Why can’t I just get on a plane and go from,
like, Montana to London, in a couple hours? I just want to experience the thrill of zooming
through the sky faster than the speed of sound? Well, if you flew on a Concorde jet back before
they were grounded — or you happen to be a fighter pilot — then you’ve probably
experienced faster-than-sound travel. And, some companies are looking to make supersonic
flight a reality again, with new commercial planes that travel faster than the speed of
sound. And someday, you might be able to fly over
the Atlantic Ocean in an hour — or even less. Problem is, most people don’t want to fly
on a plane that feels like an out-of-control rocket. And there’s also the problem of faster-than-sound
planes becoming ridiculously hot and unbearably loud. So engineers have some developing to
do. On the morning of December 17th, 1903, Orville
Wright became the first human to successfully pilot an airplane — a heavier-than-air vehicle
that was controlled, powered, and sustained. His flight lasted 12 seconds, and crossed
120 feet of a North Carolinian beach — with an average speed of almost 11 kilometers an
hour. By the end of the day, his brother Wilbur
flew the same airplane for almost a whole minute, with an average speed of almost 16
kilometers an hour. Less than a century later, in the 1970s, commercial
planes went supersonic — faster than the speed of sound. A few dozen supersonic planes were in regular
service, available in two models, the Concorde and the Soviet Tupolev. But the Tupolev only
made 55 passenger flights, from 1977 to 1978. And after a Concorde crashed in 2000, people
started to fly on them less. Eventually, they just weren’t financially
worth it anymore, and the planes were retired in 2003. 13 years later, there still aren’t any new
commercial faster-than-sound planes. But soon, there might be! There are just a
couple of improvements companies are trying to make first. The main challenge comes from getting past
what’s known as Mach 1. See, sound usually travels around 1230 kilometers
per hour, but that’s not a constant number — it depends on things like the temperature
and humidity of the air. So, when it comes to planes, it’s easier
to talk about speed in Mach numbers, which take into account the speed of sound in the
particular place where the plane is flying.. Mach 1 is just the speed of sound. Anything
slower than that is called subsonic, and anything faster is called supersonic. But switching from subsonic to supersonic
isn’t easy, because the plane has to overcome the infamous sound barrier. And that can be a problem, because the sound
barrier is sometimes strong enough to tear away at planes, and even send them crashing
to the ground. The sound barrier exists because of the way
sound waves travel: by compressing and stretching the air they travel through. The compressed air ends up at a higher pressure,
and the stretched air has lower pressure. As a plane moves, it produces sound waves
that shift the air back and forth, creating areas of lower and higher pressure. But as the plane gets faster, it starts to
catch up with those waves. New sound waves start to form on top of the
old sound waves, causing huge swings between higher and lower pressure air. Those differences in pressure can rattle and
shake planes like toys, and there’s a real danger of tearing them to pieces. Low pressure areas can also lead to drops
in temperature, condensing any moisture in the air and forming a visible cloud, sometimes
known as a vapor cone. The first plane that could get past the sound
barrier was the Bell X-1, built in 1947. It was designed to absorb 18 times the force
of gravity, and modeled after a machine gun bullet. It didn’t actually lift off from the ground
on the zone, though — it was dropped from a larger mothership plane, known as the B-29,
so it got a bit of a head start. By the mid-1970s, supersonic planes were ready
for commercial use — with the UK and France designing the concorde, and the Soviet Union
designing the Tupolev. The Concorde flew passengers from London to
New York in about three and a half hours — about half the time it would take in a plain old
subsonic commercial plane. But they only flew that one route, and there’s
a reason they spent as much time over the water as possible: the painfully disruptive
sonic boom. Like the sound barrier, sonic booms come from
a build-up of compressed sound waves, known as a shock wave. The shock wave heads away from the plane,
which you hear as a VERY loud boom — so powerful that they’re sometimes mistaken for earthquakes. And those sonic booms don’t just happen
once, like when a plane breaks the sound barrier. They continue throughout the entire supersonic
flight. That’s because the sound waves keep bunching
up behind the plane, then expanding outwards, creating a cone shape known as the Mach cone. So wherever the plane flies over land, people
hear that incredibly loud boom. So that’s why the Concorde’s supersonic
commercial flights only really happened between western Europe and eastern North America. If they flew over land, odds are people would
not have appreciated the booms. And even though you can’t fly on a Concorde
anymore, you might still be able to fly on a supersonic plane someday. NASA, for example, is looking into how to
dampen the effects of the sonic boom. One way to do that might be by moving one,
or even two engines above the wings, which would direct shockwaves upwards. So the sonic
booms would happen in the sky, rather than on the ground. Then there’s the Concorde 2, which Airbus
is working on. The Concorde 2 would first fly directly upward,
to an altitude of about 30 kilometers. Then, the plane would rotate its tail fin
in a way that would redirect the shock waves to be horizontal, so you wouldn’t feel them
as much on the ground. The Concorde 2 would be able to accelerate
up to Mach 4.5 — and at those speeds, it could take passengers from London to New York
in an hour. But maybe that’s not enough, what if you
want to go faster? The Concorde 2 would be very close to going
beyond supersonic, and into an even faster category, known as hypersonic. When people talk about hypersonic speeds,
they’re generally talking about Mach 5 or higher — more than five times the speed of
sound. Those speeds get their own category, because
that’s when the temperature of the plane becomes a bigger issue. The plane is flying through the air so quickly
that friction with particles in the air is a real problem, because it makes a lot of
heat. At hypersonic speeds, planes need to be able
to withstand temperatures over 1000 degrees celsius… but almost all of the more typical
metals would melt, or at least become very weak, at temperatures below that. The other challenge is the engine, because
a regular jet engine wouldn’t work. Standard, subsonic planes use large rotating
blades to compress incoming air, inject fuel, and then let it burn. Propelling them forward. At supersonic speeds, it becomes even easier,
because the high speeds already compress the air. In that case, the engine doesn’t even need
the blades — that’s what’s known as a ramjet engine. Ram, because the air is just rammed into the
engine. At hypersonic speeds, though, this plan doesn’t
work as well. Sure, the air is compressed, but it’s moving
so fast that there’s not enough time for it to combust and actually help move the plane. So hypersonic planes need their own fuel and
their own oxygen — which is what NASA used in the X-15, the first plane to reach hypersonic
speeds. It used a titanium skin to protect itself
from the extreme temperatures, and was able to fly at Mach 6.72. It also flew high enough that some of the
X-15 test flights are considered space flights. But the X-15 is not the kind of plane that
could be used commercially. For one thing, it burned through fuel so fast that it would
run out in less than two minutes. Also, pilots sometimes experienced 8 times
the force of Earth’s gravity, and most people wouldn’t consider that a comfortable business
trip. So, until engines became more efficient and
practical, commercial hypersonic planes are a long way from reality. And the scramjet
might be the answer. Scramjet engines work kind of like ramjets
do, but they’re designed to handle the faster-moving air. In testing, NASA’s found that they could
work at speeds up to Mach 15, at least in theory. There’s one big drawback, though: scramjet
engines only work at hypersonic speeds. The X-43A, for example, an unmanned test plane
that uses a scramjet, has to be accelerated above Mach 5 before it can fly on its own. It’s strapped to a booster rocket, which
is then loaded onto a subsonic plane. Alright, stay with me… The plane flies up to about 6 kilometers above
the ground, then releases the X-43A, along with the rocket, which gets to about 30 kilometers
up and to speeds of Mach 5. Then the X-43A can start its flight. So, it might be a while before hypersonic
planes are a practical way to get across the Atlantic. But a future where a trip to the other side
of the world involves flying faster than the speed of sound, without painful sonic booms
for the people on the ground? That might not be so far off. Thanks for watching this episode of SciShow,
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