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Aircraft Tires

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My water bottle seems to be under extra pressure when I open it inflight. Are the tires under pressure too, and do they expand much? Your water bottle experiences the result of a depressurization of its exterior as the cabin pressure decreases during climb. The interior air seems to be of a higher pressure. Of course, that is all going on inside the cabin where the cabin pressure is still about 8,000 feet at cruising altitude. However, the tires are never in a pressurized environment. When at 41,000 feet, they are nearer to space than on the ground in terms of pressure. ("Hey, what about the Space Shuttle tires?" Same as airliner tires. In fact, I think they use the same tires we do.) Filled to over 100 pounds per square inch on the ground, if they weren't strong, they'd explode for sure at altitude. The key is how they are made. Car tires have a couple of belts to add strength and durability to the tire. Otherwise, side loads and direct loads would pop the tire or push it off the wheel rim. The rubber used for tread has little strength. Some supporting structure must take the load of the vehicle. This structure is called the "carcass" of the tire. Light truck and SUV tires have 4 plies to add the strength needed to handle the stress they encounter holding up a bigger vehicle. To handle the weight of a jetliner like the 737, the tires have 28 plies! These tires are so strong they can handle the punishment of landing and braking as well as the strain under pressure at cruise altitude. With the Aramid fiber used in tires having more strength than steel (pound for pound), I doubt the tires expand too much at altitude. The tire "carcass" is so strong that it allows the airline to retread the tire several times to get better life out of them and keep the cost much lower than buying new tires all the time. You see the importance of this when you watch an airplane land because the "smoke" you see arising from the tires is vaporized tire tread. It doesn't take long before there is no tread left (and tires are inspected every time a Pilot does a walk around), but again, the steel-like carcass of the tires is what supports them.
12 Comments
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Hi Ray! FYI this link should answer your space shuttle tires question. http://www.airmichelin.com/space.html It is close to yours but I thought you used goodyears ;-P Lowest standards of unprofessional service. Ding! boy Joe
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They are also filled with nitrogen instead of air aren't they? If I remember right nitrogen doesn't expand like air.
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Ahh, "This is Your Captain Speaking" reminiscence. That is the best book ever written. Keep up the good work and the informative posts, Cap'n Ray! -Saddle Tan Fan
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I certainly enjoy all the posts, obviously! I learn a lot more reading them. These are things I don't think much about until reading. Thanks, & keep up the great work Captain Stark, & everyone else! 🙂
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Joe, Nitrogen is used in aircraft tires because it is less reactive than oxygen in regular atmosphere, no more likely to migrate through the rubber than other gasses that would be reasonable to use, and it is cheap. Rubber likes to oxidize, which decreases its integrity. High partial pressure of oxygen and high temperatures that aircraft tires experience would increase the rate of oxidization. Nitrogen keeps the rubber happy.
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Good Link!!! Commercial airliners use nitrogen. Nitrogen is more stable pressure-wise under temperature extremes, won't leak out through the rubber matrix (nitrogen molecules are too big to fit through, just like your car tires and another reason why Costco now fills your car tires with nitrogen), and is not flammable (inert) should the tire blow or overheat. Ray
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Joe, correct, although Nitrogen is primarily there to prevent excessive expansion from heat (when braking) rather than a pressure delta between ground & inflight. :o) Raphael
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For you "techno geeks" (like me) who like all the details, you might get something out of a huge compilation I have made at http://www.getonthatplane.com/forums/showthread.php?t=21 This thread involves a bunch of questions I have answered over the years with more to come monthly. Ray
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hello guys , can i inflate my rib boat with nitrogen? thanx
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The most important thing is that there is no water vapor in N
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Question for Ray Stark regarding tire pressures: If a tire is pressurized to 100 psi with dry air at sea level where the atmospheric pressure is 14.7 psig, then placed in a vacuum chamber and the chamber evacuated to 0.0 psig, what would be the change in tire pressure be if the temperature in the vacuum chamber was held constant at standard day conditions? If the test was repeated with the tire pressurized with dry nitrogen rather than dry air, what would be the change in tire pressure? If both tests were repeated with a temperature reduction near to -65 degrees F at the 0.0 psig pressure, what would be the resultant tire pressures? Would it be possible for the tire pressures in either case to be greater than 100 psig plus 14.7 psig? If so, how? What tire pressure would explode the typical aircraft tire if it had been correctly pressurized at sea level? Thanks in advance Jon Hehman Woodstock, Georgia
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Correction on my above questions. Pressures shown is psig should be shown in psia. Jon Hehman