Natesantiago88
Topic Author
Posts: 33
Joined: Fri Jan 22, 2010 4:34 pm

A346 Rejected Take-off

Mon May 17, 2010 7:02 am

I found these two videos on youtube.
http://www.youtube.com/watch?v=UocxPoUUnIQ&feature=related
http://www.youtube.com/watch?v=hRzWp67PIMw

They both are a video for testing of the 346. And I had a few question concerning the video.
Would this be considered a failed RTO?
If this was a failed test, how many tests did it take them to get a good test?
Would the damage from the incident made the plane non airworthy?
If this did make the plane non airworthy how many frames did they through?
Is this test one of the final tests to be done for the airliner?
 
tdscanuck
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RE: A346 Rejected Take-off

Mon May 17, 2010 7:16 pm

Quoting natesantiago88 (Thread starter):
Would this be considered a failed RTO?

They stopped on the runway, so it's not a failed RTO. It would probably be a failure of the max energy braking certification test, if that's what they're doing.

Quoting natesantiago88 (Thread starter):
If this was a failed test, how many tests did it take them to get a good test?

Hopefully, not more than two.

Quoting natesantiago88 (Thread starter):
Would the damage from the incident made the plane non airworthy?

Yes. I have quite a few pictures from that test and the results weren't pretty.

Quoting natesantiago88 (Thread starter):
If this did make the plane non airworthy how many frames did they through?

Non-airworthy doesn't mean non-repairable. I strongly doubt they scrapped the frame, I think they would have just fixed it and moved on.

Quoting natesantiago88 (Thread starter):
Is this test one of the final tests to be done for the airliner?

Usually, yes, because you run the risk of losing a very valuable test asset.

Tom.
 
c5load
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RE: A346 Rejected Take-off

Mon May 17, 2010 8:21 pm

Did this test cause a brake fire? The gear on the left side of the camera (right side of the airplane) was sure smoking heavily for some time. Is smoke something to be expected on a rejected t/o?
"But this airplane has 4 engines, it's an entirely different kind of flying! Altogether"
 
ANITIX87
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RE: A346 Rejected Take-off

Mon May 17, 2010 8:23 pm

Quoting c5load (Reply 2):
Did this test cause a brake fire? The gear on the left side of the camera (right side of the airplane) was sure smoking heavily for some time. Is smoke something to be expected on a rejected t/o?

What I've read (and Tom can correct me if I'm wrong) is that the fire is ok for a successful test. The fire, however, must be limited to a certain amount of time or to a certain area, in order to ensure the safe evacuation of all passengers in the event of a real RTO.

A RTO puts so much stress and heat into the braking system that, as far as I know, it's completely normal for there to be burst tires, smoke, and some flames.

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KELPkid
Posts: 5247
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RE: A346 Rejected Take-off

Mon May 17, 2010 8:24 pm

Quoting c5load (Reply 2):
Did this test cause a brake fire? The gear on the left side of the camera (right side of the airplane) was sure smoking heavily for some time. Is smoke something to be expected on a rejected t/o?

As I recall, the certification standards require that if there is a brake fire, you have to wait x seconds to put the fire out, so if it does catch fire, you have to sit there and let it burn (IIRC, it is 90 seconds...). This is to simulate ARFF response times.
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c5load
Posts: 344
Joined: Tue Sep 16, 2008 9:40 pm

RE: A346 Rejected Take-off

Mon May 17, 2010 8:37 pm

Quoting ANITIX87 (Reply 3):
A RTO puts so much stress and heat into the braking system that, as far as I know, it's completely normal for there to be burst tires, smoke, and some flames.

It would make sense to me that for the reasons of safety, tire manufacturers would have to make tires strong enough to withstand the pressure of a RTO. Same goes for brakes. Wouldn't the FAA want to er on the side of caution and puts those standards in place so there would be minimal chance of a brake fire?
"But this airplane has 4 engines, it's an entirely different kind of flying! Altogether"
 
etherealsky
Posts: 211
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RE: A346 Rejected Take-off

Mon May 17, 2010 8:52 pm

Quoting c5load (Reply 5):
It would make sense to me that for the reasons of safety, tire manufacturers would have to make tires strong enough to withstand the pressure of a RTO.

Aircraft tires employ "fusible plugs" which are designed to melt and bleed-off tire pressure before the tire itself actually bursts due to the tremendous amounts of energy (read: heat) absorbed in an RTO.

I suspect that tires and brakes aren't required to be able to completely handle a maximum-energy braking scenario because that would simply require over-engineering the landing gear. All of aviation is a balance between safety and cost/efficiency, and this is just another example of that. Airliner brakes are not small pieces of equipment as it is, and increasing their capacity to dissipate energy would mean more weight, more cost, more complexity, more maintenance, etc. etc.
"And that's why you always leave a note..."
 
tdscanuck
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RE: A346 Rejected Take-off

Tue May 18, 2010 3:26 am

Quoting c5load (Reply 2):
Did this test cause a brake fire?

Yes. Technically, it's the tires, not the brakes, that are on fire.

Quoting c5load (Reply 2):
Is smoke something to be expected on a rejected t/o?

Very much so.

Quoting ANITIX87 (Reply 3):
What I've read (and Tom can correct me if I'm wrong) is that the fire is ok for a successful test.

Correct. It's OK (almost expected) that you will get some fire. You need to have grease in the gear bearings, and the tires are rubber, and you're going to get everything way too hot to not have something catch fire. No fire is simply an unreasonable (and unnecessary) requirement. What is required is that the fire doesn't jeopardize the safety of the occupants for long enough to safety get them off the plane and/or for ARFF to arrive and put out the fire.

Quoting ANITIX87 (Reply 3):
A RTO puts so much stress and heat into the braking system that, as far as I know, it's completely normal for there to be burst tires, smoke, and some flames.

Exactly. Many "normal" RTO's do nothing more than heat the brakes, but the max energy RTO (worst case), which is the certification test, is bound to make a huge mess.

Quoting c5load (Reply 5):
It would make sense to me that for the reasons of safety, tire manufacturers would have to make tires strong enough to withstand the pressure of a RTO.

Why? It's much easier to just let the fuse plug vent the tire than to try to make a tire withstand that kind of pressure. It's more about the wheel anyone...a tire bursting is ugly...a wheel bursting is deadly.

Quoting c5load (Reply 5):
Same goes for brakes.

The brakes did exactly what they were supposed to do...safely stopped the airplane. There is no requirement, nor should there be, to be able to have no damage after a max energy RTO. Safety is the requirement, and that requirement is met by the time of certification.

Quoting c5load (Reply 5):
Wouldn't the FAA want to er on the side of caution and puts those standards in place so there would be minimal chance of a brake fire?

To what end? The certification test proves that, even in the worst case, you can safely stop the aircraft and evacuate everybody and/or put out any fire. What do you gain by increasing the requirement?

Quoting etherealsky (Reply 6):
Aircraft tires employ "fusible plugs" which are designed to melt and bleed-off tire pressure before the tire itself actually bursts due to the tremendous amounts of energy (read: heat) absorbed in an RTO.

The fuse plugs are actually in the wheel, not the tire. The main heat path is from the brakes to the wheels to the nitrogen to the tires, so having them in the wheel helps ensure they let go before the tire pressure gets critical.

Quoting etherealsky (Reply 6):
I suspect that tires and brakes aren't required to be able to completely handle a maximum-energy braking scenario because that would simply require over-engineering the landing gear.

They are required to completely handle it in the sense of safely stopping you without causing catastrophic damage to the aircraft or its passengers for a reasonable period of time. There's no requirement that they be in usable condition afterwards.

Tom.
 
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zeke
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RE: A346 Rejected Take-off

Tue May 18, 2010 4:54 am

Quoting etherealsky (Reply 6):

Aircraft tires employ "fusible plugs" which are designed to melt and bleed-off tire pressure before the tire itself actually bursts due to the tremendous amounts of energy (read: heat) absorbed in an RTO.

Airbus employs two methods, an overpressure relive valve and an eutectic plug on the wheel rim.

The overpressure relief valve, as its name suggests takes care of an overpressure situation within the tyre, the eutectic alloy plug ("fuse plug", which is like solder like material, add heat and it starts to change state) is there for a different purpose.

In the event of a brake fire, or a heavy braking event, the brakes generate a lot of heat. Airbus has a stainless steel heat shield fitted on the inner side of the rim/wheel has a to prevent the working brake temperatures radiating into the wheel and tyre, however the brakes will still radiate and conduct heat into the wheel rims. As the temperature of the rims increases, the rim strength reduces, and the possibility then exists where the rim can explode causing injury to people evacuating, RFF, rupturing fuel tanks, and to the escape chutes.

By installing the eutectic plugs into the rims, the gas (normally nitrogen) can then escape from the tyre, preventing the wheel rim from failing. On Airbus aircraft the eutectic plug should change state when the hottest part of the rim reaches 205 deg C.

Anyone who has flown classic 747 would remember that could walk away from a perfectly good aircraft only to find out about an hour later that the fuse plugs blew, this was caused by heat of the brakes getting into the rim long after the aircraft landed. The steel brakes of the older generation aircraft exhibit different thermal characteristic to today’s carbon brakes.
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etherealsky
Posts: 211
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RE: A346 Rejected Take-off

Wed May 19, 2010 4:06 am

Quoting tdscanuck (Reply 7):
Quoting zeke (Reply 8):

Ah ok, thanks for the correction- there's a lot more going on there than I had realized  
Quoting zeke (Reply 8):
By installing the eutectic plugs into the rims, the gas (normally nitrogen) can then escape from the tyre, preventing the wheel rim from failing.

So once the plugs overheat and melt, how does the release of tire pressure prevent the rims from exploding? Is the main cause of an explosion simply the tire pressure stressing the circumference of the rims while they are weakened by the heat? Even without tire pressure, you've still got the entire weight of the aircraft to handle, right?
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rwessel
Posts: 2448
Joined: Tue Jan 16, 2007 3:47 pm

RE: A346 Rejected Take-off

Wed May 19, 2010 4:41 am

Quoting etherealsky (Reply 9):
So once the plugs overheat and melt, how does the release of tire pressure prevent the rims from exploding? Is the main cause of an explosion simply the tire pressure stressing the circumference of the rims while they are weakened by the heat? Even without tire pressure, you've still got the entire weight of the aircraft to handle, right?

The increase in temperature increases the pressure and weakens the rims (and the tires). At some point the rim or tire becomes unable to contain the pressure, and the tire/rim explodes.

Note that the total pressure on the rim (or the inside of the tire) is typically several times that of the weight it will bear.

Multi-piece rims as are common on large vehicles (including aircraft), have one or more mechanical joints that need to bear much of that pressure load. Those seams usually fail first (every year several people in the US are killed by the explosion caused by trying to inflate an incorrectly assembled truck wheel).

A typical automobile wheel is a single piece and cannot fail that way (although the tire can be blown off the rim by the bead failing if the pressure is high enough, that usually does not result in a lot of shrapnel).
 
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zeke
Posts: 14057
Joined: Thu Dec 14, 2006 1:42 pm

RE: A346 Rejected Take-off

Wed May 19, 2010 4:44 am

Quoting etherealsky (Reply 9):
Is the main cause of an explosion simply the tire pressure stressing the circumference of the rims while they are weakened by the heat?

Correct, the rims are normally manufactured from an Al/Mg alloy (annealing around 400 deg C, melting around 600 deg C), as they are heated, the alloy will no longer have the strength to retain the pressure.

Please note these temperature are on the rim, not in the brakes, the brakes may well reach over 600 deg C without causing the eutectic plugs to melt.

Quoting etherealsky (Reply 9):
Even without tire pressure, you've still got the entire weight of the aircraft to handle, right?

Correct, however you do not have the air pressure behind the rim then, and if it were to fail, pieces of the rim would not become projectiles.

Think of the tyre/rim assembly as a aerosol can, put a full can in a fire, it will explode, if you were to put an empty can that had a vent hole in it into a fire, it would not explode. (Please do not do this, it is just an illustration !!!)
Human rights lawyers are "ambulance chasers of the very worst kind.'" - Sky News
 
etherealsky
Posts: 211
Joined: Fri Apr 09, 2010 6:13 pm

RE: A346 Rejected Take-off

Thu May 20, 2010 2:28 am

Quoting rwessel (Reply 10):
Quoting zeke (Reply 11):

Ah ok, that makes sense now. Thanks for responding  
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