Mainly by reducing/eliminating anything from which the radar signals can be reflected back to the station.

See http://en.wikipedia.org/wiki/Stealth_aircraft

I'm sure that there are tons of different factors that go into this, but along with being made of a material that absorbs radar waves rather than reflecting them is a variable called the radar cross section. We talked about this breifly in an Antenna course I took in college, very interesting stuff. Also see this wiki page on stealth technology.

I wonder if this is also the case using negative refractive index meta materials, much cloaking reaserch being done in that field.

Would solve the hole effect but too soon for that I believe. I heard once they can still see a reflection off the bump in refraction index from the heat trail but don't have any hard facts.

Syntetic aperture radars are amazing in inaging detail, as classified as the stealth tech, I imagine.

...said that when the F117 was first being flown on their ranges, they learned quickly to find it as a "hole in the radar space" precisely because it was TOO stealthy...

For there to be a 'hole' in the returns, the object would theoretically have to absorb or deflect reflections from objects on the same bearing, in the 'shadow cone' but that were further away. For this to be the case, any 'absorbtive' powers of the object would have to be analogous to a ferrite rod antenna 'distorting' or concentrating the field around it in order to function. Clutter (described above as 'RF noise') or other refections coming from any other sources either in front or to the side will still be evident - especially that due to multipath reflections. If a hole was detected, it had to be pretty smart operators or very clever signal processing that did it. Anyone got anything concrete on this?

And, as has been sugggested, the angular nature of the vehicle is designed to reflect whatever signature remains, away from any likely radar source. The turbine blades (an excellent reflector) are usually shrouded and tunnelled to prevent signals getting in and then out again. None of this helps the airframe aerodynamics or engine efficiency I suspect, but needs must when the devil drives.

Steve.

Stealth planes have 4 ways to reduce their reflections.

One is to use non metals in their construction. metals have an electron cloud which reflects radar

Second is to cover any metal with an absorbant/attenuative coating. This reduces the signal from the radar that reaches in the metal and also reduces the amount that emerges.

Third is to have no rounded surfaces. A round surface will reflect back in all directions, a flat surface reflects in one direction, and if that direction is upwards/rearwards/downwards then nothing goes forward to the radar.

Fourth is to have no forward facing opening (jet intakes) that can also cause a reflection.

There have been some distributed radar methods, which will have, say, 500 radar transmitters and 5000 receivers and they send a pulse to each radar and listed on each receiver, and then step through all receivers as fast as possible. Since radar goes 300,000,000 meters/second and if you want to repeat all radar transmitters 10 times/second = 5000 short pulses followed by a similar quiet listening period this would cover a circle about 25 KM in diameter. fast processing would find the intermittently reflective target as it slipped across the terrain.

more stealth stuff here

So are you saying the F-117 is not capable of escaping radar?

I don't think that was the point. Once it's acquired, it IS hard to get "un-acquired", and if you note the last sentence of the post, it was in visual all the way out. Radar stealthiness works UNLESS it's in visual acquisition, in which case, who cares what the radar says. I'm LOOKING at the bird, even if radar says it doesn't exist. Given that radar returns in favorable circumstances require astute analysis (is it a biological, is it an aircraft, is it CAT, or Cold-Air-Turbulence, is it fog, snow, ice crystals, chaff, or how many other things?), radar returns from a stealthy airframe could easily tell you "nothing here to see" while you are actually looklng at the plane with a Mark I, Mod O Eyeball device (true, bottom line, biological sensor, that!). But once you've correlated what the radar DOES see (looked like a smudge on the display, to me) with what the eyeball sees, it is much easier to keep it in site. On the other hand, if the F-117 is armed with HARM missiles, whose JOB is to take out a radar site (and it would be, for at least part of any mission it flies), you won't want to be sitting around painting the plane in the long term, since the first thing it's defensive systems are going to do is alert the pilot to the radar emitter as a target, with range, bearing, location, and probably ID. Then the next event will occur when the pilot sends a HARM missile right back down that course, and the radar shuts down, for good, catastrophically.

And the F-117 goes stealthy again.

But at the Air Show, the F-117 would know it was painted. It just wouldn't retaliate.

Bad Form to do that, as the Air Show hosts would say.

Great answer. The structure of the F117 Night Hawk is clearly built for that purpose (the third point) you mentioned. But since this principle is fairly known, what I can't understand is why there wouldn't be efforts to make all jet fighters of that design.

I could be wrong, but my guess would be that the radar-escaping structure isn't aerodynamically the best for a jet fighter (ie. it causes more drag). Would that be right?

Actually its far worse than just more drag, the plane, without its computer, could not be flown by a normal pilot.

In the F-117, the pilot tells the computer, via the controls, what he wants to do. The computer then steers the aircraft taking into account its strange flight characteristics......

That is the problem very simply put, its actually far more involved, but that is the basics.

Which is why non-stealth aircraft are still built and why the stealth aircraft are still relatively slow, none of them achieve even mach 1, except for the SR-71 of course, which I would expect to not be "stealth" anymore with modern radar....

Reading the Wiki for the SR-71 makes this a true statement with a radar area of 10 sq.meter, against that of the F-117 of a small ball bearing!! Quite a difference!!

The F-117 and the B-2 have top speeds of subsonic only....

As an aside, its quite funny to see that a Russian mathematician actually developed the maths that boosted the effectiveness of the B2 design......You can read about him if you are interested at:-

Petr Ufimtsev

Okay, I haven't understood something. The radar escaping capabilities of say a F117 is mainly due to its outer-body structure, in what way does it affect "flight characteristics"? I am not sure I understood properly.

Why do you need to know? This is confidential information.

We have evolved from homo sapiens to homo nosipaka...

RIGHT!

We can only type on our keyboards!!!

Those weird "slabby" shapes are NOT conducive to good, nor stable, flight. But they ARE conducive to stealthiness. Unfortunately, an airplane that has to sit still on the ground to avoid killing its crew in a crash is pretty useless. So the twain MUST meet, if a bird is to be stealthy AND fly.

So, slabby shapes for stealth have bad affects on flight characteristics. And the outer body structure is made up of slabby shapes.

GA - especially for sorting out the "stealth 'buzz word'" ref Blackbird.

Thanks for taking the time to type that response Micahd02. Now my knowledge in this is below novice probably, but I am making the best efforts to understand the concept here.

When I look at the F-22 and F-35, they have a structure which doesn't have sharp edges, so I can presume the "vortices" you mentioned wouldn't be produced at high speeds, so thats good. But how do they accomplish being stealthy with their structure?

Another question of the F-117, and this question probably reveals whether or not I understood anything about all that you guys have so carefully typed in responses: If we are either going to see the F-117 as a "hole" or a detected blob moving at such a speed as mach 1, a person by the screen can understand from the speed that its not a bird or something, he would have to conclude that it is a fighter. Doesn't that effectively mean it has no stealth ability? How do more modern fighters like the F-22 or F-35 deal with this problem?

If you look these planes up on Wiki, there is a lot of information that may answer your questions. Without compromising security.

The solution found to the "hole in the return" is to create just enough RF noise to eliminate the hole. The point of that part of my answer was that our early stealth attempts, vis-a-vis the F-117, were SO good we created a new, and somewhat worse, problem. The biggest takeaway from that is that when you set out to do something good, you have to, ironically, try not to be TOO good at it.

We know enough now to be a lot better at creating the right kind of noise, in the right amounts, in the right flight regimes.

And that enables us to make birds stealthy at much higher speeds. This is the confluence of stealth techniques, a la vortex elimination and such, and speed (a known turbulence enhancer) coming closer to the kind of success we need in the modern battlefield.

If you go back to that Russian MIG that was 'found to be stealthy' and look at the fuselage cross section, you may notice something of interest.

But to grasp the concept, think of it as light reflecting off, say a round Christmas tree ball, as opposed to a cube, or diamond shaped one - given the tree and balls are all silver.

The round ball always has a 'highlight' and the faceted ones sometimes 'flash' but mostly send spots everywhere else in the room.

If the transitions between facets are somewhat radiused then there is 'some small highlight' that stops it being a hole in a shiny tree background.

However, this is actually the 'stealth example' of 'hole in the sea' most of the hole argument is really derived from.

link

Thanks, great answer.

As I recall, a F117 was shot down during Clinton's escapade in Croatia because their "outdated" Soviet anti-aircraft system was able to "see" the aircraft. The stealth capacity was geared towards modern radar systems and failed with the old ones. Why is this?

I do believe that it is probably a question of frequency, just a thought!!

Also, you probably also need a skilled operator, the newer sets have been in service less time and operators are maybe not as skilled....

Recalling some MTF tests I used to perform, I believe an operator's ability to distinguish an anomaly in analog noise may be greater than thru digital noise or by a computer.

From my very limited knowledge, I would say that is eminently possible.....

Might be the same reason that old WW1 and WW2 Mine Sweepers, were built to detect Magnetic Mines-These mines were considered "Archaric".. I worked on decommissioning some of these sweepers, and lo and behold, the Chinese, 40 years ago, were still putting magnetic mines into the Straits of Formosa (They did keep a few of these sweepers on line, though..)

"Why is this?" In most defense areas soviet systems are ahead of US. They may not look shiny, or have 'sophisticated' interfaces, but functionally they're superior and a fraction of the cost.

It's ironic that the US has just recently 'invented' a guidance methodology based on that "outdated" soviet systems success. BTW 'US stealth' actually originated in 'response' to USSR development, so of course the Ruskies know how to shoot it down.

Did you know that "Stealth" was first discovered in the early '40s when the Germans started on it.

Also in the late 40's, the US built a huge flying wing, the YB-49, although the wing killed a few pilots and engineers and as an aircraft was not a success, the design was basically resurrected in the B-2 stealth bomber. You can read more details here on this link:-

YB-49 Flying Wing

Even this article does not know or understand the Stealth link fully between the two aircraft, which was kept highly secret for many years, being used again in the SR-71 "accidentally!!" in the late 50's early 60's, showing how radar signals must not be returned to source......its no accident that the SR-71 looks just like it does....many do not know that....

I don't know if the Russians knew about it any earlier than the USA (I would be most surprised!), but if they did, they appear to not have understood the implications as well as the USA did......

The US appear to have "captured" the initial technology from a German fighter aircraft of WW2, the Horten 229.

Here is an interesting link that mentions that somewhere near the end I believe:-

Horten 229

The link is VERY interesting reading and demonstrates that the technology was being worked out already in the War years.....

There is a mockup in a Museum in San Diego air museum I believe. here is a picture:-

Enjoy.

I saw a great program on Stealth some years ago on the UK TV, fascinating.

Great info Andy.

@34point5

"In most defense areas soviet systems are ahead of US. They may not look shiny, or have 'sophisticated' interfaces, but functionally they're superior and a fraction of the cost."

But it can't be true presently between the US and Russia. Presently, are there any Russian defense systems that are ahead of US'?

"Presently"

Perhaps like many, you think Russia is a 'spent force', or '2nd world', since the end of the Cold War. What She has actually been doing since 'free enterprise', is selling her 'older systems' on the open market and cashing up Her R&D to stay ahead.

As most demand comes from Nations feeling threatened by US foreign policy, the popular ones are those still 'immune' to US technology and countermeasures.

And because this is 'open market', you can even find them on Wiki.

I would tell you but the govenment will kill me. lol

The shape of the plane deflects radar away from the trasmitted point instead of back to it, the coating on the plans defuses the radar wave, and the American Pilot just bombed your SAM and radar sites and is returning to the middle of the Pacific.

Hey China, I got a taget on the 3GD, do you know how to swim???

Didn't kill this guy, so far as I know - all the answers for $5.12

Some newspapers showed engineers sat beside an odd thing "this is why the mig 25 is invisible",(Victor Belenko affaire).What was that?i was a kid.-

Interesting side note, What really advance U.S. Stealth Technology was actually taken from a technical pamphlet written by a Russian.

http://en.wikipedia.org/wiki/Petr_Ufimtsev

China is not the first to take advantage of another country's work.

Nor is this the first instance in history of great strides being made on another's work, regardless of geo-political origin.

Your point?

what point, just an interesting side note.

Ah. Thank you. I am probably oversensitive to accusations of plagiarism, or "derivative-ness" in research. Truly, very few systems or processes that make it into the practical use of the world are wholly invented/developed in one country or area. But most people seem to want it to be so.

Thanks again.

That has been already mentioned some weeks ago on this very blog!!

missed it.

Double irony in context- or is that triple?