J-20 5th Generation Fighter VII

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Bhurki said:
Let alone the rcs, even the representative size of J20 as compared to others is ill informed. It is the same length as su 57.
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We have good measurements in the 20.88 meters length / 12.95 meters wingspan range. The Su-57 is 20.1 meters long.

RCS is relatively a black box; you have Taiwanese measurements implying minimum RCS of -20 dBsm (or .01 m^2, m^2 = 10^[dBsm*.1], back conversion would be dBsm = log m^2 * 10), Carlos Kopp claiming that in 8 GHz (standard fighter radar band) the plane goes to -40 dBsm, Chinese RCS studies implying -50 dBsm max, and so on.
 
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Xsizor said:
I'm pretty sure that F35
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It's basically saying that the J-20 aims for an F-35 type RCS, which seems reasonable given how the F-35 is designed and so on.

But you also have to note, the F-35 is believed to have lower RCS than the F-22, given its size and the advancements in design and materials.

My own conviction is that the J-20 ranges in -30 to -40 dBsm in the present configuration, with a possibility to reach -50 dBsm with better RAM and the -50 to -60 dBsm range with major design modifications.

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In other words, the J-20 can be assumed to have an RCS from -30 to -50 dBsm right now in its optimum angles. The question of where the RCS is (since -30 to -50 dBSM is around a 300% range in terms of detection range) is more questionable. It is at least VLO, not LO as others might wish you to believe.
 
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stannislas

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Inst said:
We have good measurements in the 20.88 meters length / 12.95 meters wingspan range. The Su-57 is 20.1 meters long.

RCS is relatively a black box; you have Taiwanese measurements implying minimum RCS of -20 dBsm (or .01 m^2, m^2 = 10^[dBsm*.1], back conversion would be dBsm = log m^2 * 10), Carlos Kopp claiming that in 8 GHz (standard fighter radar band) the plane goes to -40 dBsm, Chinese RCS studies implying -50 dBsm max, and so on.
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Can you please provide the link or whatever of the referred “good measurements” of j-20? I saw several different version from 20.1 to 20.4 now to 20.88, all claims to be precise measurement...

and also for the su-57, if there is any good source, even wiki has different number in the same page... terribly confusing...
 
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stannislas said:
Can you please provide the link or whatever of the referred “good measurements” of j-20? I saw several different version from 20.1 to 20.4 now to 20.88, all claims to be precise measurement...

and also for the su-57, if there is any good source, even wiki has different number in the same page... terribly confusing...
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J-20 - physical parameters and other overflow from main thread

delete
www.sinodefenceforum.com

You have the source picture, and the other aircraft are J-16s (Su-30MKK clones). It's satellite, and the standard mistake working with the picture is not compensating for perspective (you need to use the centralized J-20 and a centralized J-16).
 
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stannislas

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Inst said:

J-20 - physical parameters and other overflow from main thread

delete
www.sinodefenceforum.com

You have the source picture, and the other aircraft are J-16s (Su-30MKK clones). It's satellite, and the standard mistake working with the picture is not compensating for perspective (you need to use the centralized J-20 and a centralized J-16).
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yeah, I saw that thread, and like I guessed it's the same picture, the 20.1 and 20.4 m measure from other people is also from this image as well...

Also, this is definitely not from satellite, very like DJI fly over. Depends on where the picture was taken and the lens, given the height of the picture was taken, the angle error could be much bigger than you think, 5-10% is even possible...
 
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stannislas said:
yeah, I saw that thread, and like I guessed it's the same picture, the 20.1 and 20.4 m measure from other people is also from this image as well...

Also, this is definitely not from satellite, very like DJI fly over. Depends on where the picture was taken and the lens, given the height of the picture was taken, the angle error could be much bigger than you think, 5-10% is even possible...
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Perhaps, but this is the closest we'll get to overflight. IIRC, the main errors made were based on perspective distortion, i.e, using the J-20s on the side or the J-16s on the side to do measurements (i.e, 20.1 / 20.4)

However, this is the closest we'll get to good measurements; i.e, the background is flat, the planes are on the same plane orthogonal to the viewer, etc. Software could possibly derive closer estimates than what we already have.
 
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Relative to the main plane, the center J-16 is positioned almost exactly the same as the central J-20. So we could do length vs length measurements there. IIRC that's how the numbers were derived.
 
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stannislas

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Inst said:
Perhaps, but this is the closest we'll get to overflight. IIRC, the main errors made were based on perspective distortion, i.e, using the J-20s on the side or the J-16s on the side to do measurements (i.e, 20.1 / 20.4)

However, this is the closest we'll get to good measurements; i.e, the background is flat, the planes are on the same plane orthogonal to the viewer, etc. Software could possibly derive closer estimates than what we already have.
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don't get me wrong, appreciate you provide the source, and I agree this might be the closest we could get atm in terms of the references.

But still, we could measure slightly better than this, based on the angle differences the J-16 is opened, the center of the picture in Y-axis is roughly aliasing withe the left intake of the J-16 in the middle, I don't want to measure exactly how many pixels that is but let's just say roughly 10% may occur, so the average error in width is roughly 1-2% + pixel error for a quick estimation from your measurement, and that's assuming you are using the J-20 in the middle...

To do a more precise estimation, we could roughly reverse out the height of the camera using the same idea above, and this is Step 1.

For Step 2, we need the original picture (if I'm not wrong this is a cut from a larger picture) with ISO and other information of the picture (I have DJI Mavic myself, the lens is definitely more a fisheye, so boundary stretch is big).

But assuming the X and Y axis has the same angel error (unlike, but...), and ignoring the lens stretching, for now, based on the rough length/width estimation, you might looking for a 2-4% or even 6% error in length... that's from 20.04 to 20.46 after the error compensation.

But of course, this is a very quick estimation here, and I'm not sure exactly how many % the error exactly is, just think it should be slightly more accurate the 20.88 you got from raw pixel measurement.

Inst said:
Relative to the main plane, the center J-16 is positioned almost exactly the same as the central J-20. So we could do length vs length measurements there. IIRC that's how the numbers were derived.
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yes, but the stretching and angle error on two jets are still different, not exactly useful to say...
 
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