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.
Building a low cost stealth fighter in a tight schedule.
- Thread starter lilzz
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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.
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.
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.
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RedMercury
Junior Member
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
Junior Member
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.
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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.
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
Junior Member
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!
Spread spectrum transmission is old stuff. Guess who uses it and its there in your pocket. Bluetooth.
Don't underestimate what engineers can know and can do.
Even a kid could do it.
addendum: oh and a tutorial to detect such signals.
Don't underestimate what engineers can know and can do.
Even a kid could do it.
addendum: oh and a tutorial to detect such signals.
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.
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.