reported AIM-120C losing targets easily for chaff even at close ranges

[Northstar98]

5 minutes ago, Csgo GE oh yeah said:

So we don't know what how big the search angle is for the missiles ? 
In degrees ? 

 

What do you mean by that?

 

The gimbal limits/FOV? Or the beamwidth? In any case I'd expect them both to be roughly similar, though the AIM-54 has a larger antenna.

[Csgo GE oh yeah]

Yes the gimball limit of the onboard radar

[Northstar98]

I'd expect them to be roughly the same looking at rough cutaways, at a guess (so take with a few heaps of salt) I'd say something like 90° (or 45° off of the missile boresight), it could be larger but that's my guess so far.

 

I've done a little bit of digging through the scripts file and found something called aa_missile_amraam.sch and aa_missile_amraam.sch.lyt (both found in Scripts -> Database -> Weapons -> schemes -> missiles).

 

Not sure where the HB Phoenix is defined (I'd imagine it's protected).

 

In there there's a few entries that look like they could have something to do with the seeker, but I'm kinda out of my depth. I couldn't find anything in the main database entry for the AMRAAM (which is the db_missiles.lua IIRC).

 

Spoiler

[5] = {
                ["name"] = "seeker_FOV",
                ["type"] = 2,
            },

 

Presumably refers to the seeker type, presumably 2 could mean either an active_radar, or maybe it means 2 degrees of freedom (i.e elevation and azimuth?). I'm clearly out of my depth here, maybe someone else knows better.

 

[66] = {
            ["port"] = 0,
            ["input_lead"] = "seeker_FOV",
            ["input_block"] = -666,
            ["output_lead"] = "FOV",
            ["output_block"] = 7,
        },

 

Not sure what's going on here, I wonder if "output_block" refers to the gimbal limits in 10s of degrees? So 70°, which sounds like a number that makes sense - don't know.

 

Then there's this:

 

[88] = {
            ["port"] = 0,
            ["input_lead"] = "FOV",
            ["input_block"] = 9,
            ["output_lead"] = "FOV",
            ["output_block"] = 7,
        },

 

Again, there's 7 - though again not 100% sure - I'm kinda out of my depth here.

 

Edited February 14, 2021 by Northstar98

[Tippis]

2 hours ago, Northstar98 said:

Not sure where the HB Phoenix is defined (I'd imagine it's protected).

You'll find a lot of 3rd-party entities in the CoreMods directory, under the directory of the aircraft the weapon is associated with.

 

Even if you don't own a particular module, that only stops you from flying it, not from having it appear in a mission you make (except for the WWII) stuff, and therefore, a lot of the base data needs to be available to everyone. That stuff is stored in CoreMods for exactly that purpose: they're technically separate modules, but they are also universal necessities — “core” features, if you like.

[Northstar98]

16 minutes ago, Tippis said:

You'll find a lot of 3rd-party entities in the CoreMods directory, under the directory of the aircraft the weapon is associated with.

 

Even if you don't own a particular module, that only stops you from flying it, not from having it appear in a mission you make (except for the WWII) stuff, and therefore, a lot of the base data needs to be available to everyone. That stuff is stored in CoreMods for exactly that purpose: they're technically separate modules, but they are also universal necessities — “core” features, if you like.

 

Cheers Tippis, though I had a little poke around and couldn't find anything, though I only looked for it briefly.

[Tippis]

Yeah, it's not the cleanest and most consistent storage spot for DCS data.

Each module will have its own ever-so-slightly varying directory structure, with the actual data stored or combined in its own particular set of lua files. Some stuff is will be directly under one of the aircraft modules; other will be in one of the aircraft weapon packs, or tech weapon packs, or asset packs or… (etc).

 

Without a good file searching tool, it can take quite some time to find what you want.

[GGTharos]

6 hours ago, Csgo GE oh yeah said:

So we don't know what how big the search angle is for the missiles ? 
In degrees ? 

 

We do know the gimbal limit for both.  I don't recall the exact number for either missile, but it's between 50 and 60 degrees.

Edited February 14, 2021 by GGTharos

[Csgo GE oh yeah]

Is that 50-60 to the right, and 50-60 to the left ?

 

 

[GGTharos]

Yes.

[Csgo GE oh yeah]

Ok that's a lot more than i thought. 

Years ago i read it should only be a couple of degrees , but that was a long time ago. 

[Northstar98]

1 hour ago, Csgo GE oh yeah said:

Ok that's a lot more than i thought. 

Years ago i read it should only be a couple of degrees , but that was a long time ago. 

 

That sounds more like the beam width of the main lobe (which is usually only a few degrees or less) and not the gimbal limits of the antenna. A couple of degrees off-boresight would be pretty useless - we're talking AIM-9B limits here.

[GGTharos]

3 hours ago, Csgo GE oh yeah said:

Ok that's a lot more than i thought. 

Years ago i read it should only be a couple of degrees , but that was a long time ago. 

 

The iFov is about 6 degrees for RF missiles, typically.  Technology and other factors can change that, but for most of the cases for our modern missiles the gimbals and iFoV will fall into those values.

[Csgo GE oh yeah]

Right, so what i mean is this :
What happens if a missile is in the air but isn't guided anymore by the aircraft ... Does it always automatically go active at some point ?
And also : Once it does go active, does the missile start 'scanning' for targets in that 50-60 degree range ? 

The reason i ask is because i'm watching tacviews, and notice that missiles that have been quite some time without any guidance, will 'turn on' and find targets almost 90 degrees of their nose. 

I seem to remember reading that the phoenix for instance, NEEDS a command from the aircraft to go active , but it appears that all missiles just go active no matter what. 

How is it supposed to work for amraam and phoenix ? 



 

[Northstar98]

4 hours ago, Csgo GE oh yeah said:

Right, so what i mean is this :
What happens if a missile is in the air but isn't guided anymore by the aircraft ... Does it always automatically go active at some point ?
And also : Once it does go active, does the missile start 'scanning' for targets in that 50-60 degree range ? 

The reason i ask is because i'm watching tacviews, and notice that missiles that have been quite some time without any guidance, will 'turn on' and find targets almost 90 degrees of their nose. 

I seem to remember reading that the phoenix for instance, NEEDS a command from the aircraft to go active , but it appears that all missiles just go active no matter what. 

How is it supposed to work for amraam and phoenix ?

 

Phoenix as I understand it, absolutely requires a command from the WCS to go active (which is I believe transmitted from the AWG-9 antenna, but don't quote me on that).

 

AMRAAM on the other hand will have target information saved into it prior to launch, if a track is lost and the AMRAAM stops receiving updates it should fly to the last known calculated intercept point and go active shortly prior to that.

 

The Phoenix however should go basically stupid, maybe the autopilot will keep it on the same trajectory (which might be pretty useless if the missile is lofting), I'm not sure what happens if a track is lost and then reacquired however though there is a fairly long memory mode (30s), maybe if you reacquire inside that window it'll work and update the missile. Memory mode however should work on the last known parameters of the target. If you completely lose a track though, I'm not sure what the WCS does - though I imagine it might treat it as a completely new track and the missile would be lost, never going active.

Edited February 15, 2021 by Northstar98

[GGTharos]

First, they're not finding anything when it's 90 deg off - it can be 60 and you might perceive it as 90.  Of course if you can prove that it's locking on 60, then it's a bug ... but proving this isn't easy and you must replicate it in a short track.

 

DCS vs RL:   In DCS, these missiles scan all the gimbal space.  IRL, probably not, though we don't know.

 

The real difference is in seeker movement speed.  The seeker in game moves instantly, the real one does not and you need some amount of time to search - better to search where the target probably is.

 

Again, DCS vs. RL:  In DCS, AMRAAM will begin to scan as soon as it loses support (although this may have changed now, I don't know) and unlike its IRL counterpart, for now at least it isn't range/angle/doppler-gating so it'll pick up whatever.  Of course, you'd also open the gates if enough time passed without finding a target.  The phoenix gets its go active command from the aircraft, so if it loses support it should be gone.

 

In summary, DCS used to and still does things a certain way.  Missiles depart from reality both in terms of doing things that benefit them, and things that don't.

 

32 minutes ago, Northstar98 said:

The Phoenix however should go basically stupid, maybe the autopilot will keep it on the same trajectory (which might be pretty useless if the missile is lofting), I'm not sure what happens if a track is lost and then reacquired however though there is a fairly long memory mode (30s), maybe if you reacquire inside that window it'll work and update the missile. Memory mode however should work on the last known parameters of the target. If you completely lose a track though, I'm not sure what the WCS does - though I imagine it might treat it as a completely new track and the missile would be lost, never going active.

 

If a track is lost, it's 'frozen' for 2 minutes and messages continue to be sent to the missile.  It's possible that it could re-correlate, but I doubt it.   Also if you interrupt guidance - eg. turn around or shut off the radar such that the track is not just lost but actually dropped (you can also manually drop it) - that missile datalink channel is gone (it's different and unique for each missile), so you'll never send any more messages to that missile.

Edited February 15, 2021 by GGTharos

[Northstar98]

31 minutes ago, GGTharos said:

If a track is lost, it's 'frozen' for 2 minutes and messages continue to be sent to the missile.  It's possible that it could re-correlate, but I doubt it.   Also if you interrupt guidance - eg. turn around or shut off the radar such that the track is not just lost but actually dropped - that missile datalink channel is gone (it's different and unique for each missile), so you'll never send any more messages to that missile.

 

Awesome, thanks! I didn't realise the track was frozen for that long.

[GGTharos]

1 minute ago, Northstar98 said:

Awesome, thanks! I didn't realise the track was frozen for that long.

 

If you think about it it makes sense - the maximum (guaranteed) flight time available to the 54 is 160 seconds.  If a track drops, it could be for any reason, but your target may stay on that track.  Keeping a lost track 'frozen' thus allows you to still activate the missile on a predicted point of impact and it has a small chance of acquiring the target.

[Csgo GE oh yeah]

So what do you guys think happned here :  (video quality will improve youtube is rendering)

 

[GGTharos]

Exactly what has been said above.   The missile went active, started searching, picked up the F-16 and turned towards it.  Definitely a DCSism.

 

There are two things wrong here:

 

1) Missiles shouldn't be searching this much gimbal space - this is an old DCSism from the 2000's.

2) We can't see the F-14's radar screen, but let's assume he didn't drop the track.   Despite the fact that he's been notched, the missile should be receiving instructions to look at and probably steer towards the dead track, so theoretically it should have been able to find you anyway - just slimmer chance than if it had not been notched.

Edited February 15, 2021 by GGTharos

[Csgo GE oh yeah]

But it shouldn't have gone active right ?
I mean, it looks like it's not receiving any guidance from the airplane anymore (just goes straight) , track lost meaning no 'go active' order from the airplane ?

[GGTharos]

See above for the answer.   But basically yes, it should go active if the F-14 hasn't dropped the track (it may be a dead track, but it's still valid/frozen/generating m-link data) and it should probably be steering to meet the track as well.  Unfortunately we don't know the exact details of what this missile would do in this scenario, specifically:

 

1) Dead track

2) Missile seeker can or can't see the SARH reflection from the TWS scan.  If it can, the answer is easy, it'll steer to you.  If it can't, I don't know - because the AWG-9 doesn't send missile steering commands, it sends 'look' commands plus range and doppler gates.   It's possible that the missile will guide its way to match the look command corrections here, IRL.

 

DCS is missing all of this.

Edited February 15, 2021 by GGTharos

[Northstar98]

1 minute ago, GGTharos said:

See above for the answer.   But basically yes, it should go active if the F-14 hasn't dropped the track (it may be a dead track, but it's still valid/frozen/generating m-link data) and it should probably be steering to meet the track as well.  Unfortunately we don't know the exact details of what this missile would do in this scenario, specifically:

 

1) Dead track

2) Missile seeker can or can't see the SARH reflection from the TWS scan.  If it can, the answer is easy, it'll steer to you.  If it can't, I don't know - because the AWG-9 doesn't send missile steering commands, it sends 'look' commands plus range and doppler gates.   It's possible that the missile will guide its way to match the look command corrections here, IRL.

 

DCS is missing all of this.

 

 

Sounds like the missile API and what DCS supports still has a way to go...

[Harker]

First, they're not finding anything when it's 90 deg off - it can be 60 and you might perceive it as 90.  Of course if you can prove that it's locking on 60, then it's a bug ... but proving this isn't easy and you must replicate it in a short track.
 
DCS vs RL:   In DCS, these missiles scan all the gimbal space.  IRL, probably not, though we don't know.
 
The real difference is in seeker movement speed.  The seeker in game moves instantly, the real one does not and you need some amount of time to search - better to search where the target probably is.
 
Again, DCS vs. RL:  In DCS, AMRAAM will begin to scan as soon as it loses support (although this may have changed now, I don't know) and unlike its IRL counterpart, for now at least it isn't range/angle/doppler-gating so it'll pick up whatever.  Of course, you'd also open the gates if enough time passed without finding a target.  The phoenix gets its go active command from the aircraft, so if it loses support it should be gone.
 
In summary, DCS used to and still does things a certain way.  Missiles depart from reality both in terms of doing things that benefit them, and things that don't.
 
 
If a track is lost, it's 'frozen' for 2 minutes and messages continue to be sent to the missile.  It's possible that it could re-correlate, but I doubt it.   Also if you interrupt guidance - eg. turn around or shut off the radar such that the track is not just lost but actually dropped (you can also manually drop it) - that missile datalink channel is gone (it's different and unique for each missile), so you'll never send any more messages to that missile.

Very good write-up!

One more thing, that I cannot know for sure, but I've come across from time to time, so take it with a grain of salt: IRL, after the AMRAAM goes active (with all gates optimized for the target etc), the datalink is maintained and the missile can benefit from further targeting info and correlate its own radar picture with the one received from the aircraft.

Besides the obvious guidance advantage, one more thing that this helps with is notching. If the missile is notched or otherwise decoyed, it still receives targeting info from the launch platform, potentially increasing the chance to re-acquire.

[GGTharos]

12 minutes ago, Harker said:

One more thing, that I cannot know for sure, but I've come across from time to time, so take it with a grain of salt: IRL, after the AMRAAM goes active (with all gates optimized for the target etc), the datalink is maintained and the missile can benefit from further targeting info and correlate its own radar picture with the one received from the aircraft

 

I'll help you with that ... yes, this is exactly what happens as per any -34 or other IRL weapons manual hat describes the AMRAAM's use of datalink.

 

12 minutes ago, Harker said:

Besides the obvious guidance advantage, one more thing that this helps with is notching. If the missile is notched or otherwise decoyed, it still receives targeting info from the launch platform, potentially increasing the chance to re-acquire.

 

It also helps counter ECM.

[dundun92]

2 hours ago, Csgo GE oh yeah said:

So what do you guys think happned here

Its the AIM-54 desync issue. If you looked at that clients replay youll find that it guided normally.