Name: 超音速飛行的驚人簡單的祕密 (A Surprisingly Simple Secret to Supersonic Flight)
Uploaded: 2021-01-14T10:41:23.000Z
Duration: 4 min 36 s
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When the Wright Brothers made their first flight in 1903, people had been trying to

So even though their plane didn't go much faster than 10 kilometers per hour -- basically,

running speed -- it was a major achievement.

What's maybe equally amazing, though, is that it didn't take another few centuries

Chuck Yeager became the first person to fly faster than the speed of sound --

in 1947, not even 50 years after the Wright Brothers.

But making that flight wasn't just a matter of building stronger engines.

To do it, engineers had to solve hundreds of problems -- including ditching one of the

And today, the innovation that helps keep supersonic planes from falling apart is also

the main reason why just about all commercial airplanes look the same.

At first, making a faster plane was really just about building better engines and structures.

Except, as we got better at flying and started approaching the speed of sound, we noticed

just didn't behave like they were supposed to.

Propellers act like sideways wings, and because they're moving with the plane and spinning,

they cut through air a lot faster than the rest of the aircraft.

But once propellers got moving faster than about half the speed of sound, they suddenly

stopped producing as much thrust as expected. And at high speeds, regular wings also didn't

So a plane that flew perfectly at 15% the speed of sound might fall out of the sky at 60%.

The problem lingered for about fifteen years,

until an aerodynamicist named John Stack found a fundamental flaw in the models and equations

everyone used to understand how air moved past objects.

In 1933, after looking at experiments in wind tunnels, he realized that air pressure around

a quickly-moving object drops, because, ultimately, the air is getting squeezed.

but it actually violated one of the biggest assumptions in aerodynamics.

For decades, people had assumed -- in one form or another --

It doesn't squeeze or stretch as it runs into things, but instead just glides by or

In other words, air pressure might change from place to place, but its density doesn't.

This assumption means that you don't need to worry about air interacting with itself

or how that interaction affects the rest of the world.

That makes calculations way easier, and, at slow speeds at least, it's mostly true,

Which is why people hadn't had to worry about it.

But John Stack and other researchers showed that, as you approach the speed of sound,

thinking that air is incompressible is just flat-out wrong.

And it has to do with what the speed of sound actually means.

Essentially, it's just how fast information -- like that a plane is coming -- can get

When a plane is going slowly, molecules can push each other out of the way long before

But if the plane is going close to the speed of sound, there's no time for the air to

That forms a shockwave that acts almost like a shield.

It blocks other air from smoothly moving past the plane, decreases lift, and increases drag

Which explained why wings and propellers become less effective at those high speeds.

After this realization, engineers developed all sorts of clever ways of mitigating this problem,

from stabilizers that stopped shockwaves from tearing planes apart to giving planes rocket

These innovations all culminated in Chuck Yeager's famous flight in 1947.

But supersonic or not, shockwaves still threatened to tear planes to pieces.

So before high-speed flight became a regular thing, engineers had to make a change to the

wings that you can still see on just about any fast plane today.

Originally, most planes had wings that went straight out sideways, perpendicular to their bodies.

That let air move over as much surface as possible, generating as much lift as possible.

The problem was, if a shockwave formed, air didn't have anywhere to go. It just kind

of piled up in front of the wing, which led to all those lift and drag issues.

So engineers came up with an alternative: swept wings.

They're wings that come out of the plane's body at an angle, usually with the wings pointed

The angle meant that air could get pushed along the wings instead of piling up around

them -- sort of like sliding down a ramp instead of running into a wall.

The fact that swept wings kept air moving more than made up for having slightly less

air going across the wings and actually creating lift.

And you see this design everywhere today, from military planes to commercial jets, which

These designs all fundamentally take advantage of the same clever piece of engineering, which

and why the basic airplane design hasn't changed much in the last 50 years.

Because once you've found a solution, you don't always need to keep switching things up.

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