This is a plane on final approach to the runway, did you see what just happened there?
Imagine yourself driving your car at a speed of 60 mph and suddenly you smash the brakes
completely, you will notice that the tires will produce smoke, THIS IS FRICTION.
Now, when an aircraft lands at 180 knots it creates friction too.
The reason it happens is that: exactly before the tires touch the ground it is static; its
rotational velocity is not the same as the velocity of the airplane.
So, what happens is that the tires will start skidding as it touches down trying to catchup.
The airplane essentially drags the wheels down the runway until the tires accelerate
to the level that their rotational velocity matches the velocity of the plane, so that
short time when the tire is skidding is what produces the smoke.
This is similar to drifting your car, your car tires produce smoke because the wheels
are spinning much faster than the car is supposed to be going, so the excessive friction with
the payment produces smoke.
But this makes me wonder, how do these small tires carry the weight of massive airplanes
without bursting on landing?
So now image this: the A380 is taller than a 7-story building, and it can carry as many
as 800 passengers at once, we are talking about the weight of a huge office building
here, yet when it hits the tarmac at 170 miles per hour with a weight equivalent to 400 African
elephants, and it nails it every time, these tires don’t burst.
Well, this incredible capability is because of how the tires are made and inflated, unlike
car tires, airplane tires are highly reinforced.
They're made with a combination of synthetic rubber compounds, which are paired with aluminum
steel reinforcements, nylon, and aramid fabrics.
Also, the tires are inflated twice as much as truck tires and six times as much as the
cars.
That's because the higher the pressure, the firmer the tire, and the more strength it
has to support the weight of the plane.
And they're not inflated with ordinary air, airplane tires are filled with nitrogen because
nitrogen is not affected by changes in temperatures and pressure.
What this means is that if you fill your tires to spec in your 40-degree hangar in New York
and then fly to California, the pressure in the tires will be pretty much more stable
throughout the flight and you won’t end up with over-inflated tires when you arrive
at your destination.
But even if the tires are strong enough, how many years can a plane take off and land before
reaching retirement?
Well, the short answer is: it depends.
The long answer is: the lifespan of an airliner is not measured in time, instead, it is counted
based on pressurization cycles.
Each time an aircraft is pressurized during the flight, its fuselage is subjected to stress,
the lifespan of an aircraft is reached, when there were certain metal fatigues and cracks
which may pose danger, the service life of 20 years is generally expressed by approximate
figures of 51,000 flight hours, and 75,000 pressurization cycles for most aircraft.
If an aircraft is used on long haul routes, it experiences relatively few pressurization
cycles in its life and can remain airworthiness far beyond 20 years.
And this is also why airplane windows are round because it helps with pressurization.
So how it works is that as the airplane climbs high into the sky, it is pressurized, if not
you and everyone including the pilots will pass out, so what happens up there, the outside
atmospheric pressure lower, because the plane is pressurized to keep everyone breathing,
and the pressure inside the plane will become greater than the outside pressure, this results
in a “pressure difference that causes the fuselage to expand, and go under stress.
With circular windows, the curves help distribute the stresses so that they won’t build up
a particular point.
Windows with edges will experience most of the stress at the four edges, which creates
weak points and compromises the structure of the fuselage.
Over time, those weak points will begin to crack and it has a disastrous consequence
at the higher flight levels, with the possibility of causing an explosive decompression scenario
i.e., the plane might disintegrate in mid-air.
When you look closely at the window of an airplane, at the bottom center, you will see
a hole there, it is called the bleed hole.
Well, despite the questionable name, it's there for your safety.
Airplane windows consist of three separate layers.
The outermost layer deals with the air pressure difference, while the innermost one, which
is the one you leave your prints on when you want to touch the window of an airplane to
know what it feels like, is actually there to protect the middle layer from passengers’
curiosity.
Now the purpose of the middle layer with the small bleed hole is to allow pressure to reach
equilibrium between the passenger cabin and the air gap between the layers so that the
cabin pressure during flight is applied to only the outer layer.
Wait, that’s ambiguous, okay, I’m basically saying that there is a little gap between
the middle layer and the outer layer, so the "bleed hole" is used to transfer all the pressure
from the passenger cabin to the outer layer, meaning that the outer layer takes all the
pressure while the middle layer acts as a fail-safe in case something happens to this
third layer and it gets smashed, the middle layer will be able to protect you from injuries
and lack of air pressure outside.
While this tiny hole plays an important role in keeping passengers and pilots safe, it
also helps keep the window layers from fogging up as a result of the temperature difference
between the inside and outside of the cabin, so without it, you won’t be able to stare
out into the clouds or take pictures of the airplane wing haha.
Oooohhh, we have been talking about pressurization a lot.
But, why don’t planes just fly at an altitude where they won’t need pressurization and
save all the stress and headache?
The cruising altitude of most commercial jets is about 35,000 feet, turboprops fly lower,
most of them level out at 25,000 feet or less, but why can't they fly just high enough to
avoid crashing into tall things like skyscrapers and mountains?
Well, the thing is, this altitude isn't some randomly chosen number.
Okay firstly, the higher you rise above the ground, the thinner the air becomes, so this
means that an aircraft face less air resistance at higher altitudes and the jet engine will
operate more efficiently, allowing an aircraft to travel faster whilst at the same time,
burning less fuel, here’s an example to demonstrate how the air thins out as you get
higher; imagine moving your hand through a bucket of water and a bucket of honey.
If you want to move your hand through both of these liquids at the same speed, you need
much more effort to move your hand through the honey than the water.
This is the same principle with an aircraft flying at a higher altitude when compared
to a lower altitude, so this means that the amount of work the engine needs to do at a
lower altitude to attain 500 mph is higher than the amount of work it will need to do
to attain the same speed at higher altitude.
So, it’s more fuel-efficient for a plane to fly high altitudes, also up there the skies
are clearer making it easier to navigate, so won’t have to worry about flying into
a thunderstorm, and it is smoother up there too, meaning: less turbulence.
Now, if you go to any airport and observe closely, 8 out of every 10 planes you will
see are painted white, why is it so?
I mean, I love the colorful livery of all Nippon airways, Southwest’s blue, Air New
Zealand’s black.
But, why can’t airlines paint their planes like this?
Or this?
I mean, take a good look at this, isn’t it beautiful?
Well, the thing is, the reason why most airlines chose to paint their planes white all comes
down to cost.
Yep, you heard that right.
Paint on a plane adds anywhere from 600 to 1,200 pounds to the aircraft’s weight.
This extra weight increases the amount of fuel a plane burns and is equivalent to carrying
as many as 10 additional passengers.
Removing this unnecessary weight makes the flights cheaper to operate.
The paint also costs money, both for the initial paint job and for repaints when the color
begins to dull.
Also, the white color does not fade as fast as other colors, meaning that the aircraft
has to be repainted less frequently.
Another reason airlines prefer white is because of the amount of heat an aircraft absorbs
from the sun, white paint helps to reflect the sunlight, unlike darker colors that absorb
heat, white color bounces them back and minimizes the potential harm from solar radiation.
planes have some parts made from plastic carbon fiber and fiberglass, those things, in particular,
need the most protection from a blazing sun.
That's why all the control surfaces of the plane, along with the nose cone should always
be painted white.
Modern planes that are made from composite materials need even more protection from the
sun as they can be damaged by UV radiation, which is another reason why white paint is
used.
So, this is it.
Hope you learned something today?
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See you at the next video.
Thank you.