how stralth planes stay hidden from radars?


The question above, I always wondered how that tech actually works, in a layman words of course. How does the signal absorbing paint work?

In: 0

It’s not just paint but tricky geometry and material choices.

Going over what stealth is, is reduced detection from radar and infrared(effectively heat).
Radar works by throwing signals out and getting the return. If you’re familiar with active sonar and echolocation it’s the same idea. If not, it’s like making ripples in water, and seeing how some of them return to the spot and using that info and a lot of math to determine what is out there.

Infrared checks for heat signatures relative to the background and focuses on that. Hot engines versus a cold background sky.

Radar stealth is all about making sure the radar waves that hit the plane, do not bounce back to the receiver in order for it to detect it.

The paint, which is more like a coating than just a layer of paint has material suspended in it in special ways that do not reflect the waves and instead absorb and trap them. Think like painting something matte black, but for radar waves instead of visual light.

The geometry of the aircraft is a huge thing too. [Right angles, fully flat surfaces, and fully round surfaces are avoided.]( Right angles act like two mirrors to bounce the signal back, flat surfaces act like one mirror, and round surfaces act like a disco ball where at least one section of the surface will always return to the receiver.

Material choices as well. Hard metal components will give a larger return than a soft composite material like fiberglass where the waves can pass through.

Getting into the weeds a bit more on this.

Technically stealth aircraft can be detectable. They’ll often have extremely small radar returns but still technically detectable. When there are pictures like “this has the radar cross section of a bird” it means that it the equivalent energy returned to the radar is about the same as something with the surface area of a bird. At some distance and if searching the right way, it’s possible to detect but generally it isn’t. There is a lot of random things a radar will detect and selecting for the “We occasionally have a very fast moving very weak return” is extremely hard.

There’s also the unavoidable geometry. At some angles they can be detected if at the perfect angle to find one of the few direct flat spots like the leading edges of wings. Though that’s hard to do with a fast moving aircraft that is also actively avoiding showing that angle to a radar.

Add in electronic warfare where signals are actively being disrupted by jamming and it gets even harder.

Plus when deploying weapons, it adds things like round shapes and right angles which vastly increase the radar return. This is how a stealth bomber was shot down in 1999 over Serbia. Weapons bay was open, and some very creative use of the ground radar systems. Basically at it’s very very lowest setting it could detect that something was there, not a lot of info with it, but just something. Then some luck to catch the aircraft while it was actively dropping weapons.

Imagine a guy with a tennis racket standing in front of a machine that shoots a bunch of tennis balls at him. In random places around him.

A regular player would hit the balls in a way that most would go back in the regular direction of the machine. From the regularity of the balls coming back, one could even calculate how tall the player is (more reach etc) if you expect that all players have s roughly equal skill. So a tall person with long arms might hit more balls back than a short person.

Now, imagine there is a tall person that does whatever he can to NOT shoot any ball back to the machine. For example by catching the balls or shooting them far away.

So even if he „messes up“ a ball and it goes back, the size calculator would calculate that there is something the size of a bird that was there by chance.

Same with radar.

Radar waves get sent out and hit an object. The waves get reflected and from the amount of what comes back, you can calculate the size of the object. The more comes back, the larger whatever you detected. That can range from a bird to… anything, really.

So with fancy engineering (materials and angles to name a few) you can absorb the waves or deflect them to anywhere but back to the radar station. So even if it gets messed up and an angle is bad, the radar station might just see something the size of a bird instead of the B2 bomber that’s inbound.

To understand how radar stealth works you first need to understand how radar normally works.

The usual most simple way you use radar is by having a rotating antenna send out radar pulses and listen for “echos” of these pulses coming back after being reflected of an object.

You shine a flashlight into the void to see if there is something to see.

This usually work very well.

Almost all objects will have part of their surface angled in such a way to send a part of the radar beam straight back to its source. If you have a round object you can’t really avoid that.

Stealth planes and ships and so on, don’t do round. They tend to look a bit like low polygon objects from 90s game consoles. Made up out of flat surfaces joined together at a sharp angle.

This sort of geometry limits the directions a radar signal can be reflected to quite a lot.

If you know geometry you can build things so that they limit the chances of a return signal. or you can build small object made up out of all right angles like a cats eye that guarantee a radar return.

For stealth you want to limit the chance of returns signals a lot.

There are other factors that go into it like choosing the material and the paint for the craft to make it more stealthy, but the geometry is the main thing.

Ignoring that there is already really great explanations and I can not do it half as good, do I try also.

Radar send out a signal but let’s imagine it was a bouncing ball you trow instead, if you kept trowing a bouncing ball and nothing was in front of you, would you never get the ball back, but if you then suddenly get closer to an object will you from time to time get a ball that is bouncing back, you can in that way deduce how far there is from you and to the object, by the time it takes for the ball to return.

Now to the stealth technique, the stealth object is made such that no matter where you stand in front of the object and trows the bouncing ball, will the ball never jump back to you, so for you is there no difference in if there is a stealth object or nothing because every ball gets lost and none bounces back.