Building a low cost stealth fighter in a tight schedule.

[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 :D

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.

[lilzz]

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.

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]

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.
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]

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.

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.

[kickars]

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.
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]

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.

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

http://img299.imageshack.us/img299/4796/waveey3.jpg

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]

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.

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]

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.

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.

[kickars]

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.
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]

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.

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.

[man overbored]

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.

I know this is complete fiction and I know some of the reasons why but darned if I'm going to be the guy who tells you! You could copy the external shape faithfully and never come close to the RCS reduction of the actual B-2. There is a lot of fun going on under that smooth black skin.
Now wrap your mind around the radar of the F-22. That aircraft has to be able to operate a long range search radar while not giving away even it's presence much less it's position. Hmmm, seems any radar transmitting radar ought to light up the enemy's sensors like a klieg light. it has something to do with frequency agility but that is all that is unclassified at this time. Have fun speculating. Mahalo.

[crobato]

Frequency agility isn't magic. Its as common as the device that everyone puts in their pocket, the celphone. Which by the way is also one of the LPI techniques. If your celphones don't have LPI and frequency agility, they would be jamming themselves all over, or get into cross lines where you hear other people's conversations and they will hear yours too. It doesn't require a MMIC, the latest TWTs would do. China boasts frequency agility on some of their OTH and air search ground radars as well as the seeker on the YJ-62 antiship missile. In fact, we can expect more missiles around the world to increasingly feature frequency agility and they won't set RWRs alarming once they get you as a target. Another LPI form is pulse compression, that too is common in the commercial field, can be accomplished by TWTs, and some of the recent Chinese air search radars is boasted to feature them too.

All these techniques will only make the last generation of RWRs obsolete but they can be accounted for by the next generation of RWRs.

[man overbored]

Frequency agility isn't magic. Its as common as the device that everyone puts in their pocket, the celphone. Which by the way is also one of the LPI techniques. If your celphones don't have LPI and frequency agility, they would be jamming themselves all over, or get into cross lines where you hear other people's conversations and they will hear yours too. It doesn't require a MMIC, the latest TWTs would do. China boasts frequency agility on some of their OTH and air search ground radars as well as the seeker on the YJ-62 antiship missile. In fact, we can expect more missiles around the world to increasingly feature frequency agility and they won't set RWRs alarming once they get you as a target. Another LPI form is pulse compression, that too is common in the commercial field, can be accomplished by TWTs, and some of the recent Chinese air search radars is boasted to feature them too.

All these techniques will only make the last generation of RWRs obsolete but they can be accounted for by the next generation of RWRs.

It is a touch more complicated than that. The Low Probability of Intercept capability of the radar defeats conventional radar warning receivers and ESM suites. The Raptor's radar is capable of performing an active radar search on typical RWR/ESM equipped fighter aircraft without the target knowing he is being illuminated. Unlike conventional radars which emit high energy pulses in a narrow frequency band, the Raptor emits low energy pulses over a wide frequency band using a technique called spread spectrum transmission. When multiple echoes are returned, the radar's signal processor combines the signals. The amount of energy reflected back to the target is about the same as a conventional radar, but because each Low Probability of Intercept pulse has considerably less amount of energy and may not fit normal modulation patterns, the target will have a difficult time detecting the F-22. A very clever technique that copying the shape of the F-22 will not replicate will it. Ah, if only aerospace engineering was so simple. Believe me it is not!

[crobato]

Spread spectrum transmission is old stuff. Guess who uses it and its there in your pocket. Bluetooth.

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

http://wireless.per.nl/reference/chaptr05/cdma/cdma.htm

http://www.kmj.com/proxim/pxhist.html

Don't underestimate what engineers can know and can do.

Even a kid could do it.

http://www.eetimes.com/showArticle.jhtml?articleID=190301115

addendum: oh and a tutorial to detect such signals.

http://www.tscm.com/TSCM101ss23.html

[PrOeLiTeZ]

Another factor contributing to deflecting radar signature is the thickness of the material, the thickness of the material must be exact all around, to thin or thick the radar can pick it up or draws attention.

This was one of those 2nd year physics university problems of determining the thickness of ones material properties required to reflect a certain frequency. Though stealth fighter technology is way more advance then second year university physics.

China is pretty experienced in materials, its the angle of deflections, heat dampering, and radar covering they must concentrate.

[lilzz]

I know this is complete fiction and I know some of the reasons why but darned if I'm going to be the guy who tells you! You could copy the external shape faithfully and never come close to the RCS reduction of the actual B-2. There is a lot of fun going on under that smooth black skin. Have fun speculating. Mahalo.

Well, I don't know what you trying to say? Add some technical stuffs contribution, would you?
B-2 uses alot of RAM whereas F-22 every little, that's a fact.
read carefully of what I wrote. When did I say copying the B-2??

, the target will have a difficult time detecting the F-22. A very clever technique that copying the shape of the F-22 will not replicate will it. Ah, if only aerospace engineering was so simple. Believe me it is not!

Avoiding detection of its LPI radar and its' reduction of radar RCS on enemy radar screen are two different subjects. Dude, don't mix the two. you are confused.

No double posting, use the EDIT button!

[man overbored]

Avoiding detection of its LPI radar and its' reduction of radar RCS on enemy radar screen are two different subjects. Dude, don't mix the two. you are confused.

Number one, duplicating the external shape of the F-22 will not guarantee achieving anything near it's RCS. There are a lot of passive and active features under the skin, and the paint is even tuned to suppress frequencies not otherwise suppressed by airframe and materials characteristics. What is underneath the skin and the materials are highly classified, but be certain external shape is not the primary determinate. If it were then everyone would be flying stealth fighters.
The point about the radar is that regardless of how well developed the stealth characterists of the airframe are, the radar alone could give the game away. A stealthy radar is part and parcel of the complete package. There are a lot of ways to construct what falls into the rubric of a spread spectrum radar, including those whose wave forms may appear to be white noise or pink noise to a receiver. Combined with frequency agility this could be very tough to detect. Only the transmitter will know with precision what the original wave form looks like to know what the reflection received is. Other receivers will detect fleeting ( microsecond ) transmissions of what will appear to be noise as these transmissions hop frequencies.

[lilzz]

Number one, duplicating the external shape of the F-22 will not guarantee achieving anything near it's RCS. There are a lot of passive and active features under the skin, and the paint is even tuned to suppress frequencies not otherwise suppressed by airframe and materials characteristics. What is underneath the skin and the materials are highly classified.

Number one? well, that's only your opinion.

DO you read the article "understanding stealth" I post online
suppress frequencies?? R U implying F-22 is using special RAM overall its frame. False.

Radar absorbant materials, or RAM is applied sparingly on the F-22 airframe as opposed to the entire airframe on the F-117. This is because designers have incorporated curves on crucial surfaces and edges, which lessens the need for RAM.

So R U saying those areas on F-22 /wo the special material would get exposed??
well, what you saying clearly contradict what the source I am quoting.


http://www.globalsecurity.org/military/systems/aircraft/f-22-stealth.htm

here you go. Clearly states F-22 doesn't need much RAM for frequency suppression.

For more technical discussions, pls backup your statements with some credible sources.


Edited. Calm down. No need to act agitated or insulted. He is only stating his opinions in a respectable manner and I expect you do the same. Now go on with the discussion. -crobato

[man overbored]

Number one? well, that's only your opinion.

DO you read the article "understanding stealth" I post online
suppress frequencies?? R U implying F-22 is using special RAM overall its frame. False.

Radar absorbant materials, or RAM is applied sparingly on the F-22 airframe as opposed to the entire airframe on the F-117. This is because designers have incorporated curves on crucial surfaces and edges, which lessens the need for RAM.

So R U saying those areas on F-22 /wo the special material would get exposed??
well, what you saying clearly contradict what the source I am quoting.


http://www.globalsecurity.org/military/systems/aircraft/f-22-stealth.htm

here you go. Clearly states F-22 doesn't need much RAM for frequency suppression.

For more technical discussions, pls backup your statements with some credible sources.


Edited. Calm down. No need to act agitated or insulted. He is only stating his opinions in a respectable manner and I expect you do the same. Now go on with the discussion. -crobato

Global Security has been wrong before. Example. If you ever read anywhere that Harpoons were used in Operation Praying Mantis, and you will see this everywhere, I know for a fact this is incorrect. We ( our squadron ) was given the play by play of that entire operation, detailed discussions of the ordinance involved, the limitations, etc. One point we all had a chuckle at was the choice the Navy made not to use Harpoon. Since the Iranian's did not have anything with a range greater than 25nm it was decided to use Standard SM-2 missiles in their anti-surface mode at one quarter the cost per round of a Harpoon. We depressed the Mk-13 launchers on our ships and fired the missiles in a level attitude. It worked like a charm and we disabled some Iranian frigates enough for A-6's to complete the job with Mavericks and iron bombs. The moral of the story is not to believe everything in Global Security, they get it wrong.
Under the skin of a stealth aircraft there is a lot that doesn't meet the eye. Coatings are one of these. The F-22 and F-35 have very specific paints, and these are tuned to the individual airframe ( and not tuned to any reasonable defense budget but I digress ). Put F-35 paint on an F-22 and you loose desirable stealth characteristics. You might have forgotten that with the F-35, many of the buyers will not receive all of the low observable features the US and UK will receive. For a while the Aussies were griping to us about being cut out of all the low observable features after there was some indication a person or persons in Australia's defense establishment had questionable associations with China. Shape alone is not the determinate of stealth, it is only one part. Aside from paints there other features. Consider active cancelling headphones and certain commercial radios for a vague idea of what I'm alluding too.

[lilzz]

Under the skin of a stealth aircraft there is a lot that doesn't meet the eye. Coatings are one of these. The F-22 and F-35 have very specific paints, and these are tuned to the individual airframe ( and not tuned to any reasonable defense budget but I digress ). Put F-35 paint on an F-22 and you loose desirable stealth characteristics. .


Pls provide a link to backup your comments. I not so interest in random personal opinion.

radar absorbing paint is highly frequency dependent. Now how you able to have a paint to cover you from 1hz to 20Ghz ???? As you know there are different type of radar seraching waves. pls answer this question.

http://img529.imageshack.us/img529/7038/wav2qo5.jpg

The above is from marietta scientific consulting firm.
http://mariettascientific.com/understanding/under.htm

I give you 2 credible sources which in sync with the idea the shape of the plane is most important factors in stealth, RAM materials are just supplements.

I am interest to see the source that says F-22 has the paint whereas th F-35 doesn't therefore its stealth is drastically reduced. and what range of frequency they talk about.

Because in my opinion, F-22's mid and high frequency evasion is entirely depend on its shape , line and curve, its little used RAM is to supplement the low frequency evasion portion. This makes sense bcause RAM can only works at certain frequency.

[crobato]

The thickness of the RAM also determines the frequency it absorbs. It cannot absorb wavelengths longer than its thickness. Dealing with low frequency can mean having really thick, more like a layer, of RAM, and I don't think that's possible. If you are working against low frequency, you have to work with shape.

[lilzz]

http://img401.imageshack.us/img401/1144/wavewb0.jpg

http://img401.imageshack.us/img401/8262/wave2hz9.jpg

[man overbored]

Pls provide a link to backup your comments. I not so interest in random personal opinion.

radar absorbing paint is highly frequency dependent. Now how you able to have a paint to cover you from 1hz to 20Ghz ???? As you know there are different type of radar seraching waves. pls answer this question.

http://img529.imageshack.us/img529/7038/wav2qo5.jpg

The above is from marietta scientific consulting firm.
http://mariettascientific.com/understanding/under.htm

I give you 2 credible sources which in sync with the idea the shape of the plane is most important factors in stealth, RAM materials are just supplements.

I am interest to see the source that says F-22 has the paint whereas th F-35 doesn't therefore its stealth is drastically reduced. and what range of frequency they talk about.

Because in my opinion, F-22's mid and high frequency evasion is entirely depend on its shape , line and curve, its little used RAM is to supplement the low frequency evasion portion. This makes sense bcause RAM can only works at certain frequency.

Read up on the subject of "active quieting" as used in certain high end pilot's headsets and you will start to see what I am alluding to. The military application is much more complex.

From this link on the F-35 read the paragraph "advenced stealth"

http://www.lockheedmartin.com/data/assets/corporate/press-kit/F-35-Brochure.pdf

Here is more:

http://www.aviationtoday.com/av/categories/military/845.html

These aircraft manipulate the electomagnetic spectrum to achieve certain aspects of their stealth.

Allies however will receive less low observables than US forces will

http://toyoufromfailinghands.blogspot.com/2007/11/us-developing-separate-jsf-for-foreign.html

Their plane will look the same but will be less stealthy. Shape alone does not determine stealth.