Nitrogen in tires

[patprimmer]

MJ

I would really like our Ninja Claws friend to see your last post as it reeks of field experience vs school learning. Also, quite amusing, at least to my sense of humour.

Regards
Pat
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[zdas04]

Pat,
The chance of the Ninja Claw EVER getting here is vanishingly small. I don't see a lot of entitled wankers getting into the Tech Side if you know what I mean.

David

 

[patprimmer]

David

I know exactly what you mean.

Regards
Pat
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[btrueblood]

Pat,

No, but that would probably have helped. Or N4 enhanced, perhaps. Nitro grease? Vrooom!

Seriously, though, the old dozer (Allis-Chalmers G6) my Dad ran for years (20 or 25 or so) had take-up cylinders that compensated for slack in the track links. It had a zerk fitting on the cylinder end, and a yoke to the front idler on the rod side. Every few weeks we would "fill up the tracks" with a grease gun. Silly design, until you had to change out track links, then it was a blessing (pop out the zerk fitting, and pump the opposite end of cylinder with grease gun).

 

[waross]

That design was used by a number of dozer manufacturers. Before that, there was a big screw and very big nuts. It took a long time to release or tension the front idler with the old system.
The dozers that I worked on had the zerk fitting at one end of the cylinder only. To release the tension you would remove the zerk and drive slowly into a large stone. If you try this at home, don't let anyone stand in front of the grease hole!

Bill
--------------------
"Why not the best?"
Jimmy Carter

 

[btrueblood]

Waross,

The rod-end zerk was added by the owner. Dunno if it was his idea or somebody else's that he borrowed.

 

[patprimmer]

If you try this at home, don't let anyone stand in front of the grease hole!

aww Bill why not. sounds like a hoot with the right victim.

Regards
Pat
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[WKTaylor]

Guys...

I also turned-down the N2 refill option for my plain-Jane Fusion [75$ for life from my local Ford dealer]. Cost was not justifyiable for a low/slow auto.

However, there are MANY serious reasons for using dry N2 in aircraft tires.

Some reasons are obvious, and have already been stated, IE: (a) moisture freezing inside [on one side] can create severe balance issues for massive tires rolling +150-MPH at take-off; or spinning-up from 0 to full speed in a second or two on landing; and (b) general static oxidizing effects of air on rubber and tire reinforcements.

However... that's just the beginning of the real reasons for using Dry Nitrogen in tires.

NOTE. Acft wheels are split into two halves for ease of tire installation. USAF T.O. 4T-1-3 allows use of lubricant to aid in seating beads... preferably water or A-A-52625, minimum required to seat the tire bead. The T.O. explicitly states to avoid lubricant inside the wheel Assy… So there should be minimal moisture or lube contaminating the pressurizing gas [internal atmosphere] of the tire.

High performance aircraft tires are inflated to enormously high pressures [typ 80—160-PSI, cold]. They are highly loaded in rolling ground operations and heat-up rapidly and cool-down slowly. While rolling [no braking necessary]. So, heat exposure is a real problem. Obviously dry N2 will not oxidize the interior of tires that reach 200F+ during routine ground operations… not to mention MUCH higher temps when ambient is +120F… and braking occurs. See below.

NOW… add high energy braking to the picture that can cook brakes [glowing-hot] to 1000F. In these extreme braking conditions, large acft tire/wheel combinations are in-danger of over-pressurizing and exploding. For this reason, pressure fuse plugs are in every wheel: the plugs blow-out when a specified temperature/pressure criteria is reached [+/-]. The atmosphere inside the tire/wheel can rapidly heat to 300--400-F and reach 300--500-PSI before the fuse-plugs blow-out. When the plugs finally blow out***, they release the internal atmosphere into/around composite or steel disc brakes that are glowing cherry-hot. IF the internal atmosphere is air, then hot-air [~40% oxygen] under pressure can cause massive fire/explosion potential with the brakes, leaking fluids and tire rubber… whereas N2 is pretty much inert.

*** NOTE: if fuse plugs fail to blow-out and the tires explode the danger really increases. See below…

NOW for the subtle aspects of using dry N2.

Fuse-plugs in wheels are typically a low-temperature melting alloy set to melt ~275--350F (IF memory serves me correctly). Simple… RIGHT??? NOT. Fuse plug alloys have a known problem: when oxidized [corroded] they tend to melt at a much higher that programmed temperature. In some cases these plugs fail to melt and tire/wheel explosions have been known to occur with catastrophic results due to the fragmentation and gas expansion… and would be incrementally worse if hot pressurized air was involved. Obviously if wet air is on the inside of the tire/wheel, the fuse plugs have a higher probability of oxidizing and failing to blow. Again dry N2 would provide a totally inert atmosphere inside, virtually eliminating the potential for oxidation of the wheels, fuse-plugs, rubber surfaces, reinforcement plies, etc.

Dry N2 is also MANDATORY for servicing landing gear and all pressurized accumulators [etc]. The reasons for this are simple. These pressurized components rely on the [hydraulic-oil, etc] fluid and/or dry N2 for: (a) internal corrosion protection (most of these parts are polished/bare/minimally coated metal); (b) to prevent moisture [and ice] from contaminating/clogging orifices, valves, etc; and (c) to eliminate potential for metal and rubber oxidation products [corrosion, non-metallic material deterioration] sloughing-off into the fluid, adding contaminates to the systems. If wet air mixes with the fluids, then the fluids also have the potential for moisture contamination also creating: (a) ice to block fluid flow; and/or (b) may chemically alter the fluid properties [including lubricity].

NOTE. I have seen the interiors of many steel main landing gears after they were disassembled (when they wouldn’t hold pressure). Usually, the beautiful 4—8 RA polished-steel interiors of the cylinder components [or plain bearings] are pitted/corroded/stained. The evidence leads to the fact that the component was probably serviced with wet AIR during some mental-lapse by a mechanic… or a desperate attempt to get the acft flying again at some remote location... and then not cleaned/purged afterwards [with dry N2].

It should be obvious by now, that dry N2 is an essential “fluid” for servicing all pressurized aircraft components… not just tires. For this reason alone, there should be NO pressurized AIR remotely close to the flightline. If the mechanics have a bottle of pressurized air to run power-tools [drills, etc], NOT ONLY is there a temptation to use the air-bottle for a quick servicing of a pressurized component… but the “air tools” could become contaminated with the wet air… and may freeze-up in cold climates.. or corrode internally in warm climates.

Hope this makes sense. Now… Gotta go back to work.


Regards, Wil Taylor

Trust - But Verify!

We believe to be true what we prefer to be true.

For those who believe, no proof is required; for those who cannot believe, no proof is possible.

 

[SomptingGuy]

Wow! I feel educated now. Many thanks Wil.

- Steve

 

[zdas04]

Wil,
That was an interesting combination of fact, error, and urban legend. The obvious error was that air is 40% oxygen. The number is closer to half that. Also, the idea that oxygen inside the tires will cause increased oxidation of the rubber (more than the air on the outside of the tires?) is foolish.

Now for the urban legends--If air at 500 psig and 300F would cause a fire, then introducing nitrogen at 500 psig and 300F into an environment that has 20% oxygen already would also cause a fire. The urban legend here is that oxygen is flammable. It isn't. If I fill a steel vessel with pure oxygen and create an arc, nothing will happen. If I stick a match into the oxygen environment then it will flare up in a really exciting way, because I will have strengthened the oxygen leg of the fire triangle, and the matchstick supplies the fuel. We did an experiment in grade 9 where we used electrolysis to separate water into hydrogen and oxygen. Then we tried to stick a match into the hydrogen--it flashed before we got close. Putting the match into the oxygen caused it to flare up and burn fast until the fuel was consumed. Oxygen is not flammable.

Next urban legend--oxygen in the absence of water is corrosive. It isn't. The benefit of dry nitrogen is that it is dry not that it is nitrogen (i.e. oxygen free). I can (and often do) get accelerated corrosion in the total absence of oxygen. I can't get any general or pitting corrosion in the total absence of water. There are some stress-cracking corrosion modalities that can happen without water, but I don't think that is what you were talking about.

That is it. Water vapor is the culprit, not air. I'm certain that all of the examples you pointed to were real and actual observations. Putting a few ounces of water vapor into a tire or a hydraulic system can really do ugly things. Nitrogen in and of itself doesn't cure any of these ugly things--if you saturated the nitrogen in your bottles with water vapor you would have all the problems that you've attributed to using compressed air. If you dried your compressed air to below -40F dewpoint you would get the same results you get from dry nitrogen.

David

 

[IRstuff]

Therefore, all else being equal, one might prefer using N2, because it's more likely to be dry to start with.

TTFN

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[WKTaylor]

zdas...

I kept saying DRY N2 or DRY nitrogen for a good reason. DRY. Virtually free of moisture [H2O].

OK OK OK my O2-N2 ratios are off... so I'm rusty on my atmosphere.

http://mistupid.com/chemistry/aircomp.htm

The point I tried to make with heated/compressed AIR [OXIDIZER] in tires is that it is far more reactive with intensely hot brake components [steel, carbon, rubber, asphalt, fluids, etc, THE FUEL] than ambient AIR. Obviously hot/compressed dry N2 releasing suddenly [explosively] is NOT a good thing... but not as bad as hot/compressed AIR with a fuel source.

NOTE. N2 inerting of integral fuel tank ullage [space above the liquid fuel] is a well known practice [all-be-it costly and difficult] to virtually eliminate the potential for explosions [IE: TWA Flt 800].

NOTE. The rate of chemical reactions is generally dependent on temperature and pressure. IF I remember correctly the R.O.T. was that for every +10F [or is it +10C] the RATE of chemical reaction DOUBLES. I've forgotten what the equiv was for pressure.

NOTE. The USAF has recorded ambient skin temperatures [on the ground] close to +200F for some camouflaged acft types in the desert. Add-in operational heating [engines, rolling tires, etc] and the static temperature in certain parts can be mind-boggling high.

I once had a very perplexing acrylic windshield problem: massive crazing when analysis said it shouldn't craze. The investigation revealed that the acft were sitting [for days] in desert parking seeing soaking temperatures upwards of +200F in the closed cockpits [no solar shielding]. The acft were then flown on various tactical missions, usually including hose/probe air refueling [AR]... and then returned to based and would be parked again for a few days. NOTE. during the AR disconnect most of the windshields were splashed with about a liter of JP-4 fuel. when the vendor ran tests up to ~140F with fuel dried naturally on the windshield pane, there were no problems. When the test temperatures went above 150F crazing occurred spontaneously in the fuel soaked areas... and got worse [more pervasive] as temperatures reached 180 [whole outer ply massively crazed].

In summary static temperature and static/dynamic stress combine with chemical reactivity [oxidizer + fuel] to do amazing [bad] things.



Regards, Wil Taylor

Trust - But Verify!

We believe to be true what we prefer to be true.

For those who believe, no proof is required; for those who cannot believe, no proof is possible.

 

[BigInch]

[serious ] With the amount of smoke they make on ground contact, do A/C tires really last any longer than a couple of months at best?

Let your acquaintances be many, but your advisors one in a thousand’ ... Book of Ecclesiasticus

 

[stevenal]

I don't think we need to have flammable oxygen for Wil's scenario. Fuel, O2, and ignition are required. The rubber and brake fluid provide the fuel, O2 comes from the atmosphere, and ignition heat comes from the brakes. Now we can fan this flame with pressurized air stoking the fire, or we can fan it with an inert gas tending to displace the air present. I think he has a point.

 

[zdas04]

The first time I took fire training (1971), the instructor told us that the fire extinguishers (which were at a MUCH higher pressure than we're talking about here) were good for about one office trash can worth of fire.

If brakes catch a tire on fire, spraying 25 SCF of nitrogen on it at 75 knots is going to do NOTHING. Just like spraying 25 SCF of compressed air on it. There is so much wishful thinking and urban legend in this stuff that it is really hard to let the data speak for itself.

David

 

[unclesyd]

I've heard two reason for using N2 in big race cars. On tracks where the cars use brakes a lot the is a propensity for the rim to get hot enough to melt the tire bead and tire catch fire, the problem was the inside of the tire tended to burn first. N2 was used to help mitigate this problem.

The second was that NASCAR inflates the cold tires by 1/4 psig increments and by using N2 they have less of problem with tire expansion at speeds. Fq cars preheat their tires to control the expansion.

 

[patprimmer]

Bill

A chemical reaction generally doubles in speed or thereabouts for every 10 deg C. Somewhere in my memory banks it says pressure also increases reactions in gasses, maybe because of the increase in the number of molecules in a position to react and a tighter interface between the molecules.

Water causes corrosion in some metals and hydrolysis of some materials. It does not cause oxidation.

Oxygen on the other hand causes Daaa daaa, Oxidation. This is not hydrolysis. It is a completely different reaction.

Rust only occurs where water and oxygen (or other strong oxidising agents like chlorine or fluorine and probably even iodine or bromine are present as it is hydrated iron oxide or hydrated oxidised iron.

http://en.wikipedia.org/wiki/Rust

The rubber used inside a tyre is a different compound to used outside. I am not sure how many compounds are typically used in tyres, but it is certainly at least two, and I suspect five or six.

Tyre treads, tread base bead surface, liner and reinforcement interface all have differing requirements and each area needs a compound with the balance of overall properties to suit, including cost and including the ability to bond to adjacent surfaces.

It is a bit brave in my opinion to presume the differences in properties required would still result in compounds with identical resistance to either oxidation or hydrolysis.

I do agree that the real benefit of N2 is it is much more likely to be dry.

I do agree that only one source of compressed gas greatly reduces the chance of the wrong one being used.

I also agree that air or nitrogen releasing out of a tyre onto a wheel at high speed will make a difference, but depending on speed and proximity, so little difference as to be of no consequence, however if for any unimaginable reason the red hot brake and a tyre full of compressed air where bought together just after the wheel brake assembly was confined a real difference might be present.

I certainly know that the availability of oxygen makes a huge difference to the flammability of fuels.

By your test David, neither oxygen nor fuels are flammable. Both need to be present for fire.

I have personally seen tests that showed steel to be more flammable than dynomite, so long as the dynomite sample resembled a baseball and the steel was in dust form and finely dispersed in air.

I also know that one important measure of flammability is limiting oxygen index.

Regards
Pat
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[WKTaylor]

Guys... BTW...

Transport Acft Tires are very expensive and the tread generally lasts ~200--300 operations [take-off and landing].

For this reason most acft tires are retreaded numerous times [SAE ARP4834 Aircraft Tire Retreading Practice - Bias and Radial] until the casing is no longer serviceable [by inspection/NDI].

NOTE. Since there are numerous variables, there is no set service limit [X-number**] for retreadings... only when the casing [carcass] condition deteriorates to the point is is unserviceable [slap-ass wore-out].

How many of You [us] are driving on high performance tires that have been retreaded 5-times? I am pretty safe guessing less than 1%.

Here is how abusive the worst case rejected take-off and maximum effort braking [no TR] can be to the tires...

Boeing 747-8F Performs Ultimate Rejected Take-off

http://www.youtube.com/watch?v=am392XmYBps

NOTE. I investigated a C-5A that had a max GTOW refused take-off [RTO] braking [and max/partial TR**] on a hot summer day overseas. The brakes go so hot the white paint on certain trucks was scorched and flaking... and there was balled cadmium visible with 20X magnification. Lots of wheels/tries and a couple of Trucks and brake assys were replaced.

** The C-5 crew had an unsafe TR cockpit indication just before rotation: which could have been disastrous if they had continued and the TR had deployed. So the crew elected to keep it on the ground at all cost. Acft stopped on the over-run and sizzled/smoked for several minutes.

Regards, Wil Taylor

Trust - But Verify!

We believe to be true what we prefer to be true.

For those who believe, no proof is required; for those who cannot believe, no proof is possible.

 

[Compositepro]

Here are a few more points to ponder.

Water vapor pretty much behaves as an ideal gas for our purposes here, little different from N2. In contrast, liquid water will have a vapor pressure curve that is strongly dependent on temperature. Water absorbed by rubber is somewhat like liquid water.

A cylinder containing 3000 psi air can be completely saturated with water and the air coming out will be "dry". As the gas expands so does the water vapor. In going from 3000 psi and 100% relative humidity to 300 psi, the relative humidity will drop to 10%.

Increase in gas pressure does increase reactant concentration in chemical reactions.

Oxidation is the primary reason for degradation of rubber, which is why antioxidants are almost always a part of rubber formulations. Oxidation rate increases exponentially with temperature.

 

[evelrod]

So, from what Wil and David posted, the key is "dry". Okay, I can accept that in all cases. However all I get for acft use is repeatability, DRY and, portability...The rest seems a bit urban legend to me. For racing, I can speak with a bit more authority. In auto racing it's very much monkey see, monkey do. If it is perceived that helium is the hot setup, rest assured that all teams will want helium. If, for example, Goodyear used helium in Carl Edwards car and he won a race so equipped...However, NASCAR would not allow that to happen more than once. Either ALL teams tires would be so inflated or, most probably, NONE. NASCAR likes control and if it was not their idea...

As to the chemical reactions possible, I defer to Pat. NOT my area of expertise!

And---To David's point about fire training, my last time was in the late 90's and included petroleum and rubber fire suppression with both dry chemical (probably 'purple K' or equivalent) and AFFF. In most cases the dry chemical did not do much more than temporarily controlled the bigger fires where AFFF always suppressed them, totally. Setting up on board fire control systems on acft. or even race cars is a non starter. I know of several Halon (I don't know which chemical derivative) fire suppression systems in race cars and have seen a couple deployed. In the one case where I was there to get the driver out of the car, the Halon system did not meet my expectations. Indeed, it simply 'blew' the fire up in the driver's face. I am curious how a large commercial setup like the one used by Northrup-Pico Rivera would work in a large fire.

Both my cars are equipped with multiple discharge nozzles and AFFF as a result of my experiences.

Rod