Nitrogen Tyre Inflation
 

Hi, I have recently just started flying an aircraft with Nitrogen inflated tyres. Can anyone shed any light on the reason for using Nitrogen instead of compressed air for inflation?

The use of nitrogen is primarily to reduce the risk of fire in an overheated tyre as it's an inert gas. Air contains oxygen and will therefore burn if the conditions for combustion occur.

A far better gas than compressed air, Costco over here in the UK use it for car tyres, my car has run on them for a few years now.

It is like Krystal says, Primarily to decrease risk of fire because it is an inert gas. Maybe slightly better from a corrosion point of view. But I think that filling your average car with Nitrogen is a bit over the top. Another way to squeeze out a buck or two from the customer:}

Two main reasons 'dry nitrogen' is used instead of straight compressed air, firstly it doesn't conduct heat as well as air and secondly it has no water vapour in it.

Both an advantage when the brakes get really hot and the heat starts to conduct into the wheel/tyre assembly.

The heat soak takes longer and the lack of water vapour ensures that steam is not generated in the hot wheel causing a much increased pressure.

Peak brake temps in a an airliner after a high speed rejected take off can exceed 900degC.

Concerning filling your car tyres with nitrogen, pretty much a waste of money IMO, what's already in there is 78.8% nitrogen anyway and very few car drivers will ever have peak brake temps much over a couple of hundred degrees if that.

Last time I had the tryes replaced on my car the tyre tech asked,
'Dya want nitrogen in 'em mate?"

I said,
"No thanks, I already run an 80% nitrogen mix"

"Oh" says he and wanders off. :8

Regards,
BH.

This is from an article I read a while ago (source unknown). It agrees with what I was taught as a boy, but I can claim no better authority than that.

"Nitrogen is used for a few reasons, first it is a inert gas. This means that it is a stable gas and non oxidizing. These things that are important for safety. As a non oxidizing gas, it is a fire retardant, and prevents corrizion of the rims. Second it that is has no water vapor. Water vapor can freeze at high altitudes making ice in the tire, or even worse, when landing, and the heat buildup, can cause steam which will result in a tire blow out. (Water when turned into steam, will expand over 1000x its original volume).
Third, is the ease of storage and cost. Nitrogen gas is relatively cheap compared to other inert gases, and can be stored in a metal tank for long periods of time with out any negative effects. This is the main reason N is used, even though there are many other types of inert gases.
Another reason, is that N maintains a more constant pressure 3 to 4 x longer because of the lack of oxygen and water vapor found in "shop air". ."

I think the main purpose is to remove moisture, the AMM sates:

If nitrogen is not available, Source of Clean Dry Air, maximum moisture content that isequivalent to an atmospheric dew point of -208 F (-298 C).

but being an inert gas is valid in my point of view.

I recall being told many years ago when I learned to fly that it was also because nitrogen expanded less at altitude. Never really thought about it 'til now...and can't remember my physics from school. Was I being fed a line by an engineer with a sense of humour?

One other reason for Nitrogen.
We were taught in the early 1960's (by the Royal Air Force) that during inflation pressure release of the tyre (tire) prior to disassembly of the wheel (Split or detachable rim) even if the schrader valve core had been removed, the rapid reduction in pressure could cause any moisture in the air within the tyre to freeze in the aperture of the valve causing a blockage that could lead to the false impression that the tyre was fully deflated with obvious danger of accident if the rim securing devices were released while pressure still was trapped.

From memory tyre pressures on the Handley Page 'Victor' main gear were in the region of 250 psi (around 16 bar?)

and the English Electric 'Lightning' mains 400-450 psi (30 bar?)

Always inflated for the first time in the workshop in a safety cage.

Exmek

FAA Requires it in Part 121
 

and probably in Part 25 ops.

It was about 1987 that a Mexicana 727-200 arrived at Mexico City airport with squawk of dragging brake. Departing Capt took the plane without delay, had his wife aboard and kid on his lap to depart for KLAX and Disneyland. It was a full 178 SOB, at gross.

Brake was still dragging, so he powered back to help tug move the plane. MEX is 7400' elevation, with warm to hot temps. Normal initial climbout in 727-2 there is 500'/min until cleaned up, after rotating upon reaching the red lights at the last 1,000' of 13,000.

Pilot had retracted gear right after takeoff, of course. There was a catastrophic explosion before they reached cruise.

Cause was initially thought to be a bomb. Reportedly this was the Capt wife first flight since surviving a bomb in a 727 as FA some years prior.

NTSB determined that oxygen in the tire combined with volatile gases released from the very hot rubber made an explosive mixture, and only needed a spark.
--------

A similar fate befell a DC-8 on hajj in that same year.

-------

Yes, 100% nitrogen is better than air in even your car tires. Its larger molecules won't leak out as easily, so I'm told.

Nitrogen in Tyres
 

There are several reasons why nitrogen is used, most of which have already been mentioned in other posts
- It is 'dry' therefore expands less with changes in temperature - so as tyre heats up during taxi or during an RTO the change in tyre pressure is lower. This can also be important if operating to/from airfield with very different ambients temps.
- It's inert, so if after an RTO the fuse plugs in the wheels melt to release the pressure before the wheel explodes you are not releasing any oxygen onto already red hot brakes
- The nitrogen molecule is bigger than oxygen and hence the tyre will hold it's pressure better/longer thus reducing maintenance
- Nitrogen also does not attack/degrade the membrane on the inside of the rubber tyre - the rubber is porous and the membrane makes it airtight.

Using nitrogen in car tyres is a good thing - it means you can increase cold inflation pressures and still get the same optimum hot inflation pressures. It means that the car will use less fuel on short journeys when tyres are cold as the higher inflation pressure reduces rolling resistance and for those with sports cars it means the car will handle better until the tyres warm up. The smae can be acheived with 'dry' air if you can get it.

Nitrogen
 

Used in race cars for years, in tyres and intakes.

Nitrogen is NOT an inert (Noble) gas.

It isn't used for its own qualities as much as it displaces O2 and Water
as above.

A couple of minor points...

Nitrogen molecules should be smaller than oxygen, MW=28 vs 32.

There ain't no such a thing as -298 C.

How do they get it so dry? It probably comes from air and unmixing the water vapour should be an expensive process.

After an excellent landing you can use the airplane again.

Not expensive
 

Just run air through big bottles of Stainless Steel BB's first.

AF

What is the desiccating mechanism here?

After an excellent landing you can use the airplane again!

Surface area and
 

Condensation.

In fact I see a whole bunch of methods on the www. I wonder which is cheapest?

After an excellent landing etc...

I'm pretty sure I read it in Aviation Week & Space Technology, IGh. Mexicana started using nitrogen in the tires after that.

Did you find anything on the Hajj DC-8? It was possibly a Canadian carrier, and IIRC, they had either low tire or dragging brake, and no nitrogen available at the airport, so used air.

GB

from wiki:
 

Flight 940 was operating its scheduled flight route Mexico City-Puerto Vallarta-Mazatlán-Los Angeles operated by Mexicana Airlines (Compañia Mexicana de Aviación).

On March 31, 1986, the flight departed from Mexico City utilizing a Boeing 727-264 registered as XA-MEM.

Shortly into the morning flight an over-heated tire, a part of the main landing gear unit, exploded within the gear bay. It exploded because it was filled with compressed air, rather than inert nitrogen. The explosion damaged the aircraft's hydraulic and electrical systems and caused a fire. Although the crew reported the problem and declared an emergency, the aircraft crashed near Maravatio, northwest of Mexico City.

The crash killed all 167 passengers and crew and remains the deadliest airline disaster in Mexican history and is the world's worst air disaster involving the Boeing 727.

GB

The CAA (GR16) also require with effect from 1 April 1988, all braked wheels of retractable landing gear units on aeroplanes above 5700 kgs will be required to have tyres inflated with Nitrogen, or other suitable inert gas, and maintained such as to limit the Oxygen content of the compressed gases to not greater than 5% by volume.
http://www.caa.co.uk/docs/33/CAP747.PDF

There was another case of a main tire exploding the wheel well from overheating. It was in 1973 involving a Braniff 727. The aircraft was badly damaged and landed safely at Dulles Airport in Washington DC.

I have seen photos of the aircraft, but I cannot find any thing on line now about the incident.

Perhaps someone else will have better luck.

We did have ground distance charts in the 727 with waiting times, with the parking brake not set, that you had to follow if you had a long taxi, landing distance and estimated takeoff distances were including in the calculations. I can only remember a couple of times we were ever affected by the chart in the ten years I flew 727s, so it was not much of a limiting factor. If I remember correctly if you were parked for more than an hour there was no problem.

In racing car, yes maybe, but a complete waste of time and money in road cars. You never get road tyres anywhere near hot enough to get any benefit whatsoever from it.

Thanks for all your replies to the thread, I have found the information provided very helpful and informative.
snrub :ok:

Please satisfy my curiosity. Is it true that Nitrogen inflation of tyres (tires) was an initiative of Ansett ANA, long long ago, or is it yet one more myth?

I suspect that John_Tullamarine may know the answer:confused:

Regards,

Old Smokey

SF6
 

The "best" inflation gas for aircraft tires from a performance point of view is sulfuric hexafluoride, SF6, a gas which is normally used in gas-insulated switchgear for high voltage applications (>100 kV) world wide. SF6 has excellent dielectric properties and its extinguishing capabilities are outstanding and outperforming every "competitor". Combine this with a really big molecule, Nitrogen can dust off....
Well, on the downside, SF6 is a "climate killer", so no good and therefore no large scale use in aircraft tires.
I stand to be corrected that the space shuttle still uses this gas in its tires ?

sf6
 

hi!

but doesnt it vary with the amount of pressure relative to the proportion of manufacturer's allowable "time of compression" as allotted by the ISO standards?

rnv

Please satisfy my curiosity. Is it true that Nitrogen inflation of tyres (tires) was an initiative of Ansett ANA, long long ago, or is it yet one more myth?

I suspect that John_Tullamarine may know the answer

.. at a loss here. However, next historical do at Essendon I will track down one of the old chaps and see if he can throw any light on the question.

Nitrogen molecules should be smaller than oxygen, MW=28 vs 32.

Not quite as simple as that !!!!

If it was, my life would be much easier !!!

O2 vs N2
 

Thanks for asking this question, had always meant to do so. Having always doubted the O2 bigger story in my mind dubious due to the MW being greater, have found and been corrected by (presuming it's true - sounds authentic):

www.getnitrogen.org/pdf/graham.pdf

I wouldn't think one expands more than another - physics hazy these days but I think the only time the ideal gas laws don't approximate reality is close to the liquid or sublimation points - certainly not relevant to O2 or N2 in these conditions

I asked around at Old Bold Pilots' breakfast this morning, and one ex-electrical mechanic remembers well his airline using nitrogen by the late 1960s, as he used the supply for his car tires.

Another OBP said the use of nitrogen in tires at the Bonneville Salt Flats goes back much further. How about Sir Malcolm Campbell?

GB

Even at my advanced age I learn something every day.

After an excellent landing you can use the airplane again!

WOW
 

The Bluebird and Mickey Thompson's quad Pontiac. LSR. Em were the Days. Sorry, off thread.

This thread has got me thinking, as Im just about to get some new tyres for my car.

How much heat is generated at highway speeds in 60 serries tyres, if its true that with nitrogen you could increase the PSI by say 2 PSi without having them over inflate on the highway, there might be some merit for short trips in fuel economy, by having a slightly higher inflation with nitrogen.

Any idea on how much to go up by?

Not precisely aircraft related... and some thread drift... but here's an interesting video that shows the results of welding... even for only a very short time... on an inflated light truck/pickup tyre.
This video was produced by a rim manufacturing company that became concerned about the practice of repairing steel rim cracks, in situ, on earthmovers.
At least one welder has been known to have been fatally injured by a tyre explosion caused by welding a cracked rim whilst the tyre was still inflated.
What I find interesting is how rapidly the internal fire in the tyre propagates, once started.
You can well imagine the damage caused by a tyre explosion/fire in a wheel well.

YouTube - Tire Explosion

The reason according the (still valid) AD 87-08-09:

'We did have ground distance charts in the 727 with waiting times, with the parking brake not set, that you had to follow if you had a long taxi, landing distance and estimated takeoff distances were including in the calculations. I can only remember a couple of times we were ever affected by the chart in the ten years I flew 727s, so it was not much of a limiting factor. If I remember correctly if you were parked for more than an hour there was no problem'




We avoided that problem by not having those charts !

A complete waste of time, just stick with regular air.
Most of your tyre heat is generated by the brakes as well, not by the myth of the tyre sidewalls flexing and thus causing all the heat in the tyre.

This is untrue. While obviously brake use heats a brake and wheel assembly, sidewall flex accounts for significant heat rise. In large heavy aircraft, this can have a significant impact on brake energy determinations, just from taxiing the aircraft.

The fact is that in an automobile, the underinflation is the primary cause of blow-outs, largely due to heat rise. The reason for the heat rise is sidewall flex.

In large aircraft, sidewall flex, sans brake application, causes substantial heat rise during a long taxi. At maximum weights, one can heat brakes substantially without hardly any use, due to the tires getting hot during taxi and subsequent heat transfer.

All true, however I wasn't talking about aeroplanes I made it clear I was talking about car tyres. I also did not mention underinflation but again you have to be pretty low on pressure in a car tyre to get that and also going a fair rate of speed.
Thanks for the input, Mr Mitty.

Don't even start it, Okay! :ok: