Want Nitrogen With That?

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Remember that great closing scene in The Bridges at Toko-Ri  where admiral Tarrant, upon contemplating the loss of Brubaker, ruminates, “Where do we get such men?” For all the wrong reasons, I thought of that the other week when I was talking to Dave, one of the local IAs here.

While I was fooling with the plugs in the Cub, he said, “Hey, what do you know about nitrogen in airplane tires?” My reply is that I knew as much about it as I do nitrogen in car tires, which is enough to understand that using it is yet another way to separate a customer from his money.

This had come up because a customer had come into the shop asking to have the front tire on his Cessna 172—yes, a Skyhawk—inflated with nitrogen. When the shop said it couldn’t help, the customer steamed off in a hissy, muttering that the place must not know the first thing about maintenance.

But I had been around these houses before when the local Toyota dealer offered to “freshen” the nitrogen in our Matrix tires for $5 a pop. Did I want this special service? Not just no, but hell no. Twenty bucks to top up the tire pressures? I later learned that this was a bargain. Some dealers charge as much as $179 for this “upgrade.” The idea has somehow migrated over to airplane tires, but apparently via meme, not by anything the manufacturers recommend.

The theory behind nitrogen inflation is that it retains tire pressure over time better than straight air does and this has proven to be true. But we’re talking very small differences. Consumer Reports did a yearlong test and found that nitrogen held pressure in a tire about 1.3 PSI better than straight air. That’s in tubeless tires; it might be different in the tubed tires that light aircraft use. Nitrogen is typically drier than compressed air, so it’s also thought to reduce moisture content around the metal wheel, thus limiting corrosion. But again, in an airplane, the moisture is inside the tube and never sees the wheel surface. Nitrogen acolytes also believe that because the gas is inert, it will reduce tire degradation. Well, that’s fine, but the tire is exposed to all manner of destructive UV and environmental contamination on the outside, so what’s the point of protecting the inside with a $20 top off?

There isn’t one. Or at least one that’s consistent with spending that much on a tire you’ll probably replace long before a nitrogen fill will pay off. And since it’s an airplane, we’re not really worried about fuel economy.

It is true that transport category tires are nitrogen filled; says so right in the tire specs for those big, expensive buns. But that’s not what we’re talking about here. I didn’t speak to this owner directly, but I would have liked to. Isn’t flying expensive enough without, you know, doing it to ourselves? Ain’t it funny how we talk ourselves into such things?

Comments (24)

Helium, please. I seem to remember somewhere that it made average GA tyres a whole 200 grammes lighter.
And it is so much safer than that old fashioned hydrogen at least one person I know is rumoured to use when the weight and measures tests are done.

Posted by: John Patson | September 23, 2015 4:52 AM    Report this comment

Funny that shop did not have nitrogen, given all those struts out there that need to be serviced.

Posted by: Walt Hankinson | September 23, 2015 5:35 AM    Report this comment

I always tell people I'm saving money by filling my tires with only 78% nitrogen.

Posted by: Matt Burch | September 23, 2015 6:59 AM    Report this comment

I usually fill my tires with a 78% Nitrogen 21% oxygen mixture.

Posted by: RODNEY HALL | September 23, 2015 7:43 AM    Report this comment

Agree, it's not worth the money. Keep tires inflated properly.

Posted by: Rafael Sierra | September 23, 2015 8:12 AM    Report this comment

Wow, are we running out of topics?

Posted by: Michael Kenslow | September 23, 2015 8:31 AM    Report this comment

It's funny how the same OWTs and misunderstandings are still going around, long after they should have died.

Posted by: Gary Baluha | September 23, 2015 8:34 AM    Report this comment

I'd much rather spend money on helium-filled balloons, take them to the airport with me, gulp some down, and then talk to ATC. Much better use of my money. Makes for more smiles.

Posted by: Albert Dewey | September 23, 2015 10:23 AM    Report this comment

Cow manure is an excellent source of slow-release nitrogen

Posted by: A Richie | September 23, 2015 10:25 AM    Report this comment

Wait a minute! Nitrogen is lower than oxygen on the Periodic Table and has a lower atomic number ... so nitrogen filled tires oughta weigh less !! I'm going to Firestone right now. Lemme find my wallet.

Posted by: Larry Stencel | September 23, 2015 10:27 AM    Report this comment

Ignoring minutiae is an operational error.

Posted by: Rafael Sierra | September 23, 2015 10:41 AM    Report this comment

Larry, hot air will work just fine. Do it all the time. Plenty of that in the cockpit.

Posted by: Rafael Sierra | September 23, 2015 10:46 AM    Report this comment

Because 100% nitrogen is less likely to contain vaporized Dihydrogen Monoxide, you know. We all know the horrors of Dihydrogen Monoxide.

Posted by: Steve Cornelius | September 23, 2015 1:21 PM    Report this comment

Larry is correct, nitrogen has a lower atomic mass than oxygen, but its kinetic radius is larger than O2 by about 6-8% due to its electron structure therefore making it more difficult to pass through the microscopic spaces in the rubber wall of the tire. Because of this, the permeation of O2 through a typical tire wall is 3-4 times greater than N2. Hence a tire inflated with pure N2 will leak down at a lesser rate than air (air is 78% N2 and 21% O2).

But, it's still not worth doing for little 6.00x6 tires! Besides, its a good preflight item to check them anyway.

Reference: www.getnitrogen.org/pdf/graham.pdf

Posted by: A Richie | September 23, 2015 2:04 PM    Report this comment

But what they don't emphasize is that common, every day discount air is already 78 percent nitrogen, so the benefit you're getting is only on the incremental 21 percent oxygen you're displacing.

The Consumer Reports tests validated the theory, but it costs a fair piece of change for very little gain. A reader wrote me in the background saying he's a fan of N2. I've asked him to post his views.

Posted by: Paul Bertorelli | September 23, 2015 2:11 PM    Report this comment

I fly a 414. My maintenance shop puts Nitrogen in my tires. I told him next time fill it with air, he says no, he'll keep using Nitrogen. Who's correct?

Posted by: JOHN EWALD | September 23, 2015 4:06 PM    Report this comment

He who holds the sign that reads "I-Paid!" in his hand is correct.

Posted by: Jason Baker | September 23, 2015 4:23 PM    Report this comment

Neither and both are correct. Other than cost, there's no downside to the N2. Nor is there to air. Are they uncharging for the N2? If so, what Jason said.

Posted by: Paul Bertorelli | September 23, 2015 4:32 PM    Report this comment

Using 100% nitrogen in the "go cart tire" technology that we have on our planes is just laughable. What's sad is that pilots who should know better are so easily misguided, duped, and clueless about the very stuff they fly in.

Posted by: Mark Fraser | September 23, 2015 8:09 PM    Report this comment

I am conflicted.......Should I spend my money upgrading my watch, or on a nitrogen tyre fill ?

Posted by: DAVID GAGLIARDI | September 23, 2015 8:26 PM    Report this comment

I'm going to Disneyland y'all.

Posted by: Rafael Sierra | September 23, 2015 8:42 PM    Report this comment

Why not use Argon CO2 from the MIG welder or even pure Argon? It is inert and higher on the periodic table.

Maybe, we should apply for a government grant and study the use of common and exotic gases in light aircraft tires. I think that the N2 filled tires should give better MPG. I have seen some ripoff auto repair shops that claim up to 20% better gas mileage. These are the same shops that told me that my high mileage F150 needed a complete tune up because the F150 had such a bad maintenance record. Yes, I managed almost 300K on mine with no engine repairs.

As we would say in the car business there is an a$$ for every seat.

Posted by: Leo LeBoeuf | September 23, 2015 8:43 PM    Report this comment

Seriously, this has been a good spirited blog and most informative. I now know about the benefits of N2 and what the FAA regulates. In my case, it's either N2 or compressed air but with an emphasis in correct tire air pressure. I learned that early in the morning I should check all tires for wear and air pressure and pressurize as recommended. Argon is not mentioned therefore I won't use it. Michelin wants all tires to be filled with N2 but I opt not to as it is impractical and expensive.

Posted by: Rafael Sierra | September 24, 2015 10:46 AM    Report this comment

According to Boeing*, Nitrogen inflation is required by the FAA in "braked" wheels to prevent explosions with severely overheated tires. The rubber tire will off-gas volatile compounds at high temperatures which can combine with the oxygen in air and auto-ignite, resulting in a wheel/tire explosion. At least one aircraft was lost when such an explosion occurred in the wheel well after gear retraction.

With our small, low pressure tires, I seriously doubt we need to worry about this in our aircraft.

* see boeing.com/commercial/aeromagazine/aero_05/textonly/m03txt.html

Posted by: MIKE HUTCHINS | September 24, 2015 9:15 PM    Report this comment

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