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Transport Catagory Aircraft Tire Balance

Fri Jul 04, 2003 12:38 pm

This may be a dumb question, but here it goes.
Many of you have seen chevron cutting on large aircraft tires. This occurs due to the aircraft landing on grooved runways whch results in small slices of rubber being worn away from the tires. Doesn't rubber missing on parts of the tire, coupled with high speeds, result in an unbalanced tire/wheel assembly. Automobile tires vibrate pretty badly when they are missing just a small balance weight. Wouldn't the same thing occur to an aircraft tire missing uneven patches of rubber on its surface?
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RE: Transport Catagory Aircraft Tire Balance

Fri Jul 04, 2003 1:25 pm

Chevron cutin is just that...cutting. There aren't slices of tire left on the runway.

RE: Transport Catagory Aircraft Tire Balance

Fri Jul 04, 2003 11:54 pm

Nose wheel tire unbalance can create very bad vibrations at higher speeds, I remember having aborted a takeoff at about 80 kts for that reason in a 747.
Such vibrations dont appear to be bad, when on the main gear... do not recall anyone saying "that main gear vibrates, check the tires..."
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aaron atp
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RE: Transport Catagory Aircraft Tire Balance

Sat Jul 05, 2003 12:26 am

Tire imbalances are mostly influenced by how much load is on it as well. Chevron cutting (no chunking) doesn't have nearly the effect as flat spotting on static balance.

If a rotating imbalance 1 ounce at 15 inches and causes a 300 pound upload (at some speed) on one tire on a main bogie, you won't even feel it upstairs. While the same imbalance on a car tire would make you think your car was about to fly apart

Each tire may have a load of 50,000 lbs or more, but the imbalance although seeming massive (300 pounds upwards, or a lot more!), is a very small percentage of the total load on the tire (.6%). On your car, with each tire holding a 1000 lb load, that imbalance is 30% of the load. Tire mass has a bit of influence, as do other tires on the same bogie, but it's mostly (imbalance/load)*100%

It should be easy to understand why nosewheel balance is so much more important, but I won't go into that (you generally won't see chevron cutting or flatspotting on nosewheels anyway).

It's not good for a tire to be unbalanced, but landings, takeoffs, and taxiing aren't good for them either.

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