EK156
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A380 And Wake Turbulance

Tue May 17, 2005 2:52 am

Can anyone give us more info on the wake turbulance of the A380.. Discovery channel states that the new wing design will reduce wake turbulance on the A380... by how much?? Will the A 380 have a bigger separation distance...

As far as I know, the B747 can flip a learjet upside down due to wake turbulance unless there is a sufficient separation....
 
Morvious
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RE: A380 And Wake Turbulance

Tue May 17, 2005 3:01 am

They designed the wing in a way that it wouldn't have a bigger wake turbelence then any other big jet flying already around.
Wind tunnel tests gave a positive result. I think they will or have already tested it with the original scale!

They explained why in that same program. And if I remeber correct, there is no need for a bigger seperation bewteen the A380 and the following aircraft.
Don't sue me if this info isn't correct.. I saw this at the Discovery channel.. blame them  Wink
have a good day, Stefan van Hierden
 
Glom
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RE: A380 And Wake Turbulance

Tue May 17, 2005 3:16 am

I suspect the wing fences will prevent the wake turbulence from being too high. Shame though, I was hoping for a new wake turbulence category: light, small, medium, heavy, electron degenerate.

Bigger question: what about wake turbulence from the AN-225?
 
aeropiggot
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RE: A380 And Wake Turbulance

Tue May 17, 2005 5:54 am

Quote:
They designed the wing in a way that it wouldn't have a bigger wake turbelence then any other big jet flying already around.
Wind tunnel tests gave a positive result. I think they will or have already tested it with the original scale!

They explained why in that same program. And if I remeber correct, there is no need for a bigger seperation bewteen the A380 and the following aircraft.
Don't sue me if this info isn't correct.. I saw this at the Discovery channel.. blame them

Listen gentlemen, wake turbulence is pure physics, it cannot be avoided. The airplane must generate lift to fly, and as a consequence a downwash is produce from the wings, which dissipates into the surrounding airflow as wake turbulence. The A380 weighing over 1.2 million lbs, must generate at least this amount of lift in level flight, therefore the downwash and associated trailing vortices will be greater than other commercial aircraft. The A380 will have to have a greater separation distance than the B744 from trailing aircraft, which will limit the number of takeoffs and landing from departing or arriving airports.
 twocents 
A scientist discovers that which exists, an engineer creates that which never was.
 
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Richard28
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RE: A380 And Wake Turbulance

Tue May 17, 2005 6:07 am

Quoting AeroPiggot (Reply 3):
the downwash and associated trailing vortices will be greater than other commercial aircraft. The A380 will have to have a greater separation distance than the B744 from trailing aircraft, which will limit the number of takeoffs and landing from departing or arriving airports.

Not according to Airbus, per an article in the Observer :

"Airbus insists that its unprecedented new design means the A380 will create no more wake disturbance than a 747. The company has measured the wake using computer simulation and is confident it will pass the real-world assessments."

( Source: http://observer.guardian.co.uk/travel/story/0,6903,1474063,00.html )

[Edited 2005-05-16 23:08:31]
 
AJRfromSYR
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RE: A380 And Wake Turbulance

Tue May 17, 2005 6:16 am

The A380 wing might be able to distribute the turbulence better, therefore there might not be any need for extra separation. Just a thought.
-AJR-
 
DLKAPA
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RE: A380 And Wake Turbulance

Tue May 17, 2005 6:37 am

Quoting AeroPiggot (Reply 3):

Like you say, wake turbulence is pure physics. And yes, the A380 weighs alot. In mid-flight, it will probably have a mass something on the order of 450,000kg (this is assuming some fuel has been burned off- note: fuel will be burning thus the weight will constantly change. This is just assuming somewhere in cruise). This means that gravity will be acting to pull the plane downward at a constant force of 4,410,000 Newtons. In order to sustain level flight, the wing then has to create a constant upward force of 4,410,000 Newtons. Anything less and the plane will begin to accelerate in a downward direction, anything more and it will begin to accelerate in an upward direction. To achieve this upward force, there needs to be enough airflow over the wing surface such that it is a mostly laminar flow, and the air on top has to be going faster than the air on the bottom. Basic Bernoulli's principal. When there's enough difference in speeds on the top and bottom of the wing, the faster air on top will create less of a drag force than the slower air on the bottom of the wing. This slower air pushes on the bottom of the wing, exerting more force than the faster air on top, effectively sucking the airliner into the air.

Here's where wing design comes in. At the back of the wing, where the airflow comes back together, alot of turbulence is created, aka wake turbulence. The Faster air hits the slower air and creates eddies. The challenge for airbus was to create a wing that could (using our model of mid-cruise here again) provide 4,410,000 Newtons of upward lift (just enough to resist gravity without climbing), while at the same time keeping the airflow immediately aft of the wing as smoothe as possible. To do this, they would want to create a wing that could accelerate the air at the front of the wing to a very rapid speed, slowing down as it passes to the rear of the wing, where it meets the air coming from the bottom of the wing. The closer these two airstreams match each other in airspeed, the less turbulence there is. There is always going to be wake turbulence, because if the airspeed off the top and bottom of the wing matched each other, the wing wouldn't lift. Airbus has produced a wing that can efficiently lift their airliner, without excessive wake turbulence, because of their extensive wind tunnel experiments and an efficient wing design.
And all at once the crowd begins to sing: Sometimes the hardest thing and the right thing are the same
 
VSIVARIES
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RE: A380 And Wake Turbulance

Tue May 17, 2005 6:39 am

Wake turbulence is a very complicated field that is hard to research. But there are many factors that affect it. The latest thinking suggests that large A/C actually produce more wake vortex on the ground (i.e. prior to rotation) than when airborne.
It's been discussed a lot in tech/ops before - suggest you do a search.
B/R
For every action there is always an unequal but mostly similar reaction.
 
aeropiggot
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RE: A380 And Wake Turbulance

Tue May 17, 2005 6:57 am

Quote:
Airbus has produced a wing that can efficiently lift their airliner, without excessive wake turbulence, because of their extensive wind tunnel experiments and an efficient wing design.

As you correctly mentioned above, wake turbulence is difficult to research in a lab or computationally. Flight test is truly where the "rubber meets the road", and I am curious to see if all of Airbus CFD data indicating that the A380 will have a lower wake turbulence signature than the B744 will be proven. My guess is....NOT!! The A380 should be properly called the "Typhoon", because that is what will be chasing the it, as it take off and land at the various airports around the world.
 Smile
A scientist discovers that which exists, an engineer creates that which never was.
 
DLKAPA
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RE: A380 And Wake Turbulance

Tue May 17, 2005 7:04 am

Quoting AeroPiggot (Reply 8):
NOT!! The A380 should be properly called the "Typhoon", because that is what will be chasing the it, as it take off and land at the various airports around the world.

Just because an airplane is big doesn't necessarily mean it's wake is going to be. If the difference of the speed coming from the top and bottom is great, then wake turbulence will be great also. You could have a business jet that would require heavy separation if the wing isn't an efficient one.
And all at once the crowd begins to sing: Sometimes the hardest thing and the right thing are the same
 
VSIVARIES
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RE: A380 And Wake Turbulance

Tue May 17, 2005 7:52 am

Quoting DLKAPA (Reply 9):
Just because an airplane is big doesn't necessarily mean it's wake is going to be.

Sorry but this is wrong. There are no absolutes in this area but what we do know for sure is that more weight = greater wake vortex. This isn't to say that the people in Wales haven't been able to do some clever things with the wings to make it no worse than (let's say) a 744. But sorry my old china wake vortex from biz jets is not considered in normal flying practice here, we allow for about three-five minutes separation on 737 upwards. Haven't had the pleasure of landing behind a departing A380 yet!
For every action there is always an unequal but mostly similar reaction.
 
aeropiggot
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RE: A380 And Wake Turbulance

Tue May 17, 2005 8:29 am

Quote:
DLKAPA (Reply 9): Just because an airplane is big doesn't necessarily mean it's wake is going to be

No DLKAPA, size is not the important variable here, weight is. Also remember the conservation of energy law. The heavier the airplane the more lift the wings must generate, and thus the greater the strength of the vortex. Now what do you want to do with it, to reduce the effect on other airplanes is the key. There are ways to cause the vortex to dissipate more rapidly, through destructive interference. I will not mentioned the details here, but suffice it to say, the A380 will not get with in the B744 separation distance (6 nm). In fact if Airbus had this technology, then why did they not implement it on the A346, which has wake vortex strength to rival the B744  Confused
A scientist discovers that which exists, an engineer creates that which never was.
 
B744F
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RE: A380 And Wake Turbulance

Tue May 17, 2005 9:27 am

So how exactly can you slow down the air on the top of the wing but not have adverse effects on such things as fuel efficiency? You are creating more drag on the top of the wing, at least that is what it seems. I'm sure Airbus' experts are better at this than I am, but this is probably more from their PR department stating something like it doesn't need any more separation rather than from actual flight testing.
 
speedbird128
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RE: A380 And Wake Turbulance

Tue May 17, 2005 1:36 pm

Quoting DLKAPA (Reply 9):
Just because an airplane is big doesn't necessarily mean it's wake is going to be.



Quoting VSIVARIES (Reply 10):
Sorry but this is wrong.

OK, so why then is a 757 notorious for having a wake-turbulence greater than the weight category it should have been in... It's well under the upper limit for a medium aircraft, yet as ATC we treat it as a heavy because of it's wake!?

I tend to agree with DLKAPA...
A306, A313, A319, A320, A321, A332, A343, A345, A346 A388, AC90, B06, B722, B732, B733, B735, B738, B744, B762, B772, B7
 
Areopagus
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RE: A380 And Wake Turbulance

Tue May 17, 2005 2:01 pm

The weight of the aircraft is equal to the downward force it places on the air, if the plane is flying straight and level -- no doubt about it. In order to produce lift, the air pressure over the top of the wing must be lower than the air pressure on the bottom. Out at the wing tip, the high pressure air can scoot around the tip to reach the low-pressure zone. This sets up the vortex or tornado at the wing tips. (To be sure, the air is pressed downward all along the span.)

How bad the vortex is on following aircraft depends partly on the spanwise lift distribution. If the wingtip generates a substantial part of the lift, the vortex will be strong. If the lift is concentrated more toward the center, and falls off toward the wing tips, the vortex strength is reduced. This does not change the total momentum per second transferred to the air, but it reduces the peak wind speed in the tip vortex.

Think of it this way: Would you rather be hit by a tornado for one second, or by a 20 knot wind for ten seconds?

The Spitfire had elliptical wings to achieve an elliptical lift distribution, but an elliptical wing is not the only way to do it. Wing twist and changing wing section can also do the job.

757: relatively short wing, strong vortex.
380: long wing span distributes the load to a wider swath of air, reducing the tip vortex speed.
 
DLKAPA
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RE: A380 And Wake Turbulance

Tue May 17, 2005 2:20 pm

Quoting AeroPiggot (Reply 11):
No DLKAPA, size is not the important variable here, weight is.

I guess that's why the 757 is treated by ATC as Heavy?

Quoting B744F (Reply 12):
So how exactly can you slow down the air on the top of the wing but not have adverse effects on such things as fuel efficiency? You are creating more drag on the top of the wing, at least that is what it seems.

No. Change the shape, specifically the curve of the wing. Most of the lift is generated at the front of the wing, where the top of the wing rises sharply before tapering off. This is where the airflow is fastest. By making the taper more gradual, you'd have to extend the wing farther back a little bit, but when the two airflows from the top and bottom come together, the speed will be closer at that point, and the eddies that form will generally be much weaker.

Out of Idle curiosity, has anybody here ever heard the wake behind a CR2 on short final? I've heard pretty much everything that lands at DEN, but the CR2's wake you can hear and it lasts alot longer than any other aircraft. Is it that wierd wing design that is the same reason they have to make that steep nose-down angle on landing (though that's partly also due to the lack of leading edge slats)?
And all at once the crowd begins to sing: Sometimes the hardest thing and the right thing are the same
 
wukka
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RE: A380 And Wake Turbulance

Tue May 17, 2005 2:26 pm

Even with the potential of a 99% efficient wing, the displacement of the aircraft is what it is. Bernoulli might back me up here, with his principles, as well as Archimedes and his bathtub.

If anyone wants to take bets on the mandated separation being less than or equal to a 744, I'm thinking about starting my own online betting. Perhaps 100:1 on "less than", 15:1 on "equal"... anything over equal goes to the house.

Worth my while?  Wink How many takers?
We can agree to disagree.
 
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Richard28
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RE: A380 And Wake Turbulance

Tue May 17, 2005 4:54 pm

lets not forget that the A380 wing span is longer, so the downward pressure generated is spread over a greater surface area.

Quoting AeroPiggot (Reply 11):
In fact if Airbus had this technology, then why did they not implement it on the A346, which has wake vortex strength to rival the B744

I would guess that the A346 wake turbulance fell within standard limits for normal airplane separation, so there was no need to incorporate anything fancy into the basic wing design.
 
EnviroTO
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RE: A380 And Wake Turbulance

Tue May 17, 2005 5:28 pm

I'm with the people that say the shape at the rear of the wing, the length of the wing, and the width of the wing can be altered to change exit flow characteristics while still giving the required lift. Lift is about air pressure differentials and not eddie generation. With flaps fully deployed on the A380 significant eddies would form behind the wing, but if a wing is designed with reducing wake turbulance in mind and only leading edge flaps are deployed then wake turbulance can be significantly reduced. As for the question, why not reduce wake turbulence before... probably because wake turbulence doesn't impact the economics of the aircraft in a negative way (it might actually reduce resistance behind the wing) and with the 747 already existing from a time where minimum separations were barely an issue, other aircraft built since then have only needed to match the wake turbulence of the 747. Nowadays minimum separation is a bigger deal because of the congestion at airports and the A380 probably didn't want to increase the separation or create more wake turbulence for safety reasons.
 
keta
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RE: A380 And Wake Turbulance

Tue May 17, 2005 5:29 pm

Quoting AeroPiggot (Reply 3):
Listen gentlemen, wake turbulence is pure physics, it cannot be avoided. The airplane must generate lift to fly, and as a consequence a downwash is produce from the wings, which dissipates into the surrounding airflow as wake turbulence. The A380 weighing over 1.2 million lbs, must generate at least this amount of lift in level flight, therefore the downwash and associated trailing vortices will be greater than other commercial aircraft. The A380 will have to have a greater separation distance than the B744 from trailing aircraft, which will limit the number of takeoffs and landing from departing or arriving airports.

You're an aerospace engineer? The wake turbulence of course is a function of weight, but not exclusively! The wing plays a big role. That's what I've read and I've been teached so far. I will tell you one thing: 757. It produces an enormous wake compared with its size (weight). So here you have the proof that it's not just about weight.

Quoting VSIVARIES (Reply 10):
Sorry but this is wrong. There are no absolutes in this area but what we do know for sure is that more weight = greater wake vortex

Only if the wing is the same.

Quoting DLKAPA (Reply 16):
Most of the lift is generated at the front of the wing, where the top of the wing rises sharply before tapering off

Be careful, modern jetliners use supercritical wings, and the shape of the airfoil has nothing to see with a normal airfoil. Supercritical wings are actually more bended on the bottom of the wing, the top is almost straight, and the shockwave is used to get lift.
Where there's a will, there's a way
 
BigFish
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RE: A380 And Wake Turbulance

Tue May 17, 2005 10:26 pm

Quote:
I guess that's why the 757 is treated by ATC as Heavy?

This is really sort of confusing, so I hope you're paying attention.
We do control the 57 as a heavy, but there are certain criteria that make it confusing. We control the 200 as a 757, and a 300 as a heavy due to the weight. The '57-200 has it's own rules that fit between heavy and large. The 300 is over 250k, thus the "Heavy" designation. There are 200's that have had the Max Gross Weight Takeoff increased to just over 250k, and that is reflected in their flight strip. So they will be controlled as a heavy, as well. Hope that clears that up.

Now, back to the topic. Why does everyone insist that there should be certain new rules, or allocations made for the A380? It's a big commercial airliner. However, on the scale of large aircraft, it's really not that big of a deal. THe C5 is still bigger, the AN225 is still a whole lot bigger, and there were no new rules created for them. We, as ATC, are going to apply standard heavy separation to the A380. In a radar room, he is a little green blip, with an H attached to it. And when we set him up for the final, he's going to have standard heavy separation attached to him. Unless there is something that rears its head like it did with the 757, nothing changes. And that's not my department.

Do I care what the wings are shaped like? No, not really. Do I care how it works? No, not so much. All I know is that I'm going to maintain 6 miles in trail for separation, or two miles laterally, and not put two little green blips together at the same altitude, so that I'm not responsible for killing enough people to make it look like I'm competing with the Grim Reaper. I don't see a 747, or a KC135, or a 757. I see green blips. And I seperate those green blips. So, to answer your question.. No new rules, and I'm in the business of keeping little green blips seperated, so that you can get to wherever you're going in that A380, with the really supercritical, super efficient, Bernoulli Principaled, wing fenced, vortex reducing wings. Enjoy your flight.
 
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RayChuang
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RE: A380 And Wake Turbulance

Tue May 17, 2005 10:56 pm

It will be very interesting to see what the wake turbulence of the A380 is.

You forget that besides the wing, the horizontal and vertical tail surfaces of the plane are very large. That could make the wake turbulence quite big, to say the least.
 
asteriskceo
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RE: A380 And Wake Turbulance

Wed May 18, 2005 12:00 am

I believe flap setting, wing length, and speed of the airplane also play a large role as factors of wake turbulence.
 
md80fanatic
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RE: A380 And Wake Turbulance

Wed May 18, 2005 12:23 am

The wake created depends alot on a wing's airfoil thickness and average chord length. The 380 has the thickest and longest chord wing I have ever seen....and I imagine the wake will be proportional.

I think most of the "talk" about this subject is more in the realm of "salesman's pitch" than anything in reality. When flying through fluid (fluid dynamics) there will be a wake generated and there is no known way to reduce it substantially.

Besides....if this plane will carry the load of 2 then what is the problem with giving it a little more space to operate? If I were a measly yacht.....I would elect to keep my distance from the oceanliners if I could at all avoid it.
 
jayspilot
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RE: A380 And Wake Turbulance

Wed May 18, 2005 1:32 am

it seems that this thread is a perfect example of people trying to be experts on stuff they are not. Aerodynamics is a very complicated, detailed science that has to do with a lot more then basic physics. some people on this thread have incorrectly stated statements saying they know how this wake will perform.
I am of the belief that airbus and the jaa,faa,caa ect will make sure that this plane is certified safely and that when it comes time to determine adaquate seperation requirements a lot of testing will be done on computers and real flight tests. Unless there is an aerospace engineer on this sight with real experience in wing design we are wasting our time typing.
 
Morvious
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RE: A380 And Wake Turbulance

Wed May 18, 2005 1:34 am

Airbus showed how the wake turbulence was created with images of a high speed camera. You could see where the wake was created. (at the end of the wing)

They shot a A380 model through a cloud of smoke, and this way they designed a wing that had the best result of efficiently and lower wake effects.
The wing fences played the biggest role into this.

Quoting AeroPiggot (Reply 8):
and I am curious to see if all of Airbus CFD data indicating that the A380 will have a lower wake turbulence signature than the B744 will be proven. My guess is....NOT!!

I believe no-one has ever said that.. But the wake turbulence of the A380 should be / maybe is almost identical to any other aircraft flying already around! That's what Airbus is telling, so why can't you just take their words!
have a good day, Stefan van Hierden
 
aeropiggot
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RE: A380 And Wake Turbulance

Wed May 18, 2005 1:50 am

Quote:
IL76TD Reply 20: Aeropig is quite off in most of his statements

You failed to mentioned where I went wrong in my statements above. Every thing I said is really basic aerodynamics, a subject I know a little about.

The lift required from the A380 wings will be a direct function of its weight.

The initial circulation off an airplane is a function of weight, airspeed and initial vortex separation distances.

What airbus has been saying is that the wake vortex decay will be steep so that it is claimed to be no worse than the 747-400, due to their use of technology. However from all the Studies I have seen, all attempts to reduce wake vortex has an adverse effect on other more favorable airplane charateristics (low drag, fuel consumption, low landing approach speeds etc.)

Airbus claim that the 380 wake is no worse than the 744 at the current separation in part is based on a DLR wake prediction model called D2P (deterministic 2-phase probabilistic). The model predicts a laminar diffusion phase decay which is slow, followed by a very rapid turbulent decay. The rapid decay part is the part a lot of people have questions about the model. The model has been used by airbus in various ways, including enhancing their safety arguments. There are other models such as what the FAA uses (based on NASA's AVOSS) which predict a much slower decay.
And the difference between the models is enough to make or break the business case. But again, you can only model it so far. The real thing will occur this summer, during flight test. So let it rest there for the time been, until we get the results from flight test this summer.

Hope that put Mr. IL76TD concerns to rest.  Smile
A scientist discovers that which exists, an engineer creates that which never was.
 
jush
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RE: A380 And Wake Turbulance

Wed May 18, 2005 2:08 am

Airbus will do it i promise you... I not going to tell ya why but they will meet the 744 standards.
There is one problem with airbus. Though their products are engineering marvels they lack passion, completely.
 
LongHorn2000
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RE: A380 And Wake Turbulance

Wed May 18, 2005 2:13 am

There is an important distinction to be made here. There has been a lot of talk about the flow Fields around airfoils. This does create turbulence in the air, but the length scales are small. The viscosity of the air will dissipate this sort of turbulence relatively quickly. The "wake" would not begin to cause problems for another aircraft unless it they were VERY close together.

However, the phenomenon that creates the need for separation between take offs and landings is the vortex that forms off the wing tips. This is caused by the high pressure air on the bottom of the wing trying to escape around to the low pressure areas on the top of the wing. This creates a very coherent vortex that will stay coherent for long distances. This is the danger to other AC. There has been a lot of research involving this phenomenon and I don't doubt at all that airbus has a good handle on it.
 
aeropiggot
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RE: A380 And Wake Turbulance

Wed May 18, 2005 8:46 am

Quote:
Longhorn Reply 28: However, the phenomenon that creates the need for separation between take offs and landings is the vortex that forms off the wing tips

Quite true, this is a 3D finite wing effect, and airfoil theory may be a good starting point, but cannot in of itself completely explain the phenomenon.

Quote:
Longhorn Reply 28: There has been a lot of research involving this phenomenon and I don't doubt at all that airbus has a good handle on it.

I might disagree with you here, yes a lot of research has been done, but applying that research to a commercially viable product, is not a trivial matter. We might be able to control the vortex in a lab or computationally, but good old mother nature is something else........
A scientist discovers that which exists, an engineer creates that which never was.
 
iwok
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RE: A380 And Wake Turbulance

Wed May 18, 2005 3:03 pm

Quoting LongHorn2000 (Reply 28):
However, the phenomenon that creates the need for separation between take offs and landings is the vortex that forms off the wing tips.

You are correct here. I recall seeing 737's flying through smoke to show the wingtip vortecies. I believe this is called downwash? Anyway, if all of this is true then it goes back to Morovious's statement regarding the wingtip fences aiding a lot.

AeroPiggot, thank you very much for your informative posts. I understand your point about how the disturbance that the A380 generates is directly proportional to its weight. I think there may be some truth to the wingtip fence theory.

I guess, this is one reason why the 737 blended winglets improve efficiency so much.. reduction of wingtip vortecies = more efficieny lift.

I am not an aerodynamicist, so if I have made any blatant statements, please excuse me in advance.

-iwok
 
eilennaei
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RE: A380 And Wake Turbulance

Wed May 18, 2005 3:10 pm

Pardon my interupting, but the wing does not know the weight of the plane it is attached to. The wake turbulence stems from the propulsion of the engines and the characteristics of the wing, and the weight is only indirectly linked. Likewise, people sometimes attribute the weight of the airplane to the stalling characteristics, "a heavy a/c will stall more easily", which is wrong. The most prudent way of calculation I feel would involve evaluating the total energy dissipated by the engines and the (tiny) fraction of it that is wasted at the wingtips for the wake vortex.


-Eilennaei
 
LongHorn2000
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RE: A380 And Wake Turbulance

Thu May 19, 2005 2:55 am

Eilennaei, The weight is only entering the story in that the lift generated by the wings must be equal to the weight of the AC (for level flight of course). Generally, the more lift the wings must generate (the heavier the AC) the stronger the wingtip vortex. This is particularly true at low airspeeds.

AeroPiggot, I guess we shall agree to disagree? I have seen a lot of comparisons between CFD & WT test that show some amazing capabilities. There are always surprises to be had, but CFD does a darn good job these days (at least in my experience). I would imagine that there estimates will only be slightly off.

Iwok, your statement concerning the winglets is basically correct. One way to look at the situation is that the AC is having to exert quite a lot of energy to create those massive and intense vortices. The energy required to generate them translates into lost lift and increased drag.
 
aeropiggot
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RE: A380 And Wake Turbulance

Thu May 19, 2005 4:40 am

Quote:
AeroPiggot, I guess we shall agree to disagree? I have seen a lot of comparisons between CFD & WT test that show some amazing capabilities. There are always surprises to be had, but CFD does a darn good job these days (at least in my experience). I would imagine that there estimates will only be slightly off

LongHorn, I too believe in modern CFD results, I continue to rely on it to accomplish much of my daily assignments. However wake vortex prediction is quite notorious, in trying to correlate CFD and WT data and real world events. The atmospheric conditions are a big player, and quite difficult to simulate either with code or WT testing. So I am just saying I would not be surprise if AB comes up a bit short in their optimistic predictions.

Quote:
Eilennaei, The weight is only entering the story in that the lift generated by the wings must be equal to the weight of the AC (for level flight of course). Generally, the more lift the wings must generate (the heavier the AC) the stronger the wingtip vortex. This is particularly true at low airspeeds

I also concur with your response to Eilennaei.

Thanks
A scientist discovers that which exists, an engineer creates that which never was.
 
patrickj
Posts: 88
Joined: Tue Mar 22, 2005 11:42 am

RE: A380 And Wake Turbulance

Thu May 19, 2005 1:07 pm

Quoting AeroPiggot (Reply 3):
Listen gentlemen, wake turbulence is pure physics, it cannot be avoided. The airplane must generate lift to fly, and as a consequence a downwash is produce from the wings, which dissipates into the surrounding airflow as wake turbulence.

Not necessarily true. The portion of wake turbulence that is to be avoided comes from the spanwise flow of high pressure air under the wing into the lower pressure region created above the wing. This can only occur at the wing tip hence the large cyclonic air mass that trails every aircraft that produces lift. This effect is most prominent when slow and heavy, therefore according to performance engineering standards the A380 will produce stronger wake turbulence than a B747 would.

However there are no absolutes the B757 has a much stronger wake than the heavier B767. Turns out wing area and wing loading play an important roll. If the A380 has a reduced wake it is most likely from the fact that it appears to have a low wing loading even at Max Gross Weight. No super scientific analysis here just a look at the planform of the aircraft.
 
iwok
Posts: 979
Joined: Wed Jan 26, 2005 2:35 pm

RE: A380 And Wake Turbulance

Thu May 19, 2005 5:55 pm

Quoting Patrickj (Reply 34):
This can only occur at the wing tip hence the large cyclonic air mass that trails every aircraft that produces lift.

I was thinking about this wingtip problem all day at work today (I know, I need a life) and I had an idea regarding totally eliminating the wingtip vortex, keeping the wing loading low, all the while keeping the overall wingspan minimal. My basic idea is a little complicated, so I'll attempt to draw it out.

Front View:


|
_|_
_____-----| |-----_____
[_____ | | _____]
-----|___|-----
[] []

Side View:
__
/ |
________________________/ |
/ / / /
| | | /
______________/___/___---/



So the concept would be to have a wing somewhat like a bi-plane, but with the wings connected by a connecting blended winglet at the tips. Such a concept could have a long and thin wing, with a small cord and the blended wingtips could eliminate all wingtip vortecies. According to this concept, there would still be a large enough wing area to lift the plane, but the wingspan would be about half that of a single wing. Also, since the wings are shorter, the bending moment on the root would be reduced which should help reduce weight.

Sorry for the 1970's graphics. Any merit to such a concept or is it total hogwash?

-iwok
 
ramerinianair
Posts: 1452
Joined: Tue Nov 11, 2003 6:03 am

RE: A380 And Wake Turbulance

Fri May 20, 2005 3:44 am

Iwok,
I like your idea . . . I don't know if it'll work but you are not the only one who draws silly crap like this at work or school. My design would look even funnier.
Also, I do not know if the bi-plane's wings would have enough volume to produce lift according to bernouli's theory. You cannot produce low pressure above the bottom wing due to the high pressure that would be developing under the upper wing.
-Steven
W N = my Worst Nightmare!!!!!
 
eilennaei
Posts: 1003
Joined: Tue Nov 23, 2004 8:41 am

RE: A380 And Wake Turbulance

Sat May 21, 2005 4:17 am

To those that posted on the Vortex:
yes, I'm aware the forces have to be balanced for the a/c to fly (straight & level), but that is not the end of the story by no means -- a heavier a/c is >< heavier vortex. Just judge for yourselves:
http://www.mae.cornell.edu/fdrl/research/wingvortex.html
http://www.onemetre.net/Download/Downwash/LiftLine/Liftline.htm

-Eilennaei

[Edited 2005-05-20 21:21:53]
 
RichardPrice
Posts: 4474
Joined: Sat Apr 23, 2005 5:12 am

RE: A380 And Wake Turbulance

Sat May 21, 2005 4:55 am

Quoting Iwok (Reply 35):
So the concept would be to have a wing somewhat like a bi-plane, but with the wings connected by a connecting blended winglet at the tips. Such a concept could have a long and thin wing, with a small cord and the blended wingtips could eliminate all wingtip vortecies. According to this concept, there would still be a large enough wing area to lift the plane, but the wingspan would be about half that of a single wing. Also, since the wings are shorter, the bending moment on the root would be reduced which should help reduce weight.

Sounds very much like the Box Wing concept that the USAF has debated using for inflight refueling aircraft designs, in that it reduces wingtip drag hugely and creates extra areas where the refueling booms can be strung out.
 
iwok
Posts: 979
Joined: Wed Jan 26, 2005 2:35 pm

RE: A380 And Wake Turbulance

Sat May 21, 2005 1:57 pm

Quoting RichardPrice (Reply 38):
Sounds very much like the Box Wing

Rich, thanks for the tip. I went ahead and took a look, and lo and behold the very idea that I "drew" up has already been proposed.



I can see the advantage of such a design: shorter wingspan, reduced wingtip vortecies etc. In the future if the VLA market gets real big, then you could have one of these bi-planes with a 1000-2000 pax capacity, all the while fitting into existing airport gates and slots.

If such a beast were to fly, just don't put me in one of the middle seats  Wink

-iwok
 
eilennaei
Posts: 1003
Joined: Tue Nov 23, 2004 8:41 am

RE: A380 And Wake Turbulance

Sun May 22, 2005 5:08 am

That's one of the ways composites are changing the way planes are being built. Getting back to the Wright Bros. dimensions on the thickness of the wings and .. did someone nick parts of the rear end as well?

Glad to hear someone has still got faith in the way airports cope with congestion!

-Eilennaei

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