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These days, you have to be an astronaut
or a fighter pilot to break the sound barrier.
But a few decades ago, all you had to do was buy a ticket.
Back then, we had the Concorde, the famous supersonic plane
that could get you from NYC to London in just under 3 hours.
But its reign was short-lived.
Beset by concerns over safety, cost, and emissions, it was retired in 2003.
And there was one other problem: the Concorde could only fly over the ocean.
Supersonic planes create sonic booms, which are annoying. And disruptive.
So disruptive, in fact, that many countries have passed laws
prohibiting non-military aircraft from flying faster than sound over land.
So if we want super-fast flight back, we need to
find a way to take the “boom” out of “sonic boom.”
Maybe even make it something else entirely… like a sonic thump.
And that’s what engineers are proposing. And they think they’re getting close.
[♪ INTRO]
Meet the X-59, our newest bid at commercial supersonic flight.
This funny-looking bird is part of NASA’s Quesst program,
which stands for Quieter SuperSonic Travel.
The X-59 has been in development for a long time,
in partnership with Lockheed Martin’s Skunkworks, a frequent NASA contractor.
At the time we’re making this episode,
engineers are very close to a working prototype.
Meaning they’ll have the ability to run real tests over real areas with real people.
Which is important, because it will let them evaluate the most important
and difficult part of the design: how quiet can they make a sonic boom.
So, why do things that go very fast make very loud noises in the first place?
Well our plane is flying through air, and air is (in this case)
also the medium that propagates sound.
As a plane flies, it has to nudge the air out of the way.
And this pressure is effectively also sound,
because sound is a pressure wave that our eardrums detect.
Now imagine the plane is going faster than sound, around 340 meters per second.
It's literally going faster than that pressure wave can move.
This means the pressure waves build up continuously,
creating a big old shock wave that we hear as a loud crack.
It's like the plane is doing a belly flop into a pool... again and again.
Not only is this as loud as a thunderclap. It’s extended, too.
Supersonic planes carry their booms across their entire flight path.
There’s even a risk of physical damage down below, like broken windows.
Sound waves are waves of pressure, after all.
Hence the current laws against commercial over-land supersonic flight.
And that severely limits the capabilities of a commuter aircraft.
For example, you could fly supersonic from New York to London,
but not from New York to Los Angeles.
And that brings us to sonic thumps.
That’s what the engineers of the X-59 call the aircraft’s new, quieter sonic boom.
It’s predicted to be quieter than a car door closing.
As for what it’ll sound like exactly, I am not kidding but we reached out to NASA
and they basically said they’d know when they heard it.
But joking aside, big thanks to Mark Mangelsdorf
and the X-59 team for answering our questions for this video.
Now predicting a sonic thump and realizing that prediction are two different beasts.
So, how is the team going to make it real?
Well basically, they have to figure out a way to change a belly flop into a swan dive.
Usually, a boom registers on a pressure-reading device
as an N-shaped plot with sharp points.
Now Sharp points here, equal loud noise.
But if you can figure out how to smooth out those sharp points,
you can lower the volume of the sound.
And the key, just like in diving, is shape.
The X-59 isn’t just weird-looking for no reason.
For a start, the plane’s 11.5-meter-long nose pierces through the air,
giving the surrounding air molecules more time to get out of the way.
This keeps air pressure at the front of the plane
from building up all at once, and softens the boom.
The X-59 also has no bulky cockpit window.
Instead, the pilots use two small mounted cameras
and a 4K live display to see in front of the plane.
And the bottom is super flat, so air can just flow uninterrupted.
Pretty much all protrusions are kept on top,
so that the plane can shield the ground from any boom that they might create.
Turns out there’s not a lot of folks listening from up above.
All very cool ideas, theoretically. But how do we know it’s going to work?
Well, like anything else, we test it. A lot.
The first and most repeated step in the X-59’s development is 3D modeling.
It’s a huge part of plane design, as it allows engineers to digitally
test and retest designs without having to build a whole plane.
Without it, we probably couldn’t design this kind of plane at all.
Now once researchers have a good idea of what the plane should look like,
they can move on to the wind tunnel.
There, they can test a scale model of the plane to
actually measure any booms that formed,
see how quiet those booms are, and examine how the plane works in real life.
Then, and only then, can engineers make a full-sized prototype.
Which is what’s up next for the X-59.
The engineers had to pass a few hurdles on their way to real test flights.
Obviously, they had to get through all the bumps in the design process.
But they also needed special approval from the Federal Aviation Administration
to actually do the technically-illegal flying-over-land bit.
As these tests progress, the team will have to follow certain rules.
For example, they can only fly in certain spaces,
and they have to give ample warning to those below before a flyover.
During the tests, the researchers will be able to study the flyover communities
to see how disruptive the new-and-improved boom really is.
Imagine being approached for that questionnaire.
Pardon me, but how annoying was our sonic thump? Be honest.
The team will also make use of newly-developed shock wave photography
to basically take pictures of the booms, or thumps as the case may be,
and study them in unprecedented detail.
It’s still going to be a while before this thing is finished.
And a quiet boom won’t fix everything.
After all, High operational costs and carbon output still exist.
But if it can fly over land, and not just ocean, the X-59 may actually
be cost-effective… unlike the Concorde before it.
After all, if you can fly anywhere, a whole new world opens up.
And thank you to Brilliant for supporting this SciShow video!
Brilliant is an online learning platform with thousands of
interactive lessons in math, science, and computer science.
They even have bonus puzzles in each
of those categories, like their Physics Puzzles.
These get you thinking about physics topics like pressure,
which we touched on in this video.
If you want to learn more about the mechanics of the wind tunnel experiments
I just mentioned or the waves of pressure that create those booms,
this Brilliant course is a fun way to start exploring those topics.
To try it free for 30 days, you can visit Brilliant.org/SciShow
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And thank you for watching!
[♪ OUTRO]