J-15 Carrier Multirole Fighter thread


Brumby

Major
Take these with a grain of salt (CMANO db). Frontal aspect rcs:
J-15: 7.8m2
F/A-18E: 1.4m2
Rafale-M: 0.42m2

It's well known that the Rafale has extensive LO measures implemented and it should be no surprise that it is the "stealthiest" of the three. Having said that, as Tam pointed out, aircraft RCS is highly dependent on the illuminated CS and loadout. A proper comparison (with access to classified data) would take space and effort of a master thesis.
Thanks for the numbers. It basically affirms my estimate that the F-18 has a relative RCS advantage against the J-15 by at least 5 X.

Btw, you are right in an earlier comment that there is a relationship between RCS and jamming power requirements. A lower RCS platform has a jamming advantage in terms of power requirement.
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Tam

Major
Registered Member
The question wasn't about how long it had been in testing. The issue is there are no known technical capabilities of it to begin making comparison and drawing conclusions based on nothing.​


This is what you said earlier "The difference between an F-18, Rafale to a J-15D is not likely to be that significant in the context of a powerful AESA." . How is your reply above support your earlier comment?


I can basically apply your statement unto any AESA radar and it would be generally applicable. It doesn't explain or support your assertion that the radar associated with the J-15 would necessarily be more powerful than the one on the F-18 or Rafael.


Frankly you are saying a bunch of things that may sound relevant to you but in my opinion has no connection concerning the AESA conversation. You are positing a position that the radar on the J-15 is more powerful. Please explain how do you arrive at such a view.
Simply compute the larger cross section diameter of the Flanker's nose. Once you get the square area you can compute the number of T/R elements needed by using the X-band frequency bandwidth divided by half as the spacing between each T/R.

In planes like the J-11D and likely that of the J-16, instead of a circular cross section, the total area is increased by slicing the cross section from an angle, so it becomes more of an oval.

A bigger nose will allow a larger radar, which will hold more elements, and can house a larger power transformer to power them.

It is generally common knowledge that the SU-27 has a big RCS profile. The J-15 is a reverse engineered SU-33 and a navalised variant of the SU-27 and so it basically inherits the high RCS profile. What may be debated is its more precise RCS but that doesn't change the fact that it has a higher relative RCS profile than the F-18 of between 5 to 10 X by my estimate.
Your estimate?

The Su-30MKI also inherits the Su-27 design. RCS is 4 down from 10 to 15. An F-16 is about 5 and an F-15 is a horrendous 25.

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I don't know if this is right but Su-34/35 is about 1m to 3m. J-10 is about 0.5 to 1.0. A J-7 is about 3m.

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While I do take all figures with a salt, the Su-27 basic design has plenty of room to reduce its RCS by at least a magnitude.

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This is an old document around 2004. Do you think that no one in China and Russia working in these planes already know this?

As I mentioned, the intake diverter and ducts need to be treated with RAM, which is the biggest reducer. Then the cockpit next. You can reduce the RCS further by having the radome slice at an angle, so reflections against the rim of the radome goes either up or down instead of forward, and which also allows you to create a larger cross section area for a larger AESA as I mentioned above when you have an oval or ovoid array instead of a circular one. Radar reflected at the firewall of the radome and at the array itself will be bounced upward or downward.

But they already seem to know this.

NZMNIEYXKWYORY7EH7JQCFRFVA.jpg 1634465_-_main.jpg J-11-figher-with-new-radome-1.jpg

 
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Max Demian

Junior Member
Registered Member
Btw, you are right in an earlier comment that there is a relationship between RCS and jamming power requirements. A lower RCS platform has a jamming advantage in terms of power requirement.
However, I was wrong in inferring the reduced radar detection range in presence of jamming. That would be the burn through range from the figure you posted. So between 4-5 times lower burn through range, assuming the numbers I previously posted.

The correct interpretation, as far as I understand now, is as follows.
Assume that the Rafale-M has a 17 times lower RCS than J-15. Assume both aircraft are illuminated by the same radar. Assume both aircraft are jamming the radar. Then for the J-15 to be detected at the same (max) range as the Rafale it would need a jammer 17 times as powerful as the Rafale. The detection range can be derived from the burn through equation.
 
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Tam

Major
Registered Member
You can't use a jammer that way too, because the jammer itself can become a point of detection. Your radars alone can be a point of detection. The time when Plane A detects Plane B with its radar, is also the time when Plane B simultaneously detects Plane A through its ESM/RWR.
 

Brumby

Major
Simply compute the larger cross section diameter of the Flanker's nose. Once you get the square area you can compute the number of T/R elements needed by using the X-band frequency bandwidth divided by half as the spacing between each T/R.

In planes like the J-11D and likely that of the J-16, instead of a circular cross section, the total area is increased by slicing the cross section from an angle, so it becomes more of an oval.

A bigger nose will allow a larger radar, which will hold more elements, and can house a larger power transformer to power them.
I am very familiar with the bigger radome argument because it is probably the most often use. However there are many other factors and equally important such as :
a)packaging technology which determines number of TRs that can be packed within a given space;
b)quality of TR which drives duty cycle;
c)processing gain driven by quality of digital signal processors which the US leads in tech and the Chinese aspires to acquire;
d)receiver gain;
e)US "know how:' when it has been at this much longer
Making an assumption that the J-15 will somehow have a more powerful radar simply on the basis of one factor is in my view rather selective.

Your estimate?

The Su-30MKI also inherits the Su-27 design. RCS is 4 down from 10 to 15. An F-16 is about 5 and an F-15 is a horrendous 25.

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I don't know if this is right but Su-34/35 is about 1m to 3m. J-10 is about 0.5 to 1.0. A J-7 is about 3m.

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While I do take all figures with a salt, the Su-27 basic design has plenty of room to reduce its RCS by at least a magnitude.

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The globalsecurity link has the SU-30MKI at 4 m2. Even giving you the benefit of the doubt, it is still 4X RCS advantage against the F-18 quoted at 1m2.
upload_2019-8-27_21-36-15.png

If I used the second link you provided it still had the F-18 at 1m2 and similar to the J-20 also rated at 1m2. LOL.
upload_2019-8-27_21-38-41.png
 

Tam

Major
Registered Member
I am very familiar with the bigger radome argument because it is probably the most often use. However there are many other factors and equally important such as :
a)packaging technology which determines number of TRs that can be packed within a given space;
Wrong. Its not packaging technology that determines that. Its sheer physics.

If elements are too close to each other, something called mutual coupling happens. This means radio waves from one element interferes and transfers to the next element, affecting the next element, causing a loss of efficiency and gain. To counter the effects of mutual coupling, the elements need to be separate each other.

How far can you separate the elements? If you go too far, it will result in grating lobes. To prevent grating lobes, the accepted rule is 1/2 (or just slightly over) of the frequency band used by the radar. The shorter the frequency, the shorter the spaces, the longer the frequency, the longer the space. A radar that works on a meter wavelength means the elements must be separated by half a meter from each other. Radar working on a 10 cm wavelength, means about 5 cm element separation, just for example.

Frequency used determines the distance and separation of the elements, and also of the density of the array.

b)quality of TR which drives duty cycle;
Duty cycle is determined by range of the target. Why?

Because the radar has to wait for the echo. The farther the target, the longer the radar has to wait for the echo. Only after it has received the echo can the radar transmit again. PRT is determined by range, the closer the target, the faster the pulses, the farther the object, the longer the pulses.

Mechanical fire control radars are capable of extremely fast pulse, for example, the radars used by CIWS that are used to track very close targets.

c)processing gain driven by quality of digital signal processors which the US leads in tech and the Chinese aspires to acquire;
5G is the state of the art when it comes to DSP use. Guess who is ahead.

d)receiver gain;
The bigger the array, the more receiving elements, the greater the measurable difference between elements from one side to the other, up and down, left and right.

e)US "know how:' when it has been at this much longer
The same can be said of telecom and communication technology when the AT&T monopoly was the "Huawei" of the US.

Making an assumption that the J-15 will somehow have a more powerful radar simply on the basis of one factor is in my view rather selective.
A larger plane allows for a larger radome. That's not hard to understand. Its also the same advantage the F-15 has over the F-16.

The globalsecurity link has the SU-30MKI at 4 m2. Even giving you the benefit of the doubt, it is still 4X RCS advantage against the F-18 quoted at 1m2.
View attachment 53496

If I used the second link you provided it still had the F-18 at 1m2 and similar to the J-20 also rated at 1m2. LOL.
View attachment 53497
And what is an Su-35? Its still a Flanker, and a Flanker that is getting 1m2. At 2004, meaning this is older tech than an Su-35 today and the Su-35 at that time even had canards. It may even get lower if they decided to angle the radome, or do serration on the radome rim, or add grids on the cockpit glass. Further RCS reduction is possible if you attack the RCS on the AAMs and payloads.
 

Max Demian

Junior Member
Registered Member
You can't use a jammer that way too, because the jammer itself can become a point of detection.
But it your radar is jammed, you won't get ranging information and you won't get speed information. Bearing alone is not enough for a firing solution.
 

Lnk111229

New Member
Registered Member
Off topic but see all those " huge design flaw" of J-20 write by "superior expert" journalist make me want ask. Is this true? If not than someone can tell me how stealthy of J-20. I just need simple answer like f35 stealthy is 8, f22 is 9 then J-20 is maybe 7 or 8.5? Thanks
 

Tam

Major
Registered Member
But it your radar is jammed, you won't get ranging information and you won't get speed information. Bearing alone is not enough for a firing solution.
Your ESM can triangulate location. There maybe like three points in the aircraft (or land units; ships use two) when the threat radar is received.

By comparing the angle and time of arrival of the signals on two of the receivers, you get the location. On the third receiver, which is set on a different height, you get altitude, to complete a three dimensional location.

(Ships use two ESM because they are locating the threat ship on a two dimensional surface).

The rate of radar pulses can also give away the range of the threat; faster pulse times means its closer, longer pulse times means its farther. The exact length of the pulse can give away the threat radar's range.

Not only that, the signals change when the plane changes its radar modes, like search and detect mode to track while scan, and this betrays the threat radar's intention.

Passive won't get you a firing solution for aircraft (note, for ship, it can and even over the horizon). However, it can tell your radar where to look for the enemy. Or you can send a missile on HOE mode, and it will sniff and follow the signal like a mad bulldog.

This is also true with SAM batteries. True for them against a threat aircraft, and vice versa, aircraft against threat SAMs.

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