RCS on canards can be mitigated by RAM along the leading edge and the internal spar. Second, by using a radar pass through material for the main canard itself, like composite. Third, the structural spar itself it sharp edged, there cannot be rounded, as in rounded pipe or cylindrical structures.
Boeing's sixth gen fighter proposal uses canards.
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Without knowing very detailed internal structural and materials information, it would be hard to get into specifics, which is why I was keen to keep this largely theoretical.
In terms of pure theory, it is hard to see how they could totally eliminate all possible RCS for a few key reasons.
1) all aspect stealth and internal moving parts.
With a moving surface, you need motors/actuators to drive them.
If you make the whole canard out of radar transparent materials, you have the problem of radar hitting those motors/actuators when coming from anything other than directly ahead.
That is why while radar transparent materials have been around for a long time, it’s only with supercomputers allowing the application of continuous curve shaping that allowed the likes of the F22 and J20 to be designed and built.
It’s all about compromises. You take a very small frontal RCS hit to achieve a massive side on RCS gain.
The use of radar transparent materials would be more easily applied to the J20’s vertical rails. Since all the motors and acutators that drive them are in the root structure; since that is a single piece structure with no internal moving parts, and since you need to be pretty much directly above the plane to get a return on the root motors (at which point you will be getting a huge return from the whole plane in any case), you can make the whole thing out of radar transparent materials without needing to worry about internal structures becoming reflectors, as would be the case of the F22 V tails were made entirely out of radar transparent materials.
With the new stealth nozzles, the J20’s ventricular streaks could also now be made out of radar transparent material, since the ones without stealth nozzles would likely have been RAM, as one of their main design goals would be to shield the round nozzles from radars emitting from the sides.
2) Material sciences.
All radar ‘transparent’ materials are only transparent up to a point afaik. There is perfectly radar transparent materials.
So you will always get a tiny return, and the more area you have, the bigger the return.
Now please note that all of this is theoretical. Depending on the material and design. The extra RCS from having the canards come be the equivalent of a few grains of sand. In which case it’s purely a theoretical increase that has zero real world impact.
That is the key to remember here.
A lot of the detractors of canards bring out theoretical arguments that are hard to argue with, since they are true. But whether the impact of those tiny RCS increases raises the overal RCS of the plane in any meaningful way is the real question we should be focusing on instead of trying to argue that there is zero impact.
