An average plane hits the tarmac at 170 miles per hour, which exerts about the weight of a small office building, and the entire responsibility of landing the multi-million machine along with hundreds of precious lives bears on the tiny, unimpressive looking black tires. Ever wondered how it is possible that the tires never blowout despite all the punishment they go through? Today we are going to reveal the secret.
Aircraft tires can take about 38-ton load 500 times in their lifetime before they need a re-tread, after which they are good as new. This retreading can be done for seven times in its life, meaning a single set of tires can take about 35000 landings before they need to be replaced!
If you still think the tires are “unimpressive”, get a load of this fact. Even the largest of planes don’t require too many of them to land safely. Boeing 777 utilises 14 tires, Airbus’ A380 carries have 22 of them, and the gigantic Antonov An-225 uses only 32, which when compared with its size seems highly disproportional.
So what’s the secret? As Lee Bartholomew, lead test engineer for Michelin Aircraft Tires explained, the tires get their remarkable durability by maximising the air pressure. A typical plane tire is inflated to 200 psi, while the tires on an F-16 fighter are pressurised up to 320 psi. This is about six times more than times more than what your automobile tires bear, and as Lee elaborated,
“It’s really pressurized air that’s so strong.”
The ingenious engineering behind the tire design makes this feat possible. The fact is that the tires are not very large, with the Boeing 737 using 27×7.75 R15 rubber, which is 27 inches in diameter, 7.75 inches wide, which are wrapped around a 15-inch wheel. The tires also don’t have very thick sidewalls, and the entire the strength of the tires comes from the cords embedded below the tread.
These treads, or aramid, are made from nylon, and each of its layer helps in bearing the load and in keeping the air pressure within them to such a high value.
And these tires seldom fail, as each one of them is designed by the company using extensive computer simulation and prototyping. The tires are then overloaded and oversped in the simulated flights, takeoffs, landings and taxiing. And after rigorous testing and using highest of standards, such as requiring the tire to bear at least a pressure four times its rating for three seconds, the tires are commissioned to be used for an actual flight.
Pretty cool, isn’t it?