Just going to drop this here in case anyone has seen the new simulation of Su-57's RCS, where the Su-57 doesn't seem to do so well:
In the comments below that article you can see a little thread between the author and a certain "Bart", who challenges the simulation results somewhat. The conversation ends with the author doubling down on his position, namely that the "tunnel" between the two engines on the bottom of the aircraft serves as a corner reflector for radars illuminating the aircraft from the nose aspect and that is why the aircraft has a really poor bottom nose aspect RCS.
Now, because I am, shall we say, prosopically united to Bart, and I have it on good authority that Bart cannot post any more comments on that thread due to what appears to be a ban (and Bart waited a week for any potential technical issues to be resolved, while in the meantime other people posted on other threads on that page without issue it seems), I want to answer the author's final comment here, so there is an online reference to what Bart would have said had he not been banned:I've already stated that yes, the "engine tunnel" can be regarded as a dihedral corner reflector (actually two, one for waves coming from the bottom left beam aspect and one for waves coming from the bottom right beam aspect). That does not, however, apply to waves coming from the nose aspect:
look carefully at the image you posted and you will see that the points of incidence of the rays on the two surfaces are all in a straight line (with one 90° turn at the edge where the two planes join), which traces the longitudinal middle axis of the two planes; this is because those rays are all located in the same two-dimensional plane, which intersects the dihedral reflector at that axis. So to transfer the analogy to the "engine tunnel" of the Su-57 you would have to shoot the waves in a 2D-plane perpendicular to the longitudinal axis of the aircraft, i.e. from one of the beam aspects of the aircraft, not the nose aspect.
Shooting waves from the nose aspect will mean the rays are not perpendicular and so will simply bounce off the planes and continue in the other direction; in order for them to return to the sender, you either need a dihedral reflector that is properly oriented (arguably this could be the intake and SRAAM bays, more on that in a bit) or you need a trihedral reflector, such as in the following image:See how in the above image a ray comes in, bounces off one plane, then another and then it would actually keep traveling away from the ray's source if it were not for the third plane, which makes it go back. There is no such third plane in the "engine tunnel".
Regarding the modeling of material: APA will still have to have defined an inlet shape, because they need to constrain where the "black hole" ends. They could have defined this "black hole" as being inside the engine nacelles and thus not affecting waves interacting with the outside of the nacelle; in fact, that is the most reasonable assumption about their analysis and how it's usually done if one doesn't want to model the engines.
It is correct that we just can't know the exact makeup of RAS/RAM and material distribution, so I'm not faulting you for using an all-metal model, but my point still stands: any strong return signal, such as your model and, to some degree, APA's model show in the lower frontal sector needs to be treated with suspicion, because the engineers involved in the aircraft's design will know how to conduct these kinds of analyses, too, and try to eliminate such problems (since the aircraft is supposed to have a significantly reduced signature, i.e. that's one of the design goals).
This means that returns from places that are clearly not load bearing (such as the inlets and SRAAM covers) should be suspected to have materials properties, which make them not reflect in that worst-possible way. This could be thin metal liners beneath RAS/RAM, which have a slightly different shape or it could mean that they are radar transparent. In the case of this potential dihedral corner reflector formed from the inlet side and the medial part of the SRAAM bay, a radar transparent inlet would actually completely remove the problem. In the case of the SRAAM bay as its own source of specular reflection, I suspect that RAS/RAM and some metal liner with unknown exact angle is indeed used beneath the composite material.
And finally, the DIRCM turret itself (not the cover) is actually quite small and made of unknown material; there is no reason why it couldn't be 3D-printed from some kind of plastic, for example, either completely without metal parts or with metal parts that are smaller than the pilot tubes (which the F-35 also has, btw.). So stating that modeling of the DIRCM cover as 100% metal is going to produce a lower RCS than alternatives is not true. And since it is supposed to be transparent to strong laser light, the choice of metal layers would also be limited in order to not interfere with the DIRCM function. A more reasonable assumption here is that it does not contain such a metal layer (unlike the canopy, which almost certainly does).
So now that I've defended Bart's honor in the face of this NAFO imbecile who can't understand that space has three dimensions (and what's worse, another NAFO imbecile has already started liking his posts...Lord have mercy!), I want to end on the positive note of how this whole encounter actually made me like the Su-57 even more:
If one looks at the APA results for, e.g., 6 GHz, it becomes clear that the bad returns in the above mentioned blog's simulation correspond to the "four streaks" in the middle of the following image taken from APA (somewhat vertical lines in the middle horizontally and in the third quarter from the top vertically) as well as the stronger signal directly below that:
The "four streaks" come from the corner reflector created by the apico-lateral inlet surface and the medial SRAAM surface, which is easily verifiable, e.g. by looking at an appropriate image of the Su-57 (e.g. see below, ignore the pod) and using two hand-held mirrors and a shut eye while emulating the angles (or just use your brain):
As my syn-prosopon would have pointed out, this corner reflector only works if it is assumed that the apical inlet and SRAAM bay surfaces are entirely made out of metal; even if just the first, lets say, 15 cm of the inlet are radar-transparent composite or have some RAS mitigation, the effect is lost. The stronger signal referred to above, that is in the APA image below the "four streaks", can in turn be explained by the lower apical intake lip, which would be a direct specular reflector for such angles; as it is very likely to have the same mitigation, that means this part of the RCS signature should also be disregarded.Therefore, I suspect that the Su-57 may have even better frontal aspect stealth than the F-35!
And all the NAFO trolls can do is ban/de-platform/propagandize
If anyone should agree with me and feel the need to correct the injustice of the banning of Bart, feel free to leave comments on the above linked blog...I recommend not using straight up insults, as the author has set up strict content moderation with pre-approval for new commenters and there's no need for that; instead, how about limb-style comments like:
"Has the F-35B and F-35C fixed the problem of being essentially an expensive sub-sonic aircraft yet?"
"Isn't a round nozzle on the F-35 really bad for stealth?"
"I read that the US military has said that the F-35 has failed. Why is that?"
Or, a bit less emo-marxist:
"Why does your article about stealth imply that the F-35 has smaller RCS than an insect when the pilot tubes alone are bigger than most insects?"
Or, related to Bart's above reply:
"If a bullet ricochets twice when you shoot it down a perfectly straight tunnel, does it reverse its flight path and fly back to you?"