AIM-120 loses track on cold targets even with high relative velocity.

[Default774]

The AIM-120 is prone to losing track on cold targets, even when there is sufficient doppler shift present from relative velocity. Additionally, the missile exhibits the often observed snapping after losing and regaining track on its target.

The cld3 track shows the issue most clearly, even with 200knots of relative velocity, the missile still loses track on the target. After the AI makes a slight turn while defending, the missile regains track on the target and proceeds to snap wildly losing its speed.

Disregard the missile losing track of the target completely at the end of cld1&2, this is the missiles battery running out.

All midcourse support is broken upon pitbull so the missile is completely on its own.

120_cld1.acmi 120_cld2.acmi 120_cld3.acmi 120_cld1.trk 120_cld2.trk 120_cld3.trk

Edited November 28, 2022 by Minimalist

[Default774]

Player POV tracks here. No snapping observed as missile does not reacquire at all.

120_pc3.trk 120_pc1.acmi 120_pc1.trk 120_pc2.trk 120_pc2.acmi 120_pc3.acmi

Edited November 28, 2022 by Minimalist

[Маэстро]

Quote

The AIM-120 is prone to losing track on cold targets, even when there is sufficient doppler shift present from relative velocity. 

In all tracks you have attached I see missile losing track due to almost equal velocities of missile and target. There is no any issue.

[Lurker]

30 minutes ago, Бойовий Сокіл said:

Ths should not be happening.

Why not? I mean if the missile is in a tail chase and is losing energy at some point it will match the speed of the target and there will be 0 doppler shift. Track lost. 

[Default774]

On 11/28/2022 at 3:01 PM, Маэстро said:

In all tracks you have attached I see missile losing track due to almost equal velocities of missile and target. There is no any issue.

After doing some more testing. Attached is a new track where I don't break off after the missile loses track. The missile loses track at around 1:40 into the track. You know the missile loses track because the missile launch tone stops playing on the RWR (Side note, why does this happen?). As soon as the missile loses track, there is about a 50-60kt TAS difference between the missile and the target (Tacview numbers, not very accurate). Of course I don't have access to debug tools that would show when the missile precisely loses track and why, so this is my best guess.

In this track, I keep accelerating after the missile loses track on the same trajectory. Despite the relative speed between the missile and target increasing, the missile never regains track. If the missile lost track due to near equal speed, why does it not reacquire when this is no longer the case? Does the missile have a mechanism that prevents it from reacquiring here?

 

Another side note, I know that notching behaviour is affected by whether or not the missile is looking down into the ground or the water. Notching a missile above water is (as far as I've experienced) much much more difficult than notching over land. Does the same effect not apply here?

120_spd1.acmi 120_spd1.trk

Edited November 29, 2022 by Minimalist

[Default774]

Same behaviour occurs in lookup as well. hm1&3 show the missile losing track in the defending turn which doesn't make a lot of sense to me (Separate issue?).

120_hm1.trk 120_hm2.trk 120_hm3.trk 120_hm1.acmi 120_hm2.acmi 120_hm3.acmi

Edited November 29, 2022 by Minimalist

[KlarSnow]

Battery life of the AIM-120 in DCS is 100 seconds (1:40)

[Default774]

1 hour ago, KlarSnow said:

Battery life of the AIM-120 in DCS is 100 seconds (1:40)

If you're referring to my earlier comment of the missile losing track 1:40 into the mission, the missile battery doesn't apply here at all. 

The AI fires about 20-30 seconds after mission start because my test mission has an unnecessarily large distance between the aircraft at spawn. The missile is nowhere close to 100 seconds of flight when it loses track and keeps emitting after it loses track 

Edited November 30, 2022 by Minimalist

[Hobel]

vor 17 Stunden schrieb Minimalist:

Same behaviour occurs in lookup as well. hm1&3 show the missile losing track in the defending turn which doesn't make a lot of sense to me (Separate issue?).

120_hm1.trk 96.78 kB · 2 Downloads 120_hm2.trk 116.45 kB · 2 Downloads 120_hm3.trk 87.05 kB · 2 Downloads 120_hm1.acmi 61.04 kB · 2 Downloads 120_hm2.acmi 72.59 kB · 1 Download 120_hm3.acmi 57.42 kB · 1 Download

 

is it intended that the target aircraft is so enormously fast?
I mean a 20-nm shot at a target of 1.88Mach and a defensive initiation?

For such test purposes, I would always take 1M for the firing platform and the target.
If something crazy should happen then you can evaluate it better.

[skywalker22]

Why missile looses track, is because of the puse-doppler effect and how the radar works. When speeds of missile and the target becoming more and more equal, the radar on missile (or on aircraft if still driven by aircraft) cannot see the target any longer. It is like the missile is being notched by the target. And when that happens, it looses lock. It should regain the lock again after the speed difference is becoming bigger again when missile is keep on loosing speed, but at that point it's pointless, because missile cannot reach the target anymore.

Anyway, why would someone shot an ammram on cold target without correct parameters, being not close enought, so the missile could not easily reach it. it's pointless.

Edited December 1, 2022 by skywalker22

[Маэстро]

On 11/29/2022 at 9:00 PM, Default774 said:

After doing some more testing. Attached is a new track where I don't break off after the missile loses track. The missile loses track at around 1:40 into the track. You know the missile loses track because the missile launch tone stops playing on the RWR (Side note, why does this happen?). As soon as the missile loses track, there is about a 50-60kt TAS difference between the missile and the target (Tacview numbers, not very accurate).

That's not correct to compare TAS. You need to know radial velocity (projection of closing velocity on line of sight) by which Doppler frequency shift is caused.
 

On 11/29/2022 at 9:00 PM, Default774 said:

In this track, I keep accelerating after the missile loses track on the same trajectory. Despite the relative speed between the missile and target increasing, the missile never regains track. If the missile lost track due to near equal speed, why does it not reacquire when this is no longer the case? Does the missile have a mechanism that prevents it from reacquiring here?

First of all missile has relatively narrow FOV, so it's quite easy to go out of FOV at close range(when missile does not track target). Second, there is no point to track target that missile cannot catch up.

 

On 11/29/2022 at 9:00 PM, Default774 said:

Another side note, I know that notching behaviour is affected by whether or not the missile is looking down into the ground or the water. Notching a missile above water is (as far as I've experienced) much much more difficult than notching over land. Does the same effect not apply here? 

There is no any difference between water and ground in fact.