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

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Boagrius -> IR Stealth aka (V)LO Not Modelled In-Game? (5/10/2021 3:38:58 AM)

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.

- 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

- The use of onboard fuel as a coolant alongside IR suppressant coatings (p4) to reduce the IR signature of the airframe itself

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

- 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 -> RE: [DB3K] IRST Systems Overperforming vs VLO Aircraft (?) (5/10/2021 1:56:05 PM)

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 -> RE: [DB3K] IRST Systems Overperforming vs VLO Aircraft (?) (5/10/2021 2:00:33 PM)

0014550



Boagrius -> RE: [DB3K] IRST Systems Overperforming vs VLO Aircraft (?) (5/10/2021 10:13:28 PM)

Thanks for the headsup Rory, will do.



Pygmalion -> RE: [DB3K] IRST Systems Overperforming vs VLO Aircraft (?) (5/11/2021 11:16:19 PM)

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 -> RE: [DB3K] IRST Systems Overperforming vs VLO Aircraft (?) (5/13/2021 4:29:09 AM)

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 -> RE: [DB3K] IRST Systems Overperforming vs VLO Aircraft (?) (5/14/2021 9:14:19 AM)

quote:

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.
[image]local://upfiles/72940/5B6CDF4F127F4DB39AF129B85E43233C.jpg[/image]



Boagrius -> RE: [DB3K] IRST Systems Overperforming vs VLO Aircraft (?) (5/14/2021 9:15:57 AM)

(F16 Values)
[image]local://upfiles/72940/E6DAB979C4CF4E398089F5A75E57F3F1.jpg[/image]



Boagrius -> RE: [DB3K] IRST Systems Overperforming vs VLO Aircraft (?) (5/14/2021 9:18:31 AM)

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(!).

[image]local://upfiles/72940/803DA1301E3345B1B02C1DE8AFFC3CB9.jpg[/image]



Boagrius -> RE: [DB3K] IRST Systems Overperforming vs VLO Aircraft (?) (5/14/2021 9:19:19 AM)

(baseline J10)
[image]local://upfiles/72940/B0E28AEA94C849A98D372597CC10B3A1.jpg[/image]



Boagrius -> RE: [DB3K] IRST Systems Overperforming vs VLO Aircraft (?) (5/14/2021 9:21:38 AM)

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.

[image]local://upfiles/72940/606715F155FB4DACA19130D2C160AFC8.jpg[/image]



Boagrius -> RE: [DB3K] IRST Systems Overperforming vs VLO Aircraft (?) (5/14/2021 9:22:21 AM)

(J-11 IR sig values)

[image]local://upfiles/72940/7E5800C07CAF4954BBBDB6766A97F6C0.jpg[/image]

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



Pygmalion -> RE: [DB3K] IRST Systems Overperforming vs VLO Aircraft (?) (5/14/2021 4:58:54 PM)

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 -> RE: [DB3K] IRST Systems Overperforming vs VLO Aircraft (?) (5/14/2021 10:30:21 PM)

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



Dimitris -> RE: [DB3K] IRST Systems Overperforming vs VLO Aircraft (?) (7/13/2021 8:58:58 PM)

Related post on the tactical limitations of IRSTs: https://www.quora.com/Can-5th-generation-stealth-fighters-be-detected-with-infrared/answer/Abhirup-Sengupta-5



Boagrius -> RE: [DB3K] IRST Systems Overperforming vs VLO Aircraft (?) (1/22/2022 11:45:37 AM)

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:

[image]local://upfiles/72940/3CD028D40960452EB6E9DD3F63D93652.jpg[/image]



Boagrius -> RE: [DB3K] IRST Systems Overperforming vs VLO Aircraft (?) (1/22/2022 11:48:06 AM)

[image]local://upfiles/72940/ACB33F2B70024E268A19FE35E0675E4E.jpg[/image]

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 -> RE: [DB3K] IRST Systems Overperforming vs VLO Aircraft (?) (1/22/2022 12:37:30 PM)

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 -> RE: [DB3K] IRST Systems Overperforming vs VLO Aircraft (?) (1/22/2022 6:26:33 PM)

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.



Dimitris -> RE: [DB3K] IRST Systems Overperforming vs VLO Aircraft (?) (1/27/2022 9:31:06 AM)

TL;DR version: This is a complex subject and we have various plans for improvement, but they have to wait as we are currently busy with other important items being worked on.

Slightly longer version:

There are basically 3 different aspects on this:

1) Static/nominal DB values
2) Dynamically (in-sim altered) values
3) Altering the IRST (and visual) model to curtail the "volume search" capability


1) The DB values remain to be revised. We will probably need to make some pretty significant tweaks to the signature modifiers in order to incorporate these factors. As it stands, the current modifiers do not offer the flexibility necessary for this.
These are the modifiers currently in use:
[img]https://i.imgur.com/dFBf77h.png[/img]

2) In some cases the visual & IR modifiers are indeed changed in-sim. An example of this is supersonic/hypersonic skin friction. You can see this clearly in action if, for example, you attempt IR detections (preferably head-on or side-on) on an SR-71 first at subsonic speed and then at M3+. In the latter case you should observe a substantial increase in detection range with a modern IRST.

3) The biggest handicap of the current model IMHO is not the signature details, but that fact that visual/IR sensors are allowed to function as mass volume-search sensors, which IRL is possible only at far-less-than-maximum ranges. With the exception of specialized "staring" sensors like DAS, most such sensors suffer from the "soda straw effect" which limits both their volume-search ability as well as their capacity to keep track of existing contacts. (Abhirup Sengupta describes these limitations decently here: https://www.quora.com/Can-5th-generation-stealth-fighters-be-detected-with-infrared/answer/Abhirup-Sengupta-5 . He also mentions some of the IR signature suppression techniques & modifiers that you refer to).

At the most recent CUC we presented our preliminary plans for addressing this. Here are a couple slides from the presentation:

[img]https://i.imgur.com/QGoYdqV.png[/img]

[img]https://i.imgur.com/Tn3o7pA.png[/img]

I think getting this implemented will go a long way towards balancing out the pros & cons of IR systems, and combined with suitable changes in the DB modifiers can rectify the issues described above.



BDukes -> RE: [DB3K] IRST Systems Overperforming vs VLO Aircraft (?) (1/27/2022 11:03:18 AM)

Looks good!

Mike



Boagrius -> RE: [DB3K] IRST Systems Overperforming vs VLO Aircraft (?) (1/28/2022 1:23:16 AM)

Yes thanks Dimitris, that's a great update [:)]

EDIT: The only addendum I would make is that the F22 and F35 do have all-aspect IR cooling (side + aft, not just frontal - ref OP) and I would expect this feature to appear on other 5th gen aircraft (J-20, FC-31, Su-57) as they and their powerplants mature too.




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