Airplanes are mysterious things: unimaginably heavy metal giants soaring through the sky,
jam-packed not only with people but also all kinds of electronic gizmos, and overhead bins
stuffed with their oversized luggage – and perhaps children.
No not really.
What confuses me the most however, is the airplanes tires.
Yeah really.
I mean, look at them compared to the plane’s body – they're tiny!
How can they withstand all that weight and speed?
Okay, let's check out what's happening when a plane is preparing to land on the runway.
While still in the air, its speed is becoming lower... and lower...
That's when you might feel your ears getting congested.
You also sense that the plane has seemingly started crawling at a snail’s pace, when
just a second ago, it was moving at breakneck speed.
In their flight deck, the pilots are slowing the plane down even more and getting ready
to lower the landing gear (which is often called the undercarriage).
That's a complex mechanism that consists of structural components, energy-absorbers, brakes,
hydraulics, and, of course, the wheels and tires.
From your seat, you can hear a distinct robotic noise - that's the landing gear and wing flaps
being lowered.
Then, when the airplane is about to land, its nose starts pointing upward.
If it seems counterintuitive, think about water-skis.
When a skier is moving across the water’s surface, their skis are always inclined upward.
Otherwise, both the skier and the skis would go under the water.
The same approach goes for planes: pilots must point the aircraft nose toward the sky
just before landing so that they don’t stall the machine.
Plus, exposing all that large surface area on the wings and belly will help slow the
speed of descent.
Anyway, several seconds later, all 300 tons of your airplane touch the ground while still
going 170 mph.
Imagine your typical 2-story house, fully furnished, dropping to the ground as fast
as a flying arrow - that must be quite the impact!
And STILL, those tiny (comparatively) little tires don’t pop under the tremendous pressure?
This incredible feat has to do with the materials airplane tires are made of, the gas that fills
these tires, and the way they're inflated.
To make an airplane tire, producers use a mix of different kinds of synthetic rubber.
It makes aircraft tires so strong that each of them can easily deal with a 38-ton load.
“Um, didn’t you just say 300 total tonnage?”
Hey good memory, yes I did, but remember, there can be anywhere from 14 to 22 tires
on one jumbo yet!
They’re durable too – a plane can touch the ground up to 500 times before its tires
will need to be covered with a new layer of rubber.
But what makes tires so tough is mostly nylon cords under the tread and special aluminum
steel reinforcements.
Then there’s the gas they have inside – it’s not oxygen!
At very low temperatures, oxygen can turn into ice right inside the tires.
Of course, the temperature must be extreme for this to happen, about
-360°F, but you never know with air travel!
As for high temperatures (like during braking), they can trigger a reaction between oxygen
and rubber.
When those two mix, the rubber becomes weaker.
And nobody wants weak airplane tires - they can explode!
That's why the gas that fills aircraft tires is nitrogen.
It doesn't react with rubber, which makes it a much safer choice for airplanes.
It also doesn't leak through the rubber as fast as oxygen does, meaning tires that are
filled with 95% nitrogen remain inflated a lot longer.
And it's good news because in this case, wheels need less maintenance which saves the airline's
money!
Now, the pressure in plane tires is 6 times bigger than the pressure in your car tires.
It's 200 psi (which stands for 200 lb per square inch), and that's what you’d feel
if you took a dive 450 ft underwater.
Or rather, you WOULDN'T feel because the maximum pressure a person can withstand is only 50
psi.
But if we speak about airplane tires, such high pressure makes them strong!
It's next to impossible to overinflate a tire to the point that it explodes.
It's true that overinflating can reduce traction and put more pressure on airplane wheels.
But if a popped tire situation happens, it's mostly because of the thing being underinflated.
Even if it did happen on your flight, chances are you wouldn’t even notice.
Remember, there can be plenty of wheels on large airplanes, like an Airbus A380 or Boeing
747.
And if one of the tires fails, the plane will still land safely.
There’s one more reason why aircraft tires MUST be strong and durable.
When a plane touches the ground, its tires aren't rolling at first - they're just skidding.
In other words, the plane is dragging them along the runway until it slows down enough
for the wheels to be able to rotate.
This is when you can see the tires smoking after the touchdown - at this moment, they're
accelerating to catch up with the landing speed.
This whole landing situation also led to tires having grooves cut in them.
If they had block patterns, like the ones car tires have, these blocks would simply
fall off as soon as the plane wheels touched the ground.
The most serious tire-wear happens exactly when the rubber comes into contact with the
runway.
By the way, have you noticed how tiny and skinny (compared to the huge fuselage) airplane
tires are?
Don't worry, they’re just the size they need to be!
Larger tires would be pointless since they wouldn't make landing more effective or safer.
But they would add extra weight.
You probably know that the heavier a plane is, the more fuel it uses, and the more money
an airline loses.
So, engineers try hard to make wheels as small and, at the same time, as safe as they can
be.
After plane tires are produced, they always get tested.
Manufacturers create computer simulations that check how tires will behave if they're
pushed past their speed limit or get overloaded.
They must be able to withstand pressure that’s 4 times stronger than their usual one and
should cope with this situation for at least 3 seconds.
As for the strongest tires, they shouldn't blow out even at a landing speed of 288 mph!
The same computer programs figure out how tires will react to standard landings, takeoffs,
and even taxiing, and then prototypes are created.
And still, airplane tires aren't entirely safe from bursting.
Accidents did happen in the past, and planes did skid off runways because of one of the
tires exploding mid-landing.
There were also cases of tires bursting mid-air.
If it's just an exploded tire, it's nothing too bad.
But tire fragments can get into the engine or cause serious damage to the fuselage.
That’s when the incident immediately becomes more dangerous!
Besides, when a plane lands with one or several damaged tires, the load gets uneven, and it
puts stress on the landing gear.
In the worst-case scenario, all tires (even good ones) might need replacing after such
an incident.
You can't argue that airplane wheels are cool, but sometimes, they need additional help.
I'm talking about hydroplaning - a situation that occurs when the runway is covered with
a layer of water preventing a landing plane from braking and stopping in time.
The aircraft just keeps skidding forward, unable to find traction.
(The same can happen to your car on a rainy day, by the way!)
That’s why some airports have grooves on the runway.
Water flows into these grooves, making the surface not so slippery and dropping the chances
of hydroplaning.
Pilots claim that the difference between grooved and non-grooved runways is dramatic.
And all that sounds pretty groovy to me.
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