Reggaebird
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Airbus A380 Only Has Two Thrust Reversers?

Sat Jun 26, 2010 11:36 pm

I recently filmed an Air France A380 landing ( http://www.youtube.com/user/tbird209#p/u/1/LsKa_eq3eGE ) and noted that the pilots only deployed two thrust reversers on landing. Someone replied that the aircraft only has two. That surprised me. Shouldn't it have four available for maximum stopping power in emergency or slippery conditions? Also, I then began wondering if the outboard engines are devoid of the reverse thrust mechanisms altogether or if they are just disabled when installed in the outboard positions. If the former, does that mean that operators have to stock "inboard and outboard engines" as opposed to just "engines"?
 
9V-SPJ
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RE: Airbus A380 Only Has Two Thrust Reversers?

Sat Jun 26, 2010 11:41 pm

Airbus decided to forgo the reversers on engines 1 and 4 to save weight.

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Stitch
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RE: Airbus A380 Only Has Two Thrust Reversers?

Sat Jun 26, 2010 11:48 pm

Quoting 9V-SPJ (Reply 1):
Airbus decided to forgo the reversers on engines 1 and 4 to save weight.

I also believe it is to help prevent debris being kicked up from the sides of the runway onto the runway itself.

The A380-800 with the standard 16 main wheel brakes successfully landed at a weight of 590t - 195t above her certified Maximum Landing Weight, so she has no problems coming to a stop with only two reversers and only having two reversers does not tax her braking system.
 
qslinger
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RE: Airbus A380 Only Has Two Thrust Reversers?

Sat Jun 26, 2010 11:48 pm

This link will answer your question.

Cheers

Aborted Landing: 747 Vs A380 (by Qslinger Dec 25 2007 in Tech Ops)
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Starlionblue
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RE: Airbus A380 Only Has Two Thrust Reversers?

Sun Jun 27, 2010 1:43 am

Quoting Reggaebird (Thread starter):
does that mean that operators have to stock "inboard and outboard engines" as opposed to just "engines"?

Not really. I mean the engine is the same on the "inside" if you will. Just has different parts on the outside. My guess is the pylons aren't all the same either.

Quoting Reggaebird (Thread starter):
Shouldn't it have four available for maximum stopping power in emergency or slippery conditions?

Reversers help, but the brakes are by far the most powerful devices available to stop the aircraft. Airbus even considered skipping the reversers altogether.

Even in slippery conditions, sixteen multi-disk brakes with ABS will stop you fast.
"There are no stupid questions, but there are a lot of inquisitive idiots." - John Ringo
 
StarAC17
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RE: Airbus A380 Only Has Two Thrust Reversers?

Sun Jun 27, 2010 1:52 am

I don't know if I read this on this site or somewhere else but because of the braking power available on the A380 when it was designed I believe that Airbus didn't need them but the FAA disagreed and accepted them to have 2 on the plane.
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slz396
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RE: Airbus A380 Only Has Two Thrust Reversers?

Sun Jun 27, 2010 6:15 am

Quoting Reggaebird (Thread starter):
Shouldn't it have four available for maximum stopping power in emergency or slippery conditions?

No, because reverse thrust is not to be taken into account in stopping distance calculations.

This may look weird at first, but it actually makes sense:
ever considered WHY you might be making an emergency stop? Because an engine failed during take-off roll, for instance....
They how are you going to reverse your thrust, if your engine just failed?
See the point?

Obviously, if you have them you may use them, but you don't need to have them, nor use them.

Reverse thrust shortens your stopping distance, but if you can achieve a safe stop without them, then you're fine as well.
As others have already pointed out, the outboard engines of an A380 are very close to the runway edges on runways of only 45M, so to avoid problems with debris, Airbus decided not to give the outboard engines reversers and just install them on the inboard engines.


Quoting StarAC17 (Reply 5):
I don't know if I read this on this site or somewhere else but because of the braking power available on the A380 when it was designed I believe that Airbus didn't need them but the FAA disagreed and accepted them to have 2 on the plane.

Another unfounded rumour.

There are 4 engined jet planes without reverse thrust, the Bae146/RJ comes to mind and many operators have opted to remove the reversers from their E-jets too. Airbus could have omitted the reversers on the inboard engines too, but they have decided not to do so, one of them is to reduce the use and thus wear of the brakes.

However, you can dispatch the A380 with a reverser inop should there be a technical problem with one of them...
 
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Starlionblue
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RE: Airbus A380 Only Has Two Thrust Reversers?

Sun Jun 27, 2010 6:46 am

Regarding the FAA rumor, I would think regulatory bodies only care about stopping distance, not method. Whether that is achieved with reversers, brakes, braking parachute or The Force is not relevant as long as the method is safe, reliable, within noise regs and within pollution regs.
"There are no stupid questions, but there are a lot of inquisitive idiots." - John Ringo
 
slz396
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RE: Airbus A380 Only Has Two Thrust Reversers?

Sun Jun 27, 2010 8:57 am

Indeed, not to mention the FAA only has a secondary role when it comes to the A380.

Although the A380 is also certified under FAA standards, the lead certification authority for the A380 really is EASA and whatever the FAA thinks of the A380 is secundary only.

Remember that for as long as nobody wants to register an A380 in the US, officially it needn't even have FAA certification to operate worldwide, including to/from US airports!

[Edited 2010-06-27 01:59:25]
 
tdscanuck
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RE: Airbus A380 Only Has Two Thrust Reversers?

Sun Jun 27, 2010 1:12 pm

Quoting Reggaebird (Thread starter):
Shouldn't it have four available for maximum stopping power in emergency or slippery conditions?

Not necessary...it just needs to meet the stopping performance requirements. *How* it does that is largely up to the airframer.

Quoting Reggaebird (Thread starter):
Also, I then began wondering if the outboard engines are devoid of the reverse thrust mechanisms altogether or if they are just disabled when installed in the outboard positions.

They're not there. It's a different nacelle.

Quoting Reggaebird (Thread starter):
If the former, does that mean that operators have to stock "inboard and outboard engines" as opposed to just "engines"?

No. The engine is the same, it's just the nacelle that's different, and you don't normally change the nacelle when you swap engines (except for a few unique RR designs that don't apply to the A380).

Quoting slz396 (Reply 6):
No, because reverse thrust is not to be taken into account in stopping distance calculations.

That's generally, but not universally, true. There are a couple of 737 cases (for landing only) where you do include reverse thrust.

Quoting Starlionblue (Reply 7):
Regarding the FAA rumor, I would think regulatory bodies only care about stopping distance, not method.

That's how it's supposed to be, but there are a several regulators (in all the bodies) who will just say "You need to do it this way or we're not certifying it." Sort of like arguing with border guards, it doesn't matter how right you are when they hold all the cards.

Tom.
 
slz396
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RE: Airbus A380 Only Has Two Thrust Reversers?

Sun Jun 27, 2010 2:13 pm

Quoting tdscanuck (Reply 9):
That's generally, but not universally, true. There are a couple of 737 cases (for landing only) where you do include reverse thrust.

In case of a landing on a contaminated surface for instance...

it has more to do with the fact the 737's brakes alone can't do the job under those conditions and hence the manufacturer is relying also on the reversers too to bring the plane to a full stop within reasonable distance and without overheating the brakes. The consequence is that you're obviously not able to dispatch a 737 with a reverser inop under those conditions then, which is a limitation on the plane.

The A380 doesn't have reverser inop dispatch limitations, hence is not relying on it for stopping distance.
No wonder, given the fact it has a lot of wheels with a lot of brakes... It's not the typical tricicle like mose planes.

[Edited 2010-06-27 07:17:20]
 
OldAeroGuy
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RE: Airbus A380 Only Has Two Thrust Reversers?

Sun Jun 27, 2010 3:08 pm

Quoting slz396 (Reply 6):
No, because reverse thrust is not to be taken into account in stopping distance calculations.

True for landing distance calculations on dry or wet runways. However, the takeoff distance calculations for the A380 Certification Basis do allow reverse thrust use. It does make a difference, particularly on wet runways.

For runways contaminated with snow, slush or ice, you want all the stopping power you can get, including reverse thrust.

Quoting slz396 (Reply 8):
Although the A380 is also certified under FAA standards, the lead certification authority for the A380 really is EASA and whatever the FAA thinks of the A380 is secundary only.

Remember that for as long as nobody wants to register an A380 in the US, officially it needn't even have FAA certification to operate worldwide, including to/from US airports!

Not necessarily. Many smaller nations base their certification process on the FAR's. That's why Airbus and Boeing make a practice of getting concurrent EASA/FAA Type Certification. Both OEM's need to meet the unique cert requirements of both agencies.

Quoting slz396 (Reply 10):
The A380 doesn't have reverser inop dispatch limitations, hence is not relying on it for stopping distance.
No wonder, given the fact it has a lot of wheels with a lot of brakes

Stopping power with wheel brakes is more related to the force available to each wheel. The A380 has sixteen braked wheels while the 737 has four braked wheels, a ratio of 4:1. However, the A380 MTOW is six times higher than the largest 737. It's not a given the A380 has a greater wheel brake only deceleration rate than the 737.

For icy runway operation (takeoff or landing), pilots of both airplanes will be happy to have whatever reverse thrust is available to aid stopping capability.
Airplane design is easy, the difficulty is getting them to fly - Barnes Wallis
 
slz396
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RE: Airbus A380 Only Has Two Thrust Reversers?

Sun Jun 27, 2010 4:45 pm

Quoting OldAeroGuy (Reply 11):
The A380 has sixteen braked wheels while the 737 has four braked wheels, a ratio of 4:1. However, the A380 MTOW is six times higher than the largest 737. It's not a given the A380 has a greater wheel brake only deceleration rate than the 737.

Although my remark about the large number of wheels and thus also brakes was largely anecdotical, I'd like to point out that comparing the number of brakes to the total weight like you're doing isn't really proving anything either, as a single A380 brake is far bigger and thus capable of far more individual energy dissipation than a single 737 brake.

Anyway, as others have said, the A380 has demonstrated landings at 190t ABOVE MLW, with just 2 reversers (don't even know if they have been used on that landing), so obviously, its brakes are capable of quite some energy dissipation, to say the least, and it is said Airbus could add more brakes for future weight growth even.

I'd wonder what it would take to turn this plane in a STOL-plane? 

Imagine that: an A380 at LCY... wouldn't that be great?

[Edited 2010-06-27 09:48:01]
 
tdscanuck
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RE: Airbus A380 Only Has Two Thrust Reversers?

Sun Jun 27, 2010 10:51 pm

Quoting slz396 (Reply 12):
Anyway, as others have said, the A380 has demonstrated landings at 190t ABOVE MLW, with just 2 reversers (don't even know if they have been used on that landing), so obviously, its brakes are capable of quite some energy dissipation

Landing is very rarely the critical brake situation for energy dissipation...that's a rejected takeoff at MTOW. Compared to that, essentially any landing isn't a big deal for energy (it may be for field length though).

Tom.
 
413X3
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RE: Airbus A380 Only Has Two Thrust Reversers?

Sun Jun 27, 2010 11:26 pm

it's quite simple. The outboard engines hang over so far over the runway. So if it had reverser's it would kick up a lot of debris.
 
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RE: Airbus A380 Only Has Two Thrust Reversers?

Mon Jun 28, 2010 1:50 am

Regarding wheel to weight ratio with the 737, the 380 has bigger wheels and more powerful brakes. More importantly though, more weight on the wheel enables harder braking since there is less risk of sliding. Compare with a motorbike where brake pressure on the front wheel is increased (well, should be if you're doing it right) as the braking action progresses and the suspension loads the front wheel more.
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wingscrubber
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RE: Airbus A380 Only Has Two Thrust Reversers?

Mon Jun 28, 2010 3:00 am

FYI, the world's largest airplane - the Antonov 225, has thrust reversers on all six of its engines, and the last two are hung way out - easily over the edge of some narrower runways. Although admittedly they are smaller individual engines than the a380 mills- the reverse thrust of two RR trents probably isn't much less than 6 D-18s.

http://www.air-and-space.com/19930905%20Zhukovsky/934080%20An-225%20right%20front%20landing%20l.jpg

Speaking from experience, I can tell you thrust reversers are also very thirsty where hydraulics are concerned; you can reduce the hydraulic flow demand from your engine driven pumps a great deal by eliminating them where possible, they require a large amount of fluid in a very short amount of time which the entire system has to be sized for. By getting rid of the extra TRs you do save weight in terms of the thrust reverser itself, but can you reduce the required hydraulic plumbing, your pumps can theoritically be smaller, your system accumulators can shrink and your electric motor pumps and ram air turbine can potentially be smaller too.

I was surprised myself when I found out the A380 only has two reversers, but with a great deal of braking power and an awful lot of reverse thrust available from just two engines alone, I think the Airbus engineers made a good compromise.
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RE: Airbus A380 Only Has Two Thrust Reversers?

Mon Jun 28, 2010 4:25 am

Quoting OldAeroGuy (Reply 11):
Not necessarily. Many smaller nations base their certification process on the FAR's.

Actually MOST ICAO members give the person applying for type certification the option of using the FARs or EASA requirements as their design basis.

I wonder which QF used in getting their A330 & A380s on the Oz register?

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tdscanuck
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RE: Airbus A380 Only Has Two Thrust Reversers?

Mon Jun 28, 2010 5:35 am

Quoting Wingscrubber (Reply 16):
FYI, the world's largest airplane - the Antonov 225, has thrust reversers on all six of its engines, and the last two are hung way out - easily over the edge of some narrower runways

Yes, but it's a high-wing. It's a lot harder for an An225 to suck up FOD than an A380.

Tom.
 
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RE: Airbus A380 Only Has Two Thrust Reversers?

Mon Jun 28, 2010 5:48 am

Quoting tdscanuck (Reply 13):
Landing is very rarely the critical brake situation for energy dissipation...that's a rejected takeoff at MTOW. Compared to that, essentially any landing isn't a big deal for energy (it may be for field length though).

I suspect that landing at 590t might have been one of those "rare" cases, Tom  

Rgds
 
OldAeroGuy
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RE: Airbus A380 Only Has Two Thrust Reversers?

Mon Jun 28, 2010 2:02 pm

Quoting slz396 (Reply 12):
Although my remark about the large number of wheels and thus also brakes was largely anecdotical, I'd like to point out that comparing the number of brakes to the total weight like you're doing isn't really proving anything either, as a single A380 brake is far bigger and thus capable of far more individual energy dissipation than a single 737 brake.

You're off base in your reference to brake energy. It is not the important factor in determing deceleration due to brakes. The critical factors are the contact area between tire and runway, the loading in that contact area (unit of force/unit of surface area), and the torque the brake is capable of creating on the axle to slow wheel rotation.

Quoting Starlionblue (Reply 15):
Regarding wheel to weight ratio with the 737, the 380 has bigger wheels and more powerful brakes. More importantly though, more weight on the wheel enables harder braking since there is less risk of sliding.

This is closer to the mark. Not sure what you mean by more powerful though. Do you mean how much brake torque is available?

I'll try to do a little reasearch to compare A380 and 737 tire/runway loading. The A380 does have an interesting situation in that there are 20 main gear wheels but only 16 of them are braked. The 4 wheels that aren't braked will detract somewhat from overall brake performance since they will share the runway loading with the braked wheels but will provide only rolling friction as a retarding force.
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Stitch
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RE: Airbus A380 Only Has Two Thrust Reversers?

Mon Jun 28, 2010 3:55 pm

Quoting astuteman (Reply 19):
I suspect that landing at 590t might have been one of those "rare" cases, Tom.  

True, but a customer A380-800 would never land at that weight unless the situation was so dire that they could not afford to dump fuel to reach MLW prior to landing (and even then, it would require an MTOW beyond 590t which the passenger model is not currently certified for).

Still, nice to know you have the ability.  Smile

[Edited 2010-06-28 09:15:22]
 
Fly2HMO
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RE: Airbus A380 Only Has Two Thrust Reversers?

Mon Jun 28, 2010 5:13 pm

Quoting Wingscrubber (Reply 16):
FYI, the world's largest airplane - the Antonov 225, has thrust reversers on all six of its engines, and the last two are hung way out - easily over the edge of some narrower runways

Well that's not surprising, it is designed to land on runways much smaller planes can fly into and it's a high wing, so there's a reduced risk of FOD ingestion.
 
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RE: Airbus A380 Only Has Two Thrust Reversers?

Mon Jun 28, 2010 5:44 pm

Quoting slz396 (Reply 12):
I'd wonder what it would take to turn this plane in a STOL-plane?

Imagine that: an A380 at LCY... wouldn't that be great?

Pilot's words of wisdom #172:

You can land an airplane in places where you couldn't take it off from again  

United Airlines did this one day in 1962, when they landed a DC-8 at TTD instead of PDX (a much shorter field!).

They managed to get it off again on its own, after removing the aircraft's interior and getting an FAA ferry permit to fly it to PDX on the minimum amount of fuel to get from TTD to PDX  Wow!
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astuteman
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RE: Airbus A380 Only Has Two Thrust Reversers?

Mon Jun 28, 2010 8:43 pm

Quoting Stitch (Reply 21):
True, but a customer A380-800 would never land at that weight unless the situation was so dire that they could not afford to dump fuel to reach MLW prior to landing

A rare occurrence indeed  

Rgds
 
slz396
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RE: Airbus A380 Only Has Two Thrust Reversers?

Tue Jun 29, 2010 8:32 pm

Quoting OldAeroGuy (Reply 20):
You're off base in your reference to brake energy. It is not the important factor in determing deceleration due to brakes. The critical factors are the contact area between tire and runway, the loading in that contact area (unit of force/unit of surface area), and the torque the brake is capable of creating on the axle to slow wheel rotation.


Let's not start a pissing contest here, shall we?

Quoting astuteman (Reply 24):
A rare occurrence indeed

An inextinguishable engire fire on take-off for instance... not that far-fetched at all... it's an occurance trained regularly during simulator sessions.

[Edited 2010-06-29 13:45:24]
 
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bikerthai
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RE: Airbus A380 Only Has Two Thrust Reversers?

Tue Jun 29, 2010 10:34 pm

Quoting tdscanuck (Reply 9):
There are a couple of 737 cases (for landing only) where you do include reverse thrust.
Quoting slz396 (Reply 10):
In case of a landing on a contaminated surface for instance...

So are these specific cases in relation to the capability of some of the older 737 to operate on un-improved (contaminated) surfaces?

In my days dealing with reversers, I was told that thrust reverser on commercial jets are are "nice to have" in order to reduce the wear on the brake pads. You pay in terms of complexity additional weight and costs in the nacelle.

Now, if better brake materials are available at lower prices that will last longer, then a trade could be made to not have the reverser.

bikerthai
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tdscanuck
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RE: Airbus A380 Only Has Two Thrust Reversers?

Wed Jun 30, 2010 1:14 am

Quoting bikerthai (Reply 26):
So are these specific cases in relation to the capability of some of the older 737 to operate on un-improved (contaminated) surfaces?

Contaminated is no the same as un-improved...a perfectly good runway can be contaminated by slush, water, snow, etc. And it's not just older 737's, 737NG's use the same concepts.

Quoting bikerthai (Reply 26):
In my days dealing with reversers, I was told that thrust reverser on commercial jets are are "nice to have" in order to reduce the wear on the brake pads. You pay in terms of complexity additional weight and costs in the nacelle.

That's fairly accurate...I hate thrust reversers. They're probably the single most terribly designed trade on a modern jet.

Quoting bikerthai (Reply 26):
Now, if better brake materials are available at lower prices that will last longer, then a trade could be made to not have the reverser.

This happens quite often when you have carbon brakes...you'll see a whole lot of idle reverse being used.

Tom.
 
mrocktor
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RE: Airbus A380 Only Has Two Thrust Reversers?

Wed Jun 30, 2010 4:08 pm

Quoting StarAC17 (Reply 5):
FAA disagreed and accepted them to have 2 on the plane

There is no requirement that an aircraft have thrust reversers, so there is really nothing for the FAA to agree to in this case.

Quoting slz396 (Reply 6):
many operators have opted to remove the reversers from their E-jets too

The E-jets (Embraer 170/175/190/195) all have reversers, none have been removed - though using them is of course at the operator's discretion.

The older ERJ series has units delivered with reversers and others without. I do not believe any units delivered with reversers have had them removed (though, again, using them is at the operator's discretion).

Quoting Starlionblue (Reply 7):
I would think regulatory bodies only care about stopping distance, not method.
Quoting tdscanuck (Reply 9):
*How* it does that is largely up to the airframer.

Aviation regulatory bodies have by far exceeded the scope of simply regulating the required performance of aircraft - the means to achieve the required ends are minutely regulated and have been for a long, long time.

Quoting tdscanuck (Reply 9):
There are a couple of 737 cases (for landing only) where you do include reverse thrust.

Some regulatory agencies allow separate performance charts for landing on contaminated runways taking credit for reverse thrust. Others do not allow that credit even for contaminated runway performance. No authorities allow credit for reverse thrust for clean runway RTO or landing performance.

Quoting tdscanuck (Reply 9):
That's how it's supposed to be, but there are a several regulators (in all the bodies) who will just say "You need to do it this way or we're not certifying it." Sort of like arguing with border guards, it doesn't matter how right you are when they hold all the cards.

  
 
OldAeroGuy
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RE: Airbus A380 Only Has Two Thrust Reversers?

Wed Jun 30, 2010 8:04 pm

Quoting slz396 (Reply 25):
Quoting OldAeroGuy (Reply 20):
You're off base in your reference to brake energy. It is not the important factor in determing deceleration due to brakes. The critical factors are the contact area between tire and runway, the loading in that contact area (unit of force/unit of surface area), and the torque the brake is capable of creating on the axle to slow wheel rotation.


Let's not start a pissing contest here, shall we?

I fail to see how stating the relevant factors in wheel brake stopping force is starting a "pissing contest". Please be more specific about what is troubling you.
Airplane design is easy, the difficulty is getting them to fly - Barnes Wallis
 
474218
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RE: Airbus A380 Only Has Two Thrust Reversers?

Wed Jun 30, 2010 9:18 pm

Quoting StarAC17 (Reply 5):
I don't know if I read this on this site or somewhere else but because of the braking power available on the A380 when it was designed I believe that Airbus didn't need them but the FAA disagreed and accepted them to have 2 on the plane.
Quoting slz396 (Reply 8):
Indeed, not to mention the FAA only has a secondary role when it comes to the A380.

Although the A380 is also certified under FAA standards, the lead certification authority for the A380 really is EASA and whatever the FAA thinks of the A380 is secundary only.

Remember that for as long as nobody wants to register an A380 in the US, officially it needn't even have FAA certification to operate worldwide, including to/from US airports!

The EASA and the FAA and an working agreement, aircraft certified by one agency are considered certified by the other.
 
Max Q
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RE: Airbus A380 Only Has Two Thrust Reversers?

Thu Jul 01, 2010 2:10 am

It's a bad idea, period.


There are times when you need every available stopping device working to it's utmost for you to stop the Aircraft.



You simply cannot predict what can happen, one day all the odds can stack up against you.



Airbus has saved a little weight but discarded an extra layer of redundancy and therefore, safety by reducing available stopping power.



I have landed on runways so slippery that brakes were only minimally effective, reverse thrust, the more the better was vital in these circumstances.



You just never know.
The best contribution to safety is a competent Pilot.
 
tdscanuck
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RE: Airbus A380 Only Has Two Thrust Reversers?

Thu Jul 01, 2010 2:19 am

Quoting Max Q (Reply 31):
There are times when you need every available stopping device working to it's utmost for you to stop the Aircraft.

So you feel that all engines should have reversers, all wheels should have brakes (including nose wheels), and all aircraft should have retro-rockets and drag chutes?

"Every available stopping device" is far too broad a claim, and totally unrealistic.

Quoting Max Q (Reply 31):
Airbus has saved a little weight but discarded an extra layer of redundancy and therefore, safety by reducing available stopping power.

Technically, they haven't discarded a layer, they've reduced capability in an existing layer. Pretty much the same as only having brakes on 16 of the 20 wheels.

Quoting Max Q (Reply 31):
I have landed on runways so slippery that brakes were only minimally effective, reverse thrust, the more the better was vital in these circumstances.

But, either you did that with stopping distance calculations in hand (in which case you were taking credit for your reverse thrust), or you did it without knowing if you could stop, which would be illegal to start with.

Having extra T/R's might allow you to land on a runway you otherwise couldn't, but you go into the situation knowing what devices you have. Attempting to land on a runway shorter than the plane can stop on is a pilot error, not a design error.

Tom.
 
Max Q
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RE: Airbus A380 Only Has Two Thrust Reversers?

Thu Jul 01, 2010 6:24 am

Tds,



I don't know your real background or how much experience you have in Command of Large Jets.



You are quite good at picking apart statements regarding their operation and ridiculing them.



You do this without what appears to be the normal skepticism and conservative nature that myself and my peers have gained with the benefit of decades and tens of thousands of hours of real world experience



Just what exactly is your background as a Pilot that you can come up with this, quite incredible statement ?

Quoting tdscanuck (Reply 27):
That's fairly accurate...I hate thrust reversers. They're probably the single most terribly designed trade on a modern jet.

I do not know a single (Real) Pilot that would share that opinion and once again, it makes me question your background.Why not enlighten us as to the source of your expertise ?





Every Professional Pilot I know likes to have every available stopping device installed and working.




It's always best to be prepared for the unexpected.




Max
The best contribution to safety is a competent Pilot.
 
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Stitch
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RE: Airbus A380 Only Has Two Thrust Reversers?

Thu Jul 01, 2010 11:05 am

Quoting Max Q (Reply 31):
Airbus has saved a little weight but discarded an extra layer of redundancy and therefore, safety by reducing available stopping power.

The A380-800 has successfully performed an RTO at 575t, which is a WV that will become available within the next couple of years.

So even 16 worn-to-heck brakes on their absolute last legs can stop a fully-loaded plane with no problems. How, exactly, is that discarding safety?

I don't know the brake material thickness on the A380-800 that performed a successful landing at a weight 190t above certified maximum, but at worse, an A380-800 with sixteen brand-new braking components and two thrust reversers certainly has more than enough stopping power.

True, the A380-800F would have had braking units on all 20 main wheels, but even then, that would have provided some 35t more braking power than was needed (I have heard that with 20 units the A380 can handle a "stopping weight" of 625t, which is 35t beyond the 590t MTOW of the A380-800F).

So it sounds to me like 16 units is already "redundant" for the A380-800 and adding 20 would just be more so.
 
travelavnut
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RE: Airbus A380 Only Has Two Thrust Reversers?

Thu Jul 01, 2010 2:01 pm

Quoting Max Q (Reply 34):
Airbus has saved a little weight but discarded an extra layer of redundancy and therefore, safety by reducing available stopping power.

I dont have the exact numbers, but with the already low approach speed and the facts mentioned by Stich I dont see how Airbus has "removed redudancy". It seems to me they made a logical, save and certifiable choice.

This is just mindless airbus-bashing..
Live From Amsterdam!
 
tdscanuck
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RE: Airbus A380 Only Has Two Thrust Reversers?

Thu Jul 01, 2010 2:50 pm

Quoting Max Q (Reply 33):
Just what exactly is your background as a Pilot that you can come up with this, quite incredible statement ?

That statement was actually from an engineering, not pilot, standpoint. As a pilot, my background is partial completion of private pilot training. As an engineer, I was the subject matter expert on 737NG thrust reversers. In my current job (flight test director), I do the takeoff and landing performance calculations for the tests I fly, which includes weight/runway/dispatch configurations *far* outside what are ever seen in commercial.

From an engineering standpoint, TR's are a terrible trade...they're heavy, expensive, complex, maintenance intensive, used for only about 20 seconds per cycle, and you can't even take credit for them in most situations. *If* you can achieve proper stopping performance without them, it's a huge win to get rid of them (as Airbus partially achieved on the A380).

From a pilot standpoint, I agree with you...I want all the stopping power I can get at my disposal.

Quoting Max Q (Reply 33):
Why not enlighten us as to the source of your expertise ?

3 degrees + a certificate in mech/aero/structures engineering, 5 years as subject matter expert for propulsion (mostly fuel/NGS/thrust reversers on various Boeing narrowbodies), 2 years in commercial flight test of new types, 10+ total years of doing performance calculations and the related risk/mitigation assessments.

Tom.
 
David L
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RE: Airbus A380 Only Has Two Thrust Reversers?

Thu Jul 01, 2010 5:50 pm

Quoting tdscanuck (Reply 32):
either you did that with stopping distance calculations in hand (in which case you were taking credit for your reverse thrust)

That's what I was wondering. As long as you know what's available, does it matter how many engines have reversers? It's not as though A380 crews would be expecting reverse to be available on four engines, only to find on landing that they could only apply it on two. And what about aircraft with reversers fitted to all engines that depart with one inop - i.e. with less reverse thrust than is usually available?
 
tdscanuck
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RE: Airbus A380 Only Has Two Thrust Reversers?

Thu Jul 01, 2010 6:47 pm

Quoting David L (Reply 37):
As long as you know what's available, does it matter how many engines have reversers?

I think MaxQ's issue is that you don't really *know* what's available until you actually try to use it. A T/R might fail to deploy, the runway might be slipperier than forecast, a brake might lock, etc.

Quoting David L (Reply 37):
It's not as though A380 crews would be expecting reverse to be available on four engines, only to find on landing that they could only apply it on two.

That is a possible failure mode if you have 4 reversers, albeit a really rare one. Being able to respond to such an event should be part of training, and part of the briefing. If you're in a situation where the use of reverse thrust is essential to stopping on the runway (really really rare and, I would argue, a landing that shouldn't even be attempted), you'd best be prepared with a plan of what to do if they don't all deploy.

Quoting David L (Reply 37):
And what about aircraft with reversers fitted to all engines that depart with one inop - i.e. with less reverse thrust than is usually available?

In that case, you usually take a performance penalty (e.g. on a 737NG you can't take credit for the TR's on a contaminated runway if you have an inop TR) to account for it.

Tom.
 
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bikerthai
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RE: Airbus A380 Only Has Two Thrust Reversers?

Thu Jul 01, 2010 7:08 pm

Quoting tdscanuck (Reply 36):
I was the subject matter expert on 737NG thrust reversers.

Tom,

Were you able to receive my "off-line" messages? I was curious on whether the 787 T/R reverser have insulation blankets on them.

bikerthai
Intelligent seeks knowledge. Enlightened seeks wisdom.
 
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HAWK21M
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RE: Airbus A380 Only Has Two Thrust Reversers?

Sat Jul 03, 2010 8:20 pm

Quoting KELPkid (Reply 23):

You can land an airplane in places where you couldn't take it off from again

Occured with a B747 at MAA a few yrs ago,the crew landed on an airbase,a few km away from the actual airport.They then offloaded all seats & unairworthy equipment to lighten the craft to required weight & filled 10-15mins fuel for the small distance.Got airborne & landed in a few minutes.
Amazing.
regds
MEL.
I may not win often, but I damn well never lose!!! ;)
 
wingscrubber
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RE: Airbus A380 Only Has Two Thrust Reversers?

Sat Jul 03, 2010 11:17 pm

Canuck, Fly2hmo, with the steep anhedral of the AN225 and the steep dihedral of the A380, I don't think there's really much difference between the height off the ground of their outermost engines, and btw the AN225 has a wingspan of 88.4m, compared to 79.75m for the A380, so you see there's not really a significantly reduced risk of FOD to the AN225 justifying the outboard TRs just because it's 'high wing' as you say. The difference is the AN225 uses all available stopping power regardless of FOD risk and the A380 does not.


Some examples of when some extra TR could have been helpful:
http://article.wn.com/view/2010/06/1...d_investigates_United_Express_pla/
http://www.cbsnews.com/stories/2010/04/13/world/main6391730.shtml
http://www.reuters.com/article/idUSN3029714820080530
http://www.foxnews.com/wires/2008Jun...4670,BulgariaPlaneAccident,00.html

Maybe the point I'm trying to make is that, even if the pilots opt not to use the outer TRs (as 747 pilots sometimes do) it would might still be nice to have them anyway.
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Aesma
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RE: Airbus A380 Only Has Two Thrust Reversers?

Sat Jul 03, 2010 11:36 pm

The AN-225 is irrelevant. The A380 is an airliner, meaning it's half the time flying, and has to make money, so maintenance, availability, engine life, etc., are very important. Did any airport get upgraded to handle the (only) antonov ? No. On the other end, many have been for the airbus, and that includes runways, taxiways, bridges, etc.
New Technology is the name we give to stuff that doesn't work yet. Douglas Adams
 
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Starlionblue
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RE: Airbus A380 Only Has Two Thrust Reversers?

Sun Jul 04, 2010 12:55 am

You can always argue for more stopping power. You can argue for a lot of extra safety features. In the end, though, aircraft design is a compromise.
"There are no stupid questions, but there are a lot of inquisitive idiots." - John Ringo
 
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larshjort
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RE: Airbus A380 Only Has Two Thrust Reversers?

Sun Jul 04, 2010 8:43 am

Quoting Wingscrubber (Reply 41):
The difference is the AN225 uses all available stopping power regardless of FOD risk and the A380 does not.

I haven't seen the AN-225 with a brake shute?

Every aircraft design is a compromise, and both FAA and EASA found the braking power available enough for the aircraft to have 2 thrust reversers. If every part of an airvraft was to have 100% safety, we wouldn't fly.

/Lars
139, 306, 319, 320, 321, 332, 34A, AN2, AT4, AT5, AT7, 733, 735, 73G, 738, 739, 146, AR1, BH2, CN1, CR2, DH1, DH3, DH4,
 
mrocktor
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RE: Airbus A380 Only Has Two Thrust Reversers?

Mon Jul 05, 2010 3:48 pm

Quoting 474218 (Reply 30):
EASA and the FAA (...) aircraft certified by one agency are considered certified by the other.

This is not true. Not by a long shot. There have been several cycles of harmonization but an FAA type certificate and an EASA type certificate are very different things, there is no implicit equivalence between them and it is not necessarily easy to get the other just because you have the one. Ask Eclipse.

Quoting Larshjort (Reply 44):
and both FAA and EASA found the braking power available enough for the aircraft to have 2 thrust reversers

Both the FAA and EASA found the braking power available enough for the aircraft with ZERO thrust reversers. Reversers don't count in certified performance.
 
OldAeroGuy
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RE: Airbus A380 Only Has Two Thrust Reversers?

Mon Jul 05, 2010 9:02 pm

Quoting mrocktor (Reply 45):
Both the FAA and EASA found the braking power available enough for the aircraft with ZERO thrust reversers. Reversers don't count in certified performance.

Partially true. Reversers can be used for certified takeoff field length credit on wet runways..

Please see FAR 25.109 Amend 92 Accelerate-stop distance.

(f) The effects of available reverse thrust--
(1) Shall not be included as an additional means of deceleration when determining the accelerate-stop distance on a dry runway; and
(2) May be included as an additional means of deceleration using recommended reverse thrust procedures when determining the accelerate-stop distance on a wet runway, provided the requirements of paragraph (e) of this section are met.]
Airplane design is easy, the difficulty is getting them to fly - Barnes Wallis
 
Max Q
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RE: Airbus A380 Only Has Two Thrust Reversers?

Tue Jul 06, 2010 2:38 am

All the wheels and brakes in the world won't help you much on a slippery runway. More stopping power of any kind is better, period.
The best contribution to safety is a competent Pilot.
 
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Starlionblue
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RE: Airbus A380 Only Has Two Thrust Reversers?

Tue Jul 06, 2010 4:06 am

The stopping distance calculations will take a wet runway into account.
"There are no stupid questions, but there are a lot of inquisitive idiots." - John Ringo
 
AutothrustBlue
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RE: Airbus A380 Only Has Two Thrust Reversers?

Tue Jul 06, 2010 4:16 am

Isn't the A380 fitted with runway overrun warning/protection that will alert the pilots if a runway is too short (either wet or dry)?

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