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Odd AIM120 Behaviour


Sharpe_95
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All,

I dont pretend to know very much about this at all so I apologise if I am way off - but it strikes me as odd.

 

I was just messing around with some different ranged shots in the F16 Instant Action 'Intercept' mission to get an idea of the AIM120 performance relative to the DLZ when I noticed this (see acmi - sorry no track).

 

Notice how the 4th missile pulls an excessive lead on the target jet. To my mind this is well over what I would expect to see under the circumstances. The missile was locked all the way in, I didn't snip it at all, even when it would have gone active.

 

The excessive lead seems a little odd to me? I could understand if the target pulled G to kinematically defeat the missile, or it decoyed it using countermeasures, but I would have assumed the missile would have gone behind, not ahead of the target?

 

Is this a bug or normal behaviour?

 

(Sorry, drop box link as TACVIEW not an acceptable format for upload here).

https://www.dropbox.com/s/cynxi3zeq5yqlfm/Tacview-20200429-155511-DCS-F-16C%20-%20Caucasus%20-%20Fighter%20Intercept.zip.acmi?dl=0

 

-S

PS: Sorry - I have posted this in the F16 thread as that is what I was flying - I dont know if it qualifies as an 'F16 bug' (if it even is a bug) or something else.

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Viper DLZ and ASE circle is basically a placeholder at this point and you're better off fighting by experience. You can use it as a ballpark but it's largely irrelevant, you can get kills well outside displayed Rmax under good conditions and the steering dot is straight up horrible, I tend to reference HMD designation and target track.

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Viper DLZ and ASE circle is basically a placeholder at this point and you're better off fighting by experience. You can use it as a ballpark but it's largely irrelevant' date=' you can get kills well outside displayed Rmax under good conditions and the steering dot is straight up horrible, I tend to reference HMD designation and target track.[/quote']

 

Hi Blaze,

Thanks for responding, but I think you may have been answering a different question of mine which is located elsewhere? : https://forums.eagle.ru/showthread.php?t=271694

 

This post is specifically about an AIM120c doing very odd things - not linked to the DLZ or F16 systems (i think).

 

-S


Edited by Sharpe_95
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Yep, the amraam guidence is very WIP. We were going to get a reworked missile API at the beginnin of this year but it seems ED has forgot about that. The amraam will pull insane amounts of lead and AOA if the target is beaming or changing direction even at longer ranges.

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Yep, the amraam guidence is very WIP. We were going to get a reworked missile API at the beginnin of this year but it seems ED has forgot about that. The amraam will pull insane amounts of lead and AOA if the target is beaming or changing direction even at longer ranges.

It shouldn't overcalculate the intercept/impact point. I've also seen 9Xs doing this. Passing a target in front of its flight path instead of the back, without pulling massive Gs to dodge it, which doesn't make sense. That's not how these missiles are intended to be.


Edited by Der Hirte
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Of course it makes sense.

 

These missiles are flying PN, so they'll aim further ahead while accelerating - slower speed means more lead. They then turn back into the target once they build up speed - more speed means less lead.

 

This is a direct product of proportional navigation. No impact point is calculated at all. What PN does, in layman's terms, is to constantly attempt to 'freeze the target in the FoV'.

[sIGPIC][/sIGPIC]

Reminder: SAM = Speed Bump :D

I used to play flight sims like you, but then I took a slammer to the knee - Yoda

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That fourth missile was notched. If you notice, the sudden lead occurred as the jet reached 95° of aspect, which at M 0.6 (its speed) is definitely within the doppler gate. As for why is decided to do that maneuver in particular idk, but the missile had already lost track due to notching. Nothing to do with guidance.


Edited by dundun92
Nor

Eagle Enthusiast, Fresco Fan. Patiently waiting for the F-15E. Clicky F-15C when?

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Intel Xeon W3680 (i7-980X) OC'd to 4.0 GHz, EVGA GTX 1060 6GB SSC Gaming, 24 GB DDR3 RAM, 500GB Crucial MX500 SSD. Thrustmaster T16000M FCS HOTAS, DIY opentrack head-tracking. I upload DCS videos here https://www.youtube.com/channel/UC0-7L3Z5nJ-QUX5M7Dh1pGg

 

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  • 3 weeks later...
So you believe that the AMRAAM's response to losing track is to do a 30G pull away from the bandit?

Yes, you can easily verify this. It appears to be something hard-coded. In fact, I have a tacview clip of this very thing happening (plus some other weird stuff). In these cases no chaff was used even, it was purely from the notching. https://streamable.com/7ruydj , and https://streamable.com/n50z6q.

Eagle Enthusiast, Fresco Fan. Patiently waiting for the F-15E. Clicky F-15C when?

HP Z400 Workstation

Intel Xeon W3680 (i7-980X) OC'd to 4.0 GHz, EVGA GTX 1060 6GB SSC Gaming, 24 GB DDR3 RAM, 500GB Crucial MX500 SSD. Thrustmaster T16000M FCS HOTAS, DIY opentrack head-tracking. I upload DCS videos here https://www.youtube.com/channel/UC0-7L3Z5nJ-QUX5M7Dh1pGg

 

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I'm fairly certain that there's some unhandled asymptote - I wonder if what the code is handling is going through conversions which reach infinity as the target passes through the notch.

[sIGPIC][/sIGPIC]

Reminder: SAM = Speed Bump :D

I used to play flight sims like you, but then I took a slammer to the knee - Yoda

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Yes, you can easily verify this. It appears to be something hard-coded. In fact, I have a tacview clip of this very thing happening (plus some other weird stuff). In these cases no chaff was used even, it was purely from the notching. https://streamable.com/7ruydj , and https://streamable.com/n50z6q.

 

 

Yep, active missiles actually pull the exact same amount of Gs for the same amount of time the instant they get notched... 13G if I recall correctly.

I had a heap of tacview experiments at any altitude, with or without chaff, singleplayer or multipalyer. Same behaviour every. damn. time.

You can notch a missile at 30,000 feet with zero effort by slowly turning through the notch because it will ruin its own intercept geometry with this move.

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