Tires: Air vs Nitrogen

[Lee A.]

So for a new Mooney guy, what do you inflate your tires with?   Air or nitrogen.  

Any advantage to nitrogen?

I noticed Aircraft Spruce sells a nitrogen tank/regulator/hose kit for tire inflation.  Seems like a lot of money to air up a tire.  Am i missing something?

[smccray]

I’m partial to an 80% nitrogen mix...

[rbridges]

14 minutes ago, bluehighwayflyer said:

I view the inflate-with-nitrogen argument to be the best scam since bottled water. 

Jim

It's almost as good as the Shell gasoline with nitrogen blend for cleaner engine parts.  

[Lee A.]

Ok. Got it guys!  

That is what I was thinking.  

Wanted to double check before I purchased an air compressor for the hangar.  

[201er]

59 minutes ago, bluehighwayflyer said:

I view the inflate-with-nitrogen argument to be the best scam since bottled water. 

Jim

So are you saying we don't have to pay for air or water?? 

[R4dpilot]

nitrogen is used mainly in commercial jet tires due to the temps at altitude. Tends not to draw moisture and therefore freeze. Also used in large tires on some vintage warbirds.

[rbridges]

17 minutes ago, R4dpilot said:

nitrogen is used mainly in commercial jet tires due to the temps at altitude. Tends not to draw moisture and therefore freeze. Also used in large tires on some vintage warbirds.

My 80hp Chevy spark had it from the dealership. I laughed when the salesperson told me. 

[Mooneymite]

I was looking at new cars a year ago and noticed that "nitrogen filled tires" was the latest dealer add on.  Anywhere from $75 to $125 dealer charge.....yeah, right!  I wonder who is going to check and see if those tires are really filled with 100% Nitrogen, or just 78%.  

[Hank]

1 hour ago, 201er said:

So are you saying we don't have to pay for air or water?? 

Here, the local utility charges a very few dollars per 1000 gallons of water piped to our house. Or I can go to the store and pay $1 or more per pint ($8+ per single gallon). Read the labels, some bottled water is from municipal water supplies . . . . Scam . . .

Compressed air can be had at the gas station, a quarter will buy enough time to top off all four tires. Or buy a cheap compressor and get all the air you want for mere pennies. Or go to the tire store and pay $50, $75, even $100, to inflate your tires with nitrogen. The air we are now breathing, compressed almost for free in garages throughout my neighborhood, is ~78% nitrogen. Scam!

So no, air and water aren't "free," but they sure aren't expensive unless you make them that way!  

[MB65E]

I like N2. Bottle rental is minimal. I use it several times a week at the shop. I've only changed one bottle in 10 years. 

N2 tends to last longer in tires 

N2 is more stable.

I never need to wait for the damn air compressor to turn off.

I can wheel the bottle anyware on the airport.

I don't need AC power to fill tires.

The pressure is much higher than any air comprsssor. 

But I don't fault anyone for using compressed air. It's cheap.

-Matt

[Oldguy]

Because of the various and sundry vehicles I have and the places I use them (where does the 4 x 4 have a flat? top of the mountain at the deer lease!), I sprung for the Ryobi battery powered air compressor. I throw it in the back of the plane when I am flying just because I can. I can check my tire pressure anywhere and pump up anything I need to inflate with a single battery. Sure, it may run out of power before I get a tire fully inflated from flat, but it gives me enough to get it rolling and out of the way if need be.

[Seth]

The answer is it depends.

I currently use normal air.  Most of us who stay down low really won't benefit from all nitrogen has to offer.  Turbo airplanes operating up high often, that's a major difference.

I have a hanger neighbor who flies a K model Mooney often in the flight levels and he does indeed use nitrogen.  As stated, it's more stable, it's leaks less, it's better for cold temps of flying up high, and it is not corrosive like a mixture containing oxygen could be.

If my hanger neighbor sets up a nitrogen system in his hanger as he's threatened to do (meaning mentioned he's going to), I'm going to pay him a few bucks and switch over, and maybe for my car too

 

-Seth

 

[Hank]

19 minutes ago, Oldguy said:

Because of the various and sundry vehicles I have and the places I use them (where does the 4 x 4 have a flat? top of the mountain at the deer lease!), I sprung for the Ryobi battery powered air compressor. I throw it in the back of the plane when I am flying just because I can. I can check my tire pressure anywhere and pump up anything I need to inflate with a single battery. Sure, it may run out of power before I get a tire fully inflated from flat, but it gives me enough to get it rolling and out of the way if need be.

I have those in my car, with a long cord to run off the lighter. Works decent, but not enough volume to reseat a tire, mostly good only for a top off.

Since putting Michelin Air Stop tubes, i add air to the Mooney tires generally fall and spring only, sometimes once in summer. 

[carusoam]

So for the new guy...

1) Michelin airstop tubes keeps the N2 in pretty long... many many months...

2) Nitrogen is inert, doesn't oxidize things... yay

3) Nitrogen is a larger molecule, harder to leak out... yay

4) Bottled water... high school students insist on it.  Fortunately Costco sells it for dirt cheap! Everyone is happy.

Failed tubes are the usual cause of flats. Folded tubes or separated stems are the two leading causes of a bad day....

If you have an O2 fill station, an N2 station may make some good sense. I think I need a hangar Home...

PP ideas only, not a mechanic.

Best regards,

-a-

[N201MKTurbo]

12 minutes ago, Hank said:

I have those in my car, with a long cord to run off the lighter. Works decent, but not enough volume to reseat a tire, mostly good only for a top off.

Since putting Michelin Air Stop tubes, i add air to the Mooney tires generally fall and spring only, sometimes once in summer. 

 

[Cyril Gibb]

Air is 79% nitrogen.  Oxygen (19%) leaks out faster than nitrogen.  Each time you fill (assuming you don't empty before adding) you increase the % of nitrogen remaining.  Fill a few times and the resulting nitrogen % won't be much different than filling initially with 100% nitrogen.

I haven't had any issues with moisture from an air pump during the winter.  I'm not sure what difference high altitude cold would be over winter cold, since the cold at altitude would only be temporary anyway.  I use Camguard, so maybe that's the difference.

 

[AH-1 Cobra Pilot]

51 minutes ago, Cyril Gibb said:

Oxygen (19%) leaks out faster than nitrogen.

That is interesting.  I would have thought it would be the opposite, since O₂ has a molecular weight of 32 vs. 28 for N₂.  I always thought the selling point for pure nitrogen was the avoidance of oxidation inside the tire.

[Jerry 5TJ]

45 minutes ago, Cyril Gibb said:

Air is 79% nitrogen.  Oxygen (19%) leaks out faster than nitrogen.  Each time you fill (assuming you don't empty before adding) you increase the % of nitrogen remaining.  Fill a few times and the resulting nitrogen % won't be much different than filling initially with 100% ......

I have a Nitrogen bottle in the hangar and use it to fill tires on theory it's better to use dry N2 rather than oil and water contaminated air from an air compressor.  Besides, I had the Nitrogen already from some HVAC work.  

[EricJ]

3 hours ago, Ah-1 Cobra Pilot said:

That is interesting.  I would have thought it would be the opposite, since O₂ has a molecular weight of 32 vs. 28 for N₂.  I always thought the selling point for pure nitrogen was the avoidance of oxidation inside the tire.

The Nitrogen fill argument comes up with race cars all the time, too.   A big argument in that application is N2 doesn't expand from heat like many other gases do.   Since control of inflated pressure after the tire gets hot (from friction) is critical for handling setup, this can make a big difference.   e.g., if I'm shooting for 40psi hot pressure, I may use a 32psi cold temp expecting an 8psi rise on the track as the tire heats up.   The guy with N2 just pumps it to 40 and leaves it.  Much of the pressure increase with air is due to humidity, though, and if I pump more humid air in there than I expected and wind up with 42 or 43psi hot pressure instead (due to the expansion of the additional water),  I may have just given myself a significant disadvantage.    Some of us just use driers on our compressors and not worry about it too much.

For CB racers that store their race tires inflated, the O2 migration (from the inside to the outside) will slowly harden the rubber compound of the tire (which results in less grip).   On an airplane, especially with tubed tires, I don't see this as an issue.   Airplane tires make very little grip compared to a race tire (and GA airplane brakes suck), so I don't think the difference would be noticeable to anybody.   CB racers that are more serious just store their tires deflated to avoid this.

I seem to remember reading that the SR-71 had N2-filled tires for the same reason.   With a target pressure over 400psi they didn't want the tire pressures to go up and risk a blowout as the airframe and tires heated up at cruise.   Very large, heavy airplanes with big tires may have tighter tolerances on desired tire pressure, and using N2 would help reduce the tire temperature as a variable for target tire pressure.

I don't think any of these issues are much of a concern for GA aircraft, but N2 fills certainly don't hurt anything.   If you check your tire pressures reasonably regularly, or at least do a visual inflation check, you're probably already getting the same advantage that an N2 fill might give.   And N2 won't really make much difference on leaks.   With tubed tires, I don't know how it would have anything to do with corrosion, either.

Just my dos centavos.   It is just interesting to me how this keeps coming up in different places.   I'm sad for the people who get talked into paying extra to get N2 in their car tires.

[kortopates]

The Nitrogen fill argument comes up with race cars all the time, too.   A big argument in that application is N2 doesn't expand from heat like many other gases do.   Since control of inflated pressure after the tire gets hot (from friction) is critical for handling setup, this can make a big difference.   e.g., if I'm shooting for 40psi hot pressure, I may use a 32psi cold temp expecting an 8psi rise on the track as the tire heats up.   The guy with N2 just pumps it to 40 and leaves it.  Much of the pressure increase with air is due to humidity, though, and if I pump more humid air in there than I expected and wind up with 42 or 43psi hot pressure instead (due to the expansion of the additional water),  I may have just given myself a significant disadvantage.    Some of us just use driers on our compressors and not worry about it too much.
For CB racers that store their race tires inflated, the O2 migration (from the inside to the outside) will slowly harden the rubber compound of the tire (which results in less grip).   On an airplane, especially with tubed tires, I don't see this as an issue.   Airplane tires make very little grip compared to a race tire (and GA airplane brakes suck), so I don't think the difference would be noticeable to anybody.   CB racers that are more serious just store their tires deflated to avoid this.
I seem to remember reading that the SR-71 had N2-filled tires for the same reason.   With a target pressure over 400psi they didn't want the tire pressures to go up and risk a blowout as the airframe and tires heated up at cruise.   Very large, heavy airplanes with big tires may have tighter tolerances on desired tire pressure, and using N2 would help reduce the tire temperature as a variable for target tire pressure.
I don't think any of these issues are much of a concern for GA aircraft, but N2 fills certainly don't hurt anything.   If you check your tire pressures reasonably regularly, or at least do a visual inflation check, you're probably already getting the same advantage that an N2 fill might give.   And N2 won't really make much difference on leaks.   With tubed tires, I don't know how it would have anything to do with corrosion, either.
Just my dos centavos.   It is just interesting to me how this keeps coming up in different places.   I'm sad for the people who get talked into paying extra to get N2 in their car tires.

So how does N2 violate the basic laws of physics i.e. Boyles Gas Laws where PV=nRT ??


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[mooniac15u]

28 minutes ago, EricJ said:

The Nitrogen fill argument comes up with race cars all the time, too.   A big argument in that application is N2 doesn't expand from heat like many other gases do.   Since control of inflated pressure after the tire gets hot (from friction) is critical for handling setup, this can make a big difference.   e.g., if I'm shooting for 40psi hot pressure, I may use a 32psi cold temp expecting an 8psi rise on the track as the tire heats up.   The guy with N2 just pumps it to 40 and leaves it.  Much of the pressure increase with air is due to humidity, though, and if I pump more humid air in there than I expected and wind up with 42 or 43psi hot pressure instead (due to the expansion of the additional water),  I may have just given myself a significant disadvantage.    Some of us just use driers on our compressors and not worry about it too much.

For CB racers that store their race tires inflated, the O2 migration (from the inside to the outside) will slowly harden the rubber compound of the tire (which results in less grip).   On an airplane, especially with tubed tires, I don't see this as an issue.   Airplane tires make very little grip compared to a race tire (and GA airplane brakes suck), so I don't think the difference would be noticeable to anybody.   CB racers that are more serious just store their tires deflated to avoid this.

I seem to remember reading that the SR-71 had N2-filled tires for the same reason.   With a target pressure over 400psi they didn't want the tire pressures to go up and risk a blowout as the airframe and tires heated up at cruise.   Very large, heavy airplanes with big tires may have tighter tolerances on desired tire pressure, and using N2 would help reduce the tire temperature as a variable for target tire pressure.

I don't think any of these issues are much of a concern for GA aircraft, but N2 fills certainly don't hurt anything.   If you check your tire pressures reasonably regularly, or at least do a visual inflation check, you're probably already getting the same advantage that an N2 fill might give.   And N2 won't really make much difference on leaks.   With tubed tires, I don't know how it would have anything to do with corrosion, either.

Just my dos centavos.   It is just interesting to me how this keeps coming up in different places.   I'm sad for the people who get talked into paying extra to get N2 in their car tires.

Nitrogen changes pressure with temperature just like all other gases. 

[EricJ]

16 minutes ago, kortopates said:

So how does N2 violate the basic laws of physics i.e. Boyles Gas Laws where PV=nRT ??


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That's for ideal gases.     ...edited to reduce potential confusion a bit...    

 

4 minutes ago, mooniac15u said:

Nitrogen changes pressure with temperature just like all other gases. 

Not as much.   Non-ideal gases behave to (approximately):

PV=znRT

where z is the compressibility factor.   N2 has a favorable Z.

I think it is used in airliners due to the extreme temperature change possible under heavy braking.   If you've ever seen the vids of the destructive brake testing that Boeing does, letting the tire last a bit longer before it explodes is a safety advantage.   I don't see it as an issue on a GA airplane.

 

Edited October 21, 2017 by EricJ

[mooniac15u]

4 hours ago, Ah-1 Cobra Pilot said:

That is interesting.  I would have thought it would be the opposite, since O₂ has a molecular weight of 32 vs. 28 for N₂.  I always thought the selling point for pure nitrogen was the avoidance of oxidation inside the tire.

O2 has a higher molecular weight but a slightly smaller molecular radius. 

[mooniac15u]

5 minutes ago, EricJ said:

That's for ideal gases.     ...edited to reduce potential confusion a bit...    

 

Not as much.   Non-ideal gases behave to (approximately):

PV=znRT

where z is the compressibility factor.   N2 has a favorable Z.

I think it is used in airliners due to the extreme temperature change possible under heavy braking.   If you've ever seen the vids of the destructive brake testing that Boeing does, letting the tire last a bit longer before it explodes is a safety advantage.   I don't see it as an issue on a GA airplane.

 

Conpressibility factor is not significant for either nitrogen or oxygen as both are non-polar and non-associating. The ideal gas law provides a reasonable representation of how they behave under temperature changes. 

[EricJ]

Just now, mooniac15u said:

Conpressibility factor is not significant for either nitrogen or oxygen as both are non-polar and non-associating. The ideal gas law provides a reasonable representation of how they behave under temperature changes. 

Any thoughts on why high-temp apps tend to use N2 in tires?     One thought I've heard is it's easier to keep N2 dry, but I don't know if that's even the motivator.