J-20 5th Gen Fighter Thread V

[plawolf]

The first and most important rule to any sort of data analysis is the 'golden rule' of 'trash in trash out'.

The point is that if your source data is wrong or incomplete, whatever analysis you do with that data is also going to be wrong or incomplete.

With that in mind, let's critically assess what the 'inputs' for Koop's RCS study could have been.

All he had to go with were medium resolution images at best (think back to when the he study was done). That leaves a fairly big margin for measurement error of the model he tested.

Speaking of the model, did he built a scale model? Possible, but highly unlikely. Far or likely he just built a computer model.

Next comes questions about methodology.

If he just used a software model to test against a computer model, what was the software he used to calculated RCS? How was the results validated? I highly doubt he built a scale or 1:1 model of the J20 and tested it in an Anechoic chamber or RCS range.

There is a reason even profession defence companies with years or decades of experience in designed and building stealth aircraft still do 1:1 and even live RCS testing in Anechoic chambers and on RCS ranges.

Even if he built a 1:1 model and tested it in Anechoic chambers and on RCS ranges, all he would still have is how the basic outline of the plane might register on radar. Unless he has detailed blueprints, there is no way he could account for the use of various types of composite and RAMs.

At best those RCS models are a very rough guesstimate of the possible RCS characteristics of the J20. To treat them as if they were exact figures is either disingenuous and/or critically flawed logical reasoning.

 

[Pmichael]

How would canards even be a design flaw.

Meanwhile the wings are never a topic.

 

[MwRYum]

How would canards even be a design flaw.

Meanwhile the wings are never a topic.

Something about its negative impact on the RCS performance of the airframe. BTW, this argument is something that the Taiwanese licked it up like some elixir and use whenever to dizz at J-20.

But then again, without actual RCS result of J-20 (the ONLY public flight so far was with RCS amplifier attached), so those familiar characters such as Pinkov would use things like "very loud" and "can visually see IR signature" to dizz at J-20...

Guess gotta wait till next year if POTUS Trump would deliver the long promised "Sino-US war" (regardless of everything else, his Administration is a who's-who list of China haters) then? Sure it's nonsense talk, but how else to end such endless squabble without a real war to "test things out"?

 

[coolieno99]

The only factual evidence of the J-20's steath is the Luneberg reflector attach to the underside of the fuselage. It appears in many photos of various Chinese military forum, especially CDF. It appears as small cylindrical object attached to underneath the fuselage. It's highly reflective of radar waves. It's needed because the J-20 is invisible to civilian airport radar. This enable the air traffic controller to track the J-20 in its airspace for safety reason.

 

[Pmichael]

It just doesn't make sense that if radar waves hit the canards that it would totally destroy the stealth aspect but traveling one meter further and hitting the way larger wings is okay.

 

[vesicles]

It just doesn't make sense that if radar waves hit the canards that it would totally destroy the stealth aspect but traveling one meter further and hitting the way larger wings is okay.

I've been wondering the same thing. How can a small canard be so visible when the huge wing is behind it? If the J-20 is shaped like a missile without wings, then it makes sense to me that adding additional structures like canards would mess up stealth. But the plane already has two huge wings that stick out of the fuselage... Could someone knowledgeable explain?

 

[Twix101]

I've been wondering the same thing. How can a small canard be so visible when the huge wing is behind it? If the J-20 is shaped like a missile without wings, then it makes sense to me that adding additional structures like canards would mess up stealth. But the plane already has two huge wings that stick out of the fuselage... Could someone knowledgeable explain?

Main issue is being the perpendicular angles at the joint between the moving canard and the rest of airframe. While such perpendicular angles are masked on the moving parts of the main wing, the canard joints with airframe aren't. To avoid such phenomenon, the joints between the canard should avoid such perpendicular angles.

 

[Quickie]

Main issue is being the perpendicular angles at the joint between the moving canard and the rest of airframe. While such perpendicular angles are masked on the moving parts of the main wing, the canard joints with airframe aren't. To avoid such phenomenon, the joints between the canard should avoid such perpendicular angles.

It's more than 90 degrees, even more than the angle between the wings and the airframe.

 

[Air Force Brat]

Main issue is being the perpendicular angles at the joint between the moving canard and the rest of airframe. While such perpendicular angles are masked on the moving parts of the main wing, the canard joints with airframe aren't. To avoid such phenomenon, the joints between the canard should avoid such perpendicular angles.

All of us would likely agree that the RCS of the frontal aspect of the aircraft is the most important aspect, as the aircraft is pointed in that direction. If you look at the FC-31, F-22, F-35 you see the forward fuselage, and the junction of the main wing leading edge.

On the F-22 and J-20 the leading edge of the wing has a very slight curving anhedral, just counting the Fuselage and Main wing juncture, and the verts and ventral fins, the total RCS is probably fairly similar on both aircraft??

So its not that the large canards forward of the main wing "destroy Low Observability"?? but that they are an additional forward facing surface, not masked in any way by the main wing, and they are on a completely different plane, with very significant dihedral, so they are a significant added surface area exposed to the oncoming radar beams.

In addition, if you maneuver the aircraft, those two surfaces deflect and increase the RCS even further, if you have to maneuver aggressively you could increase the forward reflective surfaces by 1/4 to possibly 3/4 in total area???

an aft mounted stabilator or elevator is masked by the main wing, even through fairly aggressive maneuvering, and even if aft edges are exposed, they are at an oblique angle, so they will never be able to contribute a significant amount to the static forward facing RCS.

So Yes, it is possible to a great degree, for an "educated eye" to look at any aircraft design, and give you a ball park figure on total RCS, from each of the significant aspect angles, in specific conditions of flight??

So, would an aircraft have a greater RCS with the landing gear UP, or with the landing gear DOWN???

 

[Lethe]

So Yes, it is possible to a great degree, for an "educated eye" to look at any aircraft design, and give you a ball park figure on total RCS?

Especially if that eye happens to emit X-band radiation.