SinoDefence Forum

lilzz

F-22 raptor's main radar stealth derived 90% from its faceting, very limit RAM are applied to the body.
Therefore if you able copy the F-22 shape, you would achieve majority of of its stealth already at least on radar signature

so instead of modifying the 3 rd generation J-11B and its wing structure to become carrier fighter, why not concentrate on building a stealth fighter body. It's not that hard. F-22 body strcuture is pretty well known already. It would be cool if China can have some F-22 lookalike planes /w foldable wings on its new carrier.

You don't need to wait for supercruise capable engine to come out. Just put in couple Ws-10 into the stealth body and use the current avionics and then you could have a low cost stealth fighter in couple yrs which would beat those Su-33 which still using the older generation body type.

the key is to copy the F-22 body shape which I don't think it's too hard.

Pointblank

Problem would be materials; stealth isn't all about shape, its about the materials used. And the Americans are very good about keeping their formulations for the panels of the aircraft secret.

crobato

There is materials _and_ shape. The materials are easier because its not hard to find out which materials are radar absorbent and which is not. Basically not much different from the material used in a radome, which is carbon fiber, with a honeycomb matrix where the spaces or the cells within are matched to the length of the frequencies.

Won't matter so much though, all stealth does is make the current generation of radars obsolete. High wattage electronic steering radars with tight beam forming is another matter.

__________________
"Lets do a thermal sweep."

lilzz

haha, I know someone would say something like that. We are not talking about B-2 in here. For F-22 90% of its stealth derive from its shape, nothing else. You can do a research on that if you don't believe.

F-22 purposedly do away with alot of those carbon based RAM due to its difficulty in maintainence.

montyp165

Also, using more advanced materials such as carbon nanotubes would improve performance for similar design layout.

Londo Molari

No it is not 90% its shape. Keep in mind, the F-35 is a LOT LESS stealthy than the F-22. The F-22 is truly a stealth fighter.

A big part of the F-22's stealth is its low thermal signature. They have designed the entire aircraft for fuel and coolant to flow throughout its body in such a way so as to keep a costant low temperature across all its outside surfaces. Then there is the low probability of interecept AESA radar. Also the materials as mentioned. All these various factors, combine with its overall shape to make something thats almost invisible to traditional sensors.

Replicating the F-22 is not just about shaping the aircraft. Not to mention that even shaping an aircraft like the F-22 also requires very complex fly-by-wire software tailored to its profile, because something with that blocky shape does not fly naturally.

crobato

Keep in mind that the B-2 is meant to be stealthy against Soviet long range low frequency volume search radar and OTH radars, while the F-22 is meant to be stealthy against high frequency fighter radars on the X-band. There is no universally stealthy shape against all bands because the shaping is determined against the physical length of the waveband. Likewise you will see this with stealth designs on ships too.

__________________
"Lets do a thermal sweep."

kickars

All F1 racing cars are looked the same. But not every car has the same performance. There's bid difference between the front grid cars and the back ones. I mean in fact 'shape' is one of the hardest thing to 'copy', unless you have all the data.

lilzz

Yes, it's. Who says F-35 is LOT less stealth? Sources only says F-35 is not as capable as F-22.
You talk about IR, yeah sure. But at radar signature far distance, IR doesn't mean a whole lot.

90% come from faceting. and 10% come from small amount of RAM applied to the wing edge against low frequency detection

I recommend you study this , it's very helpful. It talk how faceting is most important aspect in stealth.
http://mariettascientific.com/understanding/under.htm



Therefore, country can design a stealth plane from normal radar sig stand point just by having the right shape. (excluding performance, IR sig, radar sig at low frequency(RAM dependent))

lilzz

wrong, shape is easy to copy, hard to copy is the internals like supercruising engine, IR reduction,...etc.

Hey, at least the normal fire control radar have a hard time to lock on you. That's the objective of having a copied stealth shape.

Totoro

A huge part of it is also manufacturing quality, or even the manufacturing process itself. Good stealth requires as small gaps as possible between panels, very smooth surfaces, very few protrusions, etc. That is something that needs trial and error approach, meaning time and experience with construction.

crobato

Sorry the shape looks easy to copy, but its a lot lot more complicated than that. What you see as a shape is actually the product of a lot of computer simulations working to simulate radar reflections of surfaces until the perfect facet is determined. The simulations would have to be exploring a broad range of wavelengths, different aspects and directions of the plane being illuminated, following their reflections back to the receiver. What you see as a simple shape is actually a very complex 3D geometric design.

__________________
"Lets do a thermal sweep."

kickars

Maybe I didn't explain clearly. What I mean is not the overall shape of the plane. The difficult part are the surface, lines, proportions...

Well I'm not an expert on military plane design. But in automotive design, the exterior shape/surface/lines are near impossible to 'copy' them right. Sometimes the slightest difference can make a big difference. That's only to do with the look and some aerodynamics. So I would imagine for a future fighter jet every millimeter can be the difference between stealth and normal.

lilzz

Again, referring to the diagram I enclosed. at very high frequency those surface, line and edge imperfections would be critical.

but at the billardball range, this is where most of the normal microwave searching radar operating at, as long as you have the right type of angle and shape to reflect away the wave, then the job is done. So as long as you have almost the equivalent shape, you're fine.

F-22 mechanical drawing and dimension has been declassified, their numbers are out so, it's not hard to copy the equivalent shape plus nowaday, everybody has a computer simulator software, after they copied the shape, they can simulate to prefect the little imperfections.

RedMercury

Sorry, if you have a decent initialization to your search, you will find the local minimum much faster than some random guess. Even a coarse approximation to the local minimum will get you a lot of the way, and help you avoid other local minimums. Copying works, even if you don't get the final product, you get close enough to it so that the last bit is much easier. Of course, this all depends on the local smoothness of the function, but I would guess for something as complex as radar return, the function would be very bumpy on a large scale and only a little bit smoother as scale decreases. If your copy is good enough to get you to a place where the gradient is pointing towards the minimum, you're in luck.