Sponsor Message:
Civil Aviation Forum
My Starred Topics | Profile | New Topic | Forum Index | Help | Search 
A380: Mach 0.89 In Service?  
User currently offlineEg777er From United Kingdom, joined Feb 2000, 1836 posts, RR: 14
Posted (9 years 3 weeks 3 days 3 hours ago) and read 10292 times:

Whilst reading this excellent article at http://www.flightinternational.com/A...n/180/199071/Creating+A+Titan.html

I came across this quote:

Overall, Ogilvie says, “the 747 wing design is hard to beat, but we’ve put together than team that has done it.”

The distinctive double-deck fuselage presented its own unique aerodynamic challenges, not least because no-one had ever to attempted to develop such a wide, blunt-nosed and ovoid cross-section of this scale before. “One of the design objectives was to maximise the width of the cabin, but minimise any ‘bad’ flow over the fuselage. There was a lot of work done in terms of optimising the flow around the doors and windows, and we have done well,” says Ogilvie, who adds: “There is virtually no supersonic flow over speeds up to Mach 0.89, and no shockwaves, which is really important.

“Some of our customers want to belt along at M0.89, so we’ve deliberately gone out to make sure we’re shock free. We ended up playing tricks with the ovoid cross-section to get the flow to ‘go bad’ at M0.93. You have more ‘fatness’ up and down than you do in width, and the acceleration of the air from the nose is dependent on the curvature of the front fuselage. So we had to tailor the distribution of the curvature of the fuselage to maintain this acceleration,” he says. “We tried to make sure the velocity near the doors is as low as possible because the door areas can be susceptible to leaking and noise.”


Any ideas of which customers? Should put paid to the memories of slow cruising of A340s!

23 replies: All unread, jump to last
 
User currently offlineGlom From United Kingdom, joined Apr 2005, 2815 posts, RR: 10
Reply 1, posted (9 years 3 weeks 3 days 3 hours ago) and read 10253 times:

I thought 0.85 was the cruising speed of the A380.

User currently offlineN1120A From United States of America, joined Dec 2003, 26338 posts, RR: 76
Reply 2, posted (9 years 3 weeks 3 days 3 hours ago) and read 10225 times:

.85 is the design cruise of the A380, which is slower than that of the 747-400. The 744 regularly cruises at .89 issue free when conditions permit. It should not be too hard to imagine that the A380, with its design cruise, should comfortably do .89. It is just a matter of whether it will be efficient


Mangeons les French fries, mais surtout pratiquons avec fierte le French kiss
User currently offlineIkramerica From United States of America, joined May 2005, 21458 posts, RR: 60
Reply 3, posted (9 years 3 weeks 3 days 3 hours ago) and read 10225 times:

Typical cruising speed. But there are always situations where an airline needs to boost the flying speed to make up time or throw their whole operation out of whack. Most planes have this ability to some degree.

The 20 year old 747 design was hard to beat, but we put a crack team together to do it... blah blah blah.

Considering the 747 was designed the old fashioned way, I sure hope the A380 wing is more advanced and performs better.



Of all the things to worry about... the Wookie has no pants.
User currently offlineGlom From United Kingdom, joined Apr 2005, 2815 posts, RR: 10
Reply 4, posted (9 years 3 weeks 3 days 3 hours ago) and read 10168 times:

Quoting N1120A (Reply 2):
.85 is the design cruise of the A380, which is slower than that of the 747-400.

Is it? I know the 747ADV is proposed to fly at 0.86, but that's a speed boost to compensate for the A380.


User currently offlineNavion From United States of America, joined May 1999, 1010 posts, RR: 1
Reply 5, posted (9 years 3 weeks 3 days 3 hours ago) and read 10107 times:

A Mach .89 cruise speed for the A380 is just like the spas, shopping areas, lounges etc being touted...not practical in day-to-day use. Go ahead and fly at .89 and watch the fuel burn skyrocket. Go ahead and forfeit seats for lounges, spas, or bars, and watch your seat-mile costs go up. In order for the heavy A380 to make it, it has to be flown at efficient speeds with as many revenue producing seats as the traffic will bear. Airlines already know this.

User currently offlineFlyAUA From Austria, joined May 2005, 4604 posts, RR: 56
Reply 6, posted (9 years 3 weeks 3 days 3 hours ago) and read 10097 times:

Quoting Eg777er (Thread starter):
“Some of our customers want to belt along at M0.89, so we’ve deliberately gone out to make sure we’re shock free. We ended up playing tricks with the ovoid cross-section to get the flow to ‘go bad’ at M0.93. You have more ‘fatness’ up and down than you do in width, and the acceleration of the air from the nose is dependent on the curvature of the front fuselage. So we had to tailor the distribution of the curvature of the fuselage to maintain this acceleration,” he says. “We tried to make sure the velocity near the doors is as low as possible because the door areas can be susceptible to leaking and noise.”

Wow, sounds very complicated and interesting. Glad to see they've managed to get it working  Smile

Quoting Ikramerica (Reply 3):
Considering the 747 was designed the old fashioned way, I sure hope the A380 wing is more advanced and performs better.

I think they were referring to the wings of the -400, not the older versions. Wasn't this one re-engineered?

Quoting Glom (Reply 1):
I thought 0.85 was the cruising speed of the A380.

That's what they advertise, but early into the flight testing they confirmed that it can also cruise at M0.89. Nice to see that it's only at M0.93 after which it gets dangerous. Are they implying that M0.93 will be the Vne?



Not drinking, also isn't a solution!
User currently offlineB2707SST From United States of America, joined Apr 2003, 1369 posts, RR: 59
Reply 7, posted (9 years 3 weeks 3 days 2 hours ago) and read 9974 times:

M0.89 is the A380's MMO:

http://www.airbus.com/en/aircraftfam...lies/a380/a380/specifications.html

What customers ask for and what they actually use can be two different things. During the 747 design phase, Pan Am wanted a very fast (above M0.90) cruise speed, which would have required wing sweep of 45 degrees with the design technology at the time. Boeing compromised at 37.5 degrees of sweep and an MMO of either M0.89 or M0.92 (can't recall which off the top of my head). I imagine that Pan Am ended up cruising them at M0.85 along with everyone else.

--B2707SST



Keynes is dead and we are living in his long run.
User currently offlineN60659 From United States of America, joined Mar 2005, 654 posts, RR: 25
Reply 8, posted (9 years 3 weeks 3 days 2 hours ago) and read 9921 times:

Quoting B2707SST (Reply 7):
Boeing compromised at 37.5 degrees of sweep and an MMO of either M0.89 or M0.92 (can't recall which off the top of my head).

I posted this on the Tech/Ops forum some time ago:

"IIRC (this is from my foggy memory, so if I'm wrong, please correct me), the B-47, 367-80 and the 707 were built with wings swept back at 35 deg. Initially, for the 747, Boeing wanted the aircraft to cruise at M0.87 or so. Initial designs put the wing sweep angle at around 40 deg. However fears of Dutch roll and other aerodynamics related gremlins tempered the design and a compromise sweep angle (splitting the difference) of 37.5 deg was implemented."

B2707SST or anyone else with better information, please feel free to correct any factual errors.

-N60659



Nec Dextrorsum Nec Sinistrorsum
User currently offlineFlyAUA From Austria, joined May 2005, 4604 posts, RR: 56
Reply 9, posted (9 years 3 weeks 3 days 2 hours ago) and read 9909 times:

Quoting B2707SST (Reply 7):

But if they stated that the flow was only disrupted as of M0.93 doesnt that mean it would be "flyable" at M0.89? Just a question, I know very little about these things since I only did the basics of aerodynamics.

I guess it also has to do with the flow of air over the wings. An aircraft cannot fly at a speed where the airflow over the surface of any part of the aircraft would exceed M1.00. And since the Mach No of the aircraft can vary from the Mach No of the flow of air over certain parts of it, I guess M0.93 is that figure. Hence the Vne? No?



Not drinking, also isn't a solution!
User currently offlineOldAeroGuy From United States of America, joined Dec 2004, 3473 posts, RR: 67
Reply 10, posted (9 years 3 weeks 2 days 23 hours ago) and read 9663 times:

Quoting FlyAUA (Reply 9):
An aircraft cannot fly at a speed where the airflow over the surface of any part of the aircraft would exceed M1.00.

Nearly all jet transports currently flying routinely fly with wing upper surface velocities in excess of Mach 1 and have done so since the advent of the 707.

Mmo stands for Mach maximum operating. If the A380 Mmo is 0.89, it is possible to fly at that speed. However, it would rarely be done because:

1) High fuel burn makes it uneconomical. Typical Long Range Cruise speed is quoted by Airbus as 0.85M. It would be a nice flight test surprise if it turned out to be slightly higher.

2) Modern flight control systems make it nearly impossible to fly at Mmo in level flight. If you get within .005M or so of Mmo, the throttles will pull back automatically to keep the airplane from reaching Mmo. The concern is that if you operate at Mmo, a gust or a temperature change could push you to a higher Mach no. On top of that, pilots are discouraged by the airlines from manual flying near Mmo for the same reasons. Exceeding Mmo can get you a lot of trouble with the Chief Pilot and modern Flight Data Recorders are great tattle tails.



Airplane design is easy, the difficulty is getting them to fly - Barnes Wallis
User currently offlineIkramerica From United States of America, joined May 2005, 21458 posts, RR: 60
Reply 11, posted (9 years 3 weeks 2 days 21 hours ago) and read 9541 times:

Quoting FlyAUA (Reply 6):
I think they were referring to the wings of the -400, not the older versions. Wasn't this one re-engineered?

So was I. 744 was introduced in the late 80s. It was designed in the mid 80s with wing finalized basically mid 1987 at the latest, and still based on the wing of the earlier 747s, though modified. All of this was done with various levels of technological design available at that time, but none were designed in the way the 777, A380 and other such later models were. The advanced computational technology wasn't around yet.

So as I said, I would hope that a virtually designed and modeled machine like the A380 would be more efficient than the old fashioned physically modeled 744 body and wing. If it wasn't, Airbus would have some 'splainin' to do.



Of all the things to worry about... the Wookie has no pants.
User currently offlineB2707SST From United States of America, joined Apr 2003, 1369 posts, RR: 59
Reply 12, posted (9 years 3 weeks 2 days 21 hours ago) and read 9483 times:

Quoting FlyAUA (Reply 9):
But if they stated that the flow was only disrupted as of M0.93 doesnt that mean it would be "flyable" at M0.89? Just a question, I know very little about these things since I only did the basics of aerodynamics.

I guess it also has to do with the flow of air over the wings. An aircraft cannot fly at a speed where the airflow over the surface of any part of the aircraft would exceed M1.00. And since the Mach No of the aircraft can vary from the Mach No of the flow of air over certain parts of it, I guess M0.93 is that figure. Hence the Vne? No?

As OldAeroGuy mentioned, virtually all jet aircraft fly with supersonic flow over some parts of the aircraft. This is a consequence of the Bernoulli effect, which accelerates airflow over the wings and other curved portions of the airframe. The speed at which the airflow over the wings reaches sonic velocity is called the critical Mach number, and typically lies somewhere around Mach 0.75, although this will vary with the airfoil. Above that speed, the airflow is smoothly accelerated above the speed of sound, but shocks must form as it decelerates back into the subsonic regime. The shocks are wasteful of energy, causing wave drag, which increases rapidly with speed (hence the so-called "sound barrier"). They can also cause the turbulent, low-energy boundary layer above the wing to separate, which destroys the smooth airflow over that portion of the wing:


Shock-induced separation in a wind tunnel (shocks visible above and below the wing)


Since the 747 was designed, the "supercritical" or "aft-loaded" wing design developed by NASA has been adopted by both Boeing and Airbus (the A300 and 757/767 were the first commercial jets to use the supercritical cross section). Supercritical wings attempt to smooth the pressure distribution above the wing and reduce the strength of the deceleration shocks:



(Also see http://www.centennialofflight.gov/es..._Flight/Transonic_Wings/TH20G7.jpg ).

Separated boundary layers can cause buffeting of the horizontal stabilizer and other structural oscillations. Mmo is the point at which the effects of increasing drag and boundary layer separation become unacceptable for sustained flight; above Vne, they actually endanger the structural integrity of the aircraft.

Shock-induced boundary layer separation can also occur at various points on the fuselage, usually at higher speeds (the wings almost always "go critical" first). Presumably Airbus was employing supercritical-like technologies to minimize the boundary layer shock separation over the nose, which would increase drag as well as cockpit noise at high Mach numbers.

Given the resources available to the 747's designers, its wing has held up amazingly well over the years. However, supercritical wings, computational fluid dynamics, and other technologies have yielded many improvements on the 777, A380, and other modern jets.

--B2707SST



Keynes is dead and we are living in his long run.
User currently offlineKeta From Germany, joined Mar 2005, 448 posts, RR: 0
Reply 13, posted (9 years 3 weeks 2 days 15 hours ago) and read 9193 times:

Quoting Ikramerica (Reply 11):
So as I said, I would hope that a virtually designed and modeled machine like the A380 would be more efficient than the old fashioned physically modeled 744 body and wing. If it wasn't, Airbus would have some 'splainin' to do.

I thought we were talking about speed? Efficiency is another thing. The 747 wing has a higher swept-back angle than the 777 and A380, and can reach higher speeds with a less-advanced airfoil. But that doesn't mean that the 777 wing is less efficient, which, as you know, isn't.



Where there's a will, there's a way
User currently offlineN1120A From United States of America, joined Dec 2003, 26338 posts, RR: 76
Reply 14, posted (9 years 3 weeks 2 days 14 hours ago) and read 9129 times:

Quoting Glom (Reply 4):
Is it? I know the 747ADV is proposed to fly at 0.86, but that's a speed boost to compensate for the A380.

No, the 744 routinely cruises at .86 (or higher). Lufthansa for one has its base cruise for the 744 set at .86 and they fly faster if conditions dictate

Quoting FlyAUA (Reply 6):
Quoting Ikramerica (Reply 3):
Considering the 747 was designed the old fashioned way, I sure hope the A380 wing is more advanced and performs better.

I think they were referring to the wings of the -400, not the older versions. Wasn't this one re-engineered?

Actually, the 744 has pretty much the same exact wing as all other 747s, with the addition of winglets.



Mangeons les French fries, mais surtout pratiquons avec fierte le French kiss
User currently offlineEg777er From United Kingdom, joined Feb 2000, 1836 posts, RR: 14
Reply 15, posted (9 years 3 weeks 2 days 10 hours ago) and read 8889 times:

Actually if you read the rest of the article there's some interesting information about the "heritage" of the wing. It appears that the knowledge transferred during the design process is done so over a much longer time frame than is perhaps acknowledged.

Three original wing designs were considered in the 1991-2 period from three of the original Airbus partners, Aerospatiale, BAe Systems and DASA – now BAE Systems and EADS.

The wing design for the BAe AC14 concept was selected over that for the Aerospatiale ASX500/600 and DASA P502/602 concepts, and became the basis for the original “Family 1” UHCA study, which preceded the first A3XX designs in 1993. After this initial downselect, the design of the full development A3XX wing was a collaborative effort involving wing experts throughout Airbus.

The design lineage therefore extends back through the A300 to the de Havilland Comet, Trident and Sud Aviation Caravelle,, and through the A310 and A320 – it even incorporates elements from the VFW614. Thanks to experience with the A320 and A330/A340, the design also built in both aerodynamic and structural heritage features from the BAC series, including the use of integrated machined outer wing panels similar to those originally designed for the VC10 and One Eleven.


User currently offlineFlyAUA From Austria, joined May 2005, 4604 posts, RR: 56
Reply 16, posted (9 years 3 weeks 2 days 10 hours ago) and read 8829 times:

Quoting OldAeroGuy (Reply 10):
Nearly all jet transports currently flying routinely fly with wing upper surface velocities in excess of Mach 1 and have done so since the advent of the 707.

Really? Must be mistaken then. I thought that in our books we were taught that the airflow was not supposed to exceed M1.00 over any surface of the aircraft (which would dictate -for the aircraft- a lower Mach No).

Quoting OldAeroGuy (Reply 10):
1) High fuel burn makes it uneconomical. Typical Long Range Cruise speed is quoted by Airbus as 0.85M. It would be a nice flight test surprise if it turned out to be slightly higher.

This I was already aware of...

Quoting OldAeroGuy (Reply 10):
2) Modern flight control systems make it nearly impossible to fly at Mmo in level flight. If you get within .005M or so of Mmo, the throttles will pull back automatically to keep the airplane from reaching Mmo. The concern is that if you operate at Mmo, a gust or a temperature change could push you to a higher Mach no.

...but this I was not! Thanks for the info   

Quoting B2707SST (Reply 12):
As OldAeroGuy mentioned, virtually all jet aircraft fly with supersonic flow over some parts of the aircraft. This is a consequence of the Bernoulli effect, which accelerates airflow over the wings and other curved portions of the airframe. The speed at which the airflow over the wings reaches sonic velocity is called the critical Mach number, and typically lies somewhere around Mach 0.75, although this will vary with the airfoil. Above that speed, the airflow is smoothly accelerated above the speed of sound, but shocks must form as it decelerates back into the subsonic regime. The shocks are wasteful of energy, causing wave drag, which increases rapidly with speed (hence the so-called "sound barrier"). They can also cause the turbulent, low-energy boundary layer above the wing to separate, which destroys the smooth airflow over that portion of the wing

Yeah, as I was saying I had already studied this bernoulli effect as a result of the shape of certain parts of the aircraft. I just thought that the airflow had to remain below Mach 1 on subsonic aircraft. Obviously I was misinformed. Will have to go and have a look at my books again. Thanks for enlightening me with your wisdom, guys   

Quoting B2707SST (Reply 12):
Since the 747 was designed, the "supercritical" or "aft-loaded" wing design developed by NASA has been adopted by both Boeing and Airbus (the A300 and 757/767 were the first commercial jets to use the supercritical cross section). Supercritical wings attempt to smooth the pressure distribution above the wing and reduce the strength of the deceleration shocks:

Interesting... this is why I love a.net! A huge pool of many people with lots of information. I learn something new every day huh  bigthumbsup 

[Edited 2005-06-22 16:23:01]


Not drinking, also isn't a solution!
User currently offlineRayChuang From United States of America, joined Jun 2000, 7969 posts, RR: 5
Reply 17, posted (9 years 3 weeks 2 days 2 hours ago) and read 7239 times:

I think what Airbus wanted from the A380-800 was to ensure it does it economic cruise at the same speed done on the 747-400, 777-200/300 and 787-8/9: circa Mach 0.85-0.86 range. The reason is simple: Airbus got a LOT of complaints from ATC authorities due to the slow economic cruise speed of the A340-200/300 and A330-200/300 series on long flights (circa Mach 0.81), and Airbus didn't want those complaints again. Note that the economic cruise speed of the A350-800/900 is around Mach 0.84, too.

User currently offlineFlyAUA From Austria, joined May 2005, 4604 posts, RR: 56
Reply 18, posted (9 years 3 weeks 1 day 21 hours ago) and read 7096 times:

Quoting RayChuang (Reply 17):
The reason is simple: Airbus got a LOT of complaints from ATC authorities due to the slow economic cruise speed of the A340-200/300 and A330-200/300 series on long flights (circa Mach 0.81),

The speed difference you are talking about is M0.02 (very very small for ATC purposes) and they do not cruise at M0.81 but M0.83. I know this because I am involved with ATC.

Quoting RayChuang (Reply 17):
A350-800/900 is around Mach 0.84, too.

The cruising Mach No for the A350 is M0.85 (while the max. operating Mach No is M0.86), not M0.84 so it'll be just as fast as the fastest ones out there. In any case, you are talking of almost negligible differences!

Source:http://events.airbus.com/A380/Images/MME/2763.JPG



Not drinking, also isn't a solution!
User currently offlineGlom From United Kingdom, joined Apr 2005, 2815 posts, RR: 10
Reply 19, posted (9 years 3 weeks 1 day 13 hours ago) and read 6930 times:

Quoting FlyAUA (Reply 18):
The cruising Mach No for the A350 is M0.85 (while the max. operating Mach No is M0.86), not M0.84 so it'll be just as fast as the fastest ones out there. In any case, you are talking of almost negligible differences!

The link you provide gives that Mmo, but it doesn't give the best cruise mach. All other data presented here suggests it's 0.84 (presumably to compete with the 777).


User currently offlineFlyAUA From Austria, joined May 2005, 4604 posts, RR: 56
Reply 20, posted (9 years 3 weeks 1 day 11 hours ago) and read 6653 times:

Quoting Glom (Reply 19):
All other data presented here suggests it's 0.84

Present me with that data please. When I see it from a credible source I will take back what I was told  Wink



Not drinking, also isn't a solution!
User currently offlineGlom From United Kingdom, joined Apr 2005, 2815 posts, RR: 10
Reply 21, posted (9 years 3 weeks 1 day 11 hours ago) and read 6633 times:

Quoting FlyAUA (Reply 22):
Present me with that data please. When I see it from a credible source I will take back what I was told

Reply 6 gives the table of comparison and lists the A350 cruise mach as 0.840.


User currently offline0A340 From United States of America, joined Nov 2000, 266 posts, RR: 0
Reply 22, posted (9 years 3 weeks 1 day 10 hours ago) and read 6580 times:

What is the economic cruise speed of the 767?

User currently offlineFlyAUA From Austria, joined May 2005, 4604 posts, RR: 56
Reply 23, posted (9 years 3 weeks 1 day 10 hours ago) and read 6520 times:

Quoting Glom (Reply 23):
Reply 6 gives the table of comparison and lists the A350 cruise mach as 0.840.

Yeah looks like this person made a table by himself from the data on here. The only thing that is not on the airbus website which Widebodyphotog quoted in that table is the cruising speed. They have specified they Max. operating only. We will have to wait till the flight testing to see how far the normal cruise mach no. will differ from the maximum operating mach no. I guess. Unless airbus adds this bit of info soon.

And I will briefly add: When talking about a difference between 0.85 and 0.84 this is quite insignificant on a controller's radar screen. We are talking about a difference in the velocity leaders of 6kts groundspeed which is almost irrelevant when an aircraft is doing something in the range of 510kts groundspeed. When we really start worrying is when this difference becomes >12kts because then we have to either:
-lock both aircraft on speeds before exiting our sector
-coordinate with the adjacent sector to see if they will accept them not locked on speeds

And for those who will come forward with the time savings argument now: FRA-JFK (assuming direct GPS route with constant speed for comparison) will take 6.55hrs doing M0.85 or 6.63hrs doing M0.84 thus a difference of a rediculous 4.8 mins.

[Edited 2005-06-23 16:54:01]


Not drinking, also isn't a solution!
Top Of Page
Forum Index

This topic is archived and can not be replied to any more.

Printer friendly format

Similar topics:More similar topics...
AA 742 In Service? posted Wed Nov 22 2006 04:11:49 by KingAirMan
A380 Test Drive In India? posted Mon Nov 20 2006 04:41:32 by Amritpal
A380 Arrival Time In YVR? posted Fri Nov 3 2006 20:12:18 by Dimsum
Looks Like The A380 Is Now In BMI Colors posted Thu Nov 2 2006 15:59:17 by APFPilot1985
Same Price But Big Difference In Service! posted Sat Oct 28 2006 12:14:42 by RootsAir
New AZ Livery: Now In Service posted Tue Oct 24 2006 16:40:49 by Nycfly75
DC-8-50s Still In Service? posted Tue Oct 24 2006 07:07:10 by Starstream707
First Pic Of Primaris' New 757 In Service (CCS) posted Wed Oct 18 2006 05:37:42 by Luisde8cd
Lufthansa On A380 Delays, Confidence In Airbus.. posted Fri Sep 22 2006 09:48:58 by Keesje
SQ's A380 Not Put Into Service Until April 07'! posted Wed Sep 20 2006 05:15:07 by Halibut