Why nitrogen?

"Viperdoc" wrote in message
...
...

Need to see the aging data on rubber kept in air versus nitrogen.


I've seen it at work, fwiw. Some difference.

But, for car tires, I would say there is more hype than benefit.

--
Geoff
The Sea Hawk at Wow Way d0t Com
remove spaces and make the obvious substitutions to reply by mail
When immigration is outlawed, only outlaws will immigrate.

I don't know whether nitrogen alone versus plain old air would make that
much difference in supporting a fire. As I recall, the heavies have blow out
plugs in case of a hot brake, so the plug melts and lets the air (nitrogen)
out before the tire blows.

On our base they fill the KC-135 tires in a big steel mesh cage- kind of a
reminder of what could happen if it let go.

Reminds me of the time a line guy in a local airport filled the air bottle
for a Vendenyev engine (they use an air start and not an electrical starter)
with oxygen rather than compressed air. The resulting fire burned up the
whole plane. The initial start-up must have been something to watch-
ignition on, engage starter, two blades, .... then kaboom!

At least it was in a Wilga, and not an aerobatic plane. It was the aviation
equivalent of Darwinism- ridding the world of ugly airplanes.

"Viperdoc" wrote in
:

I don't know whether nitrogen alone versus plain old air would make
that much difference in supporting a fire. As I recall, the heavies
have blow out plugs in case of a hot brake, so the plug melts and lets
the air (nitrogen) out before the tire blows.

That's right. they do, but they can and do catch fire as well.

On our base they fill the KC-135 tires in a big steel mesh cage- kind
of a reminder of what could happen if it let go.

Reminds me of the time a line guy in a local airport filled the air
bottle for a Vendenyev engine (they use an air start and not an
electrical starter) with oxygen rather than compressed air. The
resulting fire burned up the whole plane. The initial start-up must
have been something to watch- ignition on, engage starter, two blades,
.... then kaboom!


wow!


At least it was in a Wilga, and not an aerobatic plane. It was the
aviation equivalent of Darwinism- ridding the world of ugly airplanes.


So, the O2 fueled an already existing fire or caused it?


Bertie

"Capt. Geoffrey Thorpe" The Sea Hawk @See My Sig.com wrote in
:

"Viperdoc" wrote in message
...
...

Need to see the aging data on rubber kept in air versus nitrogen.


I've seen it at work, fwiw. Some difference.

But, for car tires, I would say there is more hype than benefit.


Used to put it in the tires of my light plane, mostly because it was free.
I flew off grass and reckoned they'd rot before I wore them out anyway, so
I might as well get the most bang for the buck out of the tires.


Bertie

So, the O2 fueled an already existing fire or caused it?


I suspect that pumping the oxygen into the system somehow started the fi
it probably is a new definition for the term "hot start"

On Sep 16, 8:20*am, a wrote:
On Sep 15, 6:09*pm, "Viperdoc" wrote:

The thread on brakes raised a question from the past- why nitrogen in the
tires of big jets and heavies? Air is around 78% nitrogen anyway, and the
coefficient of expansion of the remaining 20% that's oxygen can't make that
much difference in volume.

Why not just use dry air? I couldn't imagine that dry air or dry nitrogen
could make that much difference in corrosion, either.

I seem to recall someone giving me the rationale for this a long time ago,
but also seem to remember thinking it didn't make that much sense at the
time.

The legend is that *the oxygen is reacting with the rubber. Even
though compressed air has the same fraction of oxygen as does the
atmosphere, the fact that it's compressed, it's been argued, increases
its reactivity. I can't validate the legend.

Thats is not a legend its a fact rubber is very prone to oxidation
which is why it contains chemical antioxidants, and the reactivity
will be proportional to the concentration , ie pressure of the
oxygen. I am not however saying that is the only reason otherwise why
dont we put nitrogen in our car tyres.
Terry

On Sep 16, 8:25*am, a wrote:
On Sep 15, 6:20*pm, a wrote:





On Sep 15, 6:09*pm, "Viperdoc" wrote:

The thread on brakes raised a question from the past- why nitrogen in the
tires of big jets and heavies? Air is around 78% nitrogen anyway, and the
coefficient of expansion of the remaining 20% that's oxygen can't make that
much difference in volume.

Why not just use dry air? I couldn't imagine that dry air or dry nitrogen
could make that much difference in corrosion, either.

I seem to recall someone giving me the rationale for this a long time ago,
but also seem to remember thinking it didn't make that much sense at the
time.

The legend is that *the oxygen is reacting with the rubber. Even
though compressed air has the same fraction of oxygen as does the
atmosphere, the fact that it's compressed, it's been argued, increases
its reactivity. I can't validate the legend.

I got curious, did a quick check. The process also reduces water
vapor, and N2 does not migrate through the rubber as fast as does O2,
so pressure stays more predictable. So it's more consistent tire
pressure, less corrosion.- Hide quoted text -

Dont see why it would reduce water vapour, dry air has no more water
than dry nitrogen. and migration or porosity is a function of
molecular size. There is not much difference between nitrogen MW 28
and Oxygen MW 32.
Terry

"Viperdoc" wrote
I suspect that pumping the oxygen into the system somehow started the
fi it probably is a new definition for the term "hot start"

In that engine, the compressed air is injected into the top of the
cylinders by an air distributor at about the same time as the spark
is fired. (it also has a "shower of sparks" system)
This sometimes results in the engine firing (and starting) before it
seems like it even turns.

In the YAK-52, the compressed air also operates the retractable gear,
the flaps and the brakes.

Bob Moore

On Sep 16, 6:39*pm, terry wrote:
On Sep 16, 8:25*am, a wrote:



On Sep 15, 6:20*pm, a wrote:

On Sep 15, 6:09*pm, "Viperdoc" wrote:

The thread on brakes raised a question from the past- why nitrogen in the
tires of big jets and heavies? Air is around 78% nitrogen anyway, and the
coefficient of expansion of the remaining 20% that's oxygen can't make that
much difference in volume.

Why not just use dry air? I couldn't imagine that dry air or dry nitrogen
could make that much difference in corrosion, either.

I seem to recall someone giving me the rationale for this a long time ago,
but also seem to remember thinking it didn't make that much sense at the
time.

The legend is that *the oxygen is reacting with the rubber. Even
though compressed air has the same fraction of oxygen as does the
atmosphere, the fact that it's compressed, it's been argued, increases
its reactivity. I can't validate the legend.

I got curious, did a quick check. The process also reduces water
vapor, and N2 does not migrate through the rubber as fast as does O2,
so pressure stays more predictable. So it's more consistent tire
pressure, less corrosion.- Hide quoted text -

Dont see why it would reduce water vapour, dry air has no more water
than dry nitrogen. and migration or porosity is a function of
molecular size. *There is not much difference between nitrogen MW 28
and Oxygen MW 32.
Terry- Hide quoted text -

- Show quoted text -

OK , I will stand corrected, on the porosity, the proper word was
permeation and nitrogen is actuallly a larger molecule than oxygen
despite its lower molecular weight. Attached link is a really good
explanation ..from an expert. oxygen does permeate 3 to 4 times
faster through rubber. I guess leakage through the tire would occur
even faster in an aircraft tire at altitude due to the driving force
of the pressure differential. But still not convinced if its the
primary reason.. I think I am leaning towards the fire risk. Anyways
its a very interesting aviation topic.
Terry
http://www.getnitrogen.org/pdf/graham.pdf

a wrote:
On Sep 15, 6:20 pm, a wrote:
On Sep 15, 6:09 pm, "Viperdoc" wrote:

The thread on brakes raised a question from the past- why nitrogen in the
tires of big jets and heavies? Air is around 78% nitrogen anyway, and the
coefficient of expansion of the remaining 20% that's oxygen can't make that
much difference in volume.
Why not just use dry air? I couldn't imagine that dry air or dry nitrogen
could make that much difference in corrosion, either.
I seem to recall someone giving me the rationale for this a long time ago,
but also seem to remember thinking it didn't make that much sense at the
time.
The legend is that the oxygen is reacting with the rubber. Even
though compressed air has the same fraction of oxygen as does the
atmosphere, the fact that it's compressed, it's been argued, increases
its reactivity. I can't validate the legend.

I got curious, did a quick check. The process also reduces water
vapor, and N2 does not migrate through the rubber as fast as does O2,
so pressure stays more predictable. So it's more consistent tire
pressure, less corrosion.

We bought a new Toyota and the salesman stated the tires were filled
with N2 since the molecule was larger and less corrosive than air which
contained O2. Now, how easy is it to find N2 around town. I can take it
to the airport where the mechanic has a tank. But, all the years of
owning a car, I never seem to really have a problem with tires going
down that quick. At the 3K oil changes they top them off anyway. I did
buy a small compressor for the hangar, but never really used it that
much. I have a couple of bikes that I have to air up before each ride.
Those tires really loose pressure. I brought the compressor home.

--

Regards, Ross
C-172F 180HP
KSWI