747Dreamlifter
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A380 Thrust Reversers?

Sun Nov 11, 2007 8:18 am

Are A380's thrust reversers available on the inboard engines only??

Thanks!
 
Geo772
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RE: A380 Thrust Reversers?

Sun Nov 11, 2007 8:28 am

Yes only on the inboards.
Flown on A300B4/600,A319/20/21,A332/3,A343,B727,B732/3/4/5/6/7/8,B741/2/4,B752/3,B762/3,B772/3,DC10,L1011-200,VC10,MD80,
 
whappeh
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RE: A380 Thrust Reversers?

Sun Nov 11, 2007 8:33 am

Any reason as to why most 4 engine aircraft do that?
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victor009
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RE: A380 Thrust Reversers?

Sun Nov 11, 2007 8:53 am

Well Intially they went with no reverse thrusters at all, Airbus was confident that aircraft was safe and would stop with just brakes and flaps, but FAA and JAA both slammed that idea. So they decided to have only on inboard engines.

cheers
XWB- The one to fly.
 
cartoonranger
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RE: A380 Thrust Reversers?

Sun Nov 11, 2007 8:59 am

Quoting Whappeh (Reply 2):
Any reason as to why most 4 engine aircraft do that?

They don't. Most quads have four reversers. The 380 is one of the few that only has 2 (VC 10 springs to mind as another) The advantage of having them only on the inboards is that if one reverser fails you can still use the other at full power as rudder can correct the assymetric thrust. That and the simple fact that you just don't need as much reverse power as you think. If you look at landing distances with and without reverse it's not significantly different. (Perhaps 1000ft as a maximum) Reverse thrust comes into it's own, where an aircraft is spending a short time on the ground between trips. (Read LCC) Not having to use the brakes so hard not only reduces wear but also reduces the brake waiting or cooling time that can be required if they are used to a high degree.
 
cloudyapple
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RE: A380 Thrust Reversers?

Sun Nov 11, 2007 9:06 am

Quoting Cartoonranger (Reply 4):
They don't. Most quads have four reversers. The 380 is one of the few that only has 2 (VC 10 springs to mind as another) The advantage of having them only on the inboards is that if one reverser fails you can still use the other at full power as rudder can correct the assymetric thrust. That and the simple fact that you just don't need as much reverse power as you think. If you look at landing distances with and without reverse it's not significantly different. (Perhaps 1000ft as a maximum) Reverse thrust comes into it's own, where an aircraft is spending a short time on the ground between trips. (Read LCC) Not having to use the brakes so hard not only reduces wear but also reduces the brake waiting or cooling time that can be required if they are used to a high degree.

Most so for the simple reason of potential FOD problem with the outboards hanging over grass. There was only a thread about it last week, to add to the millions that have come and gone.
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captainsimon
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RE: A380 Thrust Reversers?

Sun Nov 11, 2007 12:22 pm

Correct, due the size of the wing it may hang over grass at airports and the engines would throw up lot of debris.
This was the reason for no thrust reverse on the outboard engines.
 
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Faro
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RE: A380 Thrust Reversers?

Sun Nov 11, 2007 12:33 pm

Quoting Captainsimon (Reply 6):
Correct, due the size of the wing it may hang over grass at airports and the engines would throw up lot of debris.
This was the reason for no thrust reverse on the outboard engines.

One can understand the weight and complexity arguement for only having two reversers but what about safety? I would much prefer having them there for that long, slippery landing with an ugly gust kicking at the backside...

Faro
The chalice not my son
 
tdscanuck
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RE: A380 Thrust Reversers?

Sun Nov 11, 2007 5:34 pm

Quoting Faro (Reply 7):
One can understand the weight and complexity arguement for only having two reversers but what about safety? I would much prefer having them there for that long, slippery landing with an ugly gust kicking at the backside...

You really don't get as much stopping power as you might think from the reversers. The brakes are far more powerful. I'm sure we can imagine a corner case where 4 reversers would be enough but 2 wouldn't, but it's going to be very rare and probably not justify the additional cost/complexity/weight/maintenance of packing them around the other 99.999999% of the time. Also, to avoid the FOD issue (which is a safety issue in an of itself) you'd need some way to split the system so you only deployed the outboard reversers when you needed them, adding to complexity, maintenance, etc.

In a nutshell, I think if you crunch all the variables you'd find that the outboard reversers don't buy their way onto the airplane, even taking the safety factor into account. Much better to have a really robust autospoiler system and big honking brakes, which the A380 has both of in spades.

Tom.
 
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Faro
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RE: A380 Thrust Reversers?

Sun Nov 11, 2007 10:35 pm

Quoting Tdscanuck (Reply 8):
You really don't get as much stopping power as you might think from the reversers. The brakes are far more powerful.

I fully agree, they do the lion's share of stopping work.

Quoting Tdscanuck (Reply 8):
I'm sure we can imagine a corner case where 4 reversers would be enough but 2 wouldn't, but it's going to be very rare and probably not justify the additional cost/complexity/weight/maintenance of packing them around the other 99.999999% of the time.

You're probably right, it would be a corner case if the aircraft is designed to stop safely on only two reversers. Unfortunately, over the life of the , there will probably be at least one flight crew who will wish they had all four reversers going for them...

Quoting Tdscanuck (Reply 8):
Also, to avoid the FOD issue (which is a safety issue in an of itself) you'd need some way to split the system so you only deployed the outboard reversers when you needed them, adding to complexity, maintenance, etc.

Agreed but I believe the avoidance of FOD issue is not a goal in itself but rather a bonus from having a massively over-winged aircraft: this gives the A380 a relatively low wing loading for a long-range widebody, and hence low approach and landing speeds which enabled them to dispense with the outer reversers. The day they do a stretch, I'm willing to bet that all four engines will be reversing, perhaps with some fancy whiz-kit blowers on the outers (like on the CFM-powered 737's I believe) to keep the foreign objects away.

Faro
The chalice not my son
 
747Dreamlifter
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RE: A380 Thrust Reversers?

Sun Nov 11, 2007 11:07 pm

Hey Guys,

Thanks for the great tech input.....

The reason I questioned the A380 is both the A340's and 747's employs reversers on all 4 engines. I think the 380 is a rare exception to that engineering with only two units for such a large aircraft. I can't think of any 4 engine jet aircraft with only two reversers. Help! "Can anyone refresh my brains."

List of large Western built jet aircraft with 4 reversers that I know of:

Boeing 747
Airbus 340
Lockheed C-5
Boeing C-17

Does the Russian IL-76, 96 and An-124 have 4 reversers??

Thanks.
 
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Starlionblue
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RE: A380 Thrust Reversers?

Mon Nov 12, 2007 12:54 am

As mentioned above the VC-10 only has 2 reversers.

Remember that brake technology today is very different from even 15 years ago. Brakes are immensely powerful. Reversers are a (nice) bonus.

As mentioned, omitting reversers on the outboards achieves two things:
- Decreased weight.
- Decreased risk of FOD.
"There are no stupid questions, but there are a lot of inquisitive idiots." - John Ringo
 
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jetmech
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RE: A380 Thrust Reversers?

Mon Nov 12, 2007 1:31 am

Quoting Cloudyapple (Reply 5):
Most so for the simple reason of potential FOD problem with the outboards hanging over grass.



Quoting Captainsimon (Reply 6):
Correct, due the size of the wing it may hang over grass at airports and the engines would throw up lot of debris. This was the reason for no thrust reverse on the outboard engines.

I think the primary driving reason for only having two reversers on the A-380 was weight. I highly doubt it was due to fears of FOD. The A380's outboard engines are not that much further apart than a 747's outboard engines. If you are only going to have two reversers on a quad, it may as well be the inboards, as this would require less reinforcement in the wings to take the additional loads.

Regards, JetMech
JetMech split the back of his pants. He can feel the wind in his hair :shock: .
 
2H4
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RE: A380 Thrust Reversers?

Mon Nov 12, 2007 1:41 am

Quoting Starlionblue (Reply 11):
As mentioned, omitting reversers on the outboards achieves two things:
- Decreased weight.
- Decreased risk of FOD.

- Decreased maintenance, too.

2H4
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Starlionblue
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RE: A380 Thrust Reversers?

Mon Nov 12, 2007 1:41 am

Quoting JetMech (Reply 12):
If you are only going to have two reversers on a quad, it may as well be the inboards, as this would require less reinforcement in the wings to take the additional loads.

I think we're talking total weight. More weight on the outboards provides bending relief, so it may not have a big effect on the required wing strength.
"There are no stupid questions, but there are a lot of inquisitive idiots." - John Ringo
 
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jetmech
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RE: A380 Thrust Reversers?

Mon Nov 12, 2007 1:58 am

Quoting Starlionblue (Reply 14):
More weight on the outboards provides bending relief, so it may not have a big effect on the required wing strength.

True, but that would only be bending relief when airborne. Outboard reversers would add to static bending moments on the ground and during negative G operations. I was also thinking of torsional strength concerns, but I would assume that forward thrust being higher would automatically account for that. Nonetheless, I'm pretty sure the key issue for only having two reversers was weight.

Regards, JetMech
JetMech split the back of his pants. He can feel the wind in his hair :shock: .
 
tdscanuck
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RE: A380 Thrust Reversers?

Mon Nov 12, 2007 2:15 am

Quoting Starlionblue (Reply 11):
As mentioned, omitting reversers on the outboards achieves two things:
- Decreased weight.
- Decreased risk of FOD.



Quoting 2H4 (Reply 13):

- Decreased maintenance, too.

Decreased cost as well. T/R's are expensive. But I'd put the crown jewel on maintenance...T/R's are a pain in the !@$#!@$.

Quoting JetMech (Reply 12):

I think the primary driving reason for only having two reversers on the A-380 was weight.

If that's the primary reason, why do the 747 and A340 have quad reversers?

Tom.
 
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jetmech
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RE: A380 Thrust Reversers?

Mon Nov 12, 2007 2:25 am

Quoting Tdscanuck (Reply 16):
If that's the primary reason, why do the 747 and A340 have quad reversers?

Hey Tom,

I'm really not too sure. I didn't mean it as a blanket statement that quads only have two reversers to reduce weight. My comment was an A380 specific one only. I'm sure you know of all the trouble Airbus has got into, and effort that has been expended to reduce the weight of the A380 (carbon centre wing box, Glare upper fuselage, 5000psi hydraulics, aluminium wiring etc.), so I can only assume that the deletion of the outboard reversers was all part of this weight reduction program.

Obviously, the 747 and 340 could either get away with the weight of the outboard reversers, or not get away from having them due to certification requirements or less advanced brake technology. So I assume that is why these aircraft have them.

Anyway, a fair question you raise. What are your thoughts on why the A380 has no outboard reversers?

Regards, JetMech
JetMech split the back of his pants. He can feel the wind in his hair :shock: .
 
2H4
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RE: A380 Thrust Reversers?

Mon Nov 12, 2007 2:31 am

Quoting Tdscanuck (Reply 16):
If that's the primary reason, why do the 747 and A340 have quad reversers?

It has probably been determined that, thus far, the weight and maintenance to be saved aren't worth the cost and effort of reengineering and recertification.

2H4
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Starlionblue
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RE: A380 Thrust Reversers?

Mon Nov 12, 2007 3:39 am

Quoting Tdscanuck (Reply 16):

Decreased cost as well. T/R's are expensive. But I'd put the crown jewel on maintenance...T/R's are a pain in the !@$#!@$.

Good point.

Quoting JetMech (Reply 15):
True, but that would only be bending relief when airborne. Outboard reversers would add to static bending moments on the ground and during negative G operations. I was also thinking of torsional strength concerns, but I would assume that forward thrust being higher would automatically account for that. Nonetheless, I'm pretty sure the key issue for only having two reversers was weight.

Good point.
"There are no stupid questions, but there are a lot of inquisitive idiots." - John Ringo
 
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HAWK21M
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RE: A380 Thrust Reversers?

Mon Nov 12, 2007 3:43 am

Probably Airbus thought it was adequate to have The two Inboard T/Rs,considering the Weight issues faced by them on the A380 project,Any reduction of unwanted weight would def help.
Im not sure about the FOD factor but during its visit to BOM earlier the Inboard T/R did pick up a lot of dirt when deployed.Im sure the Outboard T/Rs if present would have created havoc.

regds
MEL
I may not win often, but I damn well never lose!!! ;)
 
747Dreamlifter
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RE: A380 Thrust Reversers?

Mon Nov 12, 2007 4:31 am

Hey Guys,

After reading through everyone's excellent input, my opinion is that SAVING WEIGHT was a big factor in Airbus engineering out of the norm. Besides T/R's are no substitute to an effective braking system and the A380 certainly has a massive 20 wheel boggie setup. Secondly, the 380 has huge spoilers (largest I've seen on any aircraft so far), to damper lift and increase braking efficiency. Thirdly, this aircraft will be landing only at large airports with very long runways and therefore being able to stop under a mile would not a factor.

Appreciate everyone's response......

Cheers
 
OldAeroGuy
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RE: A380 Thrust Reversers?

Mon Nov 12, 2007 5:03 am

Quoting Cartoonranger (Reply 4):
If you look at landing distances with and without reverse it's not significantly different. (Perhaps 1000ft as a maximum) Reverse thrust comes into it's own, where an aircraft is spending a short time on the ground between trips.



Quoting Tdscanuck (Reply 8):
You really don't get as much stopping power as you might think from the reversers. The brakes are far more powerful.

Thrust reversers come into their own when operating on icy runways. Under these conditions, they can be more effective than brakes.

Quoting 747Dreamlifter (Reply 21):
Besides T/R's are no substitute to an effective braking system and the A380 certainly has a massive 20 wheel boggie setup.

But only 16 main gear wheels have brakes on the A388.
Airplane design is easy, the difficulty is getting them to fly - Barnes Wallis
 
tdscanuck
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RE: A380 Thrust Reversers?

Mon Nov 12, 2007 5:37 am

Quoting JetMech (Reply 17):
I didn't mean it as a blanket statement that quads only have two reversers to reduce weight. My comment was an A380 specific one only. I'm sure you know of all the trouble Airbus has got into, and effort that has been expended to reduce the weight of the A380 (carbon centre wing box, Glare upper fuselage, 5000psi hydraulics, aluminium wiring etc.), so I can only assume that the deletion of the outboard reversers was all part of this weight reduction program.

Fair enough. That would be some nice "out-of-the-box" thinking on the part of the Airbus weight-reduction guys. Maybe it just never occured to them on the 747/340 programs and, as 2H4 noted, it's probably not worth the hassle of taking them off now.

Quoting JetMech (Reply 17):
What are your thoughts on why the A380 has no outboard reversers?

My understanding was that Airbus originally wanted no reversers (which I applaud) but EASA/FAA wouldn't go with it so two was the minimum they could go with to shut the regulators up. From that perspective, any reversers were added weight so they'd want to the minimum they could possibly certify. And, if you're only going to have two, the inboard engines are the place to put them for a lot of reasons, all previously stated in this thread.

Tom.
 
2H4
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RE: A380 Thrust Reversers?

Mon Nov 12, 2007 5:45 am

Quoting OldAeroGuy (Reply 22):
But only 16 main gear wheels have brakes

How foreign this statement would have been back in the days of the Ford Trimotor and Boeing 247.

The very notion of having 16 wheels would be one thing, but adding the word 'only' would take the perceived absurdity to an entirely different level.

2H4

[Edited 2007-11-11 21:54:33]
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Starlionblue
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RE: A380 Thrust Reversers?

Mon Nov 12, 2007 6:41 am

Quoting Victor009 (Reply 3):
reverse thrusters

Little nitpick here:
- Thrust reversers: On aircraft.
- Reverse thrusters: On the starship Enterprise.

:D

Quoting 2H4 (Reply 24):
Quoting OldAeroGuy (Reply 22):
But only 16 main gear wheels have brakes

How foreign this statement would have been back in the days of the Ford Trimotor and Boeing 247.

The very notion of having 16 wheels would be one thing, but adding the word 'only' would take the perceived absurdity to an entirely different level.

Indeed.

Quoting 747Dreamlifter (Reply 21):
Thirdly, this aircraft will be landing only at large airports with very long runways and therefore being able to stop under a mile would not a factor.

Unless you have an emergency. Then again, I wager you could put the 380 down on a runway built for DC-9s and 737s if you really really had to.
"There are no stupid questions, but there are a lot of inquisitive idiots." - John Ringo

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