Modern day fighter jets can travel faster than the speed of sound without breaking a
sweat, but until, 70 years ago on October 14 of 1947; no human had ever traveled that
fast.
Those who came close saw their aircraft become uncontrollable, or shake themselves to pieces,
leading some to believe that manned flight faster, than the speed of sound, was impossible.
There seemed to be a “sound barrier.”
And we wanted to break it.
You may be wondering why the speed of sound is important in aviation at all, and to understand
that you have to remember what sound is in the first place.
Watching a wave travel down a slinky is a good visualization.
In a gas, sound travels as a longitudinal wave, meaning that it propagates when air
molecules bunch together and then space out again.
Watching a wave travel down a slinky is a good visualization.
[pause]
As planes fly through the air, they create sound waves.
But if the planes go fast enough, they start to catch up with their own sound waves.
Air molecules get rammed into each other faster than they can get out of the way, and the
waves pile up to form a powerful shock wave -- that famous sonic boom observers hear when
a supersonic jet goes by.
But, the sudden and extreme air pressure is just the start.
As the air behind the shock wave breaks up in a turbulent wake, it can swirl and violently
slap at different parts of the plane, causing buffeting and increased drag.
For the airplanes of old, this was bad news.
First, there was the problem of the propulsion system.
As a propeller spins, the tips of the blades can actually break the sound barrier.
When that happens, the air starts swirling and increasing drag, and the prop’s efficiency
drops.
Maybe these problems could be overcome with a radically different propeller design, but
by the end of WWII, rockets had advanced and the jet engine had been invented, so there
wasn’t much point trying to force the poor propeller to do a job it wasn’t suited for.
Even with the jet engine replacing old propellers, there was another problem to overcome at speeds
close to the speed of sound: the wings.
Wings on old aircraft were straight as a 2x4 and when we were puttering around at subsonic
speeds, they worked just fine.
But when airplanes are right around that magical sound barrier, at what’s known as transonic
speeds, the airflow over straight wings does something you might not expect.
Namely, it actually goes faster than the speed of sound.
This makes sense when you consider how a wing fundamentally works.
They’ve got that curved shape on top to make the air on that side travel faster.
But if the air on top of the wing goes faster than the speed of sound it’ll form, you
guessed it, a shock wave.
And just like before, the air behind that shock wave gets all turbulent as it expands,
increasing drag dramatically and maybe even separating airflow from the wing’s surface
altogether.
Which is bad.
So, the solution was as simple as it was genius: sweep the wings back.
By placing the wings at an angle, some of the air travels down the wingspan, and the
rest accelerates across the wing more slowly, so the aircraft can fly faster before running
into the problems of a shock wave on the wing.
That means the fighter jet doesn’t have to work as hard to break through the sound
barrier completely, and when it does shock waves that form on top of the wing travel
to the trailing edge where they cause less drag.
With powerful jet engines and swept wings, the sound barrier that once seemed so solid
is now routinely smashed.
It makes you wonder what other things that seem impossible today will be routine in the
future.
For more epic stories of innovation that shaped our future, check out TheAgeOfAerospace.com
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Did you know it’s possible to create something like a sonic boom but with light waves?
No?
Trace explains how, here.
What’s the next big innovation you’d like to see in flight?
Low earth orbit passenger routes?
Affordable supersonic transport?
Wider arm rests?
Let us know in the comments and I’ll see you next time on Seeker.