edges, or technology (for design, analysis, and manufacturing) progressed to the point that the straight construction didn't pay its way anymore.

Yep. There's only one component in the structure which is significantly more difficult because of the curve.
 
tdscanuck
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RE: Kink On Trailing Edge In Airbus Vs Boeing Wings

Sat Jul 10, 2010 3:59 am

Quoting UAL747 (Reply 14):
The 747 has a definite wing sweep, that is until you get passed the outer engine pylon. The sweep changes to a lesser degree than the rest of the wing

That's an optical illusion caused by the change in flex as you cross the pylon (there's a step-change in shear at that point). If you look at a scale drawing (e.g. http://www.boeing.com/commercial/airports/acaps/7471sec9.pdf) you can see that the leading edge is dead straight and has constant sweep.

Quoting UAL747 (Reply 14):
There is a definite downward curvature to the wing around the winglet. It's more pronounced from behind since the wing looks thinner. Can anyone explain this to me?

Nobody designs for the loft on the ground; it's designed to have the right loft in flight, then they back out jig position (the position during wing assembly) from there. The position you get on the ground is just wherever the wing sags from the jig position. Given that the wing gets more flexible as you get to the tip (since it's getting thinner) and you've got a moment from the winglet, I suspect the flight position doesn't have that downward curvature at all.

Tom.
 
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Starlionblue
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RE: Kink On Trailing Edge In Airbus Vs Boeing Wings

Sat Jul 10, 2010 4:14 am

Wow. Love the answers. Love this forum.

Quoting UAL747 (Reply 14):
The 747 has a definite wing sweep, that is until you get passed the outer engine pylon. The sweep changes to a lesser degree than the rest of the wing

As tdscanuck says this is an optical illusion. You can see the same on other aircraft, for example the 330.
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MSPNWA
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RE: Kink On Trailing Edge In Airbus Vs Boeing Wings

Sat Jul 10, 2010 5:37 am

Quoting UAL747 (Reply 14):
The 747 has a definite wing sweep, that is until you get passed the outer engine pylon. The sweep changes to a lesser degree than the rest of the wing.

I've noticed that too, and I've seen it prominently in pictures when the plane is on the ground as well. I've also seen it in sketch diagrams. It's not an optical illusion. However I've yet to find out why it exists.

Quoting UAL747 (Reply 14):
There is a definite downward curvature to the wing around the winglet. It's more pronounced from behind since the wing looks thinner. Can anyone explain this to me?

I've noticed that quirk too. My guess is that it's related to the "Sutter twist". It was a late redesign of the 747 wing that twisted the wing only outboard of the outboard engine nacelles. It was to alleviate the problem of the outer wing carrying too much of the load. But, it's just a guess. Don't take my word for it.
 
tdscanuck
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RE: Kink On Trailing Edge In Airbus Vs Boeing Wings

Sat Jul 10, 2010 6:57 am

Quoting MSPNWA (Reply 19):
I've also seen it in sketch diagrams. It's not an optical illusion.

Just so we're clear, you're saying that the scaled drawings that Boeing provides to airports and airlines for planning where things will fit is *wrong*?

Quoting MSPNWA (Reply 19):
My guess is that it's related to the "Sutter twist". It was a late redesign of the 747 wing that twisted the wing only outboard of the outboard engine nacelles. It was to alleviate the problem of the outer wing carrying too much of the load.

I'm not sure that's the same thing...wing twist doesn't (normally) show up as a change in dihedral angle. The photo that UAL747 provided pretty clearly shows a drop-off in dihedral in about the last 10' or so of the wing. That's different than twist, which is a lot more pronounced and is clearly visible if you trace the wing lower surface all the way from inboard of the no. 4 pylon.

Tom.
 
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747classic
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RE: Kink On Trailing Edge In Airbus Vs Boeing Wings

Sat Jul 10, 2010 9:48 am

Quoting MSPNWA (Reply 19):
My guess is that it's related to the "Sutter twist". It was a late redesign of the 747 wing that twisted the wing only outboard of the outboard engine nacelles. It was to alleviate the problem of the outer wing carrying too much of the load. But, it's just a guess. Don't take my word for it.



You are fully correct, it's not a change in sweep but a change in twist. I always told the story of "Sutters twist" to our new 747 flight crew during type qualification, as nice background info.

During the development of the 747 the original designed wing needed additional twisting so that the aerodynamic and structural forces would become in balance.
A total wing redesign seemed necessary, but this would have meant redesigning the wing box. To save costs and time a compromise was chosen, instead of twisting the whole wing, they (Sutter and Webb) would twist only from the outer engine to the tip.
It would mean a BARELY PERCEPTIBLE BREAK in the line of the leading edge. It certainly was not elegant. But together with an other weight redistribution of the wing loads, it worked.
The outboard twist became a legendary fix, eventually known as the "Sutter twist".

From : Wide Body, the Triumph of the 747 by Clive Irving, pag. 248,249

Question : Is this break in twist also visible on the new 747-8 wing (contains the same wingbox) or is it redesigned.
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Pihero
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RE: Kink On Trailing Edge In Airbus Vs Boeing Wings

Sat Jul 10, 2010 1:05 pm

Quoting Starlionblue (Thread starter):
Is there any relation to the pronounced gulling in Airbus widebodies?

I would say yes and no.
- yes because it's the same design goal : achieve the lowest drag at the wing-to-fuselage junction. Here again one can see the different solutions both manufacturers arrive at :
Boeing strives for elegant simplicity where the wing connects to the fuselage at an orthogonal manner : the fairing is neat and simple, the designer just wants to achieve the simplest junction possible and basically, any vortices should be limited to the immediate vicinity of the fairing. ( I suspect that the 757 wash characteristics originate here ).
- no, as Airbus, on the other hand, and because of the original "smaller" wing, is obliged to extract from their design the most favourable Cl /Cd , hence a beautiful (don't think it was planned that way) exercise on 3D computer aerodynamics, involving the wing, the junction to the fuselage via a very elaborate fairing...but they too have to simplify the whole junction through an orthogonal link (very similar to the B solution), but at the same time, took advantage of that solution in reducing the gear height. It's only pronounced when you have a rear view of the aircraft. BTW, that's the Corsair solution  
Quoting tdscanuck (Reply 2):

Quoting Pihero (Reply 1):
- it provides a more efficient high speed aileron

Can you elaborate on this a little more? I hadn't heard about this benefit and I'm intrigued how it works.

The yehudi starts on the extended inboard engine strut line...and that's where the high speed aileron is placed.
According to my old aerodynamics teacher, there is no better place for it to be : the stiffest part of the wing and the benefit of using the jet exhaust on an astonishingly marked Coanda effect, which necessitates far smaller aileron movements than expected.

Got to love these aerodynamicists !
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tdscanuck
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RE: Kink On Trailing Edge In Airbus Vs Boeing Wings

Sat Jul 10, 2010 3:36 pm

Quoting 747classic (Reply 21):
Question : Is this break in twist also visible on the new 747-8 wing (contains the same wingbox) or is it redesigned.

It's not actually the same wingbox...it's structurally similar (i.e. the way it's built is basically the same) but the actual shape isn't. The whole wing was relofted.

Quoting Pihero (Reply 22):
The yehudi starts on the extended inboard engine strut line...and that's where the high speed aileron is placed.
According to my old aerodynamics teacher, there is no better place for it to be : the stiffest part of the wing and the benefit of using the jet exhaust on an astonishingly marked Coanda effect, which necessitates far smaller aileron movements than expected.

That's just cool! A blown aileron.

Quoting tdscanuck (Reply 20):
Just so we're clear, you're saying that the scaled drawings that Boeing provides to airports and airlines for planning where things will fit is *wrong*?

I stand corrected. FWI747 tipped me off via IM (thank you!) that there may be a 2 degree change in leading edge sweep as you cross the outer pylon and it's true...for the -400/-8 only! I pulled some large format wing station diagrams and slapped a ruler on them. The 747-100/200/300 has a dead straight leading edge and I originally used the first scale diagram I came across, which was a -100/200.

The -400, which is what UAL747's photo is of, has a definite change in leading edge sweep outboard of the outer pylon. The -8 has the same feature.

Tom.

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