Known as a jumbo jet, Boeing’s B747 has become the standard for jumbo passenger jets. It stretches over 230 feet in length and can accommodate nearly 500 passengers. Upon takeoff, the plane’s weight measures up to 450 tons, but it is supported by only 18 tires.
Despite the fleetingness of the takeoff and landing moments, when a massive plane touches the runway at speeds reaching 261 mph, the heat generated is so intense that it produces a smoky haze. We took a look at the secrets of aircraft tires, which must withstand these extreme conditions, at the global leader in tire manufacturing, Michelin. Over 50% of commercial aircraft operating worldwide use Michelin tires.
How Are Aircraft Tires Different Than Vehicle Tires?
The biggest difference between aircraft and vehicle tires is the need for a unique design due to specific load and speed requirements.
For example, vehicle tires have various patterns engraved on their surface depending on their use. The design of the tread, the part of the tire that touches the road, determines performance and is considered a core technology. However, aircraft tires only have a few vertical grooves. This is related to the tremendous friction that aircraft tires must withstand during takeoff and landing. The design is to dissipate the heat generated by friction during takeoff and landing and to drain water from wet runways after rain or snow. Horizontal patterns are disadvantageous when it comes to withstanding friction.
The carcass, which refers to the internal skeleton, also needs to be designed with a thick layer of rubber ply to prevent the rubber from being deformed. The sidewalls of the tire incorporate features to reduce cracks caused by ozone.
What’s the Key Point of Aviation Tires?
Depending on the situation, aviation tires can withstand approximately 300 times of flights. Each flight wears down the tire by a few grams. However, takeoff and landing are not the only extreme conditions that must be endured.
The space where tires are stored virtually has similar conditions to the outside because the temperature and pressure are not adjusted according to altitude like in an airplane. Temperatures in the air and during takeoff and landing range from -67°F to 480°F. Even in these situations, the key is to minimize the deformation of the rubber.
Unlike vehicle tires that are only filled with air, aircraft tires are filled with dry nitrogen. This allows the tire to maintain its shape at low temperatures and prevents ignition from the heat generated during landing at high temperatures. This is the same reason why racing tires are filled with nitrogen.
Just as an aircraft engine is designed to be able to take off and land even if one engine fails, tires are also designed to withstand double the load during takeoff and landing. Michelin explains that the certification tests in the aircraft manufacturing industry are thus stringent, covering all application areas.
The Bigger the Plane, the More Tires
The size difference between a B777, a large aircraft, and a mid-range B737 is huge. One engine of the B777 is as big as the body of a B737. It’s like comparing a garbage truck to a compact car.
Although aircraft tires have their own tire standards, the size of the tires does not necessarily correspond to the size of the passenger aircraft. Instead of increasing the size of the tires, the number of tires is increased to distribute the load.
For example, a B737 has two tires on each landing gear, using a total of four tires. A B747 requires 16 tires, with 4 landing gears each bundled with four tires. Adding two nose gear tires makes up the total number of tires. In some cases, like the B777, there are six in a three-wheel structure.