Ohh oops. You're right. I forgot that from y axis 0 and 180 are top and bottom.
J-20 5th Gen Fighter Thread IV (Closed to posting)
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Ohh oops. You're right. I forgot that from y axis 0 and 180 are top and bottom.
I would guess that the clipped edge threatment is mainly to deal with waves travelling along the edge
Below is a really crude pic and explanation of what I think may be happening.
Red arrow signified incomming energy direction, and purple after interacting with surface.
1 Would be a direct reflection. Which is what we don't want.
2 Would be an angled reflection, won't be picked up by the illuminating radar but may be picked up by off-boresignt passive receivers.
3 Would be diffraction when hitting corners. The energy will spread out in all directions but because it is not as focused thir magnitudes tends to be smaller. The sharper the angle, the more energy is diffracted and less is transmitted along the object's edge as creeping surface wave.
4 Would be a rounded corner, there will be some direct reflection, because at some point along the curve the surface would be normal to the incomming wave. Because the surface transition is gentle compare to an sharp corner, a large component will flow along the surface until it encounters another sharp transition such as another corner and diffraction would occur. How much energy flows along the surface and how much is shed along the way would be determined by object material's physical and electric properties as well as the size of the curve to the wavelength of the signal.
5 Would be the shaved edge example. The less sharp corner (rough rule greater than right angle) encourages more energy to flow along the edge until it reaches the second corner and more energy would bleed off as diffraction and what remains flows along still and it gets progressively smaller. The diffracted signal spreads in all directions to discourage a strong return in one particular orientation. And because there are many corners the signals will add irregularly to cancel out somewhat amongst themselves. At far enough distance from the plane, the return from all the corners would seem almost parallel which means their magnitudes are more or less the same which helps with cancellation.
So we shape for stealth by angled surface to deflect wave away from it's incomming direction. The RAM coatings will hopefully attenuate signals so that not much is reflected anyway. corners and sharp discontinuities are a problem so we shave them to make them more oblique, and we encourage the singal to bleed as it goes around different corners and 'spread the signature out' so that you don't get strong returns in one particular direction. We would also encourage controlled surface waves as they would be flowing on the RAM coatings which would attenuate them fast.
Below is a really crude pic and explanation of what I think may be happening.
Red arrow signified incomming energy direction, and purple after interacting with surface.
1 Would be a direct reflection. Which is what we don't want.
2 Would be an angled reflection, won't be picked up by the illuminating radar but may be picked up by off-boresignt passive receivers.
3 Would be diffraction when hitting corners. The energy will spread out in all directions but because it is not as focused thir magnitudes tends to be smaller. The sharper the angle, the more energy is diffracted and less is transmitted along the object's edge as creeping surface wave.
4 Would be a rounded corner, there will be some direct reflection, because at some point along the curve the surface would be normal to the incomming wave. Because the surface transition is gentle compare to an sharp corner, a large component will flow along the surface until it encounters another sharp transition such as another corner and diffraction would occur. How much energy flows along the surface and how much is shed along the way would be determined by object material's physical and electric properties as well as the size of the curve to the wavelength of the signal.
5 Would be the shaved edge example. The less sharp corner (rough rule greater than right angle) encourages more energy to flow along the edge until it reaches the second corner and more energy would bleed off as diffraction and what remains flows along still and it gets progressively smaller. The diffracted signal spreads in all directions to discourage a strong return in one particular orientation. And because there are many corners the signals will add irregularly to cancel out somewhat amongst themselves. At far enough distance from the plane, the return from all the corners would seem almost parallel which means their magnitudes are more or less the same which helps with cancellation.
So we shape for stealth by angled surface to deflect wave away from it's incomming direction. The RAM coatings will hopefully attenuate signals so that not much is reflected anyway. corners and sharp discontinuities are a problem so we shave them to make them more oblique, and we encourage the singal to bleed as it goes around different corners and 'spread the signature out' so that you don't get strong returns in one particular direction. We would also encourage controlled surface waves as they would be flowing on the RAM coatings which would attenuate them fast.
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Yano, the clipped tail and clipped canards have got me wondering why they also didn't clip the wing corners. It could be that they didn't want to affect the performance of the control surfaces, since the entire trailing edge is control surface, but I'm somewhat doubtful that a small drop in surface area would really impact aerodynamic performance?
by78
General
Wait, how do we know that they haven't clipped the wing corners? The photos and videos I've seen don't conclusively rule out that possibility.
Deino's pic in post 3009. And before that I squinted really hard at those videos. REALLY hard.
They've definitely reshaped the rear end of the fuselage to conform more with the shape of the engines.
Interesting.
Why would they use S-band? To counter AWACS?
If so, wouldnt the VLO performance raise further with the higher wavelengths?
Remember, this is just a measurement for the geometry. Other RCS reduction measures aren't included.
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