Why Are Airplane Windows Round?

The windows in our homes and cars tend to be rectangular(ish) -- so why are airplane windows always round? Learn the science in this episode of BrainStuff, based on this article: https://science.howstuffworks.com/transport/flight/modern/airplane-windows-round.htm

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Episode Transcript

Speaker 1 (00:01):
Welcome to brain Stuff production of iHeart Radio. Hey brain Stuff,
Lauren bog Obam. Here, we're used to seeing square and
rectangular windows in most building structures. There are, of course,
rounded windows or oculi in architectural parlance, that lend character
and intrigue to design. But think about airplanes and jetliners

(00:25):
always round windows. How strange would it be to walk
down the aisle of a jetliner and buckle up next
to a square window. Our ancestors may have done just
that once upon a time, as square windows were in
fact the norm in early commercial airplane manufacturing. They worked
just fine for centuries and homes and buildings, so why

(00:46):
change a perfectly good design. Unfortunately, it took a few
tragic events for engineers to take a fresh look at
aircraft window design. It was in the nineteen fifties when
commercial airliners were getting bigger, and they also started disintegrating
in mid air. Two of those were to have land Comets,
which were the first commercial airliner powered by jet engines.

(01:10):
Their debut flight was May second of nineteen fifty two
and their last was in September of nineteen eighty one.
But the two that experienced this type of failure fell
apart in flight in separate events in nineteen fifty three
and nineteen fifty four. The cause was found to be
those square windows. Engineers determined that the sharp edges of

(01:31):
the plain squared windows created natural weak spots, causing metal
fatigue failure. Metal fatigue failure is basically what happens when
a piece of metal is subjected to repeated stresses, which
cause micro cracks in the metal, which can grow to
the point that the piece of metal snaps or tears.
It can be catastrophic, but the cracks can be so

(01:53):
small that it happens without any visual warning. So the
corners of these square aircraft windows were easily stressed then
further weakened by air pressure at high altitude. By the
nineteen fifties, aircraft like that the Haveland Comets were flying
faster and higher than industry predecessors, meaning after multiple flights

(02:14):
and repeated pressurization, those square windows basically broke apart from
the pressure. Rounded windows, on the other hand, are able
to distribute the pressure evenly because they have no corners
for stressed to concentrate, reducing the likelihood of cracks or brakes.
The circular shapes are also stronger in resist deformation, making
them more able to withstand the repeated pressure differences between

(02:37):
the inside and outside of the aircraft. You might also
notice that there are multiple layers of acrylic, not glass
between you and the outside of the aircraft. Those layers
offer additional protection from weather events like rain, wind, and fog,
and that tiny hole at the bottom. Those are called
bleed holes, and they add another layer of protection, helping

(02:59):
keep the air pressure on board at a relatively constant
level by allowing the air to pass through the various
window layers. So the next time you're on a flight,
be thankful for those rounded windows, whether you're enjoying the
view or avoiding it because you don't want to be
reminded of just how high off the ground you are.

(03:22):
Today's episode is based on the article why are airplane
windows round? On how stuffworks dot com, written by Schrei's Cunningham.
Brainstuff is production of by Heart Radio and partnership with
how stuff works dot Com, and it's produced by Tyler Clang.
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