ELi5: What makes stealth planes stealthy?

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I know they’re made to go off the radar but im still here wondering if they’re anywhere close to the Helicarriers in Avengers

In: Engineering

They absorb or reflect radio waves away from the source. Stealth planes are never invisible to radar, just less detectable.

The main thing that makes them stealthy is their shape. They’re designed so that when radar hits them, it reflects at odd angles so that they appear a lot smaller than they actually are.

You can still see them with your eyes though, so they’re definitely not able to reach helicarrier levels of stealth.

Radar is light, and it bounces like light does. Radar detection works by shining radar at the sky and waiting for it to bounce off stuff. If it bounces off and comes back to your detector you can detect the presence of *something* in a particular location, and you can be reasonably confident that something is something you should take a closer look at.

Light bounces in very predictable ways, which is how radar works. Most things will bounce the radar off in a predictable direction and can therefore be detected. Stealth planes are designed to reflect radar light at weird angles, so instead of going back to the detector, they fly off somewhere else. Since the plane is never getting detected, no one knows its there. [Here’s](https://www.youtube.com/watch?v=z5cR6EA2jGY) a mouldy video that contains practical demonstrations and more detail.

So radar works by essentially sending out radio waves and “listening” to how they bounce back. Think about it like pushing a wave in water and locating rocks by the waves that bounce off of them and come back to you.

Stealth planes are shaped in such a way that they minimize this bounce back. Like a knife making minimal waves when you cut through water. Unless a government uses super sensitive equipment, it’ll be hard to locate.

There’s also a different technique they can use where they “listen” for the radar sound waves and use their own equipment to send out a sound to counter or cover up the bounce back. Although, I’m not sure how commonly used this technique is, because it’s super tricky to pull off.

Edit: I said sound waves, but it’s radio.

In addition to the rest, a stealth plane does have a radar return, but for example the F117 looks as big as a hummingbird.

In addition, to radar, they have a small thermal signature. It wouldn’t do much good for them to be invisible to radar if they looked like a bonfire to a heat-seeking missile. So the engine exhaust is on the top of the wing, screened from the ground, and mixed with more air to cool it somewhat.

In addition to the angular shape, they have special paint/texture on their surfaces that absorb radar signals. Like how black paint will absorb visible light.