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If you love flying as much as I do.
Your priority will always be getting that window seat.
Some of my favourite experiences from travelling have been experienced through the window of
a plane.
From looking down on the Burj Khalifa to returning to the green fields of Ireland.
Flying has always been a special experience for me.
So when I got a chance to fly on the Boeing 787 Dreamliner, with it’s huge windows I
was extremely excited.
I had been waiting for years to get the opportunity to fly in this ground breaking plane.
To some of you it may just look like another everyday passenger plane, but the 787 is a
revolutionary plane.
The dreamliner was the first commercial passenger plane to fly with the majority of its structure
being built with composite materials, mostly carbon reinforced plastics.
This reduced the weight of the aircraft dramatically, helping it to be around 20% more fuel efficient
than similar sized aircraft.
That 20% increase in fuel efficiency isn’t just saving you and the airline money, but
it has allowed new flight routes, that were previously financially unviable to open.
You see, the 787 is not a huge plane.
It can carry less than half the passengers than the double decker airbus A380 and fills
the size gap between the Long-Range Boeing 777 and short to mid range 737.
Boeing specifically built this plane to serve more niche routes that larger planes could
not serve, as the amount of people flying between the locations was too low to sell
the number of tickets needed to make it profitable.
Airlines call these long, thin routes.
Want to fly from Dublin to Los Angeles directly?
The 787 made that possible.
No more stopping in London or New York.
This ability may have even saved Polish airlines from bankruptcy, as the dreamliner finally
allowed them to profitably fly directly from their Warsaw hub to New York, Chicago and
Toronto.
This is great for airlines and great for any of us who live in relatively small cities
that usually have to travel to the nearest large airport to fly to our final destination.
But my favourite thing about the Boeing 787 are those huge windows.The 787s windows are
this much larger than an average airplane window.
If you are anything like me you always end up with your face crammed next to the window
trying to get the best view, but with the 787 you can see so much while sitting back
and relaxing.
It really gives your this wonderful panoramic view feeling.
It also has these electronic dimmers, which do away with the need for those crappy plastic
shutters, which people insist on opening while others are trying to sleep.
That isn’t possible on the 787 as the master dimming switch is controlled by the flight
attendants.
So you may be wondering, why are these windows so much larger than other planes?
This is another advantage of composite materials.
You may remember from my first video, early passenger planes like the De Havilland Comet
had a series of unfortunate midair explosions, due to stress concentration at the corners
of their square windows.
After intensive research the investigators discovered that the square windows were blocking
the flow of stress in the structure, making it pile up in the corners of the window.
Round windows allowed the stress to flow much more smoothly around the windows and thus
our windows have been rounded ever since, but shape is not the only thing that can elevate
stress concentrations.
The size of the window has a huge effect on it too.
A larger window means more stress has to detour around the window and thus the stress concentration
is elevated, which can result in cracks and failures over repeated cabin pressurisation
cycles.
So these large windows do result in higher levels of stress concentration around the
787 windows.
But I failed to mention one factor in that short little 2 minute video a year ago.
Fatigue.
Over the course of a plane’s life it is repeatedly pressurised and unpressurised as
it rises and falls through the atmosphere.
This means the material experiences varying stresses continually over it’s life that
can damage it.
This was the second piece of the puzzle for the De Havilland Comet mystery and it’s
engineers proved it by building this huge water tank where pressurisation test could
be done quickly . The test fuselage had undergone 1,230 normal flights and 1,830 tank flights
before the fuselage failed at the corner of the square windows.
This is why parts need to be replaced after years of use.
A part may handle a single application of a load without any problem, but after many
of cycles of loading the material will begin to weaken as tiny cracks form in the metallic
structure.
Metals like aluminium, which is traditionally used for aircraft fuselage, have a natural
tendency to form cracks over time.
This is because small defects in the crystal structure called dislocations, which are essentially
holes in the atomic structure create weakness that makes it easier to deform.
These dislocations can travel through the metal structure and have a tendency to coalesce,and
so after hundreds of cycles what was once a small defect can grow into a large defect
in the form of a crack and these cracks cause failure of the part.
Fatigue failure in composite materials is incredible complex and we still have a lot
to learn about the subject.
I have no problem admitting right now, I don’t understand it enough to teach any of you with
confidence on the details and I have a thesis specialising in the subject.
But I can say this with confidence, fatigue failure does not happen as quickly in carbon
fibre reinforced fuselages and there are many tests to prove that.
The Boeing 787 fuselage is manufactured by wrapping layer after layer of resin soaked
carbon fibre around the fuselage many times.
This creates a structure that is very resistant to fatigue as the high strength fibres are
wrapped continuously around the fuselage.
Fatigue failure will eventually occur in the plastic resin holding the fibres together,
but it takes a great deal longer than in aluminium.
This allows the carbon reinforced plastic frame of 787 to tolerate higher stresses in
the fuselage and last longer doing it.
There is still a lot to be learned about the mechanics of composite materials.
Composite materials are a difficult material to work with at the best of times and we will
be learning more about that in the next video, where we will be learning more about the history
of the material and I will be visiting a local composites factory to show you more about
the manufacturing process.
Thanks for watching!
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