By Girish Linganna
When you are sitting in an airplane cabin, you rarely feel the speed at which the plane is cruising (740-930 km/h). This allows you to look out over the clouds (at 31,000-38,000 feet) through the window and even enjoy a hearty meal or catch up on a movie onboard. But the adrenaline kicks in as you see the flight approach the runway for landing at the relatively low speeds of 240-270 km/h. And justifiably so, as most accidents tend to happen during this very phase of the flight.
In reality, it’s easier to make an airplane fly than it is to make it stop. The airplane must significantly reduce its airspeed while approaching the runway and then go on to curb its momentum fast after making a touchdown on the runway. The state-of-the-art aircraft tyres and the braking system make this possible.
During a typical landing, aircraft tyres have to brace for a huge impact at high speeds while carrying tens of thousands of kilograms in airplane weight (Antonov An-225 weighs a massive 640,000 kg). Logic would suggest that these tyres should explode during landing. But why don’t they?
The Science behind Aircraft Tyres
Tyre blowouts are fairly common on the road when it comes to cars, tractors, and motorcycles. You would imagine that such blowouts would be fairly common with aircraft tyres. But they don’t really happen because of the remarkable amount of science that reinforces the strength of aircraft tyres—impressed yet?
Part of this extraordinary strength comes from them being reinforced. These tyres are made out of proprietary synthetic compounds that are paired with nylon cords under the treads and special aluminum and steel reinforcements. This makes the tyres so strong that each of them can withstand a 38-ton load. There can be between 14 to 32 tyres on a jumbo jet, and together they help distribute the weight of the aircraft, which could go up to 300 tons and beyond.
The air pressure of the aircraft tyres also contributes to their strength. A normal aircraft tyre pressure is, on average, six times more than the air pressure in your car tyres at 200 psi. In the case of fighter jets, the tyre pressure may go up to 320 psi.
These tyres are also required to withstand an astonishing range of temperatures which can change from minus 60 degrees Celsius in the skies to extremely hot conditions when landing in the world’s warmest countries. To withstand such harsh conditions, these tyres are filled with nitrogen instead of air. Why? It’s because nitrogen does not react with rubber as high temperatures and pressure changes have less effect on it. Also, nitrogen doesn’t leak through the tyres as much as oxygen does. Tyres that are inflated with nitrogen remain inflated a lot longer, which means aircraft tyres need less maintenance and that saves airlines money
Each tyre of an airplane also uses grooves instead of the block patterns you see on your car’s tyre. This is important as the grooves help the airplane evacuate water while landing and taking off during wet conditions on the tarmac.
Small in Size for a Reason
Have you ever looked at an airplane while landing and wondered about the relatively small size of the tyres in comparison to the entire fuselage? The size of the tyres on commercial airplanes range from 27 x 7.5R (27 inches in diameter and 7.5 inches in width) in Boeing 737 to 50 x 20R in Boeing 787.
There’s a reason for this. Larger tyres have actually been proven to be no more effective than smaller tyres. Neither are they any safer. Rather, they may add extra weight to the whole structure of the plane. Heavier the plane, the more it requires in fuel, and the more it costs an airline on each flight. So, engineers have always worked on making the aircraft tyres as small and as safe as possible.
After each tyre is produced, it is put through a series of tests to ensure that it can withstand loads higher than it is expected to carry. The strongest of tyres are expected to not blow out even at a high landing speed of 463 km/h. Besides, the tyres are put through computer simulations to check how they will react to standard landings, takeoffs, and even taxiing before making a prototype of an aircraft tyre.
Aircraft tyres also have special fusible plugs that are designed to melt at a certain temperature. They act as a fuse to provide a safer failure of a tyre and prevent blowouts due to overheating. In such conditions, the plugs inside the tyre melt in a controlled manner, and minimize the risk of damage to the aircraft in cases of excessive braking.
Extending Life of an Aircraft Tyre
Aircraft tyres are highly durable too. Each one can touchdown on the runway about 500 times without requiring a new layer of rubber. But for such longevity, mechanics must conduct thorough checks throughout the lifecycle.
Heat is no friend of tyres be it for cars, motorcycles, or airplanes. But under-inflation of an aircraft tyre can increase its footprint as it rolls on the ground and couples badly with the build-up of heat. This wears the treads out more quickly than it should. In multi-tyre landing scenarios, an under-inflated tyre can force other (even properly inflated) tyres to take a lot of strain too, which over time causes these tyres to wear down too.
Aircraft tyres operate in extremely harsh conditions and consistent care is critical for their long life. The most important thing that a tyre mechanic needs to do is to maintain proper tyre inflation pressure as failure to do so can also lead to dire consequences. The grimmest of these can be a complete structural failure of the tyre.
When aircraft tyres are under-inflated or overloaded during takeoff and landing, the nylon cords in the structure of the tyre go in and out of compression as the tyre rotates. Over time, the inconsistency in the tyre pressure weakens the cords and causes the tyre structure to fail.
Apart from affecting the nylon cords, under-inflation can result in wear and tear of tyre tread. In such cases, the shear between the components of the tyre increases as it rolls in and out of contact and deforms. This can cause the rubber to revert. Reverted rubber has no strength to contain the structure, which can, over time, allow for the tyre to decompose. This can lead to tread pieces coming off the tyre and causing heavy damage to the aircraft.
Aircraft tyres can lose up to 5% of their pressure in 24 hours. Hence, it is important for aircraft mechanics to keep an eye on the pressure of these tyres.
Aircraft Tyre Industry
The pandemic grounded flights all over the globe and it had a significant impact on the travel industry. It also had a big impact on the Aircraft Tyre industry. In 2021, the industry was worth $2.59 billion in 2021, according to a report published by Global Market Insights Inc. The aircraft tyres market is expected to grow to $3.21 billion at a CAGR of 3.2% from 2022 to 2028. This growth of the industry is backed by growing job mobility, business meetings, migration, and tourism coming back as we get past the COVID-19 pandemic. Air travel being the fastest means of transit, is in high demand once again, and this spells great things for the aircraft tyre market in the near future.
The landscape is highly competitive in the aircraft tyre industry, which includes likes of Aviation Tires, Bridgestone Corporation, Desser Tire & Rubber Co., Dunlop Aircraft Tyres Ltd., Goodyear Tire & Rubber Co., Michelin, Petlas Tire Corporation, Qingdao Sentury Tire Co. Ltd., Specialty Tires of America, Wilkerson Company Inc. (Wco) Ltd., dominating.
Between 2022 and 2028, the tubeless tyre segment is slated for growth at 3.4% as there has been a rise in the application of tubeless tyres in business jets. The trend is expected to continue its upwards trajectory in the coming years.
Moving forward, the industry is showing robust recovery and fast catching up to its pre-pandemic demand levels. Especially the Asia Pacific region is seeing a huge demand for low-cost aircraft carriers. And countries including China, South Korea, India, and Indonesia are expected to play a major role in supporting the growth of the regional and global markets of the aircraft tyre industry for years to come.
(The author is Aerospace and Defence Expert & Director, ADD Engineering Components (India) Pvt Ltd (An Indo- German Company). Views expressed are personal and do not reflect the official position or policy of Financial Express Online. Reproducing this content without permission is prohibited).