CAP2008
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What Are Aircraft Tires Inflated With?

Wed Jan 16, 2008 2:34 am

After watching the episode of Mythbusters where they were dealing with the weight of air, and replacing air with helium in certain objects to reduce weight, I wonder would inflating aircraft tires with helium, especially in a 747 or a 380 gain any significant weight advantage? I know that nitrogen is used to inflate tires in some race cars and now increasingly in passenger cars, because it does not expand or contract with temperature like air does, but what about helium?
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avt007
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RE: What Are Aircraft Tires Inflated With?

Wed Jan 16, 2008 2:36 am

Nitrogen is used in aircraft. The tire pressure does change with temperature, because it isn't a pure nitrogen atmosphere inside the tire, it is mixed with the air that was in there before inflation was started. The difference hot to cold is only a few pounds, but noticeable.
 
pilotntrng
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RE: What Are Aircraft Tires Inflated With?

Wed Jan 16, 2008 2:36 am

It is Nitrogen, I certainly am not a rocket scientist and I hated chemistry, but I can recall from my ramp rat days lookin at the tires, they called for nitrogen.
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roseflyer
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RE: What Are Aircraft Tires Inflated With?

Wed Jan 16, 2008 2:49 am



Quoting CAP2008 (Thread starter):
I know that nitrogen is used to inflate tires in some race cars and now increasingly in passenger cars, because it does not expand or contract with temperature like air does, but what about helium?

Nitrogen is used because it does not contain water vapor. Air with a very low humidity will expand and contrat the same with temperature as nitrogen does. However, nitrogen is easier to use since it guarantes that no water will condense within the tire, which can have a significant effect on the pressure in the tire. Nitrogen does expand and contract though depending on temperature. The equation PV=nRT pretty much always works as long as there isn't a phase change ie. water condensing. You don't want water in the tire.
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OPNLguy
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RE: What Are Aircraft Tires Inflated With?

Wed Jan 16, 2008 2:57 am



Quoting RoseFlyer (Reply 3):
You don't want water in the tire.

True, and to the OP, here's a perfect example of why...

http://aviation-safety.net/database/record.php?id=19860331-1
ALL views, opinions expressed are mine ONLY and are NOT representative of those shared by Southwest Airlines Co.
 
KELPkid
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RE: What Are Aircraft Tires Inflated With?

Wed Jan 16, 2008 4:52 am

Nitrogen is also used because of its fire retarding properties...a fire will not burn in pure nitrogen  Smile
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Tristarsteve
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RE: What Are Aircraft Tires Inflated With?

Wed Jan 16, 2008 11:46 am



Quoting Avt007 (Reply 1):
The difference hot to cold is only a few pounds, but noticeable.

It can be a lot more than a few lbs, a tyre that is 180psi cold can be over 210psi after a braked landing. That is why we try and measure the tyre pressures as long as possible after landing.
I work in one of the colder airports on our companies network. We are forever inflating tyres that seemed to be correct at the last nightstop down in the Med, but are now too low when the OAT is below zero.
Last week I had a write up on a B777 that they had Tyre Pressure EICAS message in the cruise. On checking on the ground the pressures were OK, but at the lower end of the range. Sitting in the nose gear bay for 11 hours at M45deg , the pressure had dropped below the warning level. I inflated them to the top of the range and the message didn't reoccur.
 
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HAWK21M
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RE: What Are Aircraft Tires Inflated With?

Wed Jan 16, 2008 5:04 pm

Nitrogen is is used mainly since it is an Inert gas.
Air can be used too for inflation,but to a certain percentage & only for a small period of time.
regds
MEL
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tdscanuck
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RE: What Are Aircraft Tires Inflated With?

Wed Jan 16, 2008 5:37 pm



Quoting CAP2008 (Thread starter):
After watching the episode of Mythbusters where they were dealing with the weight of air, and replacing air with helium in certain objects to reduce weight, I wonder would inflating aircraft tires with helium, especially in a 747 or a 380 gain any significant weight advantage?

The weight difference would be very small (on the order of ten kilograms per tire). However, you'd have an issue with greatly increased diffusion through the tire, so you'd have to be pressuring it back up more often, and I suspect helium costs a lot more than nitrogen.

Tom.
 
avt007
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RE: What Are Aircraft Tires Inflated With?

Wed Jan 16, 2008 6:19 pm



Quoting TristarSteve (Reply 6):


Quoting Avt007 (Reply 1):
The difference hot to cold is only a few pounds, but noticeable.

It can be a lot more than a few lbs,

In my experience, maybe 5% would be the most I saw, changing a nominal 101 psi tire to 106, sitting on the gate.
 
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IFixPlanes
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RE: What Are Aircraft Tires Inflated With?

Wed Jan 16, 2008 7:27 pm



Quoting HAWK21M (Reply 7):
... Air can be used too for inflation,but to a certain percentage & only for a small period of time. ...

AD 87-08-09 says:

Quote:
...
a. On braked wheels, install only tires that have been inflated with dry nitrogen or other gases shown to be inert such that the gas mixture does not exceed 5 percent oxygen by volume.

b. Tires on braked wheels may be serviced with air at remote locations where dry nitrogen is not available, provided that:

i. the oxygen content does not exceed 5 percent by volume; or

ii. within the next 15 hours time-in-service, the tire must be purged of air and inflated with dry nitrogen so that the oxygen does not exceed 5 percent by volume.

...

never tell an engineer he is wrong ;-)
 
CAP2008
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RE: What Are Aircraft Tires Inflated With?

Thu Jan 17, 2008 11:35 am

Thanks for your responses guys.
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KELPkid
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RE: What Are Aircraft Tires Inflated With?

Thu Jan 17, 2008 10:35 pm

Also, I forgot: yet another reason that pure nitrogen is used is to keep the rubber compounds in the tire from degrading prematurely...Oxygen is the primary culprit in weather checking on rubber  Wink
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EssentialPowr
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RE: What Are Aircraft Tires Inflated With?

Fri Jan 18, 2008 4:11 am



Quoting KELPkid (Reply 5):
Nitrogen is also used because of its fire retarding properties...a fire will not burn in pure nitrogen

Many pure gasses other than N are inert as well...
 
KELPkid
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RE: What Are Aircraft Tires Inflated With?

Fri Jan 18, 2008 4:24 am



Quoting EssentialPowr (Reply 13):
Many pure gasses other than N are inert as well...

However, Nitrogen is the cheapest since it comprises 80% of the Earth's atmosphere.
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rwessel
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RE: What Are Aircraft Tires Inflated With?

Fri Jan 18, 2008 5:05 am



Quoting EssentialPowr (Reply 13):
Many pure gasses other than N are inert as well...



Quoting KELPkid (Reply 14):
However, Nitrogen is the cheapest since it comprises 80% of the Earth's atmosphere.

Not only are almost all the other fairly non-reactive gasses* more expensive than N2, they're mostly all heavier as well.


*Gas at the required temperatures and pressures
 
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HAWK21M
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RE: What Are Aircraft Tires Inflated With?

Fri Jan 18, 2008 8:32 am



Quoting KELPkid (Reply 14):

Quoting EssentialPowr (Reply 13):
Many pure gasses other than N are inert as well...

However, Nitrogen is the cheapest since it comprises 80% of the Earth's atmosphere.

This is Aviation.Weight is an Issue too.

regds
MEL
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tdscanuck
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RE: What Are Aircraft Tires Inflated With?

Fri Jan 18, 2008 6:45 pm



Quoting HAWK21M (Reply 16):
Quoting KELPkid (Reply 14):

Quoting EssentialPowr (Reply 13):
Many pure gasses other than N are inert as well...

However, Nitrogen is the cheapest since it comprises 80% of the Earth's atmosphere.

This is Aviation.Weight is an Issue too.

True, but weight is an issue only to the extent that it goes to cost. If your choice is cheaper and heavier or more expensive and lighter, they'll go with cheaper. The trick is that you have to roll *all* the costs, not just acquisition, into your "cheap" and "expensive" calculations.

Tom.
 
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HAWK21M
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RE: What Are Aircraft Tires Inflated With?

Fri Jan 18, 2008 7:33 pm



Quoting Tdscanuck (Reply 17):
If your choice is cheaper and heavier or more expensive and lighter, they'll go with cheaper.

Which other gases than N2 are you referring to?
regds
MEL
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tdscanuck
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RE: What Are Aircraft Tires Inflated With?

Fri Jan 18, 2008 7:55 pm



Quoting HAWK21M (Reply 18):
Quoting Tdscanuck (Reply 17):
If your choice is cheaper and heavier or more expensive and lighter, they'll go with cheaper.

Which other gases than N2 are you referring to?

I think this started back when helium was suggested. It's inert, like N2 (at the temperatures we're talking about), but lighter. But I suspect the weight improvement isn't enough to tolerate the other expense increases.

Tom.
 
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HAWK21M
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RE: What Are Aircraft Tires Inflated With?

Sat Jan 19, 2008 7:57 am



Quoting Tdscanuck (Reply 19):
I think this started back when helium was suggested. It's inert, like N2 (at the temperatures we're talking about), but lighter. But I suspect the weight improvement isn't enough to tolerate the other expense increases

No,What I meant is....Which other Inert gas has been used in service practically apart from N2?
Im referring to non experimental basis.
regds
MEL
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ThrottleHold
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RE: What Are Aircraft Tires Inflated With?

Tue Jan 22, 2008 3:31 pm



Quoting CAP2008 (Thread starter):
What Are Aircraft Tires Inflated With?

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