Compressed Air Instead of Nitrogen in Gear Strut?

I get a kick out of automotive shops that sell N for tires and tell ya it's because O2 will leak out through the rubber.

I asked one of them if that meant if I kept refilling with regular air if the tire would act like a sieve and over time I would end up with all N after slowly replacing the lost O.

He stood there with his mouth open.
 
denverpilot said:
I get a kick out of automotive shops that sell N for tires and tell ya it's because O2 will leak out through the rubber.

I asked one of them if that meant if I kept refilling with regular air if the tire would act like a sieve and over time I would end up with all N after slowly replacing the lost O.

He stood there with his mouth open.
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As you well know, the real justification for N2 in auto tires:

Benefits of Nitrogen Inflation - DEALER
New Revenue Stream
• New, trendy technology
• High profit margin
• Payback in 2-3 months
• <1 month
• Increase average ticket size​
http://www.dealersedge.com/Media/E-CommerceProductCatalog/DCF3.pdf
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Dunn Tire charges $5 per tire. So far one store in two months sold more than 1,100 nitrogen fill-ups, which adds up to about $5,500. Mr. O’Neill added that the fill-ups will pay for the equipment in a “very short period of time.”
Dunn Tire views nitrogen as an “add-on” service—one that merits the extra revenue. In his personal opinion, Mr. O’Neill said dealers should definitely charge, especially since they pay a hefty investment for the equipment.
“The industry has worked on such low margins over the last 30 years, we have to have an opportunity to be able to improve our profitability,” he told Tire Business.
“(Nitrogen) gives us the opportunity to do that. We’re selling something that’s an extra.”
http://www.getnitrogen.org/pdf/print_articles/Tire Business - N2 Inflation Good Move.pdf
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gismo said:
Methinks that's gonna be the case with the strut "fully extended" whether or not the wheel is touching the ground.:D
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I got that, but just wanted to be sure it was clear to whoever might be reading :)

Nitrogen is used because
It has less water and will not expand/contract as much as shop air with temperature changes

It also ised because nitrogen will be slower to leak through seals

And finally, it is non corrosive
 
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Is it ok if I fill mine with helium?
A dry inert gas, I believe it makes my airplane lighter than if I was using air or Nitrogen.
 
Hindenburg comes to mind.

No wait; that was hydrogen. I will go back to sleep now.
 
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dell30rb said:
Nitrogen is used because
It has less water and will not expand/contract as much as shop air with temperature changes

It also used because nitrogen will be slower to leak through seals
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Do you have a reference for those statements? I believe they are wrong.
 
Tom-D said:
Do you have a reference for those statements? I believe they are wrong.
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The only reference that matters, the CRC handbook, would make it pretty clear that you are right that he is wrong.
 
I thought they used nitrogen so you could get those cute green valve stem caps. The caps on my struts are yellow what the hale do I put in those???

There is plenty of yellow snow outside my hangar, thanks Matt.
 
From a 1976 Cessna 182 POH section 8-11:

NOSE GEAR SHOCK STRUT -- Keep filled with MIL-H-5606 hydraulic fluid and inflated with air to 55-60 PSI
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"Nitrogen in your tires?"
"Just the 78% mix, please"
"Huh?"
 
Glad to contribute! :rofl:

tmyers said:
I thought they used nitrogen so you could get those cute green valve stem caps. The caps on my struts are yellow what the hale do I put in those???

There is plenty of yellow snow outside my hangar, thanks Matt.
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Silvaire said:
From a 1976 Cessna 182 POH section 8-11:
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Good! Thus, the designers expected that air, replete with oxygen and humidity, would be present and considered that.
 
Tom-D said:
Do you have a reference for those statements? I believe they are wrong.
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#1 is common industry knowledge. I used to build/valve/tune suspension for motocross bikes, and the rear shocks are bled of all air and the fluid is put under pressure by filling a bladder (some have a cylinder with a piston) with nitrogen to 175psi. After a few hot laps those shocks get real hot. Air is a no-no in these shocks because the shocks frequently get heated to over 200 degrees, and the water vapor in the air will result in a more significant pressure increase with air than with nitrogen.

Its common knowledge that nitrogen is less reactive than oxygen, and also being free of water vapor contributes to a less corrosive environment. I can validate this first hand. Motorcycle forks contain air at atmospheric pressure when unloaded. (nitrogen not necessary, they dont heat up like shocks due to surface area) I've torn down a lot of old forks to find corrosion on the inside of the fork tubes, in the upper areas of the fork that fluid does not cover when the fork is sitting unused. I've never seen corrosion in a nitrogen filled shock.

Because aircraft do a lot of sitting, i'd imagine the inside of the upper areas of the oleos can see corrosion. Any of you A&P's able to comment on this?

As for the claim that nitrogen does not leak past rubber as quickly, my only source I have is the claim from tire-fillers that nitrogen leaks out slower than air.

This is validated by consumer reports, they filled 30 tires with air and 30 with nitrogen. The claim is validated but in a daily driver car the difference appears negligible.

The average loss of air-filled tires was just 3.5 psi from the initial 30 pressure setting. Nitrogen-filled tires lost an average of 2.2 psi from the initial 30 psi setting.
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JHW said:
It's simple. Someone who wanted to charge him for a squirt of N2 told him that.
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I don't fill my tires with nitrogen.

I could if I wanted to, I have access to all the compressed nitrogen I could want at work.
 
dell30rb said:
#1 is common industry knowledge. I used to build/valve/tune suspension for motocross bikes, and the rear shocks are bled of all air and the fluid is put under pressure by filling a bladder (some have a cylinder with a piston) with nitrogen to 175psi. After a few hot laps those shocks get real hot. Air is a no-no in these shocks because the shocks frequently get heated to over 200 degrees, and the water vapor in the air will result in a more significant pressure increase with air than with nitrogen.

Its common knowledge that nitrogen is less reactive than oxygen, and also being free of water vapor contributes to a less corrosive environment. I can validate this first hand. Motorcycle forks contain air at atmospheric pressure when unloaded. (nitrogen not necessary, they dont heat up like shocks due to surface area) I've torn down a lot of old forks to find corrosion on the inside of the fork tubes, in the upper areas of the fork that fluid does not cover when the fork is sitting unused. I've never seen corrosion in a nitrogen filled shock.

Because aircraft do a lot of sitting, i'd imagine the inside of the upper areas of the oleos can see corrosion. Any of you A&P's able to comment on this?

As for the claim that nitrogen does not leak past rubber as quickly, my only source I have is the claim from tire-fillers that nitrogen leaks out slower than air.

This is validated by consumer reports, they filled 30 tires with air and 30 with nitrogen. The claim is validated but in a daily driver car the difference appears negligible.
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I do 3 to 4 nose struts rebuilds per year, I never see the corrosion you speak of.
The main reason the struts leaks is the seals are old hard and worn by dirt debris collected in side the strut making the hydraulic fluid a grinding compound.
the dirt gets into the strut because pilots and owners will not keep the struts clean, so the dirt clings to the chrome and wears the brass scraper and enters the strut, this grinding action causes the chrome to wear, and start pitting, this pitting will accelerate the leaking problem by cutting away the rubber seals, and the alignment bushing in the lower portion of the struts.
Using N2 in struts will not add 10 minutes to the life of a strut, simply because it will fail due to other problems first.
 
Tom-D said:
I do 3 to 4 nose struts rebuilds per year, I never see the corrosion you speak of.
The main reason the struts leaks is the seals are old hard and worn by dirt debris collected in side the strut making the hydraulic fluid a grinding compound.
the dirt gets into the strut because pilots and owners will not keep the struts clean, so the dirt clings to the chrome and wears the brass scraper and enters the strut, this grinding action causes the chrome to wear, and start pitting, this pitting will accelerate the leaking problem by cutting away the rubber seals, and the alignment bushing in the lower portion of the struts.
Using N2 in struts will not add 10 minutes to the life of a strut, simply because it will fail due to other problems first.
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In GA applications, I also can't envision strut temperatures getting to the point of converting any water condensation to steam, unless someone REALLY porpoises their spam can down the entire length of a 9000' runway. ;)
 
dell30rb said:
I got that, but just wanted to be sure it was clear to whoever might be reading :)
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I figured you knew:D. However...

Nitrogen is used because
It has less water and will not expand/contract as much as shop air with temperature changes

It also ised because nitrogen will be slower to leak through seals
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I'm afraid that is pretty much BS. First of all ALL gasses obey Boyle's law
(constant volume pressure is proportional to temperature). There is some potential for a slight pressure rise as the water content changes phase but the effect is small and the air inside tires doesn't generally reach the boiling point (250-280°F).

And finally, it is non corrosive
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While this has some technical merit, I'd be surprised if internal corrosion of Oleo struts was a significant issue.
 
gismo said:
I'm afraid that is pretty much BS. First of all ALL gasses obey Boyle's law
(constant volume pressure is proportional to temperature). There is some potential for a slight pressure rise as the water content changes
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Its really more than slight. There is a reason every performance motorcycle shock i can think of since the mid 80's is filled with nitrogen. There is a reason all racing teams use nitrogen in their tires. Nitrogen is used in the tires and struts of airliners as well.

The big thing is simply that nitrogen is free of water vapor. Its also inexpensive. I can buy a fill of a large T cylinder for $11 from Praxair.

We use nitrogen to vent high-vacuum plasma chambers instead of compressed air. Why? Because it takes forever to pump down for the next cycle if we use the shop compressor and put all that water into the chamber.

Is it necessary for the strut of your piper warrior? No
 
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Keeping struts filled in a Cherokee has always been a PITA. Even getting them rebuilt is tricky as the a&p assembles them incorrectly half the time.

If Nitrogen is available and free I use it, if not I use air.

I really see no difference. Mechanic says nitrogen leaks less, ok maybe I expect less leakage but I really don't know if that is right or not.

This thread is quickly becoming overkill for the topic and nothing more than a ****ing contest. Someone is right, I do not know who. Doesn't really matter I guess.
 
denverpilot said:
I get a kick out of automotive shops that sell N for tires and tell ya it's because O2 will leak out through the rubber.

I asked one of them if that meant if I kept refilling with regular air if the tire would act like a sieve and over time I would end up with all N after slowly replacing the lost O.

He stood there with his mouth open.
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:rofl::rofl::rofl: excellent!
 
dell30rb said:
I don't fill my tires with nitrogen.

I could if I wanted to, I have access to all the compressed nitrogen I could want at work.
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My favorite tire change was on tractors. Mount the tire and ring, spray in an entire can of starting fluid and throw a match and WOOMP, the bead is seated, pressure the tire with a propane tank.:rofl::rofl::rofl: Gotta love farmers.:D
 
dell30rb said:
Its really more than slight. There is a reason every performance motorcycle shock i can think of since the mid 80's is filled with nitrogen. There is a reason all racing teams use nitrogen in their tires.
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Some use Argon...;)
 
Tell you guys what, call Rapid and price a set of struts for a Duchess,

Report back with your findings and recommendations on how often you are willing to service them.


I'll go ahead and tell you, a few years ago when I priced a set they were $9,900 each for the mains, non field reparable.:mad2:
 
OK,Once I've decided between air or nitrogen, where do I hook the hose?
 

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Skylane81E said:
Tell you guys what, call Rapid and price a set of struts for a Duchess,

Report back with your findings and recommendations on how often you are willing to service them.


I'll go ahead and tell you, a few years ago when I priced a set they were $9,900 each for the mains, non field reparable.:mad2:
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it's tough for something to be "non field repairable" when everything in it is conventional. The tube can be re-chromed, the seals can be replaced. What you're talking about is a wreck repair scenario, not a repair for a leak. But nice attempt at scare tactics aimed at the clueless.
 
JHW said:
it's tough for something to be "non field repairable" when everything in it is conventional. The tube can be re-chromed, the seals can be replaced. What you're talking about is a wreck repair scenario, not a repair for a leak. But nice attempt at scare tactics aimed at the clueless.
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What's an A&P to do when the manufacturer will not provide instructions for repair, or parts. ??

The struts that Skylane 81 was talking about are not your normal 172 nose strut.
 
Tom-D said:
What's an A&P to do when the manufacturer will not provide instructions for repair, or parts. ??

The struts that Skylane 81 was talking about are not your normal 172 nose strut.
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That's easy...........

Send it to Tom, he says a A&P can do anything, fabricate any part and perform any needed machine work operation and sign off the work at the end....:yes:;)...

Aww..
Never mind.. you ARE Tom....:D
 
N801BH said:
That's easy...........

Send it to Tom, he says a A&P can do anything, fabricate any part and perform any needed machine work operation and sign off the work at the end....:yes:;)...

Aww..
Never mind.. you ARE Tom....:D
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This is true, but you must stay with the rules of part 43.9

So what part of (a) 1 don't you understand?
 
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