J-20 5th Gen Fighter Thread IV (Closed to posting)

[Engineer]

Don't be absurd.

If you're talking a a marble to baseball sized target, you'd better build a pretty close replica. Otherwise missing specifics on things like how the internals are RCS minimized or getting the RAM composition even a bit off means you end up with a RCS of 0.005m2 instead of 0.001m2, since all those little details add up after a while.

The only thing that is absurd here is how people keep on trying to drag in reverse-engineering when reverse-engineering has nothing to do with RCS estimation. That serves no purpose other than creating a distraction.

Stealth is mostly about the exterior shaping. To quote Lockheed Martin engineer Denys Overholser, stealth is dependent on

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. The RAM coating which you are making a big deal out of is not a major factor in stealth. The coating is merely icing on the cake to further reduce the last few percents of EM energy that propagates omni-directionally and cannot be handled shaping.

Techniques are specifically employed to eliminate any possible view of an aircraft's interior by an opponent's radar. A great example on that is the conductive coating on F-22 and F-35's canopy. Another example is the engine intake duct which is curved to prevent the engine fan from being visible. There is also no such thing as internal RCS, so stop making up pseudo-scientific theories.

 

[Blitzo]

The only thing that is absurd here is how people keep on trying to drag in reverse-engineering when reverse-engineering has nothing to do with RCS estimation. That serves no purpose other than creating a distraction.

Stealth is mostly about the exterior shaping. To quote Lockheed Martin engineer Denys Overholser, stealth is dependent on

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. The RAM coating which you are making a big deal out of is not a major factor in stealth. The coating is merely icing on the cake to further reduce the last few percents of EM energy that propagates omni-directionally and cannot be handled shaping.

Techniques are specifically employed to eliminate any possible view of an aircraft's interior by an opponent's radar. A great example on that is the conductive coating on F-22 and F-35's canopy. Another example is the engine intake duct which is curved to prevent the engine fan from being visible. There is also no such thing as internal RCS, so stop making up pseudo-scientific theories.

I think "internal stealth" could be reference to very small scale details on an aircraft. For instance, serration, or the use of honeycomb structures that would serve to further absorb radar waves before bouncing back (I believe the latter was used in F-117? I cannot remember) -- and chances are there are similar other tricks that simply having a 3d representative shape of an aircraft cannot replicate. And that would constitute as shaping rather than RAM I think.

That said, if china really did hack into lockheed a few times, they might have garnered some info on how to replicate some of these measures on a representative of F-22 or F-35.

Also, even if China was able to replicate the 3/4 of F-22 or F-35's stealth via perfect replication of shaping, there's still 1/4 of RAM that needs to be accounted for, and I don't think we can really make a judgement on just how quantitatively significant a difference that will be.

 

[rhino123]

A silly question here... but I hope to be enlightened by all the experts here.

Since it is widely published or at least assumed that the RCS of F-22 was 0.0001m2, and China or anyone for that matter know basically how a F-22 looked like physically even if it was not up to the very small detail. And stealth is not totally invisible to the radar. Couldn't the Chinese just use that information to come up with a radar or avionic or whatever you choose to call, to detect, lock on and strike that target.

Unless, the target was actually resembling those of a normal sparrow, or whatever birds, that it was very difficult to determine whether the target was a F-22 or a bird and you cannot go around shooting everything that appeared on the radar screen. But I am guessing... speed is also a limiting factor... no birds can fly in supersonic speed.

 

[kwaigonegin]

A silly question here... but I hope to be enlightened by all the experts here.

Since it is widely published or at least assumed that the RCS of F-22 was 0.0001m2, and China or anyone for that matter know basically how a F-22 looked like physically even if it was not up to the very small detail. And stealth is not totally invisible to the radar. Couldn't the Chinese just use that information to come up with a radar or avionic or whatever you choose to call, to detect, lock on and strike that target.

Unless, the target was actually resembling those of a normal sparrow, or whatever birds, that it was very difficult to determine whether the target was a F-22 or a bird and you cannot go around shooting everything that appeared on the radar screen. But I am guessing... speed is also a limiting factor... no birds can fly in supersonic speed.

huh? don't understand your ?. Are you asking if one could modify a radar to look specifically for an object of a specific shape?

 

[rhino123]

huh? don't understand your ?. Are you asking if one could modify a radar to look specifically for an object of a specific shape?

Yes. That is the question. Since we know roughly (not to 100% detail) of the shape of F-22 and the RCS of 0.001m2, couldn't the radar be program to search for this shape?

 

[no_name]

Yes. That is the question. Since we know roughly (not to 100% detail) of the shape of F-22 and the RCS of 0.001m2, couldn't the radar be program to search for this shape?

At the distance involved the returning EM wave is pretty much a plane wave and thus I don't think there is much info you can extract.

It's only possible to correlate field pattern and shape in the near field region.

 

[Engineer]

Yes. That is the question. Since we know roughly (not to 100% detail) of the shape of F-22 and the RCS of 0.001m2, couldn't the radar be program to search for this shape?

Radar doesn't work that way.

 

[no_name]

Unless, the target was actually resembling those of a normal sparrow, or whatever birds, that it was very difficult to determine whether the target was a F-22 or a bird and you cannot go around shooting everything that appeared on the radar screen. But I am guessing... speed is also a limiting factor... no birds can fly in supersonic speed.

Which is why when they plan flight path for stealth missions the plane will try to fly a path tangential to the radial direction of known stations so the radial speed even if measured is low. Passive receivers that don't emit signals placed at unexpected places may pick up the intrusions - but not sure how useful they are for targeting.

 

[kwaigonegin]

Yes. That is the question. Since we know roughly (not to 100% detail) of the shape of F-22 and the RCS of 0.001m2, couldn't the radar be program to search for this shape?

no..radar works by processing signals or backscatter waves back to the 'dish' and the processor then hmm processes the signals . While the shape of an object plays a BIG role in determing the scattering of the radio waves that bounces off it, to the radar itself the shape of the object has nothing to do with anything since radar works by the amount of radio pulse it receives back not the shape of the object because it's not 'seeing' the object shape.

HOWEVER you inadverdently brought up a good discussion point because LIDAR can potentially be use to detect based on object shapes among other things since it uses light instead of radio waves for ranging and detection therefore the shape of the object can potentially be used for detection. Of course that is not possible right now.. lidar is used in atmospheric research on cloud formations etc and it uses mainly infrared and ultraviolent.. I guess you can potentially use LIDAR to track and detet exhaust fumes from an aircraft so if you know the characteristics of jet exhaust unique to a certain planes lidar can potentially identify such targets either way we're still very far away for lidar to replace radar.

 

[Totoro]

radar can indeed be used to analyze the shape of an object. That's what radar imaging satellites do, that's what modern fighter radars with Synthetic aperature mode do (albeit usually for large targets and topography), that's how longbow radar on apache identifies targets, that's how maritime patrol radars indentify their targets (ISAR is basically a similar thing, only over a longer period of looking at the target, without necesarily moving the radar in relationship to the target)

Of course, downside is that current technology isn't advanced enough to be militarily usable for what is being suggested here. Resolution of such synthetic images is still not good enough for targets with so few radar return points to be observed from a militarily useful distance. What good is it if you can look at f22 with such radar and conclude "yes, it is indeed a f-22" from only 5 or 10 km away? Those figures are just illustrative, but actual ranges are sure to be well under 100 km. One needs a big radar that has a large aperture antenna, lots of power behind it and modern processing to be able to do it with older gen aircraft at reasonable distances. Even that being said, identification of airborne targets via radar is even today a very hard thing to pull off at large distances. One needs moving parts, like helicopter rotor blades, or even roating turbine blades for aid. Even so, there's been an interesting promo pamphlet for russian buk 2me system. It says it can detect a stationary, hovering helicopter at 30 meter altitude at 15 km away. And that's with a fairly modern radar array, against a target whose RCS is oscillating a lot more than airplane's turbine blades.