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mham001
Topic Author
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Airbus Acknowledges Vortex Problem

Sat May 20, 2006 9:35 am

and Emirates blames the Americans;


http://www.timesonline.co.uk/article/0,,2-2187526.html

By Ben Webster, Transport Correspondent

Airbus, manufacturer of the 540-tonne A380, admitted that flight
tests had shown that the double-decker created a greater "wake
vortex" than its rival, the 360-tonne Boeing 747.
....
Fernando Alonso, head of flight testing at Airbus, said: "Our tests
show a slightly more intense vortex but the way it disperses depends
on the wind and it may end up being the same as for a 747."
....
Maurice Flanagan, president of Emirates, the Dubai-based airline that
has bought 45 A380s, said that the ICAO's ruling appeared to have
been influenced by the US, which is keen to protect Boeing, its
largest exporter.
 
N766UA
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RE: Airbus Acknowledges Vortex Problem

Sat May 20, 2006 9:37 am

So? It's bigger than the 747 of course it will have a bigger wake. Why is Airbus trying to pretend it won't?
 
ikramerica
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RE: Airbus Acknowledges Vortex Problem

Sat May 20, 2006 9:48 am

bite your tongue! european engineering can get around that little reality, and it's only the US politicians who are misinterpreting the data.

this was predictable years ago. in fact, some of us said years ago that this would be the ultimate case, that it would be blamed on politics and not physics.

but then again, the A380 project in the first place is more about politics than economics, about someone besides the USA making the biggest passenger jet. so how is this revelation any different?

and, some of us were pointing out for many months now that if Airbus TRULY had a case that the vortex was smaller than the 747, they would have shared those numbers immediately and not been so clandestine.

hopefully the difference is not so much that it makes for a larger separation, though i'd rather see a new class created for the 744/748/A380 that might allow for the smaller jets like 777/340/350/787 to shorten their spacing and not be lumped in with the VLA like they are now.
Of all the things to worry about... the Wookie has no pants.
 
11Bravo
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RE: Airbus Acknowledges Vortex Problem

Sat May 20, 2006 9:54 am

Quoting Mham001 (Thread starter):
"Our tests show a slightly more intense vortex but the way it disperses depends on the wind and it may end up being the same as for a 747"

I'm guessing that's probably true. How could it not be? Seems like a statement of the obvious. Given enough wind and/or time it probably has the same wake vortex as a common house fly for that matter.
WhaleJets Rule!
 
atmx2000
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RE: Airbus Acknowledges Vortex Problem

Sat May 20, 2006 12:35 pm

Quoting Mham001 (Thread starter):
Maurice Flanagan, president of Emirates, the Dubai-based airline that
has bought 45 A380s, said that the ICAO's ruling appeared to have
been influenced by the US, which is keen to protect Boeing, its
largest exporter.

So is he talking as a EK exec, wanting to ensure that EK can use their A380s without hinderance? Or is he talking as a Brit expatriate, supporting the European team?

[Edited 2006-05-20 06:02:19]
ConcordeBoy is a twin supremacist!! He supports quadicide!!
 
DfwRevolution
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RE: Airbus Acknowledges Vortex Problem

Sat May 20, 2006 12:56 pm

Quoting N766UA (Reply 1):
So? It's bigger than the 747 of course it will have a bigger wake. Why is Airbus trying to pretend it won't?

Because seperation standards are based on the B747. If the A388 requires greater seperation between other aircraft, you shoot quite a whole in the argument that the A388 is necessary to increase capacity in slot-restricted airports, or at least, the aircraft will have a scheduling headache for dispatchers and ATC.

Quoting Mham001 (Thread starter):
Fernando Alonso, head of flight testing at Airbus, said: "Our tests show a slightly more intense vortex but the way it disperses depends
on the wind and it may end up being the same as for a 747.

I doubt this will really plauge the A380-800 model to any significant degree. It's unwelcome, but that's life.

Now what will be a problem is the A380-900. I can't see how a growth version will possibly meet seperation and noise guidelines with the A388 just barely squeaking in now. That means performance enhancements and that means $$
I have a three post per topic limit. You're welcome to have the last word.
 
Lumberton
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RE: Airbus Acknowledges Vortex Problem

Sat May 20, 2006 10:33 pm

Quoting Atmx2000 (Reply 4):
So is he talking as a EK exec, wanting to ensure that EK can use their A380s without hinderance? Or is he talking as a Brit expatriate, supporting the European team?

Only Flanagan can answer that, but when you have 45 of these aircraft on order, and you have literally bet the future of the airline (and your job and, most likely, your future livelihood) on it's success, then this is a senstive subject. So naturally one looks to divert attention elsewhere. This could be extremely embarassing for Mr. Flanagan and Emirates if the wake vortex issue is not resolved quickly and to their satisfaction.
"When all is said and done, more will be said than done".
 
Glom
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RE: Airbus Acknowledges Vortex Problem

Sat May 20, 2006 10:50 pm

Numberwatch:

Quote:
Heathrow is already full during the day and BAA, the airport’s owner, had been relying on the A380 to increase annual passenger numbers from 70 million to 90 million after Terminal 5 opens in 2008.

20 million increase per year based on A380s? Let's assume the A388 slots come from 744s. Let's also dispose of the usual numbers and use numbers closer to reality.

744 - 350pax
A380 - 480pax

So we are talking an increase of 130pax by upgrading 744s to A380s. If this is to produce 20,000,000 extra pax per annum, then it requires over 150,000 A380 movements per year. That mean 420 A380s flights per day!
 
28thguy
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RE: Airbus Acknowledges Vortex Problem

Sun May 21, 2006 1:30 am

Unless the interim rules are relaxed, an A380 carrying 550 passengers would use up the same runway capacity as two 747s carrying 800 people. Tony Douglas, managing director of Heathrow, said: “If the A380 takes two slots it would cause a problem and airlines might not want to use it.”

Again Airbus forgot basic math when designing the plane.
 
NAV20
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RE: Airbus Acknowledges Vortex Problem

Sun May 21, 2006 1:44 am

Quoting 28thguy (Reply 8):
Tony Douglas, managing director of Heathrow, said: “If the A380 takes two slots it would cause a problem and airlines might not want to use it.”

By coincidence, Tony Douglas is also the guy who just confirmed that the organisation he runs is spending no less than $US850M. on accommodating the very same A380 that airlines 'might not want to use..".

"Heathrow operator BAA is spending some $850 million to upgrade the airport to accommodate the A380 and other anticipated ultra-large aircraft of the future. Other work has included runway resurfacing, upgrading runway lighting and the construction of new taxiways.

"Douglas said the airport has widened and strengthened a runway to accommodate the A380, which has a list price of $300 million. New, larger baggage carousels also have been installed at Terminal 3 to accommodate the 555 passengers that can travel on the aircraft."


http://www.forbes.com/technology/feeds/ap/2006/05/18/ap2756312.html

I rather hope (almost certainly vainly) that these 'financial genius' types do eventually have to put some of their own money where their mouths are..........
"Once you have flown, you will walk the earth with your eyes turned skywards.." - Leonardo da Vinci
 
hb88
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RE: Airbus Acknowledges Vortex Problem

Sun May 21, 2006 1:47 am

This doesn't tell us anything that hasn't been discussed ad nauseum on a.net already.

Quoting 28thguy (Reply 8):
Again Airbus forgot basic math when designing the plane.

Sorry, but this is a halfwitted comment. Wake vortices need to be tested and verified, but to assume that Airbus simply 'didn't do the math' is dumb.
 
abba
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RE: Airbus Acknowledges Vortex Problem

Sun May 21, 2006 2:32 am

Quoting 28thguy (Reply 8):
Again Airbus forgot basic math when designing the plane.

Vortex is dependent on at least two factors: the weight of the plane and the area of its wings. It seems tha the 380 has a relatively larger wing than the 747, so....

Abba
 
TWAMD-80
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RE: Airbus Acknowledges Vortex Problem

Sun May 21, 2006 2:45 am

Quoting Abba (Reply 11):
It seems tha the 380 has a relatively larger wing than the 747,

It seems to have a relatively larger weight than the 747 as well  Smile. Heavy + Clean + Slow = Big wake; throw an A380 in there and it will be interesting to see how this pans out.

TW
Two A-4's, left ten o'clock level continue left turn!
 
David L
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RE: Airbus Acknowledges Vortex Problem

Sun May 21, 2006 2:54 am

Quoting Mham001 (Thread starter):
Maurice Flanagan, president of Emirates, the Dubai-based airline that
has bought 45 A380s, said that the ICAO's ruling appeared to have
been influenced by the US, which is keen to protect Boeing, its
largest exporter.

That's a bit vague. Maybe it's true, maybe it's not but it might have been better not to mention it without citing evidence.

Quoting 28thguy (Reply 8):
Again Airbus forgot basic math when designing the plane.

Yeah, sure. Call it a gamble if you like or call it something they have to get around but saying they "forgot basic math when designing the plane"? Pity they didn't ask for the answers on A.net.  sarcastic 
 
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glideslope
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RE: Airbus Acknowledges Vortex Problem

Sun May 21, 2006 3:58 am

Quoting Ikramerica (Reply 2):
bite your tongue! european engineering can get around that little reality, and it's only the US politicians who are misinterpreting the data.

So, how is Wing Re-Design coming along?  Smile
To know your Enemy, you must become your Enemy.” Sun Tzu
 
ebbuk
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RE: Airbus Acknowledges Vortex Problem

Sun May 21, 2006 4:16 am

What does it matter anyway?

Thought the 787 is going to hub bust thus clearing slots at important airports like lhr?

So the aviation world will be able to absorb big bubble bertha with ease.

Win win
 
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keesje
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RE: Airbus Acknowledges Vortex Problem

Sun May 21, 2006 4:50 am

Quoting Ikramerica (Reply 2):
but then again, the A380 project in the first place is more about politics than economics



Quoting Atmx2000 (Reply 4):
a Brit expatriate, supporting the European team?



Quoting DfwRevolution (Reply 5):
Now what will be a problem is the A380-900



Quoting Lumberton (Reply 6):
This could be extremely embarassing



Quoting 28thguy (Reply 8):
Again Airbus forgot basic math when designing the plane.



Quoting NAV20 (Reply 9):
I rather hope (almost certainly vainly) that these 'financial genius' types do eventually have to put some of their own money where their mouths are..........



Quoting TWAMD-80 (Reply 12):
t seems to have a relatively larger weight than the 747 as well



Quoting Glideslope (Reply 14):

So, how is Wing Re-Design coming along?

Is the A380 doomed again?  yawn  Well, w´re getting used to it.



A380 video from wednesday, Berlin.

http://www.flightlevel350.net/video_streaming.php?id=6259
"Never mistake motion for action." Ernest Hemingway
 
TPASXM787
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RE: Airbus Acknowledges Vortex Problem

Sun May 21, 2006 4:56 am

I don't even understand why this is news...a quick 747/380 comparison (this is based on a 744)

747:

wingspan: 211ft 5in
height: 63ft 8in

380:

wingspan: 261ft 10in
height: 79ft

bigger votrex?

Yes!

How the hell would it not be bigger?
This is the Last Stop.
 
Morvious
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RE: Airbus Acknowledges Vortex Problem

Sun May 21, 2006 5:49 am

Quoting 28thguy (Reply 8):
Unless the interim rules are relaxed, an A380 carrying 550 passengers would use up the same runway capacity as two 747s carrying 800 people. Tony Douglas, managing director of Heathrow, said: “If the A380 takes two slots it would cause a problem and airlines might not want to use it.”

How can one test pilot of the A380 say that it is "slightly" bigger then the B747, and still take 2 slots, something ain't right here!!
have a good day,

HereThen
 
andessmf
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RE: Airbus Acknowledges Vortex Problem

Sun May 21, 2006 6:01 am

Quoting TPASXM787 (Reply 17):

How the hell would it not be bigger?

It was suppossed to be the same size as a 747. And the spacing requirements are still up in the air, but if there is more spacing required as compared to a 747, there could be some trouble.
 
OldAeroGuy
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RE: Airbus Acknowledges Vortex Problem

Sun May 21, 2006 6:09 am

Quoting Abba (Reply 11):
Vortex is dependent on at least two factors: the weight of the plane and the area of its wings. It seems tha the 380 has a relatively larger wing than the 747, so....



Quoting TWAMD-80 (Reply 12):
It seems to have a relatively larger weight than the 747 as well . Heavy + Clean + Slow = Big wake; throw an A380 in there and it will be interesting to see how this pans out.

Actually, vortex strength is proportional to four factors:

Vortex Strength> (Weight*Config. Factor)/(Wing Span*Approach Speed)

In a 2001 presentation to the FAA, Airbus related the relative vortex strengths of the A380 to the 744 using these ratios assuming both airplanes were at an approach speed of 165 kts:

Wt. Ratio = (95% of A380 MZFW/95% of 744 MZFW) = 340.1t/239.1t = 1.422

Span Ratio = (A380 Span/744 Span) = 79.8m/64.4m = 1.239

Combining the terms:

A380 Wake Strength/744 Wake Strength = 1.422/1.239 = 1.148

By this measure, the A380 wake is about 15% stronger than the 744 wake assumming that the Speed and the Config Factor are equal.

Since that time, flight testing has shown that the A380 Vref is 138 kts. The 165kt Approach Speed for the earlier calculation is representative of Vref + 10kt for the 744 at MLW. On the same basis, Vref +10kts for the A380 would be 148kts.

So the approach speed ratio would be:

Approach Speed Ratio = Vapp A380/Vapp 744 = 148/165 = .897

Accounting for the different Vapp, the relative vortex strengths now become:

A380 Vortex Strength/744 Vortex Strength = 1.147/.897 = 1.279

The implication is that the A380 wake vortex is 28% stronger than the 744 assuming that the Config. Factor is equal. That's quite a bit and could well impact A380 separation requirements.

Config. factors are difficult to assess, but the 744 discontinuous trailing edge flap probably promotes more rapid vortex decay than the A380 continuous trailing edge flap. The A380 flap design is great for noise and low drag, but it will be interesting to see what its vortex decay characteristics are.

That's why I can't wait to see the results of the Istres test data Airbus has indicated they will announce in July.

[Edited 2006-05-20 23:11:45]
Airplane design is easy, the difficulty is getting them to fly - Barnes Wallis
 
Glom
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RE: Airbus Acknowledges Vortex Problem

Sun May 21, 2006 6:16 am

Quoting OldAeroGuy (Reply 20):
Config. factors are difficult to assess, but the 744 discontinuous trailing edge flap probably promotes more rapid vortex decay than the A380 continuous trailing edge flap. The A380 flap design is great for noise and low drag, but it will be interesting to see what its vortex decay characteristics are.

What does that mean for the 748, which will be changing the flaps?
 
OldAeroGuy
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RE: Airbus Acknowledges Vortex Problem

Sun May 21, 2006 6:20 am

Quoting Glom (Reply 21):
What does that mean for the 748, which will be changing the flaps?

From what I've seen, I'd guess the 748 flap will be worse than the 744 for vortex decay, but better than the A380.
Airplane design is easy, the difficulty is getting them to fly - Barnes Wallis
 
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kc135topboom
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RE: Airbus Acknowledges Vortex Problem

Sun May 21, 2006 6:50 am

Quoting Mham001 (Thread starter):
Fernando Alonso, head of flight testing at Airbus, said: "Our tests
show a slightly more intense vortex but the way it disperses depends
on the wind and it may end up being the same as for a 747."

No, that is not true. You have to use the same wind factor for both the A-380-800 and B-747-400 to get a fair comparison.

The approach and enroute spacing the ICAO and FAA uses for the B-747, all models, is 5nm. Departure spacing is 5nm or 2 minutes. But, interestingly enough, the B-747-400 has a slightly smaller wake turbalance factor than any of it's earlier sisters. This is because of the winglets on the -400 and a more effecient wing that the B-747-100/-200/-300 don't have.

The A-380-800 is equipped with those small upper and lower wingtip fences, not a true winglet. Perhaps retrofitting true winglets will lower the turbalance factor to that of the B-747-200, but I doubt to that of a B-747-400.

The A-380 is much closer in a wake turbalance and seperation factor to the An-124, not the B-747.

The two factors that cause wake turbalance are wing design and weight. The A-380 grosses out 28% heavier (1.2M lbs) than the heaviest B-747 (915K lbs). The A-380 wing is 6' (1.9m) longer, but has a much thicker cord, and more of a supercritical design than the B-747-400 wing. The A-380 wing design is much closer (but of course much bigger) to the B-757 wing, than the B-747. You already know the B-757 has a spiecal wake turbalance speration requirement, even though it is not a "heavy" (300,000 lbs or more) jet.

So, the seperation factor behind the A-380 will be based on physics and prior experience, and not US politics, just as the B-757 seperation factor is. If there is any politics being played here, it is from Airbus and based on their desire to sell more A-380s.

Boeing continued to sell the B-757 for about 12 years after the wake turbalance factor behind it was identified. So with proper ATC management, any increase in spacing behind the A-380 should be manageable.

Quoting AndesSMF (Reply 19):
It was suppossed to be the same size as a 747

Numbers indicate that will never happen, for the current B-747s. When the new B-747-800 begins to fly, with it's supercritical wing design, raked wingtips, and higher gross weight (over the current B-747 models), I think the spacing requirements behind it will increase over the current B-747s.
 
atmx2000
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RE: Airbus Acknowledges Vortex Problem

Sun May 21, 2006 7:52 am

Quoting OldAeroGuy (Reply 20):
Config. factors are difficult to assess, but the 744 discontinuous trailing edge flap probably promotes more rapid vortex decay than the A380 continuous trailing edge flap. The A380 flap design is great for noise and low drag, but it will be interesting to see what its vortex decay characteristics are.

I suppose they could come out ahead if the NIMBYs try to push noise reduction through fewer flights. Maybe Airbus should secretly fund NIMBY lawsuits.  stirthepot 
ConcordeBoy is a twin supremacist!! He supports quadicide!!
 
PolymerPlane
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RE: Airbus Acknowledges Vortex Problem

Sun May 21, 2006 8:53 am

Quoting OldAeroGuy (Reply 20):
Since that time, flight testing has shown that the A380 Vref is 138 kts. The 165kt Approach Speed for the earlier calculation is representative of Vref + 10kt for the 744 at MLW. On the same basis, Vref +10kts for the A380 would be 148kts.

Out of curiosity, since I am not an aircraft engineer and do not know anything on Vref determination, Why can't A380 increse its Vref to reduce the vortex?. Is there any negative effect on faster approach?

I have always thought that slower Vref is better for every point of view, but I guess I was wrong. So if lower Vref is detrimental to problem, why did Airbus boast about lower Vref than expected?

Cheers,
PP
One day there will be 100% polymer plane
 
2H4
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RE: Airbus Acknowledges Vortex Problem

Sun May 21, 2006 9:05 am




Quoting PolymerPlane (Reply 25):
Is there any negative effect on faster approach?

Even a modest increase to Vref would result in a significant increase in inertia. At A380 weights, dissipating all of that energy might not be worth the lower vortex that might result. Just one possible negative that comes to mind.




2H4


Intentionally Left Blank
 
mham001
Topic Author
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RE: Airbus Acknowledges Vortex Problem

Sun May 21, 2006 9:23 am

Quoting Hb88 (Reply 10):
This doesn't tell us anything that hasn't been discussed ad nauseum on a.net already.

Au contraire, monsuer. This is a significant statement from Airbus. They previuously stated it would match the 747 and indignantly claimed they would prove it with their own tests and drag the 777 into the fracas as well. This appears to be the first statement about those tests.
 
warreng24
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RE: Airbus Acknowledges Vortex Problem

Sun May 21, 2006 9:27 am

I am sure that 35 years ago, the exact same things were said about the 747. Apparantly it was also billed as a potential "folly"

And, I am sure that all of the "doom and gloom" was said about the DC-10 and L-1011 as well.
 
FFlyer
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RE: Airbus Acknowledges Vortex Problem

Sun May 21, 2006 9:58 am

Every time I see the name of this guy, Fernando Alonso - I just can't help smiling. It's a funny image of this young Spanish guy with thick eye-brows piloting an Airbus plane in Renault overalls. After all, the F1 World Champion must be the better-known Fernando Alonso.
 
OldAeroGuy
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RE: Airbus Acknowledges Vortex Problem

Sun May 21, 2006 1:34 pm

Quoting PolymerPlane (Reply 25):
Out of curiosity, since I am not an aircraft engineer and do not know anything on Vref determination, Why can't A380 increse its Vref to reduce the vortex?. Is there any negative effect on faster approach?

I have always thought that slower Vref is better for every point of view, but I guess I was wrong. So if lower Vref is detrimental to problem, why did Airbus boast about lower Vref than expected?



No reason they couldn't fly faster when wake vortex reduction would be desireable. It's just more wear and tear on the tires and brakes. Flying faster could also be required to integrate the A380 better into ATC approach patterns.

It also spoils the Vref marketing advantage the A380 has over the 744.
Airplane design is easy, the difficulty is getting them to fly - Barnes Wallis
 
abba
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RE: Airbus Acknowledges Vortex Problem

Sun May 21, 2006 6:09 pm

Quoting Mham001 (Reply 27):
Au contraire, monsuer. This is a significant statement from Airbus. They previuously stated it would match the 747 and indignantly claimed they would prove it with their own tests and drag the 777 into the fracas as well. This appears to be the first statement about those tests.

No - they have said that for about a year now. The quotation for this article is pretty old. And no doubt also second hand. I have followed this discussion closely as this seems to be the only potentially substantial problem that the 380 might have as it seems to otherwise exceed the gurantees that Airbus has given. Do not forget that most of those commeting on this issue has as little a clue about the realitry of things here as I have. And that is next to nothing (which do not prevent them from their customary (by now rather boring) doom and gloom talking in spite of people knowing what they are talking about for the most part seems to considder the case rather minor. Including AC people with very good knowledge (if not first hand working experience) of the operations of LHR)

There is abosolutely nothing new whatsoever in this article.

ABBA
 
bayareapilot
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RE: Airbus Acknowledges Vortex Problem

Sun May 21, 2006 6:41 pm

Quoting Mham001 (Thread starter):
the ICAO's ruling appeared to have
been influenced by the US, which is keen to protect Boeing, its
largest exporter.

Sure, it had nothing to do with those minor details that the US has the busiest ATC system in the world and has had a fatal crash due to a wake encounter.
 
Oryx
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RE: Airbus Acknowledges Vortex Problem

Sun May 21, 2006 6:50 pm

Vortex strength behind the wing is only depending on physics. But two items are not: vortex deccay and separation standarts. What is determing for the following aircraft is not the vortex strength right behind the trailing edge of the leading plane, but at the position of the trailing aircraft. To calculate this strength measurements and numerical simulations are performed. Finally apropiate separation distances are determined. This is the point where the politics get into the game. Which model is used for numerical simulations? How to interpret the measurements - mean values, max values, standart deviations etc.? And last but not least: at what vortex strength open up a new class. This leads to the two questions on which has to be agreed: How strong is the wake at the position of the trailing aircraft and does this requiere to open up a new class of aircraft "bigger than B747"?
 
hb88
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RE: Airbus Acknowledges Vortex Problem

Sun May 21, 2006 7:29 pm

Quoting Glideslope (Reply 14):
So, how is Wing Re-Design coming along?

Blimey you must know a lot more than us poor people at Airbus Filton.

Wing redesign? uh huh....

a.net A380 folklore #5 in a series. Collect them all.
 
art
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RE: Airbus Acknowledges Vortex Problem

Sun May 21, 2006 8:18 pm

Quoting Glom (Reply 7):
So we are talking an increase of 130pax by upgrading 744s to A380s. If this is to produce 20,000,000 extra pax per annum, then it requires over 150,000 A380 movements per year. That mean 420 A380s flights per day!

I can just see Heathrow becoming an A380 only airport. Smile

Quoting NAV20 (Reply 9):
rather hope (almost certainly vainly) that these 'financial genius' types do eventually have to put some of their own money where their mouths are..........

Financial gurus like to demonstrate their genius using other people's money. If they lose it, they still get paid. If they don't lose it, they get bonuses. Why trade a 0% risk "win/win a lot position" for a >0% risk "win a fortune/lose a fortune" position? Unless, of course, you really are a financial genius.
 
Pihero
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RE: Airbus Acknowledges Vortex Problem

Sun May 21, 2006 10:00 pm

If the determination of the energy of a wake were as simple as OldAeroGuy and KC135TopBoom describe, really, I don't see any reason for all the most advanced research labs in the world to spend litterally tens of millions to study it.
Some of the fallacies :
1/- the bigger the airplane, the stronger the wake .WRONG as a NASA study in the '80s discovered that the DC-10 had a stronger vortex than a C5 A Galaxy.
2/- the longer the span, the stronger the wake . Once again, we need to qualify that statement. Performance gliders disprove it.
3/- the slower the airplane, the more powerful the wake : Although it has been demonstrated that for one given type and at a given weight, the wake is the strongest on a clean configuration at low speeds[, I find it quite excessive to generalise that finding to two different types of airplanes flying in vastly different flap / gear / weight /geometry /aspect /speed configurations .

Quoting OldAeroGuy (Reply 20):
Config. factors are difficult to assess, but the 744 discontinuous trailing edge flap probably promotes more rapid vortex decay than the A380 continuous trailing edge flap

I agree on that statement.
Regards.
Contrail designer
 
NAV20
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Joined: Thu Nov 27, 2003 3:25 pm

RE: Airbus Acknowledges Vortex Problem

Sun May 21, 2006 10:06 pm

This seems to be a simply-written summary of the situation. Though, as I understand it, no-one knows everything about wake vortices:-

"The intensity or strength of the vortex is primarily a function of aircraft weight and configuration (flap setting etc.). The strongest vortices are produced by heavy aircraft, flying slowly, in a clean configuration. For example, a large or heavy aircraft that must reduce its speed to 250 knots below 10,000 feet and is flying in a clean configuration while descending, produces very strong wake. Extra caution is needed when flying below and behind such aircraft."

http://www.asy.faa.gov/safety_products/wake.htm#problem
"Once you have flown, you will walk the earth with your eyes turned skywards.." - Leonardo da Vinci
 
OldAeroGuy
Posts: 3928
Joined: Sun Dec 05, 2004 6:50 am

RE: Airbus Acknowledges Vortex Problem

Sun May 21, 2006 11:25 pm

Quoting Pihero (Reply 36):
If the determination of the energy of a wake were as simple as OldAeroGuy and KC135TopBoom describe, really, I don't see any reason for all the most advanced research labs in the world to spend litterally tens of millions to study it.
Some of the fallacies :
1/- the bigger the airplane, the stronger the wake .WRONG as a NASA study in the '80s discovered that the DC-10 had a stronger vortex than a C5 A Galaxy.
2/- the longer the span, the stronger the wake . Once again, we need to qualify that statement. Performance gliders disprove it.
3/- the slower the airplane, the more powerful the wake : Although it has been demonstrated that for one given type and at a given weight, the wake is the strongest on a clean configuration at low speeds[, I find it quite excessive to generalise that finding to two different types of airplanes flying in vastly different flap / gear / weight /geometry /aspect /speed configurations .

I never said any of this was simple. The equation I presented merely shows how the terms interact and mis-interpretation does not help.

For instance, where did anyone say that the longer the span, the stronger the wake? Span loading, W/b, is an important predictor of vortex strength. At the same Weight, a greater span reduces vortex strength.

As far as speed goes, your third comment shows that experiment confirms theory. Slower speeds for the same configuration do produce stronger vortices. Differences between configurations are still important though.

The main point is that the A380 has the potential, based on its first order geometric and operating characteristics, to produce a significantly stronger wake than airplanes currently in operation.

Let's see what the July release of the Istres data have to say.
Airplane design is easy, the difficulty is getting them to fly - Barnes Wallis
 
Pihero
Posts: 4318
Joined: Mon Jan 31, 2005 5:11 am

RE: Airbus Acknowledges Vortex Problem

Sun May 21, 2006 11:34 pm

Quoting OldAeroGuy (Reply 38):
where did anyone say that the longer the span, the stronger the wake?



Quoting KC135TopBoom (Reply 23):
The A-380 wing is 6' (1.9m) longer, but has a much thicker cord, and more of a supercritical design than the B-747-400 wing. The A-380 wing design is much closer (but of course much bigger) to the B-757 wing, than the B-747.

That's what I gathered from that post (dimensions seem to be in error, too.).

Quoting OldAeroGuy (Reply 38):
The main point is that the A380 has the potential, based on its first order geometric and operating characteristics, to produce a significantly stronger wake than airplanes currently in operation

Yes, I agree on that. But to try and quantify it is beyond my knowledge.

Regards.
Contrail designer
 
OldAeroGuy
Posts: 3928
Joined: Sun Dec 05, 2004 6:50 am

RE: Airbus Acknowledges Vortex Problem

Mon May 22, 2006 1:09 am

Quoting Pihero (Reply 39):
Quoting KC135TopBoom (Reply 23):
The A-380 wing is 6' (1.9m) longer, but has a much thicker cord, and more of a supercritical design than the B-747-400 wing. The A-380 wing design is much closer (but of course much bigger) to the B-757 wing, than the B-747.

That's what I gathered from that post (dimensions seem to be in error, too.).



Quoting Pihero (Reply 36):
Quoting OldAeroGuy (Reply 20):
Config. factors are difficult to assess, but the 744 discontinuous trailing edge flap probably promotes more rapid vortex decay than the A380 continuous trailing edge flap

I agree on that statement.
Regards.

I think he was saying that the continuous span flap of the A380 has more in common with the 757 flap system than the 744 system. You agreed with me that A380 was likely to have worse vortex decay characteristics than the 744 due to the continuous nature of its flap. The A380 increased span was not being said to increase vortex strength.

As an aside, airfoil sections have little, if any impact, on approach wake characteristics. The more advanced A380 supercritical airfoil isn't a player in its approach wake signature.
Airplane design is easy, the difficulty is getting them to fly - Barnes Wallis

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