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


Air Force Brat

Brigadier
Super Moderator
J-20 is longer and heavier than American stealth fighter jets. J-20 are designed for long distance missions ??
Now you're in trouble, LOL no actually the J-20 only weighs 15,000 lbs and is only 40 ft long! LOL have fun Dude

Well, I'll be a nice guy, they say the J-20's empty weight is only 3/4's of the empty weight of an F-22, and its shorter than a Flanker! (this last may be true if we are looking at the tail sting on the Flanker, anyway, this is an older thread.....
 

Inst

Senior Member
J-20 is longer and heavier than American stealth fighter jets. J-20 are designed for long distance missions ??
Range is fairly optimized on the J-20, compared to the F-22. The Su-57 likewise is designed for extended ranges.

There's a rumor going around that the J-20 needs to hit 5500 km ferry range, which would allow it to be deployed in any portion of China from any other portion of China. This is achievable with 4 drop tanks, or in other words, with 7.5 tons of additional fuel.

Counting an 8% penalty, and assuming 12,500 internal fuel load, you'd get roughly 5940 km without drag and weight penalties, you'd get basic ferry range without tanks of 3712.5 km. Multiply by 40% to get 60% fuel (standard combat fuel capacity), and you'd get 1485 km of combat radius on the J-20, unrefueled.

The internal fuel, of course, is an unknown factor, but going between 8000 to 12500 kg, you go from 1230 km to 1500 km, and we're still assuming the 5500 km range with 4 tanks is correct.

A comparison point would then be the F-35C, which has 1300 km of range with enormous internal fuel tanks. The J-20, in comparison to the F-35C, would still have good internal tank combat radius without going into 0.9 T/W at 50% fuel; the J-20 by comparison would be in the 1.04-1.1 T/W range.

===

As a second point of comparison, the A6M2, a WW2 turboprop, had 1300-1500 km of range depending on whether you ran 60% or 50% fuel for combat radius with an auxiliary tank.
 

stannislas

Junior Member
Registered Member
Looking back at the underlying thread, it's roughly the reverse, i.e, 20.87 + 12.94 for wingspan. My own measurements are 20.84 l 12.93 w.

More surprisingly, the wing area has been overlooked, a recent measurement I took showed about 76 m^2 in terms of effective wing area including LERXed areas. This gives a loaded wing loading of 395 m^2 under 30000 loaded weight and 345 m^2 at 26200 (18,000 empty wight + 60% of 12000 fuel with 1000 kg of munitions). This is inferior to the F-22 and Su-57.

Measurements:

Using this set of coordinates:

Frontal triangle apex:

256 539

Front wingspan

390 659

392 421

Rear wingspan

417 658

419 422

Rear triangle apex

443 541

We get roughly 136 pixels of length for the front triangular segment, 27 pixels of length for the central rectangular section, and 25 pixels of length for the rear triangular segment. Using 402.1 for Flanker length (21.94), and double counting the 27 central rectangular section, we get roughly 75.8 m^2 wing area.

Picture in use:

like I said in the other thread
we could see the photo was taken in pretty low angle, so angle error could be pretty huge

we can see the picture was taken roughly in the middle in terms of uh...Y-axis, but for X-axis is slightly difficult to say... and that's how the different length measured...
 

Inst

Senior Member
like I said in the other thread
we could see the photo was taken in pretty low angle, so angle error could be pretty huge

we can see the picture was taken roughly in the middle in terms of uh...Y-axis, but for X-axis is slightly difficult to say... and that's how the different length measured...
They literally parked the aircraft on a grid, you know? The measurements I'm getting have an error of roughly 3%, depending on plane you're using and the measurement method.

If you use the grid method (72x90 pixel length per chart, assume 4x5 meter runway tilings), you get roughly 21.3 meters length vs 13.1 meters wingspan. The wingspan is still 97.5% of the lowest wingspan you can derive from the picture.
 
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stannislas

Junior Member
Registered Member
n
They literally parked the aircraft on a grid, you know? The measurements I'm getting have an error of roughly 3%, depending on plane you're using and the measurement method.

If you use the grid method (72x90 pixel length per chart, assume 4x5 meter runway tilings), you get roughly 21.3 meters length vs 13.1 meters wingspan. The wingspan is still 97.5% of the lowest wingspan you can derive from the picture.
no, can you show me what grid you are referencing to? if you are talking about the brick on the runway....than you are facing a bigger error than simply pixel measurement. The size of the brick is unknown and as a building material, it has a much bigger error than a jet... I will say

So to measure the exact size of the brick, you have to use the number of J-16 (assuming identical to Su-27) which then back to the pixel measurement...... so what's the point?
 

Inst

Senior Member
n

no, can you show me what grid you are referencing to? if you are talking about the brick on the runway....than you are facing a bigger error than simply pixel measurement. The size of the brick is unknown and as a building material, it has a much bigger error than a jet... I will say

So to measure the exact size of the brick, you have to use the number of J-16 (assuming identical to Su-27) which then back to the pixel measurement...... so what's the point?
It's reasonable to assume bricks are built in standard sizes, and the ratio of the brick dimension (5:4) is relatively standard.

If, say, this were an architectural structure, then we could reasonably assume that the bricks are non-standard in dimensions, but since this is airfield concrete tiling, we can assume it's 5x4 m.

This gives us roughly a larger figure than the basic J-20 figures, it'd imply the aircraft is about 21.3 meters long, and 13.1 meters wide in wingspan.

The grid, likewise, is usable in terms of determining perspective effects. Since the brick is uniform, we can use variations in the measurement of the brick to determine the effect of perspective distortion, which seems less than 2% from edge to center.
 

Inst

Senior Member
On casual inspection, I accepted the forums dogma that the canard on the J-20 is plane-aligned to the opposite wing, and that the ventral fin on the J-20 is plane-aligned to the opposite tailfin. However, doing measurements, it's obvious that this isn't actually the case.





On the preceding image, we have wing measurements:


The line formed by the wing is 36x348 pixels, giving us a ratio of 0.10344827586206896551724137931034 or about 5.9377724516054286242797916868402 degrees.

On the subsequent image, however, we have canard measurements:



The line formed by the canard is 61x332 pixels, giving us a ratio of 0.18373493975903614457831325301205 or about 10.587385565866989310103810801075 degrees.

That's a difference of roughly 5 degrees, and too great to be the result of measurement error. A measurement of the opposite canard from a different picture, shows a greater difference of 6 degrees, but the canard in that picture is not in that resting position. It is possible that the canard in the original picture isn't in rest position either, but the difference is only 1 degree based on minor disalignment.

This is something reasonable to assume based on the J-20's engine deficit; i.e, the airframe can't fully align the canards with the main wing without causing significant penalty to the canard-wing aerodynamic alignment, or further reducing the effective wing area on the J-20 due to increasing the anhedral even further.

The next set of measurements would be for the ventral fin vs the tailfin alignment.



Here, we have 179x345 pixels for the tailfin. This is a ratio of 0.51884057971014492753623188405797 or 31.25 degrees (measurement error would allow +-1 degree).



For the ventral fin, however, we have 104x211 pixels. That's a ratio of 0.49289099526066350710900473933649 or 29.5 degrees, or in other words, there's a 1.75 degree difference between the ventral fin and the tailfin.

So what we have to conclude is that the J-20 does enjoy some plane alignment features, especially when viewed from the z-axis, but on the y-axis the set formed by the canard-wing planes and the set formed by the ventral-tailfin planes aren't internally aligned.

This isn't a big problem insofar as with WS-15, it'll be possible to rework the aircraft, especially if the ventral fins can be entirely replaced by TVC.
 

stannislas

Junior Member
Registered Member
It's reasonable to assume bricks are built in standard sizes, and the ratio of the brick dimension (5:4) is relatively standard.

If, say, this were an architectural structure, then we could reasonably assume that the bricks are non-standard in dimensions, but since this is airfield concrete tiling, we can assume it's 5x4 m.

This gives us roughly a larger figure than the basic J-20 figures, it'd imply the aircraft is about 21.3 meters long, and 13.1 meters wide in wingspan.

The grid, likewise, is usable in terms of determining perspective effects. Since the brick is uniform, we can use variations in the measurement of the brick to determine the effect of perspective distortion, which seems less than 2% from edge to center.
Clearly, you don't have much knowledge in engineering, especially in civil engineering. How could you assume the brick is exactly is 5x4m, the process for you to get those numbers is pretty unreasonable, based on " relatively standard ", what standard? Like I repeated many times, it's a construction material, I won't be surprised if their error to be more than 10cm differences between each. And if you won't read what other people wrote then, I'm done discussing this with you.

Also, more importantly, known how runway is constructed, those are not actually "brick", normally they will do the entire runway in concrete and after the concrete is dry, they use some machine to cut out each channel for the concrete to be able to expand in the summer and shrink in the wintertime. And if you have any idea about the civil engineer, trust me, their minimal error is measured in cm, whereas 1mm (mostly even much less) in jet production.

So I will say your pixel measure will be much accurate than the grid approximation, just need some additional error correction to get the estimation more reliable.
 

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