Nitrogen?
Joined: Mar 2000
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From: Bothell WA
Air has a certain moisture content and it is generally very hard to remove this moisture. If an airplane tires were filled with air, at the flight altitude ice would form inside the tires since the temp up there is about -55 degrees C. Landing with a chunk of ice in the tire would make it out of balance and change the tire pressure. Tires would probably burst.
On the other hand, nitrogen doesn't form a liquid till -173C and pure nitrogen has almost no moisture.
In addition, consider if the brakes overheat and cause a fire. The nitrogen will not burn, but air has oxygen which will feed the fire. Jet airline tires are fused. When the fuse is heated it deflates the tire so they don't explode.
. .The huge tires on aircraft are expensive, and difficult to mount and dismount. They are also subjected to tremendous forces on landing when they must accelerate very quickly. The friction on touch-down creates great heat within the tires and produces very high stresses in the walls of the carcass.
Therefore, every effort is made to reduce or eliminate the deterioration caused over time by oxidation.
Since normal atmospheric air is approximately 20% oxygen, the tires are inflated with 100% nitrogen - a relatively inert gas.
On the other hand, nitrogen doesn't form a liquid till -173C and pure nitrogen has almost no moisture.
In addition, consider if the brakes overheat and cause a fire. The nitrogen will not burn, but air has oxygen which will feed the fire. Jet airline tires are fused. When the fuse is heated it deflates the tire so they don't explode.
. .The huge tires on aircraft are expensive, and difficult to mount and dismount. They are also subjected to tremendous forces on landing when they must accelerate very quickly. The friction on touch-down creates great heat within the tires and produces very high stresses in the walls of the carcass.
Therefore, every effort is made to reduce or eliminate the deterioration caused over time by oxidation.
Since normal atmospheric air is approximately 20% oxygen, the tires are inflated with 100% nitrogen - a relatively inert gas.
Joined: Nov 2001
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From: Near LGW
seem to remember only braked wheels require nitrogen ... nose wheels probably can be pumped up with air if reqd ... [quote] <hr></blockquote>and there was me thinking that I was at the centre of the universe ..!
Joined: Nov 2001
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From: LSZH
An other gas which outperforms nitrogen and can be used for aircraft tires is sulfuric hexafluoride, i.e. SF6. The molecule is huge compared to nitrogen and leakage rate is extremely low. An other big advantage of SF6 is the excellent extinguishing performance in case of fire.. .However, since SF6 is a global warming gas, its use will be quite limited in the future.. .SF6-gas is also used in gas-insulated switchgear for electrical high voltage insulation applications and in the sport shoe markets, e.g. nike air cushions are filled with SF6.
Cheers
CB
Cheers
CB
Joined: Aug 2000
Posts: 65
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From: Dubai, United Arab Emirates
Not sure I fully agree with TR4A's comments about freezing at altitude, the thickness of the tyre wall would prevent the onset of any freezing inside the tyre. The tyre would have to cold soak for many many hours to have any appreciable effect on the inside temperature of the tyre, this can be confirmed by a glance at the tyre pressure page on the EICAS/ECAM during a long haul flight, the temperature ( and pressure ) drop is marginal. Many manuals allow a tyre to be filled with air as a ' get you home ' measure until the tyre can be purged and refilled with N2.
Joined: Aug 2000
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From: Dubai, United Arab Emirates
Yes Redtail, you are correct. It was a DC8 super 60 series owned, I think, by the now defunct Canadian charter airline, Nationair. It burst an underinflated wheel that had been inflated with air taking off from Jeddah on a Haj charter in 19XX ? The gear was retracted when the overheated wheel rim split and burst through the pressure floor causing control cable loss and a subsequent fire. All on board perished when the aircraft crashed about 2 kms short of it's return approach . . . .
Joined: Apr 2000
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From: USA
I thought so, thanks for reminding me. We had to watch a training film long ago, for reasons I forget, and that was one of the examples. The flight engineer had a warning lights for various systems, but kept telling the other crew members that "It's ok, it's ok". There was also some other instances. The FAA tends to react slowly sometimes.
Joined: Mar 2000
Posts: 8,571
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From: Arizona USA
Nitrogen is also used in the landing gear strut to avoid corrosion. Very high pressures indeed, especially when the strut is compressed.. .SV had an incident with the TriStar, when after a very long taxi and takeoff, one of the main gear wheels burst, disabling three of the four hydraulic systems and the aircraft landed at Doha with only half of 'D' system remaining.. .The idea of..treat your copilot with respect...comes to mind as in the TriStar with only 'D' system remaining....only the First Officer has control.
Iconoclast
Joined: Sep 2000
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From: The home of Dudley Dooright-Where the lead dog is the only one that gets a change of scenery.
Here is a story in an allied vein and deals with gasses and what they are used for.
Many years ago on an USAF fighter base a mechanic sent a compressed gas cylinder to tech supply for filling. The bottle was painted black and gray and was stenciled indicating it was for nitrogen gas only. The bottle although being used for nitrogen gas was stamped on the neck for oxygen service only. In order to allow an oxygen bottle to be used for nitrogen service the technician had to cobble up a bunch of fittings to allow the oxygen bottle that had left hand threads to be able to connect to a nitrogen charging system that had right hand threads. The accompanying paper work requested that the bottle be charged with 2200-psi nitrogen. When the technician at tech supply received the bottle he obviously disregarded the color coding of the bottle and the stencil as well as the accompanying paperwork and zeroed in on the stamping on the bottle neck which stated for oxygen service only. He then cobbled up several fittings, which would allow connecting of the oxygen supply cylinder, which had left hand threads to the bottle, which had right hand threaded fittings. The bottle was charged and returned to the originating technician.
The originating technician attached a charging line and a set of pressure gages and proceeded to inflate a nose gear strut on an F-86. When the oxygen hit the hydraulic fluid it exploded killing the technician and starting a fire that nearly wiped out a whole squadron of F-86 aircraft in the aircraft hangar.
The following question begs answering. Who was wright and who was rong?
[ 18 February 2002: Message edited by: Lu Zuckerman ]
[ 18 February 2002: Message edited by: Lu Zuckerman ]</p>
Many years ago on an USAF fighter base a mechanic sent a compressed gas cylinder to tech supply for filling. The bottle was painted black and gray and was stenciled indicating it was for nitrogen gas only. The bottle although being used for nitrogen gas was stamped on the neck for oxygen service only. In order to allow an oxygen bottle to be used for nitrogen service the technician had to cobble up a bunch of fittings to allow the oxygen bottle that had left hand threads to be able to connect to a nitrogen charging system that had right hand threads. The accompanying paper work requested that the bottle be charged with 2200-psi nitrogen. When the technician at tech supply received the bottle he obviously disregarded the color coding of the bottle and the stencil as well as the accompanying paperwork and zeroed in on the stamping on the bottle neck which stated for oxygen service only. He then cobbled up several fittings, which would allow connecting of the oxygen supply cylinder, which had left hand threads to the bottle, which had right hand threaded fittings. The bottle was charged and returned to the originating technician.
The originating technician attached a charging line and a set of pressure gages and proceeded to inflate a nose gear strut on an F-86. When the oxygen hit the hydraulic fluid it exploded killing the technician and starting a fire that nearly wiped out a whole squadron of F-86 aircraft in the aircraft hangar.
The following question begs answering. Who was wright and who was rong?
[ 18 February 2002: Message edited by: Lu Zuckerman ]
[ 18 February 2002: Message edited by: Lu Zuckerman ]</p>
Union Goon
Joined: Feb 2000
Posts: 1,097
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From: New Jersey, USA
Redtail,
Its okay Its Okay was the Saudia L1011 with the cabin fire that burned up killing all 400 or so people on it. The captain was singing and the engineer had THICK glasses and they didnt stop the jet quickly, instead they taxied the whole length of the runway with the fire trucks chasing them. They never depressurized so they couldn't get the door open. All lost aboard after a successful if deliberate return to the airfield by severe mishandling of the A/C by the captain...
Cheers. .Wino
Its okay Its Okay was the Saudia L1011 with the cabin fire that burned up killing all 400 or so people on it. The captain was singing and the engineer had THICK glasses and they didnt stop the jet quickly, instead they taxied the whole length of the runway with the fire trucks chasing them. They never depressurized so they couldn't get the door open. All lost aboard after a successful if deliberate return to the airfield by severe mishandling of the A/C by the captain...
Cheers. .Wino
Joined: Aug 2001
Posts: 28
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From: UK
It is an AD requirement that Transport Aircraft tyres are filled with Nitrogen only!! Should be a placard of each landing geat leg. And yes SV had a tyre blow out not related to the item above, took the floor out of the a/c and I believe a row of seats c/w pax sitting on them...not the best thing to happen.
Joined: Sep 2000
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Well can't speak for F1, but certainly use nitrogen on my mates race car, much less pressure fluctuation between hot and cold pressures. With air we were inflating to about 20 psi cold for a hot pressure of about 30 psi. Reduced down to about 25 psi for a hot pressure of 30 psi with nitrogen. we do have to deal with contaminants though, as trundling around a nitrogen cylinder to club racing events is not seen as terribly good form <img src="wink.gif" border="0"> , so mionr adjustments are made with air. In fact we just popped down to a Halfords garage, where they will purge and replace with dry nitrogen for £1 a tyre
Joined: Sep 2001
Aviation Qualifications: CPL
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From: Toronto
There were two L1011 accidents in the Arabian peninsula around that time.
In one case the tire burst in the wheel well and occupants were ejected (one or more children among them), but the a/c landed safely with the remaining passengers.
In the other case, a cabin fire was reported and all occupants died after a successful landing as described. Discussion at the time indicated that hajj pax have a tendency to light up a camp stove and brew up in the aisles. Carry extra extinguishers.
In one case the tire burst in the wheel well and occupants were ejected (one or more children among them), but the a/c landed safely with the remaining passengers.
In the other case, a cabin fire was reported and all occupants died after a successful landing as described. Discussion at the time indicated that hajj pax have a tendency to light up a camp stove and brew up in the aisles. Carry extra extinguishers.