AIM-120 guidance - Are CFDs Accurate?

Its not just AIM120s. Their ordinance FM is a little off …… (FF 45 secs)

It most definitely looks off - but may I suggest starting a separate thread and attaching a track or Tacview file to the report? This one is related to a specific issue with a specific weapon.

Whatever it is tracking is outside the seekers field of view in the beginning for sure.

Bump. Fox 3s need attention. Guidance is so weird and unpredictable.

I have noticed multiplayer desync exacerbates the problem, which is why it's much easier to replicate in multiplayer. Especially on contacts that 'sync' just as the missile approaches.

Very frustrating in even moderately populated servers.

Bumping this too. I've noticed this in about a quarter of all shots I take now, MP and SP.

This was with both the Hornet and Eagle in various radar modes. The 120 will track perfectly with a solid radar lock and at some point in its flight will just dart off in a totally different direction just long enough so that the shot is wasted. Tonight I had this happen to me when the target was maybe 500 feet away. It's like the missile had a collision avoidance system and just skirted around the target.

Also just to add:

When firing a FOX1 on something and retaining a solid lock all the way through ..

The missile has no chance in hell to go for chaff! ... Just saying.

It has in DCS.

... of course it has a chance to go for chaff. Why wouldn't it? The radar will be illuminating it for a significant amount of time, and the seeker itself is tracking with a doppler gate that can be taken advange off by chaff + maneuver. Not to mention the guiding radar itself being perfectly capable of switching targets.

It should be harder once the missile's own seeker is locked on, compared to CMs in the air before lock/launch, but nowhere near 'no chance in hell'.

With Fox1's wouldn't it be more the case that so long as the main radar is locked onto the target (and stays that way) the missile will perceive the target to grow in apparent size dragging the aim point behind the target? With ofc this being dependent on aspect, range, Doppler gate size, and if the missiles has filters specifically to reduce the s/n (if that's the correct term) from chaff.

To reduce gain a lot is probably difficult with chaff. For dragging the aimpoint behind, I agree - this is how I've always seen it though I don't think it's the only mode of decoying.

CMs are combined with maneuvers for a number of reasons: putting the missile on the beam eliminates the doppler gate filter, flying through the notch while dispensing probably throws the doppler gate for a loop, and chaff is perfectly capable of causing the prox fuze to go off IRL, even vs. heat seekers.

How effective/useful is all this stuff? I have no idea - a better understanding sits behind paywalls (I have seen such research when I had journal access), and specific weapon/sensor knowledge is likely a secret.

Yeah I don't have much on its effectiveness just tidbits here and there from different papers and textbooks:

The top one in there is Radar Homing Guidance by DA James right?

Iirc he talks about different ways of biasing modern PD filters as well to e.g. eliminate clutter appearing behind the direction of the tracked object or outside track plane of motion.

There's a lot of ways in which the effect of chaff can be reduced. As GGTharos said chaff without a manoeuvre is mostly useless or at least, extremely easy to CCM.

Don't forget that chaff is combined with jammers and other forms of electronic warfare. The goal is to deteriorate signal-to-noise ratio and reduce seeker sensitivity to the extent that it just can't acurrately track the target anymore.

Within DCS this is very poorly represented. I get the simplification of chaff-as-flares... it's not too far-fetched as an approach. But the fact it has the same effectiveness at 30,000 feet as it does at 300 feet AGL, as well as the fact that it remains an effective countermeasure without aggressive manoeuvring LONG after it has been dropped is something that could definitely do with some serious tweaks.

Chaff in game shouldn't last more than 5sec IIRC. Maybe it sticks around a little longer these days, but chaff gets cleaned up pretty fast in DCS.

The 4-5 seconds it is in DCS is still absurdly long compared to the short time it would have before it enters the doppler gate. From what I've read the main return is caused by the expansion of the cloud, after they lumped into the clutter filter for PD sensors due to their near-zero angular velocity.

Still mess up pulse radars something fierce at that point though. RIP your daily weather report.

^ that's the other thing in DCS... pulse and PD response to chaff is identical...

I think one of the worst issues is that seeker 'see' chaff outside of their mainbeam, as if they are not suppressing antenna sidelobes but only for chaff.

This has been a main complaint for the R-27, and likely affects all SARH. ARH can pick up a chaff cloud during its scan and at this point the doppler filter might be 'fail wide' ... which isn't exactly what happens in DCS - in DCS the guidance locks onto an object in the computer science sense, without trying to go through the motions of figuring out if it should, IMHO. Or, at least this processing is minimal.

I think one of the worst issues is that seeker 'see' chaff outside of their mainbeam, as if they are not suppressing antenna sidelobes but only for chaff.

Yup: https://forums.eagle.ru/showthread.php?t=242215

New Aim-120 Model - Are CFDs Accurate？

As you all may be aware of, ED made a new model about AMRAAM, which heavily involves CFD-based calcuations.

According to their News page,( https://forums.eagle.ru/showthread.php?p=4367841) It seems they are using some code affiliated with Cartesian Mesh.Are there more information about ED performed their CFD approach in their AMRAAM Development, and how accurate are those results?

I've never seen ED posting any verification results regarding to their CFD calcuations, and If I recall correctly, current cartesian codes are usually not well-known for transonic and supersonincs Calcuations , especially in terms of drag estimates.

Or alternatively ED developeds their own in-house CFD code? (I consider that being unlikely)

IASGATG performed his AMRAAM approach in Fluent though.

ref:http://www.zaretto.com/sites/zaretto.com/files/missile-aerodynamic-data/AIM120C5-Performance-Assessment-rev2.pdf

This is getting academic... me likes :D

Following

IASGATG report was much more thorough. In my own Mechanical B.Sc final project I've used FEA and of course when you write down the report you you go deep regarding the mesh you've used, the assumptions , the exact method (what method used at what phase, what are the advantages and disadvantages) etc. ED update was more like the poster you do to show your work. You don't get into the smallest details... You show the conclusions and only the key things.

So, you can't judge the quality of their work only by their "poster". I doubt they wrote a full academic report regrading their work because only the writing is a LOT of work.

Seems like they took this project very seriously and it's hard not appreciate that. Without reviewing their work in detail - you can't compare it.

Did ED do any validation tests for its new CFD

I am curious the small write up given to us about the new CFD didn't go into the depth that IASGATG went into which leads me ask did ED do any validation tests for its CFD? If so i'd love to see the results.

Thanks! Edit - one more question do amraam's loft profile get updated during midcourse based on what a target does (for example a split S)? Or is it set at launch only currently (I haven't been able to test this unfortunately way to busy recently)