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Topic: A380 Overperforms Says Tim Clark Of EK
Username: art
Posted 2012-11-22 02:05:57 and read 33050 times.

“I kind of looked at the A380 as a late, overweight aircraft,” he says. “But when she flew, she was faster, more fuel-efficient and more aerodynamical and still is.” Clark points out that “the faster you fly [the A380], the more fuel-efficient she gets; when you fly at [Mach] 0.86 she is better than at 0.83.”

Also, Emirates has observed a very low degradation factor: The first aircraft delivered in 2008 would normally perform around 2.5-3% less efficiently than in the beginning, but according to Clark the degradation has been only around 1%.

http://www.aviationweek.com/Article....e-xml/awx_11_21_2012_p0-519980.xml

Seems remarkable that the the aircraft burns less fuel at mach 0.86 than at mach 0.83. How does that come about? Any engineers able to offer an explanation?

Airbus appears to have come up with an aircraft that exceeds expectations. I guess that is rather useful to Airbus where an airline is debating the proportion of big twins/A380's it wants in its fleet mix. I guess it also means that in the absence of an all new VLA appearing within 15 years, Airbus can look forward to a large number of orders for delivery in the 2020's as existing customers turn over their fleets.

Topic: RE: A380 Overperforms Says Tim Clark Of EK
Username: EagleBoy
Posted 2012-11-22 02:20:15 and read 32945 times.

Interesting info on the lower level of degradation in the fleet.
The future of secondhand market for A380 has been debated a few times on A.Net. EK have 90 on order, the assumption being that the last 25-33% are to replace the first 25-33%. A lower level of degradation may slow the need to replace and/or maintain the used value of the airframe.

Topic: RE: A380 Overperforms Says Tim Clark Of EK
Username: francoflier
Posted 2012-11-22 02:22:40 and read 32916 times.

Quoting art (Thread starter):
How does that come about?

The extra fuel flow required to go faster is lower is compensated by the shorter flight time.

I didn't think the A380 would be 'comfortable' .86 cruiser. I imagined it more in the .84~.85 range.

The 744 is also very comfortable at .86. Some operators apparently didn't even bother with cost index or FMC econ cruise and just flew around at.86 everywhere. It just likes it there.

Topic: RE: A380 Overperforms Says Tim Clark Of EK
Username: nighthawk
Posted 2012-11-22 02:26:50 and read 32872 times.

Quoting art (Thread starter):
Seems remarkable that the the aircraft burns less fuel at mach 0.86 than at mach 0.83. How does that come about? Any engineers able to offer an explanation?

Don't forget if you fly at 0.86 you get there faster. I'm guessing the extra fuel used to fly at 0.86 is more than offset by the shorter flight time and therefore less overall fuel use.

Topic: RE: A380 Overperforms Says Tim Clark Of EK
Username: JU068
Posted 2012-11-22 02:32:41 and read 32767 times.

What about the other operators? Have any of them been this impressed by this bird?

Topic: RE: A380 Overperforms Says Tim Clark Of EK
Username: brightcedars
Posted 2012-11-22 02:42:56 and read 32641 times.

Actually one should do the math to see if it isn't most efficient to fly at a certain speed when the plane is heavily loaded with fuel soon after take off and more slowly when it's lighter and cruising later in flight.

Topic: RE: A380 Overperforms Says Tim Clark Of EK
Username: swallow
Posted 2012-11-22 02:43:24 and read 32645 times.

Classic TC ....putting the screws on Airbus by negotiating in the press. As he has done before, he casts doubt on the product, hoping to get better pricing on future orders. At least he has the temerity to admit he was wrong regarding the 388. Didn't stop him ordering stacks of them.

I think his main target is the 3510. I highly doubt that Airbus would have changed its specs without consulting EK, one of her main customers. Tellingly, JL does not publicly contradict TC's claim that he was not consulted.

Since the 359 is becoming to small for his needs, I think TC is looking to convert some 359 orders to the 3510

Topic: RE: A380 Overperforms Says Tim Clark Of EK
Username: rwy04lga
Posted 2012-11-22 02:55:14 and read 32488 times.

Quoting swallow (Reply 6):
As he has done before, he casts doubt on the product, hoping to get better pricing on future orders.

Claiming overperformance doesn't sound like he's casting doubt on the product. If anything, Airbus could say that if he likes it so much he should be willing to pay more on future orders.

Topic: RE: A380 Overperforms Says Tim Clark Of EK
Username: flipdewaf
Posted 2012-11-22 02:57:22 and read 32479 times.

Quoting art (Thread starter):
Seems remarkable that the the aircraft burns less fuel at mach 0.86 than at mach 0.83. How does that come about? Any engineers able to offer an explanation?

It may well burn more fuel (have more drag) at M0.86 but if the fuel flow required to fly ~0.36% faster is less than 0.36% then you will travel further on the same fuel.

This seems like good news for the whale but Tim Clark always seems to have a reason up his sleeve for saying things.

Fred

Topic: RE: A380 Overperforms Says Tim Clark Of EK
Username: swallow
Posted 2012-11-22 03:08:38 and read 32332 times.

Quoting rwy04lga (Reply 7):
Claiming overperformance doesn't sound like he's casting doubt on the product.

Per the linked article, he is doubting the 35J not the 388

Emirates Airline President Tim Clark says the carrier’s current order for the Airbus A350-1000 is “in limbo at the moment,” but he is not ready to step back from it .

The aircraft is “overweight and late,” Clark tells Aviation Week. “Let’s just see what she is like when she flies,” he adds. “At the moment there are issues.”


Notice he remains committed to the order, and actually thinks the 350 will do well

we got a pleasant surprise with the A380, maybe we also get a pleasant surprise with the A350-900 and -1000,” Clark says.

Topic: RE: A380 Overperforms Says Tim Clark Of EK
Username: art
Posted 2012-11-22 03:12:12 and read 32275 times.

Quoting brightcedars (Reply 5):
Actually one should do the math to see if it isn't most efficient to fly at a certain speed when the plane is heavily loaded with fuel soon after take off and more slowly when it's lighter and cruising later in flight.

Forgot that: the faster you fly, the faster you have less weight to push throught the air (because you are burning fuel faster).

I see narrowbodies tend to have m 0.8 as their advertised cruise speed. Can they also be flown faster without increasing fuel burn from A to B or is this a phenomenon seen only in (some?) long range aircraft? I don't understand why the advertised cruise speed would be less than the speed.that burnt the least fuel between origin and destination. Lower engine maintenance cost? Some other factors?

Topic: RE: A380 Overperforms Says Tim Clark Of EK
Username: par13del
Posted 2012-11-22 03:29:03 and read 32111 times.

No mention of the effect on the engines, I guess it may be too early to judge the effect.
Derate takeoffs and lower cruise speeds was not only about fuel but also about preserving the time on the wing for a/c enhines which is also a huge cost and take a/c out of service for a day or so, never mind the capital cost of a replacement engine.

Good news all around for the A380.

Topic: RE: A380 Overperforms Says Tim Clark Of EK
Username: Zkpilot
Posted 2012-11-22 03:38:33 and read 32006 times.

Quoting art (Reply 11):
I see narrowbodies tend to have m 0.8 as their advertised cruise speed.

This is because they spend a much greater proportion of their lives taking off, climb, descent and landing with much less cruise time than wide-bodies.

Topic: RE: A380 Overperforms Says Tim Clark Of EK
Username: HiJazzey
Posted 2012-11-22 04:06:42 and read 31498 times.

Quoting Zkpilot (Reply 13):
This is because they spend a much greater proportion of their lives taking off, climb, descent and landing with much less cruise time than wide-bodies.

True, although they're flying longer these days. The newer generation NBs like the NEOs and Max's should probably be optimised for longer stage lengths

Topic: RE: A380 Overperforms Says Tim Clark Of EK
Username: lightsaber
Posted 2012-11-22 04:12:37 and read 31345 times.

I would love to know how the A388 CASM is versus expectation. Lower fuel burn is great, but how is the maintenance (other than the wing cracks)?

Quoting par13del (Reply 12):
Good news all around for the A380.

That is is. Now if only the production rate could speed up.

Lightsaber

Topic: RE: A380 Overperforms Says Tim Clark Of EK
Username: worldrider
Posted 2012-11-22 04:14:08 and read 31279 times.

Soo EK has 50 A359 and 20 A350-100 on the order book.. counting the total of 388s "soon delivered" that makes
the astonishing number of 160 A widebodies! hmm no B787s? ?

its very likely some of the 359s will be converted the bigger variant (to become the ultimate 777 replacement) aka CX..
nice 380 publicity    i enjoy flying them.

Topic: RE: A380 Overperforms Says Tim Clark Of EK
Username: flyingturtle
Posted 2012-11-22 04:15:50 and read 31280 times.

Quoting art (Thread starter):
Also, Emirates has observed a very low degradation factor: The first aircraft delivered in 2008 would normally perform around 2.5-3% less efficiently than in the beginning, but according to Clark the degradation has been only around 1%.

How does that happen? Does the A/C put on weight over the years, do the wings and fuselage deform into a less aerodynamic state, like the wrinkles on heavily used B-52, for example?


View Large View Medium
Click here for bigger photo!

Photo © Frank J. Mirande



Or is it the engine wearing out?


David

Topic: RE: A380 Overperforms Says Tim Clark Of EK
Username: Zkpilot
Posted 2012-11-22 04:21:36 and read 31099 times.

Quoting flyingturtle (Reply 17):

How does that happen? Does the A/C put on weight over the years, do the wings and fuselage deform into a less aerodynamic state, like the wrinkles on heavily used B-52, for example?

Parasitic Drag (Friction drag), every time an aircraft flies through some rough weather at the right temp etc those little ice crystals dent, scratch, chip away at the aircraft. Screws etc are replaced but don't always give 100% the same fit as a brand new aircraft. Yes they gain weight from bits and pieces and the engines do become less efficient over time.
Some bad turbulence or hard landings can also cause some minor forms of deformation which also add up.

Topic: RE: A380 Overperforms Says Tim Clark Of EK
Username: justloveplanes
Posted 2012-11-22 04:25:04 and read 30972 times.

Quoting flyingturtle (Reply 17):
How does that happen? Does the A/C put on weight over the years, do the wings and fuselage deform into a less aerodynamic state, like the wrinkles on heavily used B-52, for example?

It may be the GE engines that maintain durability. Clark has mentioned similar characteristics about the EK 77W, that they are resistant to degrading.

Topic: RE: A380 Overperforms Says Tim Clark Of EK
Username: GCT64
Posted 2012-11-22 04:41:54 and read 30567 times.

Quoting EagleBoy (Reply 1):
Interesting info on the lower level of degradation in the fleet.
The future of secondhand market for A380 has been debated a few times on A.Net.

Remember that EK probably has more incentive than anyone else in the world in promoting the value of secondhand A380s and that includes both current and future, owned and leased aircraft as this will feed into the lease rates / finance deals they can negotiate.

Topic: RE: A380 Overperforms Says Tim Clark Of EK
Username: lightsaber
Posted 2012-11-22 04:43:23 and read 30526 times.

Quoting flyingturtle (Reply 16):
How does that happen? Does the A/C put on weight over the years, do the wings and fuselage deform into a less aerodynamic state, like the wrinkles on heavily used B-52, for example?

Aircraft put on a tremendous amount of weight (tons) per year. One reason the carpets are replaced is even with wear they gain weight (yes, yuck). Another thing is patches to fix damage.

I'm a bit surprised at the baseline number. That is higher than I've heard as the rule of thumb, but perhaps Clark knows more than I.  
Quoting flyingturtle (Reply 16):
Or is it the engine wearing out?

Engines degrade with time. On widebodies in long haul service, that often sets the overhaul interval.

Lightsaber

Topic: RE: A380 Overperforms Says Tim Clark Of EK
Username: imiakhtar
Posted 2012-11-22 04:45:05 and read 30434 times.

Quoting par13del (Reply 12):
Derate takeoffs and lower cruise speeds was not only about fuel but also about preserving the time on the wing for a/c enhines

Derate takeoffs and cruise speeds are independent of each other. A higher cruise speed will have negligible engine EGT deterioration.

Quoting flyingturtle (Reply 17):
Or is it the engine wearing out?

That's correct.

Over time (or over Flight Hours:Flight cycles in the aviation context), an engine will undergo Exhaust Gas Turbine (EGT) deterioration. Consequently, the engine will suffer from higher fuel burn. When you factor in DXB's sandy locale and high ambient temperatures, you can see why operations in such an environment are torture for the engines.

Quoting lightsaber (Reply 15):
but how is the maintenance (other than the wing cracks)?

That is what I would like to know too.

A few years ago, the GE90-110/5 in EK service on the 77L/W had an EGT deterioration of around 9degC per 1000 flight cycles versus an engine brochure figure of 10degC/1000FCs - a surprising difference given the multiple regional sectors the 77Ws are used on.

It would be interesting to see how the GP7200 compares.

{edited-sorry for confusion)

[Edited 2012-11-22 04:57:05]

Topic: RE: A380 Overperforms Says Tim Clark Of EK
Username: kaitak
Posted 2012-11-22 04:46:24 and read 30354 times.

Quoting swallow (Reply 6):
Classic TC ....putting the screws on Airbus by negotiating in the press. As he has done before, he casts doubt on the product, hoping to get better pricing on future orders. At least he has the temerity to admit he was wrong regarding the 388. Didn't stop him ordering stacks of them.

I think his main target is the 3510. I highly doubt that Airbus would have changed its specs without consulting EK, one of her main customers. Tellingly, JL does not publicly contradict TC's claim that he was not consulted.

Since the 359 is becoming to small for his needs, I think TC is looking to convert some 359 orders to the 3510

Sure is typical of him; Airbus, while being pleased at his A380 comments, must also be pretty incandescent about his A350 comments (although I really can't blame TC if he was not consulted!).

However, one thought flashed through my mind (it happens at least once a week): could this also be a message to Boeing as well: "the only thing that's keeping the A350 on our books is your failure to launch the 777X". Just a thought ...

Topic: RE: A380 Overperforms Says Tim Clark Of EK
Username: PIEAvantiP180
Posted 2012-11-22 04:48:05 and read 30306 times.

Quoting flyingturtle (Reply 17):
How does that happen? Does the A/C put on weight over the years, do the wings and fuselage deform into a less aerodynamic state, like the wrinkles on heavily used B-52, for example?

The aircraft does put on weight over the years due to many different factors. If you have skin repairs due to ramp rash is just one example. I can't give you a definite answer if the fuselage and the wings deform but with the previous example the plane will loose aerodynamic performance with skin repairs and adding different antennas for Fifi, GPS, and satellite dishes for entertainment. As for wrinkles in the skin, its a normal occurrence. If you can stand on top of a plane when its sitting on the ground you will see ripples in the skin from one rib to another, once the plane is in the sky and its pressurised it will smooth out.

Topic: RE: A380 Overperforms Says Tim Clark Of EK
Username: AmericanAirFan
Posted 2012-11-22 04:54:30 and read 30147 times.

It's great to hear the A380 out perform its' promise. Maybe this will lead to more carriers in the future trying to place the A380 in their fleet.

Topic: RE: A380 Overperforms Says Tim Clark Of EK
Username: AmericanAirFan
Posted 2012-11-22 04:57:31 and read 31337 times.

Quoting flyingturtle (Reply 16):
Does the A/C put on weight over the years, do the wings and fuselage deform into a less aerodynamic state, like the wrinkles on heavily used B-52, for example?

Funny you say that. The picture you posted has the following remark:

"and the conspicuous skin wrinkles, which are often mis-identified as evidence of aging, but were actually present when factory fresh and are due to tension from wing flex and weight (called Wagner Tension Field). "

However, aircraft do put on weight over the years as others have said. The A380 being a composite airframe though shouldn't wrinkle like the aluminum birds.

Topic: RE: A380 Overperforms Says Tim Clark Of EK
Username: flyingturtle
Posted 2012-11-22 05:11:02 and read 30853 times.

Quoting Zkpilot (Reply 17):
Quoting justloveplanes (Reply 18):
Quoting lightsaber (Reply 20):
One reason the carpets are replaced is even with wear they gain weight (yes, yuck).
Quoting imiakhtar (Reply 21):
Quoting PIEAvantiP180 (Reply 23):

Thanks for the answers, and especially for the yucky one!  
Quoting AmericanAirFan (Reply 25):

Well, I looked for an example image - a fuselage with wrinkles... I could have pulled up E-2 Hawkeye picture for that matter. 

On one aspect you're wrong... the A380 still has an aluminium frame & skin. See http://en.wikipedia.org/wiki/Airbus_A380#Advanced_materials  


David

Topic: RE: A380 Overperforms Says Tim Clark Of EK
Username: astuteman
Posted 2012-11-22 05:20:47 and read 31249 times.

Quoting swallow (Reply 6):
Since the 359 is becoming to small for his needs, I think TC is looking to convert some 359 orders to the 3510

Funny, isn't it. But the article is about the A350-1000 being "in limbo", and yet the type that looks most threatened by his comments is the A350-900

Quote:
the A350-900 “is starting to look a bit marginal to us because of size,” he adds. “Gauge is the way we grow, you cannot get any more aircraft into the Dubai hub

Sounds to me like that might actually make the A350-1000 more appealing, not less.

Quoting swallow (Reply 6):
Classic TC ....putting the screws on Airbus by negotiating in the press

Tend to think that's how it looks.
I can see early build A350-900's being overweight.
I can equally see most of the weight issues having been worked out of the system by the time the A350-1000 hits the streets - Steve Udvar Hazy certainly thinks there's a viable plan being worked to do this, if his recent comments are anything to go by.

Interesting to note that Airbus and EK between them have taken 5 TONNES of weight out of their A380's. I know Airbus were targetting having 3 tonnes off the base airframe by 2013
That's a LOT of weight   

If they've brought their A380 dry operating weight down from c. 300 tonnes I believe the early frames were at, to c. 295 tonnes, that's very significant in terms of the longer sectors that EK fly. Especially when that gain is applied to the 573 tonners they will get next year.

Nice to see the A380 exceeding TC's expectations, even if that in itself fails to live up to a large part of A-Net's expectations...  

Rgds

Topic: RE: A380 Overperforms Says Tim Clark Of EK
Username: EPA001
Posted 2012-11-22 05:27:22 and read 30904 times.

Quoting lightsaber (Reply 14):
I would love to know how the A388 CASM is versus expectation. Lower fuel burn is great, but how is the maintenance (other than the wing cracks)?

That would indeed be very interesting to know.

Quoting par13del (Reply 11):
Good news all around for the A380.

Yes it is.   Makes you wonder which versions of the A380 EK will get in 2013?  .

http://www.flightglobal.com/news/art...ewest-a380-weight-variants-379235/

Topic: RE: A380 Overperforms Says Tim Clark Of EK
Username: EPA001
Posted 2012-11-22 05:31:02 and read 30766 times.

Quoting astuteman (Reply 27):
Nice to see the A380 exceeding TC's expectations, even if that in itself fails to live up to a large part of A-Net's expectations...  

It is indeed. And the part of A-nets expectations that can now lo longer be upheld, well I guess these people have to adjust their opinions and expectations regarding the A380?  .

Topic: RE: A380 Overperforms Says Tim Clark Of EK
Username: AmericanAirFan
Posted 2012-11-22 05:47:13 and read 30328 times.

Quoting flyingturtle (Reply 26):
Well, I looked for an example image - a fuselage with wrinkles... I could have pulled up E-2 Hawkeye picture for that matter.

On one aspect you're wrong... the A380 still has an aluminium frame & skin. See http://en.wikipedia.org/wiki/Airbus_A380#Advanced_materials


David

Awesome. Thanks for the correction. I don't know why I thought the whole frame was composite.  

Topic: RE: A380 Overperforms Says Tim Clark Of EK
Username: sunrisevalley
Posted 2012-11-22 05:48:06 and read 30301 times.

Quoting astuteman (Reply 27):
If they've brought their A380 dry operating weight down from c. 300 tonnes I believe the early frames were at, to c. 295 tonnes,

Not quibling but Piano-X has an OEW of 299t. for what is termed a "uae" version. Is it possible that the DOW on these frames is nearer 306t ? The OEW for a "generic" 569t MTOW A380 is shown as 285t. For what it terms a "reu" version with 840- seats, 282t.

Topic: RE: A380 Overperforms Says Tim Clark Of EK
Username: swallow
Posted 2012-11-22 05:49:06 and read 30319 times.

Quoting worldrider (Reply 15):
the astonishing number of 160 A widebodies! hmm no B787s?

In the rarefied atmosphere that is EK management, the 787 is considered too small. TC already considers the 359 to be marginal!

That said, TC has publicly praised the 77W and 388 for exceeding expectations.

I expect airline CEO's to say the same about the 787

Nice to see these new aircraft programs beat expectations despite some of the doom and gloom that surrounded their genesis

I look forward to seeing the 350 prove her chops, like the 77W, 388 and 787 before her

Topic: RE: A380 Overperforms Says Tim Clark Of EK
Username: KC135TopBoom
Posted 2012-11-22 06:01:25 and read 30004 times.

I just don't see where cruising at .86M as opposed to .83M will save fuel. On a mission from DXB to LAX you save about 30 minutes flying time. For an A-380, that is about 15,000 lbs of fuel saved due to the 30 minutes less flying time. But fuel flow per engine would increase by about 1%, per engine, for the 15 hour flight, per hour, at FL-330. That comes out to around 18,000 lbs of additional fuel burn because of the higher cruise airspeed. From LHR-BOS or JFK it is about 10 minutes due to the higher cruise speed.

This doesn't take into account your initial take off will be at a higher gross weight, thus a heavier airplane throughout the entire mission. Or it means taking less cargo/pax so you can load more fuel.

Yes, airplanes do grow in weight as they age. Engine efficency also degrades as the engine ages, too. But it is not 2.5%-3% per year as Mr. Clark is saying, and the airplane OEMs know this, it is typically anywhere from .25% to 1% per 10,000 flying hours or 5,000 cycles (unless the airplane is damaged). So, EK's 4 year old A-380s are somewhere between 1% and 4% less efficent today than the day they were delivered. The only A-380 I can think of that is less efficent than that is the QF bird (Nancy Bird-Walton, VH-OQA?) that had the engine explode and now has patches and repairs that have made it heavier (about 100 kg?) than when it was delivered.

Topic: RE: A380 Overperforms Says Tim Clark Of EK
Username: squared
Posted 2012-11-22 06:18:46 and read 29450 times.

Quoting KC135TopBoom (Reply 33):
But it is not 2.5%-3% per year as Mr. Clark is saying,

"The first aircraft delivered in 2008 would normally perform around 2.5-3% less efficiently than in the beginning, but according to Clark the degradation has been only around 1%."

He never says 2.5-3% per year... He says 1% from the beginning - which is on the low end of the scale.

Topic: RE: A380 Overperforms Says Tim Clark Of EK
Username: MattH
Posted 2012-11-22 06:27:22 and read 29219 times.

Quoting flyingturtle (Reply 16):
do the wings and fuselage deform into a less aerodynamic state, like the wrinkles on heavily used B-52, for example?

Please read the description of the photo - those wrinkles aren't from wear........

Topic: RE: A380 Overperforms Says Tim Clark Of EK
Username: art
Posted 2012-11-22 06:33:31 and read 29019 times.

Quoting KC135TopBoom (Reply 33):
I just don't see where cruising at .86M as opposed to .83M will save fuel. On a mission from DXB to LAX you save about 30 minutes flying time. For an A-380, that is about 15,000 lbs of fuel saved due to the 30 minutes less flying time. But fuel flow per engine would increase by about 1%, per engine, for the 15 hour flight, per hour, at FL-330. That comes out to around 18,000 lbs of additional fuel burn because of the higher cruise airspeed. From LHR-BOS or JFK it is about 10 minutes due to the higher cruise speed.

This doesn't take into account your initial take off will be at a higher gross weight, thus a heavier airplane throughout the entire mission.

Interesting to hear. Thanks.

Topic: RE: A380 Overperforms Says Tim Clark Of EK
Username: Stitch
Posted 2012-11-22 06:49:59 and read 28703 times.

If the A350-900 is now "marginal" for EK, it would explain why the airline has expressed interest in the 777-8X as it is longer and wider than the A350-900 so it would allow EK to increase capacity by at least 40 seats over the 777-200ER / A350-900 in a 10-abreast configuration (so 330 passengers vs. 290).

Topic: RE: A380 Overperforms Says Tim Clark Of EK
Username: art
Posted 2012-11-22 07:06:22 and read 28084 times.

Quoting Stitch (Reply 37):
If the A350-900 is now "marginal" for EK, it would explain why the airline has expressed interest in the 777-8X as it is longer and wider than the A350-900 so it would allow EK to increase capacity by at least 40 seats over the 777-200ER / A350-900 in a 10-abreast configuration (so 330 passengers vs. 290).

I remember EK ordering A350-10. Unless my memory fails me, Clark said something like if Airbus was late he would take their legs off at the kneecaps. Additional lift WHEN NEEDED to fit expansion plans is really important to EK is the message I got. Would a 777-whateverX be available fast enough for EK? Suppose Boeing launched a "new" 777 today, when could EK start scheduled services with it?

Topic: RE: A380 Overperforms Says Tim Clark Of EK
Username: flyingturtle
Posted 2012-11-22 07:07:00 and read 28070 times.

Quoting MattH (Reply 35):

...and as I have written in #26.....  


  

David

Topic: RE: A380 Overperforms Says Tim Clark Of EK
Username: sunrisevalley
Posted 2012-11-22 07:09:38 and read 28045 times.

Quoting KC135TopBoom (Reply 33):
I just don't see where cruising at .86M as opposed to .83M will save fuel

PIANO-X says that a 569t MTOW/285tOEW version , 60t payload, 7000nm sector burns 188.268t of fuel at M.83 and at M.86, 192.531t

Topic: RE: A380 Overperforms Says Tim Clark Of EK
Username: Stitch
Posted 2012-11-22 07:13:39 and read 27941 times.

Quoting art (Reply 38):
Suppose Boeing launched a "new" 777 today, when could EK start scheduled services with it?

If Boeing pushed, I expect 2018-2019.

Topic: RE: A380 Overperforms Says Tim Clark Of EK
Username: astuteman
Posted 2012-11-22 07:30:10 and read 27543 times.

Quoting KC135TopBoom (Reply 33):
I just don't see where cruising at .86M as opposed to .83M will save fuel.

EK operates 27 of them. They should know

Quoting KC135TopBoom (Reply 33):
But it is not 2.5%-3% per year as Mr. Clark is saying, and the airplane OEMs know this, it is typically anywhere from .25% to 1% per 10,000 flying hours or 5,000 cycles (unless the airplane is damaged). So, EK's 4 year old A-380s are somewhere between 1% and 4% less efficent today than the day they were delivered

If you actually read the article, he states 1% since EIS, which is a different thing altogether.
And certainly fits with the bottom end of your projection.
I suspect a lot more 4 year-old aircraft than just Nancy Bird Walton fit into the "less efficient than that" category..  
Quoting art (Reply 36):
Interesting to hear. Thanks

Wasn't it?  
Quoting sunrisevalley (Reply 40):
PIANO-X says that a 569t MTOW/285tOEW version , 60t payload, 7000nm sector burns 188.268t of fuel at M.83 and at M.86, 192.531t

Again, I'd ask how many A380's do PIANO-X fly, compared to Mr. Clark?

Good though it may be, at the end of the day it's a modelling tool. It's not reality x 27

Rgds

Topic: RE: A380 Overperforms Says Tim Clark Of EK
Username: TVNWZ
Posted 2012-11-22 07:58:00 and read 26642 times.

When you are buying, the product sucks. When you own them for awhile and have to eventually sell them, the product is great! Classic buy low. Sell high.

Topic: RE: A380 Overperforms Says Tim Clark Of EK
Username: autothrust
Posted 2012-11-22 08:06:13 and read 26421 times.

Quoting flyingturtle (Reply 26):

On one aspect you're wrong... the A380 still has an aluminium frame & skin

The upper shells/skins are GLARE not aluminium.


However anyone has some info about the Wagner Tensions Field?

Topic: RE: A380 Overperforms Says Tim Clark Of EK
Username: brilondon
Posted 2012-11-22 08:21:51 and read 26021 times.

It is the same with your car. Your engine has a maximum efficiency at a certain speed, so the aircraft is more efficient at .86 vs. .83. It also depends on the winds, the actual weight, etc. which I am sure has alot to do with it.

Topic: RE: A380 Overperforms Says Tim Clark Of EK
Username: flyingturtle
Posted 2012-11-22 08:40:04 and read 25474 times.

At least some migratory birds use two "most" efficient airspeeds. One that gives them the least energy expenditure per hour flown, and one that yields the least energy expenditure per distance flown. When they migrate, they use the latter.

Now, what exactly is optimized when the A380 is flown at 0.86 M vs. 0.83 M? Tim Clarke mentions fuel efficiency, but what is the exact metric?


David

Topic: RE: A380 Overperforms Says Tim Clark Of EK
Username: N14AZ
Posted 2012-11-22 09:32:43 and read 24059 times.

This is actually not new - Airbus or EK (don't remember who it was) reported about this effect some years ago.

Topic: RE: A380 Overperforms Says Tim Clark Of EK
Username: Alnicocunife
Posted 2012-11-22 09:33:51 and read 24162 times.

Quoting art (Thread starter):
Seems remarkable that the the aircraft burns less fuel at mach 0.86 than at mach 0.83. How does that come about?

Could be similar to the DC-10. When flying .082 or less the tail dropped causing more drag. Flying faster allowed the tail to flight higher (aircraft level in cruise). Less drag, less fuel burned or the same fuel burned but you are moving faster.

Topic: RE: A380 Overperforms Says Tim Clark Of EK
Username: art
Posted 2012-11-22 10:14:53 and read 22991 times.

Quoting Alnicocunife (Reply 48):
Quoting art (Thread starter):
Seems remarkable that the the aircraft burns less fuel at mach 0.86 than at mach 0.83. How does that come about?

Could be similar to the DC-10. When flying .082 or less the tail dropped causing more drag. Flying faster allowed the tail to flight higher (aircraft level in cruise). Less drag, less fuel burned or the same fuel burned but you are moving faster.

Interesting to know but did Douglas give the cruise speed as mach 0.82 whereas the aircraft would burn less fuel cruising from A to B at a higher mach number? I'm confused why Tim Clark mentions A380 is more efficient at mach 0.86 than at mach 0.83 unless this is an overall assessment of all costs and benefits at mach 0.83 versus the same at mach 0.86.

Topic: RE: A380 Overperforms Says Tim Clark Of EK
Username: swallow
Posted 2012-11-22 10:21:45 and read 22902 times.

Quoting KC135TopBoom (Reply 33):
I just don't see where cruising at .86M as opposed to .83M will save fuel

I found this explanation on another website. Hope it makes sense.

The A380 was designed to have an economical cruise speed, and a high speed cruise. The design turned out such that the fuel burn was higher than expected at the economical cruise speed (due to the lower than desired aspect ratio of the wing) and so they tend to only use the high speed cruise of around 0,86. There are no/ minimal gains by cruising slower in the A380 unless the aircraft is partially filled. You will see that Airbus is changing the wing twist from next year, and increasing the washout by another 1.5 degrees in order to try and resolve this problem.

The basic problem stems from the fact that you want to carry 555 pax, making this a large aircraft, so you need a certain wing area, but you are restricted in span due to existing airport infrastructure. The net result is that the wing chord is increased, with a fixed span, so the aspect ratio of the wing reduces. Induced drag is inversely proportional to aspect ratio. So they have a bit of a problem!


Source: http://www.avcom.co.za/phpBB3/viewtopic.php?f=1&t=98712

Topic: RE: A380 Overperforms Says Tim Clark Of EK
Username: art
Posted 2012-11-22 10:43:55 and read 22273 times.

Quoting swallow (Reply 50):

Thanks. I think I may be starting to understand.  

Topic: RE: A380 Overperforms Says Tim Clark Of EK
Username: Stitch
Posted 2012-11-22 11:11:30 and read 21713 times.

So the fuel savings from the wing twist comes from allowing a slower cruise speed, which reduces engine thrust and SFC?

Topic: RE: A380 Overperforms Says Tim Clark Of EK
Username: Revelation
Posted 2012-11-22 11:30:10 and read 21189 times.

Quoting HiJazzey (Reply 13):
True, although they're flying longer these days. The newer generation NBs like the NEOs and Max's should probably be optimised for longer stage lengths

Might be why Boeing is finding it worthwhile to clean up the tail cone on the 737.

Quoting sunrisevalley (Reply 31):
For what it terms a "reu" version with 840- seats, 282t.

I imagine the name came from the company that planned to fly two A380s in cattle-class configuration to Reunion Island.

Topic: RE: A380 Overperforms Says Tim Clark Of EK
Username: MauriceB
Posted 2012-11-22 12:02:53 and read 20316 times.

Maybe the fact that it performs better at a higher mach. number comes from the fact that the faster a plane is able to fly, the less induced drag it creates. Higher speed also means that the profile drag numer is higher. But probably the plane is so aerodynamic that the extra speed+less induced drag makes up for the extra profile drag.

Incredible it only performs 1% less after years of operation, shows once again that the A380 is a game changer.

I can imagine that future, composit planes, will also have less degradation in performance as it is less funurable to damage due to rocks, weather, and fluctuating cabin pressure...


Let's see if the 787 will perform even better!


Maurice

Topic: RE: A380 Overperforms Says Tim Clark Of EK
Username: art
Posted 2012-11-22 12:26:01 and read 19826 times.

Quoting Revelation (Reply 53):
Quoting sunrisevalley (Reply 31):
For what it terms a "reu" version with 840- seats, 282t.

I imagine the name came from the company that planned to fly two A380s in cattle-class configuration to Reunion Island.

"Cattle class" sounds disparaging to me. I know the term is used but one should not forget that 50 years ago air travel was very, very expensive in Europe and had it remained so, there would be relatively few travellers and hundreds of thousands/millions less people employed in the aviation industry . If cramming 840 people into an A380 saves each pax $200 for 20 hours flight, I think most of those pax would be very pleased to experience the additional discomfort. For some it would make the difference between taking the trip/not taking the trip.

Topic: RE: A380 Overperforms Says Tim Clark Of EK
Username: tommytoyz
Posted 2012-11-22 14:48:29 and read 17209 times.

The SR-71 burned less fuel per mile traveled the faster it flew. Going Mach 3.5 was more economical than flying at Mach 3.2.

Why? Beats me. No idea.

But that's a huge speed differential of Mach 0.3. Here with the A380 it's only a speed differential of Mach 0.03.

To turlte:

The wrinkles on the B-52 have been there since she rolled out of the factory:

the conspicuous skin wrinkles, which are often mis-identified as evidence of aging, but were actually present when factory fresh and are due to tension from wing flex and weight (called Wagner Tension Field).

Topic: RE: A380 Overperforms Says Tim Clark Of EK
Username: tdscanuck
Posted 2012-11-22 15:20:20 and read 16645 times.

Quoting art (Thread starter):
Seems remarkable that the the aircraft burns less fuel at mach 0.86 than at mach 0.83. How does that come about?

ASM production goes up more (due to higher speed) than CASM (due to higher fuel burn).

Quoting art (Reply 10):
I see narrowbodies tend to have m 0.8 as their advertised cruise speed. Can they also be flown faster without increasing fuel burn from A to B

Typically not.

Quoting art (Reply 10):
I don't understand why the advertised cruise speed would be less than the speed.that burnt the least fuel between origin and destination. Lower engine maintenance cost? Some other factors?

Design cruise speed was selected *way* back in the development phase before all the testing (especially NAMS) was completed.

Quoting autothrust (Reply 44):
The upper shells/skins are GLARE not aluminium.

GLARE is an aluminum/fiberglass laminate. So it's correct to refer to it as composite, but not correct to say it doesn't have any aluminum.

Quoting autothrust (Reply 44):
However anyone has some info about the Wagner Tensions Field?

Here's a good paper:
http://diablo221.altervista.org/Tension-field%20Theory.pdf

It's also called "diagonal tension" or "intermediate diagonal tension". It's been used in aircraft design for decades. It works really well when you're not so worried about displacement as strength.

Quoting MauriceB (Reply 54):
Maybe the fact that it performs better at a higher mach. number comes from the fact that the faster a plane is able to fly, the less induced drag it creates.

Be careful; the faster you fly, the less induced drag *coefficient* it creates. The induced drag force goes up because the dynamic pressure goes up faster than the induced drag coefficient drops.

Quoting tommytoyz (Reply 56):
The SR-71 burned less fuel per mile traveled the faster it flew. Going Mach 3.5 was more economical than flying at Mach 3.2.

Why? Beats me. No idea.

At those speeds, the SR-71 was in pure ramjet mode. Ramjet efficiency goes up with increasing speed. So, as the airplane accelerated, the engine thrust could go up faster than the drag.

Tom.

Topic: RE: A380 Overperforms Says Tim Clark Of EK
Username: musang
Posted 2012-11-22 15:30:32 and read 16572 times.

Quoting lightsaber (Reply 20):
Aircraft put on a tremendous amount of weight (tons) per year

In the mid '80s AirLanka was using one of Royal Jordanian's TriStar 500s. It became apparent during an overhaul that there was (I'm sure any figure bandied around at the time was exaggerated) a rediculous amount of sand in the belly, presumably dropped off ULDs, pallets and ground staff shoes over the years.


View Large View Medium
Click here for bigger photo!

Photo © AlainDurand



musang

Topic: RE: A380 Overperforms Says Tim Clark Of EK
Username: flyingturtle
Posted 2012-11-22 15:46:43 and read 16241 times.

Quoting tommytoyz (Reply 56):


For a thorough discussion of the topic at hand, please refer to my posting #39.   




David

Topic: RE: A380 Overperforms Says Tim Clark Of EK
Username: zeke
Posted 2012-11-23 00:31:34 and read 11390 times.

Quoting francoflier (Reply 2):

The extra fuel flow required to go faster is lower is compensated by the shorter flight time.

That is part of it, with the newer aircraft they have transonic wings and have rather flat drag polars, M0.83 would be closer to maximum endurance for the A380, and 0.86 closer to normal long range cruise, i.e. best MxL/D.

Quoting francoflier (Reply 2):

I didn't think the A380 would be 'comfortable' .86 cruiser. I imagined it more in the .84~.85 range.

The A380 was designed for a long range cruise of 0.85/FL360, it might have turned out a bit better than design, i.e. 0.855/0.86.

Quoting JU068 (Reply 4):
What about the other operators? Have any of them been this impressed by this bird?

QF & SQ have made similar comments before.

“In terms of technical performance, specifically fuel burn, the aircraft is performing better than Airbus promised. In seat/mile terms we achieve overall a 20% better fuel burn than our 747-400s.“ Chew Choon Seng, CEO Singapore Airlines ATW online, Dec 13th 2007

“The A380 has met or exceeded all the original performance, noise and fuel burn guarantees made by Airbus at the time the aircraft purchase decision was made.” Lyell Strambi, Group Executive - Qantas Airlines, Operations Airline Fleet Management , July 2009

Quoting flyingturtle (Reply 16):
How does that happen?

The airframe degrades over time, a number of items that change over time include the paint, seals on the slats, damage from lightning strikes/birds, damage from ground equipment, erosion in the engine, etc.

Quoting flyingturtle (Reply 46):
Now, what exactly is optimized when the A380 is flown at 0.86 M vs. 0.83 M? Tim Clarke mentions fuel efficiency, but what is the exact metric?

0.86 would be close to the tangent to the drag polar, which is the best specific range (nil wind).

To work this out, the aircraft automatically records the engine and airframe parameters during the cruise, these parameters are sent back to the operator back via ACARS/QAR data. Airbus produces as part of the performance engineering software a inflight flight planning (IFP) software, that is the baseline virtual "A380" which every operator bases their flight planning on.

The performance monitoring software takes a whole series of the aircraft parameters, weight, altitude, TAS, and mach, N1, from various flights, weights, times, conditions from that it will look at the IFP to come up with the theoretical fuel flow (FF) for those parameters. Next it takes the same parameters, this time using the actual N1, and uses a theoretical engine for that altitude and mach to come up with a new calculated FF, the calculated FF is compared to the theoretical FF, the difference in the model is the airframe degradation (i.e. a given amount of thrust at a given altitude is required to overcome the drag in the IFP). It does another loop where the actual FF is compared to the theoretical FF, we already know what the airframe degradation is from the previous step, so any additional fuel flow is the engine degradation contribution.

This is a very statistical approach, both for generating the engine and airframe model in the IFP as well as the recording the in service data. The data shows trends, not absolutes. Also I believe the wing and some of the fairings on the initial test aircraft were slightly different to the production aircraft, which would result in some of the flight test data being a little more conservative.

Topic: RE: A380 Overperforms Says Tim Clark Of EK
Username: maxter
Posted 2012-11-23 00:45:21 and read 11169 times.

Quoting flipdewaf (Reply 8):
This seems like good news for the whale but Tim Clark always seems to have a reason up his sleeve for saying things.

For goodness sake, can't we just accept that this aircraft may just be all TC and many others say it is rather that somehow cast doubt as to it's actual abilities by insinuating that TC might not be on the level?

Topic: RE: A380 Overperforms Says Tim Clark Of EK
Username: autothrust
Posted 2012-11-23 01:33:10 and read 10593 times.

Quoting tdscanuck (Reply 57):
GLARE is an aluminum/fiberglass laminate. So it's correct to refer to it as composite, but not correct to say it doesn't have any aluminum.

I haven't said it doesn't have any aluminium. I was just pointing out the upper shells not being normal aluminium so less prone to Wagner Tension Field.



Anyone knows if GLARE 2 will be used on the next A380's?

Topic: RE: A380 Overperforms Says Tim Clark Of EK
Username: PlaneInsomniac
Posted 2012-11-23 01:57:23 and read 10360 times.

Quoting maxter (Reply 61):
For goodness sake, can't we just accept that this aircraft may just be all TC and many others say it is rather that somehow cast doubt as to it's actual abilities by insinuating that TC might not be on the level?

Well, yeah, remember that this is about the A380.

According to some poeple:
If somebody who really should know what he's talking about says the plane is consistently performing better than projected, this can only mean:
a) the plane is really underperforming for some bizarre, illogical "technical" reason or
b) that person is lying for political reasons.

Nothing new, really. The same game we have played here for a decade or so. Some people just never get tired, I guess.

Topic: RE: A380 Overperforms Says Tim Clark Of EK
Username: flyingturtle
Posted 2012-11-23 02:09:26 and read 10194 times.

Keep clicking through, there will be some diagrams about the Wagner tension field:

http://www.docstoc.com/docs/74843498...S-OF-DIAGONAL-TENSION-FIELD-ACTION

Quoting autothrust (Reply 62):

You have confused me by mentioning "upper shells"... huh, what part of the A/C is that? It can't be part of the fuselage...    
Quoting zeke (Reply 60):

Thank you for sharing your knowledge!


David

[Edited 2012-11-23 02:11:33]

Topic: RE: A380 Overperforms Says Tim Clark Of EK
Username: N14AZ
Posted 2012-11-23 03:11:14 and read 9836 times.

Quoting swallow (Reply 50):
I found this explanation on another website. Hope it makes sense.

The A380 was designed to have an economical cruise speed, and a high speed cruise. The design turned out such that the fuel burn was higher than expected at the economical cruise speed (due to the lower than desired aspect ratio of the wing) and so they tend to only use the high speed cruise of around 0,86. There are no/ minimal gains by cruising slower in the A380 unless the aircraft is partially filled. You will see that Airbus is changing the wing twist from next year, and increasing the washout by another 1.5 degrees in order to try and resolve this problem.

The basic problem stems from the fact that you want to carry 555 pax, making this a large aircraft, so you need a certain wing area, but you are restricted in span due to existing airport infrastructure. The net result is that the wing chord is increased, with a fixed span, so the aspect ratio of the wing reduces. Induced drag is inversely proportional to aspect ratio. So they have a bit of a problem!
Quoting Stitch (Reply 52):
So the fuel savings from the wing twist comes from allowing a slower cruise speed, which reduces engine thrust and SFC?

Given the fact that I was lousy in Physics I also would appreciate if somebody could explain the link between the wing twist and the speed.

So if Airbus now ncreases the wing twist by 1.5 degree, the wing span is actually a little bit smaller, correct? (seems as if I was lousy in mathemtics as well...).

Topic: RE: A380 Overperforms Says Tim Clark Of EK
Username: lightsaber
Posted 2012-11-23 05:51:43 and read 9396 times.

Quoting francoflier (Reply 2):
Quoting musang (Reply 58):
In the mid '80s AirLanka was using one of Royal Jordanian's TriStar 500s. It became apparent during an overhaul that there was (I'm sure any figure bandied around at the time was exaggerated) a rediculous amount of sand in the belly, presumably dropped off ULDs, pallets and ground staff shoes over the years.

My prior employer purchased a used 747 for ground based testing. When it took too long to prepare the aircraft, they weighed the trash cans of scapped off food (tarred for a empty trash can) to show the executives why we were behind schedule. 3.5 TONS of scrapped food later, it was ready.

And by yuck on the carpets... absorbed food and such. They weighed about twice what they did when installed.

Note: I don't know about the seats. They were worth money and thus removed as we weren't going to pay what they were worth.

Quoting imiakhtar (Reply 21):
It would be interesting to see how the GP7200 compares.

   And the Trent too... But the real numbers will be hard to find.

Quoting maxter (Reply 61):
For goodness sake, can't we just accept that this aircraft may just be all TC and many others say it is rather that somehow cast doubt as to it's actual abilities by insinuating that TC might not be on the level?

There is certainly enough sales demand, for the long lead times, to imply the A380 will make money.   

Lightsaber

Topic: RE: A380 Overperforms Says Tim Clark Of EK
Username: swallow
Posted 2012-11-23 06:07:54 and read 9255 times.

Quoting N14AZ (Reply 65):
Given the fact that I was lousy in Physics

Me too   

Quoting N14AZ (Reply 65):
I also would appreciate if somebody could explain the link between the wing twist and the speed

My layman understanding is that wing twist decreases induced drag at cruise. Adding twist makes the wing more efficient.

I suppose it follows that less induced drag translates into faster speed.

Quoting Stitch (Reply 52):
So the fuel savings from the wing twist comes from allowing a slower cruise speed, which reduces engine thrust and SFC?

Methinks the fuel savings come from lower induced drag at cruise, but I'll defer to the engineers on this board.

[Edited 2012-11-23 06:08:41]

Topic: RE: A380 Overperforms Says Tim Clark Of EK
Username: 2175301
Posted 2012-11-23 06:29:53 and read 9138 times.

Quoting lightsaber (Reply 66):
There is certainly enough sales demand, for the long lead times, to imply the A380 will make money.

At least for most of the companies operating them.


Have a great day,

Topic: RE: A380 Overperforms Says Tim Clark Of EK
Username: Stitch
Posted 2012-11-23 06:56:04 and read 9000 times.

Quoting Stitch (Reply 52):
So the fuel savings from the wing twist comes from allowing a slower cruise speed, which reduces engine thrust and SFC?
Quoting swallow (Reply 67):
Methinks the fuel savings come from lower induced drag at cruise, but I'll defer to the engineers on this board.

Which is essentially what I meant, I just worded it poorly.

Topic: RE: A380 Overperforms Says Tim Clark Of EK
Username: autothrust
Posted 2012-11-23 07:05:17 and read 8938 times.

Quoting flyingturtle (Reply 64):
You have confused me by mentioning "upper shells"... huh, what part of the A/C is that? It can't be part of the fuselage..

Sorry for confusing  
Quoting flyingturtle (Reply 64):
there will be some diagrams about the Wagner tension field:

Thanks for the Links.

Topic: RE: A380 Overperforms Says Tim Clark Of EK
Username: tdscanuck
Posted 2012-11-23 07:33:27 and read 8805 times.

Quoting zeke (Reply 60):
The A380 was designed for a long range cruise of 0.85/FL360, it might have turned out a bit better than design, i.e. 0.855/0.86.

This seems to have been a trend since the mid 90's for both OEM's. I think that better CFD tools (they're really really good for high speed aerodynamics now) haven't quite caught up with the conservatism from the aerodynamics guys. Always a pleasant surprise when you get to actual testing.

Quoting autothrust (Reply 62):
I haven't said it doesn't have any aluminium. I was just pointing out the upper shells not being normal aluminium so less prone to Wagner Tension Field.

Diagonal tension is an intentional design; it's nothing particular to aluminum. As far as I know, nobody is currently building large airliners with diagonal tension skins so the fact that you don't see wrinkles isn't because it's GLARE, it's because they didn't design it in. Several current design do go into diagonal tension when they're over limit load but you never see that in service.

Quoting N14AZ (Reply 65):
Given the fact that I was lousy in Physics I also would appreciate if somebody could explain the link between the wing twist and the speed.

Wing twist determines how much lift each piece of the wing is generating. This, in turn, determines the spanwise lift distribution, which determines induced drag. So altering the wing twist can alter the induced drag for the same amount of lift. The normal induced drag expression is:
C_di = C_l^2 / pi / Aspect Ratio / e

e is called "Oswald's Efficiency Factor" and is where you roll in all the effects of twist, sweep, taper, planform, etc.

Quoting swallow (Reply 67):
Methinks the fuel savings come from lower induced drag at cruise, but I'll defer to the engineers on this board.

Lower induced drag *coefficient*. Absolute induced drag still goes up but not enough to offset the faster trip (you burn more fuel per unit time but do it for less time).

Tom.

Topic: RE: A380 Overperforms Says Tim Clark Of EK
Username: flyingturtle
Posted 2012-11-23 10:26:26 and read 8143 times.

Quoting tdscanuck (Reply 71):
Diagonal tension is an intentional design; it's nothing particular to aluminum. As far as I know, nobody is currently building large airliners with diagonal tension skins so the fact that you don't see wrinkles isn't because it's GLARE, it's because they didn't design it in. Several current design do go into diagonal tension when they're over limit load but you never see that in service.

How are E-2 Hawkeyes and B-52 built, if they form these wrinkles? I'm looking for "stringers B-52", but can't find anything...


David

Topic: RE: A380 Overperforms Says Tim Clark Of EK
Username: tdscanuck
Posted 2012-11-23 11:07:04 and read 7991 times.

Quoting flyingturtle (Reply 72):
How are E-2 Hawkeyes and B-52 built, if they form these wrinkles?

The wrinkles don't form until you load the structure. They're build with normal skins and techniques. The difference between this and more conventional semi-monocoque structures is whether you let the skin go past its buckling load...if you do, it wrinkles. Sometimes you'll only see the wrinkles when the load is on and they'll come out when it relaxes. Sometimes it doesn't come out and you see airplanes that are "permanently" wrinkled. It's not really permanent, in the sense that the material never went past it's yield point, but the structure never relaxes enough for the wrinkles to come out. At least in theory, if you could return the aircraft to jig position, the wrinkles would come out.

Quoting flyingturtle (Reply 72):
I'm looking for "stringers B-52", but can't find anything...

Search on "intermediate diagonal tension" and you'll get lots of hits. The stringers aren't winkling, it's the skin that's wrinkling. The skin basically gives up all compression capability in one direction (perpendicular to the wrinkles) and that compressive load tranfers into the stringers and frames. The skin is carring predominantly tension (parallel to the wrinkles). In a diagonal tension design, if the stringers or frames buckle (wrinkle) you're screwed because now you've got nothing to carry compression. In theory, you could have intermediate diagonal tension beams for stringers or frames but I'm not aware of any design actually doing that.

Tom.

Topic: RE: A380 Overperforms Says Tim Clark Of EK
Username: autothrust
Posted 2012-11-23 11:25:03 and read 7911 times.

Quoting tdscanuck (Reply 71):
Diagonal tension is an intentional design; it's nothing particular to aluminum. As far as I know, nobody is currently building large airliners with diagonal tension skins so the fact that you don't see wrinkles isn't because it's GLARE, it's because they didn't design it in. Several current design do go into diagonal tension when they're over limit load but you never see that in service.

Thanks for the explanation.

Wouldn't you see wrinkles in a 787?

Topic: RE: A380 Overperforms Says Tim Clark Of EK
Username: flyingturtle
Posted 2012-11-23 13:56:50 and read 7407 times.

Quoting tdscanuck (Reply 73):
The stringers aren't winkling, it's the skin that's wrinkling.

Thank you, your answer is really helping me to understand. I was looking for a picture of a "skinned" B-52 or E-2, and I was wondering if the stringers and longerons are placed differently in comparison to, say, a 777 or a 330. The latter ones don't seem to wrinkle...

So it only depends on how much load the skin is carrying, in comparison to the internal structure like stringers and longerons?



David

Topic: RE: A380 Overperforms Says Tim Clark Of EK
Username: tdscanuck
Posted 2012-11-24 10:31:13 and read 6376 times.

Quoting autothrust (Reply 74):
Wouldn't you see wrinkles in a 787?

You shouldn't. As far as I know, the 787 doesn't have any intermediate diagonal tension design in the composite. It's all shear-resistant. Also, when you have the ability to tailor directional strength with fibers (as you do in GLARE or CFRP) then weight advantage isn't as large.

Quoting flyingturtle (Reply 75):
I was looking for a picture of a "skinned" B-52 or E-2, and I was wondering if the stringers and longerons are placed differently in comparison to, say, a 777 or a 330. The latter ones don't seem to wrinkle...

As far as I know, the placement (in terms of frame or stringer spacing) isn't significantly different. The major difference would be skin thickness relative to stringer/frame spacing...for similar loading with a diagonal tension design, you'd have either a significantly thinner skin or significantly more spaced out frames/stringers but not necessarily both.

Quoting flyingturtle (Reply 75):
So it only depends on how much load the skin is carrying, in comparison to the internal structure like stringers and longerons?

It depends on how much load the skin is carrying relative to its bucking load. In a shear resistant design, you keep the skin loads below the skin bucking load so it doesn't wrinkle (wrinkling is the 2D version of 1D column buckling). In a diagonal tension design you intentionally let the skin go above buckling load so it wrinkles; the skin loses it's ability to handle compression perpendicular to the wrinkles so you need stringers/frames that can handle the shifted compression load. In return, you can use a much thinner skin and, in general, you don't need to increase the stringer/frame weight as much as you save on the skin. So you have an overall lighter structure for a given load capability. This is especially useful when you're covering the gap between limit and ultimate load; if you are shear-resistant up to limit load you can get a lot of post-limit capability via diagonal tension and so make it all the way to ultimate load without a lot more structure. Since, at least in theory, you'll never go over limit load in service, the presence of wrinkling usually isn't that big a deal. You see this concept a lot in, for example, floor beams.

You typically don't see this type of design outside aerospace because the wrinkling results in large deflections...in something like a building or bridge those are highly undesirable (and weight savings isn't nearly so important).

Many of the current types, including 787/A350/A380 may exhibit this wrinkling behavior between limit and ultimate load but you're unlikely to ever see it in normal operation. For aerodynamic reasons, you don't want skin wrinkles in normal operation. The B-52 had...less stringent...fuel burn requirements.

Tom.

Topic: RE: A380 Overperforms Says Tim Clark Of EK
Username: ferpe
Posted 2012-11-24 12:48:45 and read 6086 times.

Quoting flyingturtle (Reply 46):
Now, what exactly is optimized when the A380 is flown at 0.86 M vs. 0.83 M? Tim Clarke mentions fuel efficiency, but what is the exact metric?

Tom has answered that in a brief way, here a bit more on why the A380 can be more efficient when flown at 0.86 instead of 0.83:

In general the drag on an aircraft has this dependence of speed (from one of the aircraft design books):

http://i298.photobucket.com/albums/mm262/ferpe_bucket/Totaldragcurve.jpg

As can be seen induced drag (or drag due to lift) is dominating at low speed (it is 80% of the problem at start for instance) and parasitic drag (or drag independent of lift, mainly friction drag ) raises as your speed increases. This diagram ignores one important drag component however, transonic drag. This stays really low (under 1% of total drag) up to cruise speeds and then shoots up very steeply at or just after max cruise speed (due to the stronger wing shockwaves beating the boundary layer to let go) .

Now the A380 has 2 specific characteristics, it has a rather big wing area (good for transonic drag rise if you do the profile right) and rather short span (for a modern wing ) due to the 80m restriction. So induced drag is higher then normal and transonic drag has the potential to be kept low longer then normal (which A seems to have achieved). So by flying faster you increase the parasitic drag as normal, you lower the induced drag more then normal and your transonic drag does not shoot up as usual, voila the TC effect  Wow!  . Of course your total drag increases and therefore you need more engine = higher fuel burn but the time decrease for the leg compensate as others have explained.

Here as a reference the drag data for the A380 at cruise compared to the 787, both modern wings (look at the ratios not the absolute values):

Drag lbf..........Induced...%.....Parasitic..%...Transonic..%
A380...............25,000...48......26,000...50........1,000...2
787...................8,700...37......14,300...61...........500...2


What A is now trying to do with the added wing twist is to lower the high induced drag of the A380 as much as the wing allows, apparently their flight test data told them they could tweak the e (the Oswald thing per Toms post) a tick further   .

[Edited 2012-11-24 13:10:54]

Topic: RE: A380 Overperforms Says Tim Clark Of EK
Username: astuteman
Posted 2012-11-24 23:50:12 and read 5402 times.

Quoting ferpe (Reply 77):
transonic drag has the potential to be kept low longer then normal (which A seems to have achieved).

They did.
During flutter testing, they were expecting to have to dive at a 6 degree angle to achieve M0.96, but only required a 4 degree angle.

I have no link, but I've been advised that part of this was also due to the (infamous) long forehead working better than was predicted to avoid transonic shock waves as the air was accelerated over that huge fuselage..

(during testing they also reduced take-off and landing speeds by 4 kts, but that's a different matter)

Rgds

Topic: RE: A380 Overperforms Says Tim Clark Of EK
Username: kaitak
Posted 2012-11-25 01:38:02 and read 5196 times.

Emirates pushing for A389?

http://www.arabianbusiness.com/emira...-for-up-800-passengers-480685.html

Although the -900 isn't specifically mentioned, an 800 seater (triple deck!) aircraft is; the EK executive concedes that the technology for such an aircraft is over a decade away, but K will be interested in it when it happens.

Does anyone know if there is any firm detail yet on the A380, e.g. dimensions (or length of the intended fuselage plugs to lengthen the A388?).

It would surprise me very much if EK were not at the head of the queue for the A389, particularly with so many undelivered A388s, orders for which would be converted to A389s?

I guess the big issue there would be whether other carriers would be willing to take that jump; CX and VS have expressed interest in the -900, though I think it's anyone's guess whether VS actuall flies any A380s at all.

Topic: RE: A380 Overperforms Says Tim Clark Of EK
Username: Zkpilot
Posted 2012-11-25 01:53:11 and read 5130 times.

Quoting kaitak (Reply 79):

I guess the big issue there would be whether other carriers would be willing to take that jump; CX and VS have expressed interest in the -900, though I think it's anyone's guess whether VS actuall flies any A380s at all.

Me thinks part of the reason why QF deferred its last 8 A380 deliveries to the end of the decade was to get the A389...

Topic: RE: A380 Overperforms Says Tim Clark Of EK
Username: scbriml
Posted 2012-11-25 02:03:45 and read 5099 times.

Quoting kaitak (Reply 79):
It would surprise me very much if EK were not at the head of the queue for the A389, particularly with so many undelivered A388s, orders for which would be converted to A389s?

IMHO, Airbus would be insane to launch the -900 for EIS before EK has taken delivery of nearly all their A388s.

Topic: RE: A380 Overperforms Says Tim Clark Of EK
Username: art
Posted 2012-11-25 02:05:58 and read 5099 times.

Quoting kaitak (Reply 79):
It would surprise me very much if EK were not at the head of the queue for the A389, particularly with so many undelivered A388s, orders for which would be converted to A389s?

I guess the big issue there would be whether other carriers would be willing to take that jump; CX and VS have expressed interest in the -900, though I think it's anyone's guess whether VS actuall flies any A380s at all.

It's been debated but the big issue for Airbus may be that airlines ordering A389 would have ordered A388 anyway.

Topic: RE: A380 Overperforms Says Tim Clark Of EK
Username: Stitch
Posted 2012-11-25 07:37:30 and read 4516 times.

There will be no real need for Airbus to launch an A380-900 until a smaller plane equals or beats it's CASM and I don't expect that to be possible until Boeing launches their next generation large widebody twin (the Y3).


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