J-20 5th Gen Fighter Thread V

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plawolf

Lieutenant General
People seem to be forgetting those giant vertical stabilisers the F22 have compared to the J20.

In terms of actual real estate, the F22's vertical stabilisers' have much more reflective area than the J20's verticals and side steaks combined.

Please explain how canting makes the F22's giant vertical stablizers irrelevant in terms of RCS, but the same canting makes the J20's tiny side streaks lumberg lenses.

In terms of engine arrangement, well maybe all these overnight stealth masters popping out of the woodworks should be explaining the total folly of round nozzles and the unparalleled benefits of stealth nozzles to LockMart, because they must not have gotten that memo to go from awesomesource stealth nozzles on the F22 to go back the using noob round nozzles on the F35.
 

b787

Captain
People seem to be forgetting those giant vertical stabilisers the F22 have compared to the J20.

In terms of actual real estate, the F22's vertical stabilisers' have much more reflective area than the J20's verticals and side steaks combined.

Please explain how canting makes the F22's giant vertical stablizers irrelevant in terms of RCS, but the same canting makes the J20's tiny side streaks lumberg lenses.

In terms of engine arrangement, well maybe all these overnight stealth masters popping out of the woodworks should be explaining the total folly of round nozzles and the unparalleled benefits of stealth nozzles to LockMart, because they must not have gotten that memo to go from awesomesource stealth nozzles on the F22 to go back the using noob round nozzles on the F35.
J-20 has ventral fins for a ground radar is a reflector F-22 has vertical large fins but has shielded engines and no ventral fins add the ventral fins to the dorsal fin and the J-20 has no small surface, even in the F-35 is better to J-20, the chinese jet needs ventral fins because the dorsal fin area is not enough to control the jet, and the jet is huge
 

plawolf

Lieutenant General
J-20 has ventral fins for a ground radar is a reflector F-22 has vertical large fins but has shielded engines and no ventral fins add the ventral fins to the dorsal fin and the J-20 has no small surface, even in the F-35 is better to J-20, the chinese jet needs ventral fins because the dorsal fin area is not enough to control the jet, and the jet is huge

So we are now talking about ground based radars instead of just air based? See that hole in the ground in front of you? That's where your goal posts used to be.

Ground radar would also see the F22 and F35's horizontal tails, which are far larger than the J20's ventral fins, and those tails are also not as well angled to reflect radar energy again from the transmitter as the canted J20 fins. They also need to flap around to help control flight, which I seem to remember someone mentioning was bad for stealth.

The J20's ventral fins also actually block radar seeing the far more vulnerable engines from both air and ground for all but a limited range of aspects.

The F35 especially shows its round engines far more easily than the J20, yet I don't remember people saying anything about it having stealth issues.
 

Richard Santos

Captain
Registered Member
People seem to be forgetting those giant vertical stabilisers the F22 have compared to the J20.

In terms of actual real estate, the F22's vertical stabilisers' have much more reflective area than the J20's verticals and side steaks combined.

Please explain how canting makes the F22's giant vertical stablizers irrelevant in terms of RCS, but the same canting makes the J20's tiny side streaks lumberg lenses.

In terms of engine arrangement, well maybe all these overnight stealth masters popping out of the woodworks should be explaining the total folly of round nozzles and the unparalleled benefits of stealth nozzles to LockMart, because they must not have gotten that memo to go from awesomesource stealth nozzles on the F22 to go back the using noob round nozzles on the F35.

A single large surface is not a problem in itself. The important thing is how the edges of the surfaces are oriented, how the flat surface is oriented, and whether any part of the edge or surface forms and angle reflector with other parts of the aircraft. Having many surfaces oriented at different angles is a problem, because it becomes difficult to really align them all so they all only reflect only in very few narrowly focused directions. Having many differently oriented surfaces means the aircraft likely have many more directions into which it would reflect any incoming radar beam.

The ventral stabilizers on the j20 is not in itself a problem. Where it becomes a problem compared to the control surface layout of f22 is it presents more surfaces, not bigger surfaces, than on the f22. This is particularly an issue because the ventral surfaces are visible across a wide arc from beneath the aircraft. So the j-20 is likely to possess vulnerable directions to radars searching for it from beneath. While this is an issue, it doesn't necessarily present a crippling issue. If j20's threat warning system is very good in picking up and identifying the direction of threatening radar receivers, and the signals from these warning receivers are integrated into the autopilot to enable the aircraft to always maneuver to direct reflections away from radar emitters, it could become in effect as stealthy from a mission perspective as the f22.

However, if the enemy possesses low probability of intercept radar, or possess radar receivers that are geographically separated from radar emitters, then there is nothing j-20's threat receivers and avionics can do to compensate for its extra number of reflecting surfaces compared to the f22.
 

PikeCowboy

Junior Member
but aren't the ventral fins aligned with the contralateral fuselage and dorsal fin?
reflections from the ventral fins should go in the same direction as that from the contralateral fuselage?

and about the single flat surface, my impression is that it reflects radiation pretty well, just in an easier to control direction... you would still need to know the position of opposition radar emitters and receivers for you to achieve effective "stealth"

does the j20 ventral fin add an extra direction of radar reflection compared with its fuselage?
 

vesicles

Colonel
Not sure if we should look at all these surfaces acting in an additive manner, meaning that do 5 surfaces always reflect more signals than 3 surfaces? What about some kind of synergistic way, either preventing signal reflection or enhancing it?

Is there any simulations on the J-20's stealthiness?
 

plawolf

Lieutenant General
A single large surface is not a problem in itself. The important thing is how the edges of the surfaces are oriented, how the flat surface is oriented, and whether any part of the edge or surface forms and angle reflector with other parts of the aircraft. Having many surfaces oriented at different angles is a problem, because it becomes difficult to really align them all so they all only reflect only in very few narrowly focused directions. Having many differently oriented surfaces means the aircraft likely have many more directions into which it would reflect any incoming radar beam.

The ventral stabilizers on the j20 is not in itself a problem. Where it becomes a problem compared to the control surface layout of f22 is it presents more surfaces, not bigger surfaces, than on the f22. This is particularly an issue because the ventral surfaces are visible across a wide arc from beneath the aircraft. So the j-20 is likely to possess vulnerable directions to radars searching for it from beneath. While this is an issue, it doesn't necessarily present a crippling issue. If j20's threat warning system is very good in picking up and identifying the direction of threatening radar receivers, and the signals from these warning receivers are integrated into the autopilot to enable the aircraft to always maneuver to direct reflections away from radar emitters, it could become in effect as stealthy from a mission perspective as the f22.

However, if the enemy possesses low probability of intercept radar, or possess radar receivers that are geographically separated from radar emitters, then there is nothing j-20's threat receivers and avionics can do to compensate for its extra number of reflecting surfaces compared to the f22.

Good post. But the problem is everything is all too theoretical and circumstantial.

My point isn't to 'prove' how stealthy the J20 is, because we simply don't have the data to make such a claim. Which is my entire point of easily poking holes in the arguments of those making bold claims about the J20's stealth characteristics with nothing but feelings, vague general principles and other intangibles as back-up.

At the end of the day, you cannot change physics.

If we hold all else equal, a bigger surface will yield a bigger radar return compared to a smaller surface. Same with more surfaces yield higher RCS than fewer surfaces.

But if we are moving goal posts and talking about ground based radar, then all the arguments about the F22 and F35 hiding their horizontal tails behind their main wings also go out the window, since those would also be visible to ground based radar and come into play for RCS.

What we cannot know is how much the RCS will compare with two big sets of surface against 3 much smaller sets, as the aspect towards the planes change.

It would take a massive, detailed dataset; supercomputers and advanced bespoke software to work out the actual RCS difference between a J20's layout and that of the F22/35 from the same radar source from the same angle and as that angle change.

That's why I find all those human eyeball RCS readers so silly and untrustworthy.

I'm no mind reader, but I get the strong feeling the whole reason a lot of the people making bold claims about the J20 are doing so about RCS is also precisely because of how hard it would be to prove it one way of the other - it makes it almost impossible to conclusively call them on their made-up claims.
 
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AssassinsMace

Lieutenant General
It's funny how people talk about the ventral fin when the F-22 has a huge tailfin combined with the angle created with the horizontal stabilizer and you have a huge radar return.
 
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