FLIR , IRST in air to air mission

I don't think so. The matter being that the J-20 and J-31 have larger RCS compared to the F-35 and F-22.

For instance the J-20 should have a RCS of 0.05 square meters (and this is already in a good case scenario). And even taken a somehow conservative scenario that the APG-81 can detect a 1 square meter target/aircraft at a range of 260 km this means that the same APG-81 would detect a J-20 at a range of 122 km or almost 66 Nautical Miles and this in a wide search.

And even if the J-20 or other aircraft (like the J-31) have a RCS of 0.01 square meters this would translate in a detection range of 82 km or around 44 nautical miles with the APG-81 radar.

Any of the values above would be much higher than possible with the IRST's (specially during wide search).

I'm not so sure that their RCS is that high. There's a lot of speculation about their optimal RCS but we have zero credible information on what the RCS polar plots look like, how effective their materials are in relevant frequencies nor how good they are at building to and maintaining the required tolerances. I think it's a mistake to believe that they are significantly inferior. I've heard speculation about the J-20 being in the -30 dBsm range and that seems quite reasonable to me. I do suspect that side and rear aspect RCS will be higher, perhaps significantly higher on that airplane. But IMO its all speculative at this point. I'd rather prepare for the worst and hope for the best than writing them off because this is their first VLO platform...

I'm not so sure that their RCS is that high.

And I'm not sure that their RCS is that low (compared to the values that I posted earlier).

Or resuming, the RCS values that I posted are IMO best case scenarios for those Chinese planes. I'll explain below.

There's a lot of speculation about their optimal RCS but we have zero credible information on what the RCS polar plots look like, how effective their materials are in relevant frequencies nor how good they are at building to and maintaining the required tolerances. I think it's a mistake to believe that they are significantly inferior. I've heard speculation about the J-20 being in the -30 dBsm range and that seems quite reasonable to me. I do suspect that side and rear aspect RCS will be higher, perhaps significantly higher on that airplane. But IMO its all speculative at this point. I'd rather prepare for the worst and hope for the best than writing them off because this is their first VLO platform...

The thing is, even the Russians admit that their Su-57 has an RCS of 0.1 to 0.5 square meters (no, that's not a typo). Another evidence of this was the fact that the Indians bailed out as partners of the PAK-FA/Su-57 program and the main reason seem to have been that the aircraft didn't have an RCS nearly as low as the Indians expected.
And the experience that the Chinese have in designing LO/VLO aircraft is similar if not smaller compared to the Russians. Of course that the Chinese have access to vast amounts of resources/cash which should give them an edge over the Russians. As such I believe that the Chinese aircraft (J-20/J-31) will be better - RCS speaking - than the Russian SU-57 but definitely not so good as the American designs (F-35 and F-22). And -30 dBsm range (around 0.001 square meter) for the Chinese aircraft would put them very close to the F-35 for instance, this in terms of RCS.
Hence why I put the Chinese in the range of 0.01-0.05 square meters in terms of RCS.

I'm not so sure that their RCS is that high.

And I'm not sure that their RCS is that low (compared to the values that I posted earlier).

Or resuming, the RCS values that I posted are IMO best case scenarios for those Chinese planes. I'll explain below.

There's a lot of speculation about their optimal RCS but we have zero credible information on what the RCS polar plots look like, how effective their materials are in relevant frequencies nor how good they are at building to and maintaining the required tolerances. I think it's a mistake to believe that they are significantly inferior. I've heard speculation about the J-20 being in the -30 dBsm range and that seems quite reasonable to me. I do suspect that side and rear aspect RCS will be higher, perhaps significantly higher on that airplane. But IMO its all speculative at this point. I'd rather prepare for the worst and hope for the best than writing them off because this is their first VLO platform...

The thing is, even the Russians admit that their Su-57 has an RCS of 0.1 to 0.5 square meters (no, that's not a typo). Another evidence of this was the fact that the Indians bailed out as partners of the PAK-FA/Su-57 program and the main reason seem to have been that the aircraft didn't have an RCS nearly as low as the Indians expected.
And the experience that the Chinese have in designing LO/VLO aircraft is similar if not smaller compared to the Russians. Of course that the Chinese have access to vast amounts of resources/cash which should give them an edge over the Russians. As such I believe that the Chinese aircraft (J-20/J-31) will be better - RCS speaking - than the Russian SU-57 but definitely not so good as the American designs (F-35 and F-22). And -30 dBsm range (around 0.001 square meter) for the Chinese aircraft would put them very close to the F-35 for instance, this in terms of RCS.
Hence why I put the Chinese in the range of 0.01-0.05 square meters in terms of RCS.

Rough but fair assumption....

This is true, it takes at least 1.5 pixels x 1.5 pixels to detect something with good probability. Then it takes at least 6x6 pixels for recognition (tank, aircraft, person, ship). Identification requires at least 12x12 pixels. So identification range is usually almost ten times shorter than detection range using the same optics.

This is another interesting point, i.e. there's a substantial difference between so called "blob detection" and a weapons quality track. This 10:1 estimation from detection to positive ID is more than would have thought was necessary but makes sense. This would suggest that countering LO/VLO threats is going to end up with some sporty, close in engagements.

One thing is that IRST systems usually have narrow FoV/higher magnification for identification and wide FoV for searching and detecting targets. So the difference usually is not 10:1 but something like 3:1 or so. One extreme is F-35 with DAS and EOTS where the identification range for EOTS is probably longer than detection range of DAS. This is because DAS is very wide FoV (something like 95 degrees or more for spherical capability) sensor and EOTS has very narrow FoV (probably under 1 degree) like all modern targeting pods have. Even EOTS itself might have similar range for detection and identification due to different FoV for each task. However I bet that EOTS could be used for cued search with narrowest FoV for really impressive range but naturally the search area will be extremely small. But could still be useful in some situations.

I'm not so sure that their RCS is that high. There's a lot of speculation about their optimal RCS but we have zero credible information on what the RCS polar plots look like, how effective their materials are in relevant frequencies nor how good they are at building to and maintaining the required tolerances. I think it's a mistake to believe that they are significantly inferior. I've heard speculation about the J-20 being in the -30 dBsm range and that seems quite reasonable to me. I do suspect that side and rear aspect RCS will be higher, perhaps significantly higher on that airplane. But IMO its all speculative at this point. I'd rather prepare for the worst and hope for the best than writing them off because this is their first VLO platform...

I haven't seen speculation or evidence to suggest that the J-20 has achieved a level of signature reduction in the .001m^2 class. It's no doubt superior to the Su-57, but it's doubtful it's several orders of magnitude stealthier.

Rough but fair assumption....

Thanks! That was exactly my intent and purpose with my last post

I haven't seen speculation or evidence to suggest that the J-20 has achieved a level of signature reduction in the .001m^2 class. It's no doubt superior to the Su-57, but it's doubtful it's several orders of magnitude stealthier.

Exactly!
There's also an additional piece of 'evidence' (note the quotes - 'indication' is likely a better word than evidence) that seems to point out that the J-20 isn't nearly as stealthy or almost as stealthy as for example the F-35 and this also comes from India as well. It seems that the Indians don't seem to be particularly terrified or impressed with the J-20 RCS/stealth capabilities.
They (Indians) have even hinted in the recent past that their Rafales could successfully take on the Chinese J-20s. Of course that I don't believe such claim (it seems to be a nationalistic claim in order to try to publicly assert some superiority over the Chinese) but at least this seems to be a sort of indication that the J-20 RCS shouldn't definitely have a level of RCS in the 0.001 square meter.

There's also an additional piece of 'evidence' (note the quotes - 'indication' is likely a better word than evidence) that seems to point out that the J-20 isn't nearly as stealthy or almost as stealthy as for example the F-35 and this also comes from India as well. It seems that the Indians don't seem to be particularly terrified or impressed with the J-20 RCS/stealth capabilities.
They (Indians) have even hinted in the recent past that their Rafales could successfully take on the Chinese J-20s.

For once we are not in disagreement.

The Indian Air Force has on many occations pushed back on the politicians if the IAF is in disagreement, for instance we have seen their lack of enthusiasm for the LCA Tejas and preference for Western 4.5 gen fighters. If they had believed that Rafale would not cut it I am sure they would have pushed hard for F-35. Instead they express confidence that Rafale is good enough And I am sure they are right -- Rafale seems far superior to any non-Western fighter. Excellent sensors, probably the best 4.5 gen sensor fusion on the planet, excellent missiles (including Meteor), and the OSF with laser rangefinding is brilliant. Also excellent HMI. The integrated EW suite based on GaN AESA is very good. And although it is no stealth plane it does have several RCS reduction measures, and the engines have some IR reduction measures. Rafale F4 will be very close to the perfect 4.5 gen fighter jet IMHO.

For once we are not in disagreement.

The Indian Air Force has on many occations pushed back on the politicians if the IAF is in disagreement, for instance we have seen their lack of enthusiasm for the LCA Tejas and preference for Western 4.5 gen fighters. If they had believed that Rafale would not cut it I am sure they would have pushed hard for F-35. Instead they express confidence that Rafale is good enough And I am sure they are right -- Rafale seems far superior to any non-Western fighter. Excellent sensors, probably the best 4.5 gen sensor fusion on the planet, excellent missiles (including Meteor), and the OSF with laser rangefinding is brilliant. Also excellent HMI. The integrated EW suite based on GaN AESA is very good. And although it is no stealth plane it does have several RCS reduction measures, and the engines have some IR reduction measures. Rafale F4 will be very close to the perfect 4.5 gen fighter jet IMHO.

Perhaps we're not quite in agreement here as well.

I don't believe for a second that the Rafale or any other 4.5th gen fighter aircraft for that matter has much of a chance against the J-20, this with both aircraft on "equal footing" (on typical head-to-head BVR situations).
My point with the above was to show that the J-20 RCS isn't that low when compared to its US counterparts (F-22 and F-35) and definitely not to hint or argue that an aircraft like the Rafale could detect a J-20 first than otherwise (something that again I definitely not believe in)

I don't believe for a second that the Rafale or any other 4.5th gen fighter aircraft for that matter has much of a chance against the J-20, this with both aircraft on "equal footing" (on typical head-to-head BVR situations).
My point with the above was to show that the J-20 RCS isn't that low when compared to its US counterparts (F-22 and F-35) and definitely not to hint or argue that an aircraft like the Rafale could detect a J-20 first than otherwise (something that again I definitely not believe in)

I am not so sure -- Sensors, sensor fusion, EW suites, quality and sensitivity of RWR, quality of missiles. It is all a package. Low RCS is not enough. If Rafale does not stand a chance against J-20 then I am sure IAF would be much more vocal in getting a 5. gen fighter jet ASAP. Currently they are not. I think they know quite a lot about the technology level of J-20.

If Rafale does not stand a chance against J-20 then I am sure IAF would be much more vocal in getting a 5. gen fighter jet ASAP. Currently they are not. I think they know quite a lot about the technology level of J-20.

I would say that the IAF isn't more vocal in getting a 5th gen fighter aircraft because in reality they simply can't get one.
Actually the only 5th gen fighter aircraft that they (IAF) could get is the PAK FA/Su-57 which as well all know wasn't deemed to be stealthy enough by the Indians and as such there's no more 5th gen options out there for them.
And no, the F-35 is not an option for the IAF independently of what some people (including Trump himself apparently) may have said in the past or recent past.

So and since they can't get a 'proper' 5th gen fighter aircraft then they had to settle with a sort of a "half-truth" in the face of the threat posed by a 5th gen fighter aircraft (Chinese J-20) where they stated that the J-20 RCS isn't that super-low (which would be accurate) and as such that their Rafales - which granted, have some advantages like the ones you described - could handle it (which would not be accurate). Typical political "chit chat"...

If Rafale does not stand a chance against J-20 then I am sure IAF would be much more vocal in getting a 5. gen fighter jet ASAP. Currently they are not. I think they know quite a lot about the technology level of J-20.

I would say that the IAF isn't more vocal in getting a 5th gen fighter aircraft because in reality they simply can't get one.
Actually the only 5th gen fighter aircraft that they (IAF) could get is the PAK FA/Su-57 which as well all know wasn't deemed to be stealthy enough by the Indians and as such there's no more 5th gen options out there for them.
And no, the F-35 is not an option for the IAF independently of what some people (including Trump himself apparently) may have said in the past or recent past.

So and since they can't get a 'proper' 5th gen fighter aircraft then they had to settle with a sort of a "half-truth" in the face of the threat posed by a 5th gen fighter aircraft (Chinese J-20) where they stated that the J-20 RCS isn't that super-low (which would be accurate) and as such that their Rafales - which granted, have some advantages like the ones you described - could handle it (which would not be accurate). Typical political "chit chat"...

I wouldn't at all be surprised if the Rafale (especially once in the F4 configuration) has superior sensors/avionics/EW/weapons to J-20s. The J-20s primary advantage will be in RCS, whereas the F-35 combines having lower RCS + superior sensors/sensor fusion.

I wouldn't at all be surprised if the Rafale (especially once in the F4 configuration) has superior sensors/avionics/EW/weapons to J-20s.

Sure, I also agree with you above.
But I just don't think that the Rafale's better/superior sensors/avionics/EW and weapons are enough to overcome the J-20 advantage in terms of (lower) RCS.

I wouldn't at all be surprised if the Rafale (especially once in the F4 configuration) has superior sensors/avionics/EW/weapons to J-20s.

Sure, I also agree with you above.
But I just don't think that the Rafale's better/superior sensors/avionics/EW and weapons are enough to overcome the J-20 advantage in terms of (lower) RCS.

Perhaps not, but it also won't have the overwhelming superiority of having both, that the F-22/35 bring.

I wouldn't at all be surprised if the Rafale (especially once in the F4 configuration) has superior sensors/avionics/EW/weapons to J-20s.

Sure, I also agree with you above.
But I just don't think that the Rafale's better/superior sensors/avionics/EW and weapons are enough to overcome the J-20 advantage in terms of (lower) RCS.

Perhaps not, but it also won't have the overwhelming superiority of having both, that the F-22/35 bring.

Exactly! That was basically my point when I first replied to BDF here in this thread.

One thing is that IRST systems usually have narrow FoV/higher magnification for identification and wide FoV for searching and detecting targets. So the difference usually is not 10:1 but something like 3:1 or so. One extreme is F-35 with DAS and EOTS where the identification range for EOTS is probably longer than detection range of DAS. This is because DAS is very wide FoV (something like 95 degrees or more for spherical capability) sensor and EOTS has very narrow FoV (probably under 1 degree) like all modern targeting pods have. Even EOTS itself might have similar range for detection and identification due to different FoV for each task. However I bet that EOTS could be used for cued search with narrowest FoV for really impressive range but naturally the search area will be extremely small. But could still be useful in some situations.

Totally get that. What I’m getting at is that, based on your comment on initial detect, to type of target to positive ID that you wrote earlier, is a what I was referring to when discussing a 10:1 ratio. I.e. a point of positive ID whereby there is a high confidence that you that the track is hostile and can now shoot it. This being a detection to ID ratio vice a detection range ratio (i.e. the 3:1 ratio when comparing cued to volume search modes.) It seems to me then, that when relying solely on IRST data, that the limiting factor is the range at which the target can be positively identified and this strikes me even more limiting than say the reduced detection ranges when conducting a volume search. Of course, other systems can assist in target ID potentially.