AIM-120 Strange post chaff behaviour

[Default774]

Look up notch is performed in the tracks to make the missile go for chaff. After the missile gets chaffed, the guidance becomes abnormal, repeatedly snapping between the targeted aircraft and the chaff which decoyed the missile. This doesn't seem intentional.

120_postchaff1.trk 120_postchaff2.trk 120_postchaff1.acmi 120_postchaff2.acmi

Edited November 27, 2022 by Minimalist

[Default774]

Additional track to look at with other angle and background, might matter . In this track the notch was especially poor (~100deg relative angle) and the missile still seemed to get decoyed by chaff.

120_postchaff3.acmi 120_postchaff3.trk

Edited December 1, 2022 by Default774

[Маэстро]

Sorry, can't do a thing with current chaff mechanics. It's requires complete reworking to become more realistic. So that's not a bug, but a task for the future.

[AeriaGloria]

On 12/1/2022 at 2:20 PM, Default774 said:

Additional track to look at with other angle and background, might matter . In this track the notch was especially poor (~100deg relative angle) and the missile still seemed to get decoyed by chaff.

120_postchaff3.acmi 32.1 kB · 1 download 120_postchaff3.trk 78.79 kB · 1 download

 

Notching isn’t determined only by aspect, but by difference between TAS of the radar and the closure rate of the radar and target. The doppler filter in many planes usually covers about 50-100 knots from the TAS of the radar. If the closure speed is within that range, it will notch. 

[Default774]

1 hour ago, AeriaGloria said:

Notching isn’t determined only by aspect, but by difference between TAS of the radar and the closure rate of the radar and target. The doppler filter in many planes usually covers about 50-100 knots from the TAS of the radar. If the closure speed is within that range, it will notch. 

I know this. Looking at the relative angle is a quick and dirty way to see if I was roughly in the right direction with my manoeuvre. Just taking the TAS of both the missile and target isn't entirely correct either, but it's whatever.

How closely you get to zero relative radial velocity doesn't really seem to matter here either way as far as I have seen. The chaff behaviour in these tracks is exceedingly rare, I'm talking countless amounts of test runs for these three tracks. It seems to me you just have to be roughly in the notch and have to get very lucky with the chaff rng.

In the end, I don't have any subject matter expertise or design documents, so I can't really say for certain how the missile is and isn't supposed to work, or exactly how the 120 works for that matter. The conclusion I drew about this matter could be completely wrong for all I know. All I can go off is a surface level knowledge of radars and the hundreds of test runs I must have done for the 120 by this point. 

I will probably end up making a tacview add-on to show relative radial velocity properly eventually.

[Hobel]

vor 3 Stunden schrieb AeriaGloria:

Notching isn’t determined only by aspect, but by difference between TAS of the radar and the closure rate of the radar and target. The doppler filter in many planes usually covers about 50-100 knots from the TAS of the radar. If the closure speed is within that range, it will notch. 

F16 radar sees targets with 0 closure rate in a clean environment.
 

Edited December 8, 2022 by Hobel

[AeriaGloria]

20 hours ago, Hobel said:

F16 radar sees targets with 0 closure rate in a clean environment.
 

 

That is different. 

Lets says, you are in F-16 following a F-18. Both traveling at same speed, 700 knots TAS. 
 

Your ground speed is 700, but the closure speed is 0 knots. That’s a 700 knot difference! Pretty easy for a radial velocity gate to not filter that out. 
 

But if your ground speed is 700, and the F-18 makes an instant 90 degree turn, no matter the speed of the F-18, your closure speed is now equal to your TAS, 700 knots. Since the difference between ground speed and closure speed is 0 knots, the F-18 falls within the notch/radial velocity filter. 
 

There is equal speed gates, range gates, and doppler filter. The doppler filter is only based on 0 knots closure speed if your F-16 is flying at 0 knots. Without being able to hover or 200 knots winds, just flying in formation behind someone with 0 knot closure won’t be enough to make them fall in the notch. 

Edited December 8, 2022 by AeriaGloria