I believe you have a typo in your second situation, you mentioned that 91N6 target detection radar can acquire the F-35 at 94Km but I think you mean 49Km instead (you have it correct in the first situation).

The RCS of the F-35 is said to be in the order of 0.0014 square meters which is area of a standard a golf ball. So rounding the number it gives 0.001 square meters.
However this RCS value is an average value considering all angles (frontal, sides, rear) of the F-35 and it's known that for example the F-35 RCS in its frontal arc is below that 0.001 square meter value.
Actually it was officially acknowledged by the USAF that the F-35 is stealthier than the F-22 when both aircraft are compared in their respective frontal arcs (This was mentioned my USAF Gen. Hostage if I'm not mistaken).
So if the F-35 is traveling towards a S-400 site, the F-35 RCS to be considered (if we would want to be extremely rigorous) should be much lower than 0.001 square meters.

But even considering the "conservative" 0.001 square meter RCS number (which favour "less" the F-35) there are large (I would say huge) problems with any of your scenarios for the S-400 side. For example:
- At just above 49Km there are a number of weapons that the F-35 can employ well outside the 49Km range. Most notably, is the Small Diameter Bomb (SDB) in both it's variants, the SDBI and the SDBII (the later, granted is still in development but soon to be deployed and the SDBI is ).
JSOW is an another (and current) weapon that the F-35 could easily employ against the S-400 and well outside its detection range.
- The F-35 has it's own EW suite which can perform EW warfare against any radar (including the S-400). The F-35 with its stealth and EW could likely employ the shorter range JDAMs against the S-400 without the S-400 ever detecting it, or resuming it's extremely possible that the F-35 with its stealth and EW combo wouldn't be detected at the "theoretical" 49Km "maximum" range but well below (shorter) than that!
- The F-35's DAS (Distributed Aperture System) would detect any incoming missile launched by the S-400 granting it early warning and a much better ability to avoid and evade incoming missiles.

I can only see the S-400 having some success against the F-35 in an ambush style tactic where the S-400 radars would only be turned on when an incoming F-35 is flying well within the 49Km detection radius. Of course the challenge would be knowing where the incoming F-35 really is and as such if any F-35 is or not within the "effective" range of a certain S-400 system.

However I do agree that the S-400 would be a "killer" or extremely dangerous for any 4.5gen fighter aircraft (like the Super Hornet, Typhoon or Rafale).

Last edited by ricnunes; 12/11/16 05:06 PM.