What trap may I know? Until now you have not answer j20blackdragon enquries. Or you are the one not able to answer about the plantform alignment of J-20? The picture alignment from j20blackdragon makes sense. Come on, give us some sensible answer. We are reasonable people. Simple enquiry with simple answer? Difficult? Or you chicken off
You unwittingly dug a trap for yourselves. If you are in mainland China, you would be a conscript reject just like your friends. So take your time and read what comes next. You will learn something, no matter how little.
First of all...There is nothing wrong with the canards. By themselves, each is just another structure. But when it is speculated that the canards are questionable regarding the J-20's radar cross section (RCS), it is about their relationship to other major structures nearby.
According to 'Chinese physics'...
The U-turn arrow on the wing is the exact and only behavior by surface traveling waves on any expanse. This is what the Chinese members here believes and there are no possible arguments against this belief. For the J-20's canards, and all other major structures for that matter, the only scattering behavior is back scatter. No such thing as forward scatter. Therefore, under 'Chinese physics', bi-static radar is not possible since the bi-static triangle requires forward scattering.
But for those who subscribes to real physics, here is why the J-20's canards are questionable.
When an impinging radar transmission cone is bisected by an edge, what is called a 'Keller cone' (keyword search) is created.
Note: Believers of 'Chinese physics' does not see a radar transmission as a cone but exactly as a straight line/arrow as illustrated.
For believers of real physics, this is what a radar transmission would look like...
It does not matter if the transmission is from an antenna. Real physics says that even specular reflection is effectively a transmission, in other words, real physics says that
ALL radar transmission are either conic or fan in shape, depending on the transmitting antenna, of which a wing's leading edge by merely reflecting is effectively an antenna.
Following the production of the Keller Cone are surface traveling waves.
Radar cross section calculations of traveling surface waves
The traveling surface wave phenomenon, a significant echo mechanism for long, smooth bodies, manifests itself in the radar cross section (RCS) pattern of realistic targets for horizontal polarization and grazing angles of incidence.
The body here is the canard and it is a finite structure. Its surface expanse is called the 'electrical path'. The longer the surfave traveling wave remains on this path, the greater the energy loss thru 'leaky waves'.
In RCS control, the first rule is to limit the
AVAILABILITY of surface disruption or surface discontinuity. Any body is a finite body to start so it is inevitable that there will be at least one and the first available surface disruption. For an aircraft, aerodynamics take highest priority so there must flight control surfaces. This give other available surface discontinuities such as main wings, horizontal and vertical stabilators, and additional stabilizating/control structures such as non-moveable fins, if necessary. Some designs, based on whatever mission they were intended to do, may have more or less of these surface discontinuities.
For example, the B-2 bomber...
If we discount minor surface discontinuities such as communincation antennas or panel gaps, we can see the B-2 have the least quantity of major available surface disruptions. The B-1 is next and the B-52 have the highest. The combination of advanced aerodynamics and mission intention enabled the B-2 to have, essentially, just one major surface disruption. The B-2 is a flying wing (singular) design and as such, it does not have a fuselage as commonly understood. It does not have two wings but only one. Or that its wing is its fuselage. But no matter which descriptor, the B-2 have only one major surface discontinuity -- itself. Then the discussion can move on to lesser surface disruptors such as panel seams, engine intakes, communincation antennas, air data probes, etc. All of these lesser surfave disruptors are common throughout all aircraft designs anyway.
So if we abide by the first rule about controlling the availability of surface disruptions, or radiators, regarding major structures, then the J-20 is a superior target than the F-22. Superior as in the higher quantity of radiators.
- The F-22 have six major radiators: two wings, two horizontal stabilators, and two vertical stabilators.
- The J-20 have eight major radiators: two canards, two wings, two underside stabilizating fins, and two vertical stabilators.
Sooner or later on a finite body, surface traveling waves must exit, if they are not attenuated (lost) in some ways. That loss could come from long electrical path that causes minute quantities of leaky waves that may be (not definite) lost inside the clutter rejection threshold. Additional losses could come from absorber but absorbers do have their own limitations and belongs to another discussion.
Now comes the 'Rayleigh Criterion' (keyword search).
Rayleigh Criterion | COSMOS
The Rayleigh criterion specifies the minimum separation between two light sources that may be resolved into distinct objects.
https://www.boundless.com/physics/wave-optics/diffraction-2/rayleigh-criterion-2/
According to the criteria, two point sources are considered just resolved (just distinguishable enough from each other to recognize two sources) if the center of the diffraction pattern of one is directly overlapped by the first minimum of the diffraction pattern of the other. If the distance is greater between these points, the sources are well resolved (i.e., they are easy to distingiush from each other). If the distance is smaller, they are not resolved (i.e., they cannot be distinguished from each other).
The astronomy sources may say 'light' sources, but the principle is applicable to non-visual EM wavelengths as well. Not sure what 'Chinese physics' say about this.
What this mean is that diffracted signals from the canards that impact the wings can be resolved by the seeking radar if the incident angle is sufficiently large.
Or put it another way:
- The canard produces its own returns from its leading edge.
- The diffracted signals from the trailing edge impact the wing.
- The wing's leading edge produces its own returns from two source signals: from the seeking radar and from the canards' diffracted signals.
- If the incident angles from all sources are sufficiently apart, each structure will be distinctively resolvable by the seeking radar.
From the image above containing the Rafale, the MIG 1.44, and the J-20, we can see diverse incident angles from two mechanisms:
- The cant angle of the canards in relation to the wings.
- The elevation difference between the canards and the wings.
For the Rafale, we have cant angle and elevation difference. For the 1.44 we have elevation difference. For the J-20 we have cant angle. The seeking radar will definitely resolve the canards and the wings for the Rafale and 1.44, and highly probable for the J-20 for the same major structures.
The reason I am willing to concede to 'highly probable' for the J-20 is because its canards have roots that are in the same plane as the wings, unlike the Rafale. But their cant angle seems to be very similar so their trailing edge diffracted signals will arrive at the wings at different incidence compare to the F-22.
