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 zoomingthrough the sky faster than the speed of sound? Well, if you flew on a Concorde jet back beforethey were grounded — or you happen to be a fighter pilot — then you’ve probablyexperienced faster-than-sound travel.
And, some companies are looking to make supersonicflight a reality again, with new commercial planes that travel faster than the speed ofsound.
And someday, you might be able to fly overthe Atlantic Ocean in an hour — or even less.
Problem is, most people don’t want to flyon a plane that feels like an out-of-control rocket.
And there’s also the problem of faster-than-soundplanes becoming ridiculously hot and unbearably loud.
So engineers have some developing todo.
On the morning of December 17th, 1903, OrvilleWright became the first human to successfully pilot an airplane — a heavier-than-air vehiclethat was controlled, powered, and sustained.
His flight lasted 12 seconds, and crossed120 feet of a North Carolinian beach — with an average speed of almost 11 kilometers anhour.
By the end of the day, his brother Wilburflew the same airplane for almost a whole minute, with an average speed of almost 16kilometers an hour.
Less than a century later, in the 1970s, commercialplanes went supersonic — faster than the speed of sound.
A few dozen supersonic planes were in regularservice, available in two models, the Concorde and the Soviet Tupolev.
But the Tupolev onlymade 55 passenger flights, from 1977 to 1978.
And after a Concorde crashed in 2000, peoplestarted to fly on them less.
Eventually, they just weren’t financiallyworth it anymore, and the planes were retired in 2003.
13 years later, there still aren’t any newcommercial faster-than-sound planes.
But soon, there might be! There are just acouple of improvements companies are trying to make first.
The main challenge comes from getting pastwhat’s known as Mach 1.
See, sound usually travels around 1230 kilometersper hour, but that’s not a constant number — it depends on things like the temperatureand humidity of the air.
So, when it comes to planes, it’s easierto talk about speed in Mach numbers, which take into account the speed of sound in theparticular place where the plane is flying.
Mach 1 is just the speed of sound.
Anythingslower than that is called subsonic, and anything faster is called supersonic.
But switching from subsonic to supersonicisn’t easy, because the plane has to overcome the infamous sound barrier.
And that can be a problem, because the soundbarrier is sometimes strong enough to tear away at planes, and even send them crashingto the ground.
The sound barrier exists because of the waysound 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 wavesthat shift the air back and forth, creating areas of lower and higher pressure.
But as the plane gets faster, it starts tocatch up with those waves.
New sound waves start to form on top of theold sound waves, causing huge swings between higher and lower pressure air.
Those differences in pressure can rattle andshake planes like toys, and there’s a real danger of tearing them to pieces.
Low pressure areas can also lead to dropsin temperature, condensing any moisture in the air and forming a visible cloud, sometimesknown as a vapor cone.
The first plane that could get past the soundbarrier was the Bell X-1, built in 1947.
It was designed to absorb 18 times the forceof gravity, and modeled after a machine gun bullet.
It didn’t actually lift off from the groundon 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 readyfor commercial use — with the UK and France designing the concorde, and the Soviet Uniondesigning the Tupolev.
The Concorde flew passengers from London toNew York in about three and a half hours — about half the time it would take in a plain oldsubsonic commercial plane.
But they only flew that one route, and there’sa reason they spent as much time over the water as possible: the painfully disruptivesonic boom.
Like the sound barrier, sonic booms come froma 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 happenonce, like when a plane breaks the sound barrier.
They continue throughout the entire supersonicflight.
That’s because the sound waves keep bunchingup behind the plane, then expanding outwards, creating a cone shape known as the Mach cone.
So wherever the plane flies over land, peoplehear that incredibly loud boom.
So that’s why the Concorde’s supersoniccommercial flights only really happened between western Europe and eastern North America.
If they flew over land, odds are people wouldnot have appreciated the booms.
And even though you can’t fly on a Concordeanymore, you might still be able to fly on a supersonic plane someday.
NASA, for example, is looking into how todampen 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 sonicbooms would happen in the sky, rather than on the ground.
Then there’s the Concorde 2, which Airbusis working on.
The Concorde 2 would first fly directly upward, to an altitude of about 30 kilometers.
Then, the plane would rotate its tail finin a way that would redirect the shock waves to be horizontal, so you wouldn’t feel themas much on the ground.
The Concorde 2 would be able to accelerateup to Mach 4.
5 — and at those speeds, it could take passengers from London to New Yorkin an hour.
But maybe that’s not enough, what if youwant to go faster? The Concorde 2 would be very close to goingbeyond 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 ofsound.
Those speeds get their own category, becausethat’s when the temperature of the plane becomes a bigger issue.
The plane is flying through the air so quicklythat friction with particles in the air is a real problem, because it makes a lot ofheat.
At hypersonic speeds, planes need to be ableto withstand temperatures over 1000 degrees celsius… but almost all of the more typicalmetals would melt, or at least become very weak, at temperatures below that.
The other challenge is the engine, becausea regular jet engine wouldn’t work.
Standard, subsonic planes use large rotatingblades 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 needthe blades — that’s what’s known as a ramjet engine.
Ram, because the air is just rammed into theengine.
At hypersonic speeds, though, this plan doesn’twork as well.
Sure, the air is compressed, but it’s movingso fast that there’s not enough time for it to combust and actually help move the plane.
So hypersonic planes need their own fuel andtheir own oxygen — which is what NASA used in the X-15, the first plane to reach hypersonicspeeds.
It used a titanium skin to protect itselffrom the extreme temperatures, and was able to fly at Mach 6.
It also flew high enough that some of theX-15 test flights are considered space flights.
But the X-15 is not the kind of plane thatcould be used commercially.
For one thing, it burned through fuel so fast that it wouldrun out in less than two minutes.
Also, pilots sometimes experienced 8 timesthe force of Earth’s gravity, and most people wouldn’t consider that a comfortable businesstrip.
So, until engines became more efficient andpractical, commercial hypersonic planes are a long way from reality.
And the scramjetmight be the answer.
Scramjet engines work kind of like ramjetsdo, but they’re designed to handle the faster-moving air.
In testing, NASA’s found that they couldwork at speeds up to Mach 15, at least in theory.
There’s one big drawback, though: scramjetengines only work at hypersonic speeds.
The X-43A, for example, an unmanned test planethat uses a scramjet, has to be accelerated above Mach 5 before it can fly on its own.
It’s strapped to a booster rocket, whichis then loaded onto a subsonic plane.
Alright, stay with me.
The plane flies up to about 6 kilometers abovethe ground, then releases the X-43A, along with the rocket, which gets to about 30 kilometersup and to speeds of Mach 5.
Then the X-43A can start its flight.
So, it might be a while before hypersonicplanes are a practical way to get across the Atlantic.
But a future where a trip to the other sideof the world involves flying faster than the speed of sound, without painful sonic boomsfor the people on the ground? That might not be so far off.
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