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Starlionblue
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RE: Why The Airbus A380 Has Only Two Thrust Reverser?

Thu Jul 13, 2006 6:20 am

Quoting Prebennorholm (Reply 49):
And remember, there is only one reason for airline companies to exist: To please their shareholders.

Did I say something wrong? No, I don't think so.

I thought it was to keep the threads in polls_and_opinions going...

Quoting Prebennorholm (Reply 49):
Always keep your number of landings equal to your number of take-offs, Preben Norholm

Not when you're skydiving.
"There are no stupid questions, but there are a lot of inquisitive idiots." - John Ringo
 
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Jetlagged
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RE: Why The Airbus A380 Has Only Two Thrust Reverser?

Thu Jul 13, 2006 6:48 am

Quoting Prebennorholm (Reply 49):
If we call Airbus and order an A380 with four reversers, then I'm pretty sure they will say "Thank you Sir".

I doubt that. Life is much more complicated these days, compared to the days of the VC10 and Comet (both of which had two out of four reversers). The VC10 originally had four, but two were removed optionally later (due in part to their proximity to each other I understand).

However, adding two reversers to the A380 is more complex than deleting them (as per the VC10). If nothing else, the ECAM synoptic displays would have to be modified, unless they are already programmed as if four are fitted, but two disabled. Not to mention the additional wiring, etc. It's a big design change, unless four reversers were intended initially  Smile

Airbus already seem to be having significant wiring problems with customers customising the aircraft. So unless a blue chip customer like SIA or Emirates demanded it, I suspect the answer might be a polite but firm "Non".
The glass isn't half empty, or half full, it's twice as big as it needs to be.
 
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zeke
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RE: Why The Airbus A380 Has Only Two Thrust Reverser?

Thu Jul 13, 2006 8:53 am

Quoting Jetlagged (Reply 51):
Airbus already seem to be having significant wiring problems with customers customising the aircraft. So unless a blue chip customer like SIA or Emirates demanded it, I suspect the answer might be a polite but firm "Non".

The wiring problems as far as I understand are in the cabin, not to do with flight controls or powerplants.

In my view no additional wiring would be needed for this, as far as I understand just about everything on the aircraft is done on a bus, the reverse logic and monitoring would be just additional data on the bus.
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prebennorholm
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RE: Why The Airbus A380 Has Only Two Thrust Reverser?

Fri Jul 14, 2006 5:25 am

Quoting Starlionblue (Reply 50):
Quoting Prebennorholm (Reply 49):
Always keep your number of landings equal to your number of take-offs, Preben Norholm

Not when you're skydiving.

Okay, Always keep your number of landings equal to or greater than your number of take-offs  bigthumbsup 
Always keep your number of landings equal to your number of take-offs
 
n8076u
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RE: Why The Airbus A380 Has Only Two Thrust Revers

Fri Jul 14, 2006 6:28 am

Quoting Starlionblue (Reply 47):
I still don't buy the argument that the plane is less safe without outboard reversers.

I don't really buy the argument either, but I think I understand what he's trying to say. According to the theory, a 747 is also "less safe than it could be" in its present design than if it had 6 or 8 of its current engines with 6 or 8 reversers, as it could possibly stop a little faster. On a very basic level, this is true as far as the physics involved are concerned, but in the real world, the aircraft's weight will be the limiting factor, and 4 or 6 or 8 reversers won't matter in the calculations at all. Both the 4 and 8 engined 747, at the same landing weight and all other things being equal, will have identical runway length requirements, and both will be equally landing-weight restricted on shorter fields or in bad weather conditions that affect traction or landing speed (tailwind, for instance). And both aircraft still need to be able to stop without any reversers at all, which is what the calculations are based on.

The original 747 came with reversers for both the fan air and the core flow. The core reversers were later deactivated. Did that make it less safe? Besides, less safe does not mean "unsafe". So perhaps "less room for error" or "less cushion" is more appropriate than "less safe" which implies that safety is somehow compromised.

Chris
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Starlionblue
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RE: Why The Airbus A380 Has Only Two Thrust Revers

Fri Jul 14, 2006 7:33 am

N8076U. Thank you for the excellent example of the 8 engined 747 with 6 reversers.

This reminds me of the joke about the B-52 declaring an emergency with an engine out and coming in for landing. A single-engine Cessna pilot is told to hold for the B-52. He replies: "Ah yes, the dreaded seven engine landing!"


From a broader perspective, there is an obsession in the modern world with making everything as safe as it can possibly be. While this is a good idea in principle, at a certain point practicality must set in. Otherwise our cars would cost a million dollars and speeds on the highways would be restricted to thirty miles an hour. Safe? Certainly. Practical? Not reallly.

Seen from another perspective: My daughter, all of nine months old, crawls around a lot. She'll find drawer handles and pull herself up until she is kneeling. Every now and then she slips and bumps her head on a handle, followed by a surprised expression for a few seconds, and then a fit of crying. Now, we could stop her from grabbing the handles, but at a certain point you have to accept the greater good involved (learning to stand) and deal with the occasional accident.
"There are no stupid questions, but there are a lot of inquisitive idiots." - John Ringo
 
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RE: Why The Airbus A380 Has Only Two Thrust Reverser?

Fri Jul 14, 2006 8:26 am

Dear N8076U, the number of reversers have nothing with safety to do. It is about operational parameters.

Sure an A380 would be able to operate on shorter runways with four reversers than with two, especially on a wet or slippery runway.

But the A380 will hardly be operated from runways which are not already dimentioned for the 747. And since the 380 has that lower take-off and landing speed, and the full 747-length runways are already there, then why not take advantage of that? Every single reverser adds empty weight and reduces payload.

If they ever produce a 1.4 million lbs MTOW A380-900 with the same wing geometry, then take-off and landing speeds will grow to 747 level and four reversers may become the norm as on the 747.

The 747 is not exceptionally fast on take-off or landing. It's in the same league as A346 and MD-11. But the A380 is just considerably slower than those great planes when taking off or landing.
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Jetlagged
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RE: Why The Airbus A380 Has Only Two Thrust Reverser?

Sat Jul 15, 2006 4:36 am

Quoting N8076U (Reply 54):
According to the theory, a 747 is also "less safe than it could be" in its present design than if it had 6 or 8 of its current engines with 6 or 8 reversers, as it could possibly stop a little faster.

Who said anything about 6 or 8 engines on a 747? That is not my contention (or "theory") and never was. I won't repeat the whole argument again, but summarising: if you have reverse thrust it should be on all engines if at all possible. It was not about having extra engines just in case.

I accept that the lower Vref argument is a big safety factor, but what about circumstances where some or all the flaps cannot be deployed, raising landing speed? As I have said, it's about combinations of problems and circumstances, not single failures.

Yes, early JT9Ds had core reversers, but with the fan reverser only at least the total net thrust on each engine is negative. The core reversers added a small proportion of reverse thrust for a lot of extra complexity.

Quoting Zeke (Reply 52):
In my view no additional wiring would be needed for this, as far as I understand just about everything on the aircraft is done on a bus, the reverse logic and monitoring would be just additional data on the bus.

You might be able to add the reverser data to existing buses to the FADECs. However some non-bus connection is almost inevitable, so additional wiring would probably be necessary to install the reverser control and indication signals.

Even if no wiring were involved, it certainly would not be a trivial matter to install outboard reversers as a customer option, unless the aircraft had been provisioned for outboard reversers all along. Airbus aircraft are much less customised than Boeing, for example, so I doubt Airbus would consider the idea, unless all aircraft were to be modified.
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Starlionblue
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RE: Why The Airbus A380 Has Only Two Thrust Reverser?

Sat Jul 15, 2006 4:48 am

Quoting Jetlagged (Reply 57):
if you have reverse thrust it should be on all engines if at all possible

By this logic, zero out of four is better than the current two out of four. Kidding  Wink

Seriously though, there's no specific reason why you need reverse on ALL engines.


Quoting Jetlagged (Reply 57):
I accept that the lower Vref argument is a big safety factor, but what about circumstances where some or all the flaps cannot be deployed, raising landing speed? As I have said, it's about combinations of problems and circumstances, not single failures.

If the flaps can't be deployed, you find a long enough runway and land anyway. Granted, an added two reversers would make a (pretty small) dent in the stopping distance, but we are far from the realm of "we're all gonna die" for a flap failure. I'll repeat that the extra two reversers don't have a huge effect on stopping distance. The runways planned for landing and diversion are plenty long enough to stop a 747 with no flaps and the 380 has at least equivalent performance.

Safe as it is, flying entails a (very small) calculated risk. The risk is mitigated by operational and design characteristics. If airplanes were built "as safe as possible" they would be way overweight and cost ten times as much as today. The thread about giant parachutes comes to mind.
"There are no stupid questions, but there are a lot of inquisitive idiots." - John Ringo
 
pygmalion
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RE: Why The Airbus A380 Has Only Two Thrust Reverser?

Sat Jul 15, 2006 4:50 am

I'm sure if a customer wanted to add a couple more reversers to the A380... Airbus would say yes... but it will cost you 30 million a copy (or more) Its not as simple as some synoptic display changes... its a complete new thrust lever housing with new handles, new flight manuals, certification testing, new outboard struts designed for increased weight and loads, not too mention wing gage changes etc... It not a matter of just installing a few parts from the inboards to the outboards. Airplanes are complex systems of equipment that all have to be designed together... if it was easy, the Chinese would not be buying aircraft from A and B... they would be building them themselves.

[Edited 2006-07-14 21:57:17]
 
n8076u
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RE: Why The Airbus A380 Has Only Two Thrust Reverser?

Sat Jul 15, 2006 5:02 am

Quoting Jetlagged (Reply 57):
Who said anything about 6 or 8 engines on a 747? That is not my contention (or "theory") and never was. I won't repeat the whole argument again, but summarising: if you have reverse thrust it should be on all engines if at all possible. It was not about having extra engines just in case.

Sorry if I misunderstood what you were trying to say. I was just trying to make a point, that's all, and it had nothing to do with "extra engines", as I just used that as an example. But, if the 747 had been designed with 8 engines and only four had reverse thrust capability, your "contention" would be the same, right?

Quoting Prebennorholm (Reply 56):
Dear N8076U, the number of reversers have nothing with safety to do. It is about operational parameters.

Sure, I know what you're saying, but aren't the operational parameters in place primarily for safety's sake?

Quoting Prebennorholm (Reply 56):
Sure an A380 would be able to operate on shorter runways with four reversers than with two, especially on a wet or slippery runway.

I thought minimum runway length calculations don't take the reversers into account at all? At least that's what I understood from other topics I've read recently on A.net.

Chris
Don't blame me, I don't work here...
 
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Jetlagged
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RE: Why The Airbus A380 Has Only Two Thrust Reverser?

Sat Jul 15, 2006 10:46 pm

Quoting N8076U (Reply 60):
But, if the 747 had been designed with 8 engines and only four had reverse thrust capability, your "contention" would be the same, right?

Yes, but that's a big, pointless, hypothetical if. As I said, if you're going to have a reverse thrust system, have it on all engines you install, unless there's a very good reason not to.
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RE: Why The Airbus A380 Has Only Two Thrust Reverser?

Sat Jul 15, 2006 11:41 pm

Quoting Jetlagged (Reply 61):

Yes, but that's a big, pointless, hypothetical if. As I said, if you're going to have a reverse thrust system, have it on all engines you install, unless there's a very good reason not to.

I still don't see the logic behind this argument. What is the reason for having to mount reverse on all engines as opposed to only two if you can get the desired reverse thrust from only two?
"There are no stupid questions, but there are a lot of inquisitive idiots." - John Ringo
 
2H4
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RE: Why The Airbus A380 Has Only Two Thrust Reverser?

Sat Jul 15, 2006 11:52 pm




Quoting Starlionblue (Reply 62):
I still don't see the logic behind this argument.

I agree. The logic seems to be "If a feature exists to reduce landing distance, it should be used"....which suggests every airliner should be equipped with drag chutes as well as reversers on all engines.

Drag chutes, of course, are not commonly used, because the cost and effort to use and maintain them does not outweigh the advantage that could be gained by using them. The same can be said for the two nonexistent reversers on the A380.




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Starlionblue
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RE: Why The Airbus A380 Has Only Two Thrust Reverser?

Sat Jul 15, 2006 11:55 pm

Quoting 2H4 (Reply 63):

Quoting Starlionblue (Reply 62):
I still don't see the logic behind this argument.

I agree. The logic seems to be "If a feature exists to reduce landing distance, it should be used"....which suggests every airliner should be equipped with drag chutes as well as reversers on all engines.

Drag chutes, of course, are not commonly used, because the cost and effort to use and maintain them does not outweigh the advantage that could be gained by using them. The same can be said for the two nonexistent reversers on the A380.

More drag chutes! And cowbells! While we're at it, let's have retro-rockets and splitting control surfaces doubling as airbrakes (like on the Space Shuttle).
"There are no stupid questions, but there are a lot of inquisitive idiots." - John Ringo
 
777-200
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RE: Why The Airbus A380 Has Only Two Thrust Reverser?

Sun Jul 16, 2006 12:29 am

Quoting 747400sp (Thread starter):
Do not get me wrong an A380 looks cool at landing but safe out rules cool.

Just my Two Cents

PS: Please do not trun this into an A vs B topic I like all four engines airliners.

Heh, I'm pretty shure the Airbus engineers know alot more than your about the safety of the aircraft...
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2H4
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RE: Why The Airbus A380 Has Only Two Thrust Reverser?

Sun Jul 16, 2006 12:48 am




Quoting Starlionblue (Reply 64):
More drag chutes! And cowbells! While we're at it, let's have retro-rockets and splitting control surfaces doubling as airbrakes

Heck, according to the media, the global transport-category aircraft fleet is already equipped with "reverse thrusters", so we're halfway there!  bigthumbsup 




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Jetlagged
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RE: Why The Airbus A380 Has Only Two Thrust Reverser?

Sun Jul 16, 2006 3:17 am

Quoting 2H4 (Reply 63):
The logic seems to be "If a feature exists to reduce landing distance, it should be used"....which suggests every airliner should be equipped with drag chutes as well as reversers on all engines.

Once again, no that isn't the logic. Read the posts again. I said if an aircraft has a reverse thrust system, it probably should be fitted to all engines if practical. This would improve redundancy, commonality, symmetry of operation, simplicity of operation, etc. It increases safety margins. What's wrong with that?

I did not say all available means to stop should be installed, including drag chutes, arrester hooks, retro rockets, boat anchors and chains, etc. You may not agree, but please take it seriously.

Don't seem to be too many pilots commenting on this and they are the ones you'd expect to have the most valid opinion.
The glass isn't half empty, or half full, it's twice as big as it needs to be.
 
2H4
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RE: Why The Airbus A380 Has Only Two Thrust Reverser?

Sun Jul 16, 2006 3:24 am




Quoting Jetlagged (Reply 67):
What's wrong with that?

Well, as you specified:

Quoting Jetlagged (Reply 67):
if practical.

...Doing so is not always practical.  Wink




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Starlionblue
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RE: Why The Airbus A380 Has Only Two Thrust Reverser?

Sun Jul 16, 2006 4:08 am

Quoting Jetlagged (Reply 67):

Once again, no that isn't the logic. Read the posts again. I said if an aircraft has a reverse thrust system, it probably should be fitted to all engines if practical. This would improve redundancy, commonality, symmetry of operation, simplicity of operation, etc. It increases safety margins. What's wrong with that?

It may be economically wrong, AKA impractical. Also, if FOD ingestion is an issue, it may make operation LESS safe.
"There are no stupid questions, but there are a lot of inquisitive idiots." - John Ringo
 
n8076u
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RE: Why The Airbus A380 Has Only Two Thrust Reverser?

Sun Jul 16, 2006 7:54 am

Quoting Starlionblue (Reply 69):
if FOD ingestion is an issue,

I'm wondering if, like others have said, because the outboard engines on the A380 are so far out there, and put out roughly twice the thrust of a 747 engines, that it was found that there is a high possibility of blowing dirt, grass or other debris from the overhanging areas onto the runway when using higher thrust settings during reverse thrust. In itself, this may not seem like it would affect that A380 that's using reverse thrust directly as long as it was above a certain speed (70kts or whatever). But this would possibly cause hazard to any aircraft passing the same area after the fact.

Airbus may have felt that deleting the reversers altogether on the outboards to save the weight was more worthwhile than keeping them and restricting the outboards to only idle reverse or a low reverse thrust setting.

Chris
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Starlionblue
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RE: Why The Airbus A380 Has Only Two Thrust Revers

Sun Jul 16, 2006 8:10 am

Quoting N8076U (Reply 70):
I'm wondering if, like others have said, because the outboard engines on the A380 are so far out there, and put out roughly twice the thrust of a 747 engines, that it was found that there is a high possibility of blowing dirt, grass or other debris from the overhanging areas onto the runway when using higher thrust settings during reverse thrust. In itself, this may not seem like it would affect that A380 that's using reverse thrust directly as long as it was above a certain speed (70kts or whatever). But this would possibly cause hazard to any aircraft passing the same area after the fact.

Indeed. Also, if you blow crap straight back through the engines it only moves more or less along the runway or taxiway. No huge problem. If crap bounces through the reversers it will now be moving sideways, potentially hitting aircraft and other vehicles on taxiways, or even the wings and fuse of the 380 itself. I can see it now: "Passenger killed on new SuperJumbo when discarded fuel tank filler cap is propelled through his head by reverse thruster. Investigators point fingers at HAWK21M, notorious ramp rat. Says co-worker, 'this isn't the first time HAWK21M has been acting dangerously. He also asks questions about forbidden knowledge. It has landed us in trouble before."

MEL, hope you don't mind me poking some fun.  Wink
"There are no stupid questions, but there are a lot of inquisitive idiots." - John Ringo
 
n8076u
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RE: Why The Airbus A380 Has Only Two Thrust Reverser?

Sun Jul 16, 2006 8:26 am

Quoting Starlionblue (Reply 71):
He also asks questions about forbidden knowledge.

And uses a period at the end of his question, rather than a question mark to mask that fact.  Wink

Chris
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2H4
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RE: Why The Airbus A380 Has Only Two Thrust Revers

Sun Jul 16, 2006 8:33 am



Quoting Starlionblue (Reply 71):
Says co-worker, 'this isn't the first time HAWK21M has been acting dangerously. He also asks questions about forbidden knowledge. It has landed us in trouble before."

HAWK21M has since replied with a letter, questioning the charges brought upon him. The letter, however, was thrown out by the investigation team. Says Chief Investigator, Henry Wiggens, "The complete and total lack of question marks rendered the letter unreadable. We were simply unable to make any sense of it."





2H4



Blast....76U beat me to it....  biggrin 

[Edited 2006-07-16 01:34:22]
Intentionally Left Blank
 
n8076u
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RE: Why The Airbus A380 Has Only Two Thrust Reverser?

Sun Jul 16, 2006 9:38 am

Quoting 2H4 (Reply 73):
Blast....76U beat me to it....

Oops, sorry!  Smile
Don't blame me, I don't work here...
 
bri2k1
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RE: Why The Airbus A380 Has Only Two Thrust Revers

Sun Jul 16, 2006 10:42 am

Wow...we went from 8 engines on a 744 to poking fun at HAWK21M??? (Not that I mind, of course  Smile)

This just goes to prove that "reverse trusters" make everyone here at A.net completely loco! Probably has something to do with chemtrails. Or a treadmill.
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2H4
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RE: Why The Airbus A380 Has Only Two Thrust Reverser?

Sun Jul 16, 2006 3:33 pm




Quoting Bri2k1 (Reply 75):
Probably has something to do with chemtrails. Or a treadmill.

Surely, it must somehow involve several thousand birds, as well....




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Starlionblue
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RE: Why The Airbus A380 Has Only Two Thrust Revers

Sun Jul 16, 2006 9:49 pm

Quoting 2H4 (Reply 76):

Quoting Bri2k1 (Reply 75):
Probably has something to do with chemtrails. Or a treadmill.

Surely, it must somehow involve several thousand birds, as well....

If the birds are flying upstairs or downstairs in the 380, will it make a difference to lift. (<- period used as per a.nut standards).

[Edited 2006-07-16 14:50:06]
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OldAeroGuy
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RE: Why The Airbus A380 Has Only Two Thrust Reverser?

Sun Jul 16, 2006 9:54 pm

Quoting N8076U (Reply 60):
I thought minimum runway length calculations don't take the reversers into account at all? At least that's what I understood from other topics I've read recently on A.net.

See Reply 39. The rules have changed.
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HAWK21M
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RE: Why The Airbus A380 Has Only Two Thrust Reverser?

Mon Jul 17, 2006 1:52 am

Quoting Starlionblue (Reply 71):
Investigators point fingers at HAWK21M, notorious ramp rat. Says co-worker, 'this isn't the first time HAWK21M has been acting dangerously. He also asks questions about forbidden knowledge. It has landed us in trouble before."

MEL, hope you don't mind me poking some fun.



Quoting 2H4 (Reply 73):
HAWK21M has since replied with a letter, questioning the charges brought upon him. The letter, however, was thrown out by the investigation team. Says Chief Investigator, Henry Wiggens, "The complete and total lack of question marks rendered the letter unreadable. We were simply unable to make any sense of it."



Quoting N8076U (Reply 72):
And uses a period at the end of his question, rather than a question mark to mask that fact



Quoting Bri2k1 (Reply 75):
Wow...we went from 8 engines on a 744 to poking fun at HAWK21M??? (Not that I mind, of course )

Thanks to the Lack of Support,HAWK21M was considering losing the Bet with 5 months to spare & type in the Forbidden Question Mark.But then since Hes as Stubborn as a Dogs Tail,He decided Against It  biggrin 
BTW whose Henry Wiggins The guys who does not use Exclamation marks  Smile

To stay on topic.....How many A380s are Currently Flying right now.

regds
MEL
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CSMUK
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RE: Why The Airbus A380 Has Only Two Thrust Reverser?

Mon Jul 17, 2006 3:26 am

I think it makes sense the Airbus A380 only has two engines that engage into reverse thrust when so many Boeing 744 pilots in my company only seem to use engines 2 & 3 for reverse thrust after landing…

Reverse thrust is mostly ‘complementary’ breaking right? I mean the wheel breaks do most of the work?

Dana
 
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HAWK21M
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RE: Why The Airbus A380 Has Only Two Thrust Reverser?

Mon Jul 17, 2006 3:48 am

Quoting CSMUK (Reply 80):
when so many Boeing 744 pilots in my company only seem to use engines 2 & 3 for reverse thrust after landing…

Is this common with Most B747 Pilots.
regds
MEL
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kaddyuk
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RE: Why The Airbus A380 Has Only Two Thrust Reverser?

Mon Jul 17, 2006 3:49 am

Quoting CSMUK (Reply 80):
I think it makes sense the Airbus A380 only has two engines that engage into reverse thrust when so many Boeing 744 pilots in my company only seem to use engines 2 & 3 for reverse thrust after landing…

Reverse thrust is mostly ‘complementary’ breaking right? I mean the wheel breaks do most of the work?

On the B744, all four engines are reversed when landing but with only idle power and brakes doing most of the work. If then required reverse thrust is already active and all the pilots need to do is increase power.
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RE: Why The Airbus A380 Has Only Two Thrust Reverser?

Mon Jul 17, 2006 4:02 am

Quoting CSMUK (Reply 80):
Reverse thrust is mostly �complementary� breaking right? I mean the wheel breaks do most of the work?

Correct. If the brakes are applied fully, pax would be bang their heads pretty hard on the seat in front of them.
"There are no stupid questions, but there are a lot of inquisitive idiots." - John Ringo
 
kaddyuk
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RE: Why The Airbus A380 Has Only Two Thrust Reverser?

Mon Jul 17, 2006 7:19 am

Quoting Starlionblue (Reply 83):
. If the brakes are applied fully, pax would be bang their heads pretty hard on the seat in front of them

You dont need to apply the brakes fully... on a 12000ft runway, touchdown 1000ft down, leaving you with 11000ft of useable tarmac... plenty of room for even the larger jets...
Whoever said "laughter is the best medicine" never had Gonorrhea
 
vikkyvik
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RE: Why The Airbus A380 Has Only Two Thrust Reverser?

Mon Jul 17, 2006 8:54 am

I heard something about birds, so I thought I'd poke my head in here, and what do I see? A bunch of guys ragging on the poor Indian guy!

Quoting Kaddyuk (Reply 84):

You dont need to apply the brakes fully... on a 12000ft runway, touchdown 1000ft down, leaving you with 11000ft of useable tarmac... plenty of room for even the larger jets...

I think he was just trying to show that brakes are quite capable of stopping an aircraft by themselves, and would typically do so in a relatively short distance IF applied fully.

Anyway, we're supposed to be talking about trust! Man....84 (now 85) off-topic replies talking about airplanes! I think we all missed the point of the thread.

~Vik
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bri2k1
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RE: Why The Airbus A380 Has Only Two Thrust Reverser?

Mon Jul 17, 2006 9:58 am

Quoting Vikkyvik (Reply 85):

Anyway, we're supposed to be talking about trust!

Funny story...I asked about that, and my post got deleted!

Guess no one cares about reverse trusters anymore. Sad...
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Starlionblue
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RE: Why The Airbus A380 Has Only Two Thrust Reverser?

Mon Jul 17, 2006 10:11 am

Quoting Kaddyuk (Reply 84):
Quoting Starlionblue (Reply 83):
. If the brakes are applied fully, pax would be bang their heads pretty hard on the seat in front of them

You dont need to apply the brakes fully... on a 12000ft runway, touchdown 1000ft down, leaving you with 11000ft of useable tarmac... plenty of room for even the larger jets...

As Vik says, I was just trying to illustrate a point about the relative importance of breaks and reverse trusters. Ahem... I mean...
"There are no stupid questions, but there are a lot of inquisitive idiots." - John Ringo
 
n8076u
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RE: Why The Airbus A380 Has Only Two Thrust Reverser?

Mon Jul 17, 2006 4:39 pm

I found out something interesting in another post:
A380 Main Landing Gear (by WingedMigrator Jul 17 2006 in Tech Ops)

Not only does the A380 have only two thrust reversers, but out of the 20 main landing gear wheels, only 16 have brakes, as the rear two body gear axles (2 wheels each) are brakeless.

Chris
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speedracer1407
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RE: Why The Airbus A380 Has Only Two Thrust Reverser?

Mon Jul 17, 2006 7:33 pm

Quoting N8076U (Reply 88):
Not only does the A380 have only two thrust reversers, but out of the 20 main landing gear wheels, only 16 have brakes, as the rear two body gear axles (2 wheels each) are brakeless.

After reading this thread for a couple weeks now, it's this information that has me quite a bit more perplexed than the thrust reverse. Carbon brakes or not, tire-to-pavement friction is friction, and I'm surprised that the A380, with 300,000 lb greater MTOW than a 744 has the same number of braked tires. Of course, the A380 shouldn't have to land anywhere near MTOW under normal circumstances. But are there, or will there be some sort of stipulations that make A380 overwieght landings more difficult or impossible because of this?

Btw, I don't mean to be a chicken little; it's just that the sheer size of this new plane begs new questions about otherwise worn-out assumptions.
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Starlionblue
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RE: Why The Airbus A380 Has Only Two Thrust Revers

Mon Jul 17, 2006 8:50 pm

Quoting N8076U (Reply 88):

Not only does the A380 have only two thrust reversers, but out of the 20 main landing gear wheels, only 16 have brakes, as the rear two body gear axles (2 wheels each) are brakeless.

So is the center wheel pair on the 342/343. It's no biggie.

Also, "ONLY 16 out of the 20" [my emphasis]. That's still 80%.

Quoting Speedracer1407 (Reply 89):

After reading this thread for a couple weeks now, it's this information that has me quite a bit more perplexed than the thrust reverse. Carbon brakes or not, tire-to-pavement friction is friction, and I'm surprised that the A380, with 300,000 lb greater MTOW than a 744 has the same number of braked tires. Of course, the A380 shouldn't have to land anywhere near MTOW under normal circumstances. But are there, or will there be some sort of stipulations that make A380 overwieght landings more difficult or impossible because of this?

Since landings are slower than for a 744, you would theoretically need less braking capability per kg of mass. but that there is plenty to go around.

I have no doubt the aircraft has enough braking to meet certification and operator requirements. Do you really think Airbus would be allowed to design and build and aircraft which made overweight landing impossible?

Quoting Speedracer1407 (Reply 89):
Btw, I don't mean to be a chicken little; it's just that the sheer size of this new plane begs new questions about otherwise worn-out assumptions.

This is a misconception. The size of the plane is quite sometihng, but systems are simply scaled up to size so it's not a problem. There are not really new issues. Simply larger ones.
"There are no stupid questions, but there are a lot of inquisitive idiots." - John Ringo
 
kaddyuk
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RE: Why The Airbus A380 Has Only Two Thrust Reverser?

Mon Jul 17, 2006 10:08 pm

The airbus has larger wheels than the boeing and so has larger brakes...

Just accept that this aircraft has enough braking power to stop the airframe...
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Starlionblue
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RE: Why The Airbus A380 Has Only Two Thrust Reverser?

Mon Jul 17, 2006 11:22 pm

Quoting Kaddyuk (Reply 91):
The airbus has larger wheels than the boeing and so has larger brakes...

Just accept that this aircraft has enough braking power to stop the airframe...

I can see it in front of me. The first SQ landing at LHR.

"Here she comes in for landing... Long roll... She is now thundering into the BA maintenance facilities... She just decapitated a 747... Manufacturer rivalry perhaps?... There comes the boom... Nice fireworks..."

As Kaddyuk says, we can all safely assume that the Airbus people has done their homework. We can also safely assume that the JAA and FAA, like good teachers, will check the homework.
"There are no stupid questions, but there are a lot of inquisitive idiots." - John Ringo
 
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Jetlagged
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RE: Why The Airbus A380 Has Only Two Thrust Reverser?

Tue Jul 18, 2006 1:30 am

Quoting 2H4 (Reply 68):
...Doing so is not always practical.

I said that to cover myself, but I can't think of a current airliner, with reverse thrust, that doesn't have it installed on every engine (except the A380 naturally).

Quoting Kaddyuk (Reply 91):
Just accept that this aircraft has enough braking power to stop the airframe...

On ice, without reverse thrust? How do you know? With a slippery runway reverse thust might just make the difference between a safe stop and an overrun. Remember the SWA 737 at MDW last year. If reverse had been selected early enough, maybe it might not have overrun.

Quoting Starlionblue (Reply 92):
As Kaddyuk says, we can all safely assume that the Airbus people has done their homework. We can also safely assume that the JAA and FAA, like good teachers, will check the homework.

I certainly hope so, but such complacency does occasionally bite designers in the rear end. The certification rules should be continuously reviewed and novel configurations given special attention. By anyone's standards the A380 is novel from a size viewpoint alone, let alone only having 2 out of 4 engines with T/R.

Quoting Starlionblue (Reply 90):
The size of the plane is quite sometihng, but systems are simply scaled up to size so it's not a problem. There are not really new issues. Simply larger ones.

Did you tell Airbus it was that easy? Perhaps they wouldn't have had so many problems if they'd known  Smile
Finally, in case anyone missed the point in all the sarcasm, braking on a heavily contaminated runway has nothing to do with installed braking power. You can't apply maximum braking on ice, the anti-skid won't let you. It is almost entirely dependent on the available runway coefficient of friction and the braked rubber in contact with it. However reverse thrust works just fine, regardless of the runway friction level, which is why it is so important on contaminated runways. It would be interesting to have a 744 pilot like Philsquares view on this.
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RE: Why The Airbus A380 Has Only Two Thrust Reverser?

Tue Jul 18, 2006 1:37 am

Quoting Jetlagged (Reply 93):
The certification rules should be continuously reviewed and novel configurations given special attention.

This problem will take care of itself. The first time an A380 overruns a runway, the fleet will be grounded until the outboards are reverse-equipped.

Then, the next time one overruns a runway, all planes will be grounded, everywhere, until the weather shapes up and starts behaving right.
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Starlionblue
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RE: Why The Airbus A380 Has Only Two Thrust Reverser?

Tue Jul 18, 2006 1:44 am

Quoting Jetlagged (Reply 93):
Quoting Starlionblue (Reply 90):
The size of the plane is quite sometihng, but systems are simply scaled up to size so it's not a problem. There are not really new issues. Simply larger ones.

Did you tell Airbus it was that easy? Perhaps they wouldn't have had so many problems if they'd known

The problems are more related to making the aircraft meet weight and production targets. It seems to have no problems flying around and landing.

Quoting Jetlagged (Reply 93):
Finally, in case anyone missed the point in all the sarcasm, braking on a heavily contaminated runway has nothing to do with installed braking power. You can't apply maximum braking on ice, the anti-skid won't let you. It is almost entirely dependent on the available runway coefficient of friction and the braked rubber in contact with it. However reverse thrust works just fine, regardless of the runway friction level, which is why it is so important on contaminated runways. It would be interesting to have a 744 pilot like Philsquares view on this.

The view of this non pilot is that a pilot would divert to a runway long enough and with enough friction to handle the job. Just like a 744 or any other aircraft. If the pilot is surprised by the low friction at the time the wheels hit the runway, he's already a bit behind wouldn't you say?

Quoting Jetlagged (Reply 93):
Quoting Starlionblue (Reply 92):
As Kaddyuk says, we can all safely assume that the Airbus people has done their homework. We can also safely assume that the JAA and FAA, like good teachers, will check the homework.

I certainly hope so, but such complacency does occasionally bite designers in the rear end. The certification rules should be continuously reviewed and novel configurations given special attention. By anyone's standards the A380 is novel from a size viewpoint alone, let alone only having 2 out of 4 engines with T/R.

There are larger aircraft flying, albeit not pax aircraft. Certification rules are continously reviewed. In any case, as long as Airbus can demonstrate that the 380 can land on a wet/icy runway in the same distance as a 744 (multiple tests for reverser or non) the whole question should go away.

There have been aircraft with 2 reversers out of 4 before. For example the VC-10.
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speedracer1407
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RE: Why The Airbus A380 Has Only Two Thrust Reverser?

Tue Jul 18, 2006 1:46 am

Quoting Starlionblue (Reply 90):
Do you really think Airbus would be allowed to design and build and aircraft which made overweight landing impossible?

No, and I should have included that I ASSUME airbus would have desinged the world's largest passenger transport aircraft to brake properly.

Quoting Kaddyuk (Reply 91):
Just accept that this aircraft has enough braking power to stop the airframe

I accept.

But for me, it's jut another marvel to ponder. After all, bigger wheels/bigger brakes do not equal more friction between the tires and pavement. Thust, I assume Airbus probides enough braking power to stop the airframe by taking advantage of larger brake diameter, advanced brake material, and advanced anti-skid programing to achieve acceptable stopping distances with roughly the same tire contact patch as a lighter 747.
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Starlionblue
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RE: Why The Airbus A380 Has Only Two Thrust Reverser?

Tue Jul 18, 2006 1:56 am

Quoting Speedracer1407 (Reply 96):
Quoting Starlionblue (Reply 90):
Do you really think Airbus would be allowed to design and build and aircraft which made overweight landing impossible?

No, and I should have included that I ASSUME airbus would have desinged the world's largest passenger transport aircraft to brake properly.

Quoting Kaddyuk (Reply 91):
Just accept that this aircraft has enough braking power to stop the airframe

I accept.

Ok. I also accept. But here's the thing. I don't really really know. I just trust that the certification authorities and the operators wouldn't put the aircraft into service if they couldn't operate it safely.

Misplaced trust? I don't think so. They're not infallible, but they will certainly do their level best.
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vikkyvik
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RE: Why The Airbus A380 Has Only Two Thrust Reverser?

Tue Jul 18, 2006 2:32 am

Quoting Starlionblue (Reply 97):
Misplaced trust?

How about.....REVERSE trust???

I think you just brought the thread full circle  Smile
I'm watching Jeopardy. The category is worst Madonna songs. "This one from 1987 is terrible".
 
Klaus
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RE: Why The Airbus A380 Has Only Two Thrust Reverser?

Mon Jul 24, 2006 3:58 am

Quoting Speedracer1407 (Reply 89):
After reading this thread for a couple weeks now, it's this information that has me quite a bit more perplexed than the thrust reverse. Carbon brakes or not, tire-to-pavement friction is friction, and I'm surprised that the A380, with 300,000 lb greater MTOW than a 744 has the same number of braked tires

I'd expect the MLG to have been designed with a) the forthcoming cargo version and b) the full-sized version (-900) in mind (although the latter might potentially get an additional center bogie).

So there could very well be enough "headroom" left in the current "light and small" -800 version for saving the weight, complexity and maintenance of the special braking linkages the steerable body gear axes would require...

If the landing speed is actually slower than the one of the 747-400, even just 16 of the enlarged wheels and brakes could be very well able to handle the braking load without any passenger needing to panic...!

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