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Message started by JayG on Feb 21st, 2011 at 5:11pm

Title: Re: Lou - STORIES
Post by LOU on Dec 28th, 2019 at 4:15pm
The other day a person asked me how many landings would you expect to get out of a tire on the 757?  That is a very good question since aircraft tires are a lot different from your average car tire.

Most car tires are 4 ply and inflated to somewhere in the mid 30 psi with air.  The tires on the 757 are either 28 or 32 ply and inflated to 200 psi with dry nitrogen.  Why dry nitrogen you ask?  Well, air contains moisture, and at altitude the water would freeze into a lump at one place in the wheel. If you were to land in a cold place, the wheel would still be frozen and the unbalance in the wheel could destroy the tire on landing. 

As for the number of landings out of a set of tires, that depends on the pilots and their landing skill.  These wheels are fairly heavy and don't spin-up instantly on touchdown.  Really smooth landings actually do more to shorten the tire life since the wheel tends to slide on the runway and take longer to spin-up causing a part of the tire to melt due to the friction. That's why you see all the black marks in the touchdown zone of the runway. Our manual would actually teach a solid touchdown to cause the wheel to spin-up faster and lessen the wear on the tire.  Getting the wheel to spin-up faster increased the coefficient of friction of the tire on the pavement giving you better control on the roll out.  That is why the plane's anti-skid system really tries hard to avoid getting the wheel to stop turning.  If the wheel stops spinning, the coefficient of friction goes to zero.

I seem to remember around 200 landings on a set of main wheels before the tire was removed and sent for re-capping.  If the tire was too worn, that would make it less able to be re-capped.

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