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Society & Success

The magic that is aeroplane tyres

Nitrogen is used for inflation since it does
Nitrogen is used for inflation since it does not support a fire. PHOTO | FILE 

One of the facts I found surprising when I started flying was the small size of the aeroplane tyres. Even the small planes weigh about a tonne yet the size of their tyres is like that of a wheelbarrow.

The situation isn’t much different on the larger planes. A Boeing 737 has a 16.5 inch rim which is really the size of the rim on a mid-sized sports utility vehicle. Of course when you add the tyre the total wheel diameter is larger but still a lot less than what you would expect from what is essentially the only thing supporting 80-tonne plane.

This is all because apart from the same outward appearance, airplane tyres are different from that of cars. What kind of mission are designed for? For a start, these tyres have to withstand up to six times the load of an automotive tyre.

Desert airport

They have to withstand high speeds necessary for takeoff. Most airline tyres are rated at speeds of approximately 370kph which are necessary for takeoff at some of the higher weights. On landing, they both have to absorb much higher forces as well as spin up to the airplane speed in seconds.

They have to withstand a wide range of environmental conditions so that a plane taking off from a winter location does not have to change tyres when it arrives in a hot desert airport.

Add to all these the fact that planes do not always have unlimited room to manoeuvre. For example, in the typical West African airport, there are no parallel taxiways which results in planes having to do tight 180 degree turns at the end of runways.

This will mean that some tyres will be stationary while fully supporting the load of the plane as it turns, thus generating heat.

While most of these conditions are transient, a typical plane tyre will experience extreme centrifugal forces, heat and other stresses than those faced by even the most heavily overloaded Mombasa-Malaba truck.

Consequently, an aviation tyre carcass is much stronger. It is also typically pressurised to 200 pounds per square inch as opposed to just 30 for a car tyre.

Nitrogen is used for inflation since it does not support a fire and won’t react with the inner lining of the tyre. An additional safety measure is that these tyres are usually fitted with fusible plugs that melt and deflate the tyre when tyre temperatures exceed safe limits. Tyre care is very important in aviation.

Debris accidents

Not only will a poorly maintained tyre wear out quickly, thus increasing expenses but it will also pose a safety risk. In fact, debris cast from disintegrating tyres rotating at high speed have been implicated in several accidents the most famous of which was the Concorde accident in Paris.

Dr Ondieki is a pilot with an international airline.

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