Nitrogen in tires

[BigInch]

Looks like Will Taylor sized it up pretty well, "For those who believe, no proof is required; for those who cannot believe, no proof is possible." Amen!

Interesting about the C5A tires, but I'm not clear what performance statistics would be different between air or N2 and by how much.

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

 

[WKTaylor]

Folks...

Another forum-site with a virtually identical discussion...

http://www.pprune.org/tech-log/365043-nitrogen-tyre-inflation-3.html

From comment #50... situation with transport catagory acft tire is more serious from a fire/explosion perspective than even I considered...

...
"It's also a certification standard ("dry nitrogen or other gases shown to be inert") and requirement for large aircraft, as found in 14 CFR (code of federal regulations--the "FAR's) 25.733(e):

(e) For an airplane with a maximum certificated takeoff weight of more than 75,000 pounds, tires mounted on braked wheels must be inflated with dry nitrogen or other gases shown to be inert so that the gas mixture in the tire does not contain oxygen in excess of 5 percent by volume, unless it can be shown that the tire liner material will not produce a volatile gas when heated or that means are provided to prevent tire temperatures from reaching unsafe levels."
...
...
"Advisory Circular AC 25-22, Certification of Transport Airplane Mechanical Systems, under Section 25.733, provides the reason that the regulation 25.733 requires nitrogen or other inert gas:

b. Intent of Rule. This rule specifies type certification requirements for both design and performance of tires used on transport category airplanes. The tire must be of proper fit and have approved speed and load ratings for a particular airplane application. The maximum static ground reaction for the condition specified must not exceed the maximum static load rating of each tire. Retractable gear system tires must have adequate clearance from surrounding structure and systems. The tire inflation medium is to be an inert gas to avoid explosions. Tires installed on landing gear axles with multi-wheels (main wheel tires only), must have a 7% load margin included in their rating. Tire performance standards are contained in Technical Standard Order (TSO) TSO-C62. A TSO approval is not approval to install tires on the airplane. The airframe manufacturer/user must conduct the applicable airplane certification tests and receive FAA approval for installation.

The same advisory circular goes on to explain:

(6) Amendment 25-78 (March 29, 1993) added paragraph § 25.733(e) to require that for airplanes with a maximum certified takeoff weight of more than 75,000 pounds, the tires mounted on braked wheels be inflated with dry nitrogen or other inert gases so that the tire does not contain oxygen in excess of 5 percent by volume to prevent tire explosions. The 75,000 pounds weight limit was based on a review of the service difficulty reports indicating that tire explosions, as opposed to tire bursts, tend to occur on the larger, heavier airplanes. The 5 percent by volume limit for oxygen content was based on a series of laboratory tests indicating that an abrupt auto-ignition could occur for oxygen concentrations of 10 percent or more.

(a) There had been several cases where tire explosions had occurred in transport category operations. A tire explosion differs from a tire burst, which can occur when an overheated or over inflated tire fails and releases the high pressure air contained therein. Protection against tire burst is required under § 25.729(f). A tire explosion is the result of a chemical reaction occurring when gases released from overheated tire material mix with oxygen in the inflation air and ignite. In 1987, the FAA issued an airworthiness directive (AD 87-08-09) requiring use of nitrogen for tire inflation to ensure that the tires on braked wheels of airplanes do not contain more than 5 percent oxygen. Amendment 25-78 was intended to accomplish the same purpose for new airplanes."
...

These folks also get into a row as to why dry nitrogen is now recommended for auto tires... just like us...

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.

 

[Ron]

Was driving through Tallahassee, Florida last week and saw a sign at at tire dealer for "Nitrogen fill $29.95"....first one I've seen thus far. Across the street was a convenience store with a coin operated compressor....$1.25. Didn't need either, but know which I would choose!