Nitrogen tires

727 is my favorite Boeing. What a plane. Too bad you couldn't have crammed a high bypass in the center engine :-(

Tough day for Boeing

I've posted this on a couple of other forums. When I was at Boeing, I was in the landing gear/tires/brakes engineering group for several years. We started a project to stretch the 727, and ran afoul of a new FAA requirement that we had to certify that a tire burst on a main gear tire, after retraction, wouldn't endanger the airplane.

There had been one fatal accident with a Swissair Caravelle where a tire burst had brought down the airplane, resulting in 70 fatalities. There had also been an accident which totalled a USAF C-5A, but only minor injuries to the crew and one with a 727 where an 18" hole had been blown into the bulkhead separating the wheel-well from the pressurized aft cargo compartment. In that one, three USPS mailbags jammed in the hole and slowed the decompression rate so that there was no big structural failure. The Mexicana wreck was later than my research and shouldn't have happened. Maybe they didn't get the word, who knows?

Common to all these incidents were very hot brakes and gear retraction before they had cooled sufficiently. I did a detailed study on the 727 incident. Structural cables that made up the bead of the tire had failed in tension and there was extensive burning of the inside of the tire carcass. We eventually concluded that there had been a spontaneous explosion inside the tire, reaching a pressure of almost 12,000 psi to cause the bead failure.

It turned out that the airplane had taxied a long way at the airport because the take-off direction had been reversed because of a wind shift. One of the brakes was dragging and got very hot, particularly during the takeoff run. At the time, that particular airline was still using air for tire inflation. Boeing put out an immediate recommendation to switch to nitrogen, which cannot support combustion/explosion.

You only NEED to use nitrogen if your RV can accelerate to 150mph with a dragging brake and then you retract the wheels into a closed box. If you WANT to spend the extra money, that's up to you. Even using air at gas stations these days costs money, so I carry a small compressor to keep my RV tires at the correct pressure.

I beileve that all should stop over-thinking this and go camping!

CapriRacer wrote:

paulcardoza wrote:
OK.... I tried to not comment on this ridiculous thread, but......
How does water evaporate from inside a sealed tire? :h

The same way it evaporates in an open container - into the non-saturated air. The only difference is that the water VAPOR then has to migrate through the rubber - which it does due to the "Law of Partial Pressure of Gases". The water will always be in a vapor form unless the air inside the tire reaches 100% humidity - then the water condenses out.

The article of capriracer and an article of J.C.Daws ackowledged my suspicion that Oxigen and water when it a gas, can go from outside to inside the tire , against the high pressure. A while before this I supposed it in a Dutch topic, but it was rediculed away bij comparing it to electric curent, wich is one way.

I rather talk about water as a gas , because vapor is the same as damp, and that are verry little water drops.

My new suspicion is that liquid water or vapor water does not or much less diffuses trough the rubber as Water as a gas, wich it is in lower then 100% humidity air. Water as a gas does go trough the rubber the same as all gasses, would like to know at wich speed comparing to Nitrogen for instance. Oxigen , i once or more read, goes 5 times faster trough the rubber then Nitrogen.

This can cource that by temperature chanches and humidity-chanches of the outside air, whatever effort you take to get as less water in the tire as possible, there will be getting more water in it, or the inside tire gets dryer in the long run. That is something I want to find out. like to get wiser on that.

If there is liquid water in the tire, Oxigen and mayby carbondioxide, and even Nitrogen can dissolve in that water , wich lowers the pressure because of less vollume gas total. The gas inside the tire that is dissolved in the water, takes less space then in the gas.

For oxigen in any case, there is always a percentage of total ,belonging to the pressure , that the tire-inside will work its way to.
Going from 20% Oxigen in the outside air, it will be about 5% for 3 bar/44psi, 4% when 4bar/59psi?, 2% for 9 bar/ 130 psi, and 10% for 1 bar/14.5 psi.
At that moment the partial pressure of Oxigen is inside the tire the same as outside the tire ( 0,2 bar /3psi), and there will be going oxigen in to the tire yust as fast as it is going out, so there is a balance.
At that moment only Nitrogen diffuses out trough the tire.
Leaking is another thing , there are no little holes in the rubber.

jrw1550 wrote:
Let me give the real facts related to nitrogen inflation of tires. The nitrogen atom is larger then the oxygen atom and with tire rubber being porous the oxygen atom is small enough to get through the tiny holes in the rubber. This is the cause of tire pressure going down. The solution is to use the larger nitrogen atoms only. You should be asking yourself how this is done. It is very simple if we remember that the air we breath is about 78% nitrogen so continue to use normal air to inflate and the left over 22% of space that is usually oxygen gets replaced by nitrogen. When you first fill the tire is it 78%/22% mix, the next time it is 80%/20%, then 82%/18%, etc. And yes the percentage changes by 2% each time you refill for low pressure. So in reality losing the oxygen atoms is a good thing in tires. You will know you have reached 100% nitrogen when the tire pressure remains unchanged. Of course if you remove the tires from the rims you are back to the 78%/22% ratio and back to square one in the process. Just a little 4th of July humor for everyone!!!

Glad you are trying to be funny.........

I use helium in my TT tires. It just seems to float behind me.

Thank You Mr Science

Let me give the real facts related to nitrogen inflation of tires. The nitrogen atom is larger then the oxygen atom and with tire rubber being porous the oxygen atom is small enough to get through the tiny holes in the rubber. This is the cause of tire pressure going down. The solution is to use the larger nitrogen atoms only. You should be asking yourself how this is done. It is very simple if we remember that the air we breath is about 78% nitrogen so continue to use normal air to inflate and the left over 22% of space that is usually oxygen gets replaced by nitrogen. When you first fill the tire is it 78%/22% mix, the next time it is 80%/20%, then 82%/18%, etc. And yes the percentage changes by 2% each time you refill for low pressure. So in reality losing the oxygen atoms is a good thing in tires. You will know you have reached 100% nitrogen when the tire pressure remains unchanged. Of course if you remove the tires from the rims you are back to the 78%/22% ratio and back to square one in the process. Just a little 4th of July humor for everyone!!!

Allworth wrote:
How does this BS survive year after year??

Because there is a new sucker born every minute.

paulcardoza wrote:
OK.... I tried to not comment on this ridiculous thread, but......
How does water evaporate from inside a sealed tire? :h

The same way it evaporates in an open container - into the non-saturated air. The only difference is that the water VAPOR then has to migrate through the rubber - which it does due to the "Law of Partial Pressure of Gases". The water will always be in a vapor form unless the air inside the tire reaches 100% humidity - then the water condenses out.