How is the B2 bomber stealthy?

I know that most people won’t know and those that do won’t be able to disclose it, but my understanding is that with the F117A jagged edges were used to reflect RADAR waves in all directions in order to minimise it’s RADAR signature. This doesn’t appear to be the case with the B2. A RADAR wave hitting the underside of the bomber as it flew over an installation would have a large area to hit, surely?

I heard that a special paint was developed that absorbed RADAR waves, yet, if this is true, why not paint more planes than the B2 with it? Surely it would be safer for all pilots to be flying around in planes coated with a RADAR absorbing paint?

So, do any aerospace engineers have any vague ideas as to how the B2 does it?

A number of things:

  • Top coating (paint)
  • Under-coating
  • Elastomer compound used between the panels
  • Shape
  • Thermal signature

My recollection, backed up zero facts, is that when the F117A was designed, the maths for calculating the radar reflections was so complicated that they had to use flat surfaces to be able to do them at all. By the the time of the B2, the computers/techniques had advanced to where they could use proper curves.

It’s a combination of factors, it’s shape still being a primary one. The F-117 uses sharp (but not 90 degree) angles because they scatter, rathar than reflect, radar waves. Well, so does the B-2’s shape. In the time between the F-117 and the B-2, they found a way to scatter the waves while not having to resort to the funky angles.

In addition, the paint is slightly absorbant, but antother big key is the materials, and the way that it’s masks its exhaust.

From here:

So yes, the actual materials and specifics about the gemotry are claffified, but they do let us know that the flying wing desingn and the angles and so forth of the curves play a big part.

Heck, I don’t think the F117 is all that stealthy. I saw one at an airshow in Chicago and it about put my eardrums out…

(I know, I know, they fly higher than that, and probably fast enough that by the time you hear anything, you’ve already been dead five minutes).

Or now that I look at a picture, perhaps it was a B2 after all…

As to why they don’t do it for all military planes? Look at the pricetag for a single B2 bomber. IIRC, it’s approx $2 billion per plane. :open_mouth:

Also you don’t have to absorb all the radar waves… you just musn’t reflect them in a way that makes it possible to detect your airplane.

Rumors are that the Russians have developed better radar to detect “stealth” planes… beggining of a stealth tech race ?

I thought it was the opposite? My understanding was that radio waves will reflect off flat panels, and very little of it gets back towards the source. (Unless the surface is perpendicular to the radio wave, which is unlikely.) Complex curves (like on conventional aircraft) will scatter radio waves, and some of it gets scattered back towards the source, where the detection system is. The F-117 is made up of flat surfaces.

Hasn’t British Aerospace already developed one? I seem to remember a report on the news of them successfully tracking a B2 as it flew over at a British airshow. This was a few years ago, now. The USAF claimed that the paint wasn’t working properly or had been washed off.

But remember that stealth planes aren’t “radar invisible”, they just have a low radar visibility compared to conventional planes. The idea is that a radar with given characteristics that could detect a conventional plane at distance X would only detect a stealth plane at distance X/Y, X and Y being top secret values.

If you suspect the presence of a stealth plane, if you know exactly where to look, a stealth plane IS detectable. But a radar station looking for stealth planes is going to have to investigate a lot of clouds, flocks of birds, computer errors, etc as it looks for the faint signals from stealth planes.

Forgive the long post. I have some work experience in detection of aircraft by radar and feel like talking.

Radar works by detecting radio-frequency (RF) energy. General types are active radars, which transmit RF energy, and passive, which do not, using environmental sources instead. Active radars are either monostatic, where the transmitter and receiver are co-located, bistatic, where the transmitter and receiver are separated, or multistatic, which has one transmitter and many, dispersed receivers. Whatever the type, the energy from the aircraft must be distinguishable (by intesity, location, and/or frequency-shift due to motion) from all the other energy received by the radar. Most operational radars are active and monostatic.

To avoid detection by a radar, you must minimize the amount of energy it receives. There are many ways to do this:[ol]
[li]Reflect the energy away from the receiver. Thus the sloped shapes and smooth surfaces of stealthy aircraft. Even the pilot’s head/helmet is considered. []Absorb the energy, by wise choices of materials. []Avoid the RF energy by using terrain and the curvature of the earth. Fly low, and behind mountains. []Increase the clutter by releasing chaff or decoys. []Confusing the receiver with energy (jamming). One aircraft, at a safer distance, will transmit energy at the radar to blind it or confuse its signal processing, preventing the detection of other aircraft. Stop the radar from transmitting and/or receiving. Often by either destroying it or scaring them enough to not turn it on. [/ol][/li]
Radar cross section (RCS) is a measure of how much energy is returned from any given look angle. A large-RCS aircraft is easy to detect, while a low-RCS aircraft is much more difficult. Designers of low-RCS aircraft must make engineer trade-offs about where to reflect the energy. You cannot minimize reflections from all angles. Typical stealthy designs minimize the reflections for, in priority, the front, front-low, front-high, rear, rear-low, rear-high, sides, beneath, above.

On specific questions/points:
A RADAR wave hitting the underside of the bomber as it flew over an installation would have a large area to hit, surely?
Yes, aircraft usually have large a RCS from beneath. But aircraft do not fly directly above hostile radars (unless attacking them), and surveillance radars typically point out, not up. It’s more important to avoid detection while approaching and leaving, than while above it. The targeting radars of surface to air missiles (SAMs) can sometimes detect aircraft above them, but no one flies directly above a SAM (more than once :wink: ).

I heard that a special paint was developed that absorbed RADAR waves, yet, if this is true, why not paint more planes than the B2 with it?
The paint is expensive to maintain and has some environmental restrictions. The surface shape and the material underneath the paint are more important. No paint would make an F-16 stealthy.

Rumors are that the Russians have developed better radar to detect “stealth” planes… beggining of a stealth tech race?
Stealth can be negated several ways. A radar with a powerful transmitter, sensitive receiver, sophisticated signal processing, and proper doctrine can potentially detect a lot. Bistatic radars can circumvent stealth by detecting the energy that’s reflected away from the transmitter. Passive radars have a similar advantage. However, these anti-stealth technologies will not make stealthy aircraft obsolete. It’s always better to be a smaller target. And there’s other options for mitigating radars (see points 3-6). So, yes, there’s tech race, as always.

I thought it was the opposite? My understanding was that radio waves will reflect off flat panels, and very little of it gets back towards the source. (Unless the surface is perpendicular to the radio wave, which is unlikely.) Complex curves (like on conventional aircraft) will scatter radio waves, and some of it gets scattered back towards the source, where the detection system is.
In radar terminology, “scatter” is the preferred term for any reflection. “Reflection”, and especially “specular reflection” (which no one has used, but I think is what’s in mind here), is more a term for the optical limit (i.e., short wavelengths). Just use “scatter”.

On preview: Lemur866 is exactly right. Stealthiness is a continuum, not an either-or. In the industry, we use the term “low-observable” not “stealth”.

The answer is simple, then…

Kill all the birds. Anything moving must be a stealth aircraft.

Awesome post, Pleonast.

This is some great dope. Hats off.

After it overflew you?

I saw a show about stealthy aircraft that mentioned that sound baffling is only engineered ahead of the plane. They showed a plane approaching the camera, and all was silent. As it flew overhead and past the camera, the roar was deafening.

I have heard this exact explanation as well, possibly on the same show I referenced above.

Quite possible, given that it was the Russians that invented radar stealth in the first place.

Russian scientist Pyotr Ufimtsev invented the theory, and was actually permitted to pubish it in a Russian scientific journal. Because neither he nor the KGB(?) realized that it was actually feasable to do this in practice. It just requires much computing power, more than was generally available in Russia at the time.

People at Lockheed’s famous ‘Skunk Works’ eventually realized that it was possible to actually build a stealth plane using this theory, and did so. They had a hard time convincing the Defense Department that it actually worked, even after they had the plane designed!

As it was classified, the Russian inventor never knew that his theory had actually been used to build stealth aircraft until years later, when he had emigrated to the US and was invited to tour the Lockheed facility.


As far as detecting it, in theory, it is possible to detect such planes with mutiple, syncronized radar sites. As I understand it, you basically track the ‘hole’, the spot where radar transmissions are disappearing and NOT being reflected back. To work, this would probably require several radar sites, distantly located, tightly syncronized, and a good deal of computing power to analyze the signals.

      • I heard this in a similar way: when the F-117 was designed, the engineers assumed that all the radar waves in every direction had to be diverted. By the time of the B2, they had found out that this was not so, that most of the radar image reflected comes off of only certain types of edges. So now you see planes (like the B2 and F22) that have rounded top & bottom surfaces, but lots of attention is paid to the “circumferential” edges.
  • Also do note: the B-2’s radar-absorbing paint is not waterproof; if it flies through rain it has to be stripped and repainted, at a cost of -a lot of money-. I dunno exactly (-who does?-) but it’s a few million dollars or something. B-2’s are never allowed to get wet if it can possibly be avoided.
  • You can make stealth paint yourself by getting some clear laquer and adding lots of powdered iron. The paint used on the stealth planes is also IR-radiant as well, but you could figure something for that, powdered copper perhaps. Some handbooks on radio operations describe formulas for RF-absorbing coatings that you can mix and paint onto surfaces, but as I have been casually told, the powdered iron in a non-conductive binder (clear laquer) is the main two ingredients.
    ~

the real paint has an iron compound, not iron, as iron I would suspect would just act like a normal metal and reflect?

" Radar absorbing paint, or RAM (Radar Absorbent Material) coating, especially on the edges of metal surfaces. The RAM coating, known also as “iron ball” paint, contains tiny spheres coated with carbonyl iron ferrite. Radar waves induce alternating magnetic field in this material, which leads to conversion of their energy into heat. Early versions of F-117A planes were covered with neoprene-like tiles with ferrite grains embedded in the polymer matrix, current models have RAM paint applied directly. The aircrafts must be painted by robots, because the solvent used is highly toxic."

from http://en.wikipedia.org/wiki/Stealth_technology

More comments:

Kill all the birds. Anything moving must be a stealth aircraft.
Bird don’t fly at aircraft speeds. Because of Doppler shifts in the energy boucing off a fast-moving aircraft, signal processing techniques make it easy to distinguish birds from aircraft. Of course, that’s for a large-RCS aircraft. If the scatter is small enough, it’ll be lost in the clutter no matter what speed it’s going.

As far as detecting it, in theory, it is possible to detect such planes with mutiple, syncronized radar sites.
Yes, it is possible. See below.

As I understand it, you basically track the ‘hole’, the spot where radar transmissions are disappearing and NOT being reflected back.
This is nonsense. Almost the entire volume being scanned is a “hole”. A “perfect” stealth aircraft that absorbed all RF energy would look exactly like air. (I’m over simplifying, but the hole explanation is just wrong.)

To work, this would probably require several radar sites, distantly located, tightly syncronized, and a good deal of computing power to analyze the signals.
Yes, this is true. The radars would work by forming a large multistatic network. Stealth can be mitigated because most of the energy is scattered in some direction, and if you have a receiver there, bingo! This type of network requires a huge data bandwidth and computional number-crunching. But with Moore’s law it’ll be here sooner rather than later.

Awesome post, Pleonast. This is some great dope. Hats off.
Thanks! I’m not an expert so much in stealth as in radar/air defense. It’s always fun to talk about what you know. :slight_smile:

Hmm, is it possible that the price tags for stealth planes include budgets for decoys, which get into air shows and magazine covers? Otherwise, couldn’t someone try to build one based on the dimensions from the pictures?