IR Stealth aka (V)LO Not Modelled In-Game?

[Boagrius]

Thought I would submit this one for further investigation:

Modern VLO aircraft like the F22, F35 and J-20 have significant infra-red signature reduction measures built into their designs that are (arguably) just as elaborate as those in the RF spectrum. For example, the F35 features:

- The use of divertless supersonic inlets with serpentine inlet ducts to block the line of sight to the engine’s hot interior from the forward hemisphere.

http://www.f-16.net/forum/download/file ... &mode=view

https://www.google.com/url?sa=i&url=htt ... AdAAAAABAD

- The use of fuselage air “scoops” to mix cooler outside air with the engine exhaust so as to rapidly cool it and in turn reduce the IR signature of the engine plume.

http://www.f-16.net/forum/download/file ... &mode=view

- The use of onboard fuel as a coolant alongside to reduce the IR signature of the airframe itself.

https://www.researchgate.net/publicatio ... e_Aircraft

link=https://www.jmargolin.com/laser/ref7_AW ... -IR-bw.pdf]IR suppressant coatings (p4)

- Recessed positioning of the nozzle so that the jet’s fuselage and tailfins block a direct line of sight to it in all but the aft-most sector.

http://www.f-16.net/forum/download/file ... &mode=view

- The use of a serrated nozzle derived from the Low Observable Axisymmetric Nozzle (LOAN) program to further reduce the signature of the engine and assist with mixing cool air with the exhaust plume (p4).

Other (V)LO jets feature similar IR sig reduction measures, but this does not appear to be reflected by in-game IRST performance. Consider the air battle depicted between New Caledonia and Vanuatu in the scenario attached, where the opposing F35s, J-20s and J-31s routinely track and fire on each other (using IRST alone) from well in excess of 70nm, even when the target is out of afterburner. This far outstrips the performance of their onboard radars, and does not appear to reflect their likely real world detectability in the IR spectrum. AFAIK no airborne IRST has been documented either detecting or tracking (with targeting quality data) a VLO aircraft of this kind at these sorts of ranges, and certainly not when afterburner is disengaged.

[Rory Noonan]

Hi,

Please read this explanation of why putting your own tags in your post subject makes it much more likely your issue will be missed.

[WSBot]

0014550

[Boagrius]

Thanks for the headsup Rory, will do.

[Pygmalion]

Thanks for the report!

We did some digging to see what might be behind those weird detections. In the save file you provided, it appears that the F-35s are being initially detected by the J-31s at about 50nm. The distant J-20s are then passed contact info; only then are they able to close with, detect, and engage the F-35s. This multi-unit cooperation seems to be the cause of what would in isolation be excessively long-range detection by the J-20's IRST sets.

In test scenarios where the aircraft are isolated (single J-20 vs single F-35), those 70+nm IRST detections don't occur.

With that said, while investigating, we did discover a few points on which to improve: there was some inconsistency between IR detection modifiers on different versions of the same aircraft, which we've now fixed. We also aren't completely happy with how afterburners affect IR detection when engaged, and have begun internal discussions on how best to modify those values. So you should see some tweaks to IRST performance soon, even if they're not exactly the ones you expected!

Again, thanks for the report, and let us know if you come across anything else weird.

[Boagrius]

Hi Pygmalion,

Thanks for the response! Yes I had assumed there must have been some data sharing at play, however even the 50nm range for the J31's IRST may be quite generous (and vice versa for EOTS on the F35) when faced with a front or even side aspect F35 (or J20/31) that isn't in afterburner. As I said in the OP, VLO jets like the F35 are heavily signature reduced in the IR spectrum as well as the RF spectrum.

That said, I do acknowledge that modeling IRST performance accurately is a significant challenge, since atmospheric IR attenuation is so heavily influenced by things like humidity/weather/cloud and target contrast, while hard data on the relevant platforms and systems is naturally kept secret. Nevertheless, I am not aware of any OSINT documenting a VLO jet being detected by an IRST beyond about ~20nm (radar cued PIRATE vs F22 with luneberg lenses IIRC), certainly not without being directed by an onboard radar first.

Appreciate you taking the time to investigate, as the scenario playing out with VLO aircraft lobbing purely IRST cued missile shots at each other from over 50nm did not compute with my understanding of modern 5th gen CONOPS.

[Boagrius]

ORIGINAL: Pygmalion
With that said, while investigating, we did discover a few points on which to improve: there was some inconsistency between IR detection modifiers on different versions of the same aircraft, which we've now fixed. We also aren't completely happy with how afterburners affect IR detection when engaged, and have begun internal discussions on how best to modify those values. So you should see some tweaks to IRST performance soon, even if they're not exactly the ones you expected!

Hi again Pygmalion,

I did some further digging in the database and I think I found the source of the problem - the IR signature reduction features found on 5th gen/VLO fighters do not seem to be modelled at all. Instead, the IR signature values roughly correspond to the size of the aircraft in question, creating some signature values that are almost certainly off by a wide margin. For example:

The IR signature for the F35 is modelled as inferior to the F16, which essentially has no IR sig reduction features to speak of.

[Boagrius]

(F16 Values)

[Boagrius]

The same is true for the J10 and J31, with the 4th gen aircraft (using comparatively modest IR sig reduction features) showing the better IR signature values(!).

[Boagrius]

(baseline J10)

[Boagrius]

Also note the similarity in values between the baseline J11 and the most modern J20 variant. Again, this seems to be based largely on the size of the aircraft instead of taking their (vastly different) IR sig reduction features into account.

[Boagrius]

(J-11 IR sig values)



Based on the above I think it is reasonable to conclude that the current in-game modelling is flawed, warranting correction. I'd suggest that it may be worth consulting whatever SME's you guys have at your disposal on the subject? Appreciate you taking the time on this one.

Regards,

Boagrius

[Rory Noonan]

Thanks for the updates; please stop messing with the subject of your post. This is not the first time someone has reported a problem, you do not need to redefine our processes for us.

[Pygmalion]

We spotted those weird values as well.

Part of the aforementioned adjustments we're discussing internally involve better distinguishing IR detection disparities between VLO and non-VLO aircraft. Once we decide on a path forward, these values ought to better reflect the real world. So, in short: rest assured, we're looking into it!

Thanks again!

[Boagrius]

No worries, thanks again for taking the time to look into it!

[Dimitris]

Related post on the tactical limitations of IRSTs: https://www.quora.com/Can-5th-generatio ... Sengupta-5

[Boagrius]

Hi there,

I just wanted to check in to see if there has been any update on this question?

Additionally, I did some more investigating based on suspicions I had while playing around in the editor and discovered that CMO does not appear to model IR signature reduction in modern cruise missiles either. Compare, for example, the IR signature values for the VLO subsonic LRASM vs the ramjet powered(!) supersonic Kh-31:

[Boagrius]

Thought this was also worth investigating! As you can see the IR signature values are quite comparable (rear aspect values are just downright odd), but the IR signature reduction features are not even close in the real missiles. One is a subsonic (inherently cooler due to less heating of the missile body/nose cone via friction with the air), turbojet powered (much cooler exhaust) cruise missile, while the other is an older (no significant IR sig reduction features to speak of) supersonic, ramjet powered (comparatively massive and sustained IR engine plume) ASM. Compare:

LRASM

Kh-31

[AndrewJ]

The picture you linked for the Kh-31 may be a bit misleading. The 'massive plume' you're seeing there is the exhaust from the solid fuel booster motor which is used to accelerate the missile to supersonic speeds before the ramjet ignites. That only lasts a few seconds. Once the ramjet ignites that big white plume is gone, and the missile becomes less conspicuous.

[Boagrius]

Yes I am aware of that, but I am not referring to the Kh-31's smoke plume (or any other attributes related to optical detectability), I am referring to the infra-red emissions of both missiles in flight.

Surely the point holds that the difference in IR signature between an active supersonic ramjet vs a subsonic turbojet (fitted to a more modern stealthy cruise missile) is unlikely to be in any way comparable.

Both the Kh-31 SRM booster and the ramjet itself are much more substantial and incandescent sources of IR radiation than anything the LRASM would generate in any phase of flight. Eg.

https://youtu.be/UFkT8jWtVYs

The only potential caveat to this would be surface launched LRASMs that also briefly use an SRM booster to gain their initial altitude and speed (albeit one that is still merely subsonic).

Again, this is before considering the supersonic heating of the missile itself (and associated IR emissions) vs that of a subsonic weapon that has been heavily signature reduced from its (more recent) inception.