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AIM-120 still can not chase simple Split S manuever.


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2 hours ago, NineLine said:

Hence the reason for the white paper, and for the interaction here. To show the design consideration, what we can and cant do based on info we have, etc. I see a lot of assumptions throughout all this, so I don't know where it will all land or how some of you will accept that some of this stuff is just unknown. I see some who want this spectacular missile so to get kill after kill, and some that want to see it be trashed easy. It will end up at some point in between. 

While I hope this will help, I am afraid that it may exacerbate the disconnect between what players are expecting to see and what your (ED's) intent is. Adding one line features in change logs that affect (or don't affect) the entire gameplay system without any real in-depth explanation of what exactly is going on really does not help. This is a community that thrives on documentation. So please document changes and updates in how these mechanics work. What exactly type of radar is missile X using, what's its detection range, what techniques are you using to mitigate problem X problem Y, what is its notch size..... etc..... all of these parameters need to be clarified so they don't have to be parsed from random threads and general user knowledge in these forums. And it needs to be updated as things change.

 

If we know what you are trying to do from the outset and what assumptions you are using for each change, that at least lets us know with every update what the working as intended state is. "added range gates" or "fixed range gates" tells us absolutely nothing when you go out and the exact same behavior as before the patch is still there.

I understand that ya'll probly don't like having every single update constantly scrutinized like this, exposing each change in detail will at least give everyone a common ground to start with, and if you updated us on the progress of things, more frequently that would immediately cage expectations or at least give everyone an understanding of what is going on. 

Yes this will probably also lead to a lot of concern and feedback about decisions and design assumptions, that already happens, but right now we have no idea if any of it is as intended or a bug, and most of the time concerns that things aren't working correctly or that theories are being applied wrong are just dismissed out of hand with a Correct as is. You cannot properly test if something is working correctly if you do not know how it is designed to work. All you have to go on is why does my missile miss so much in these situations.

You might understand why this is all very frustrating and does not lead to a lot of trust between you (ED) and the community when it comes to this stuff. 

A roadmap (much like you have implemented for the F-16 and the hornet) for how the missile API is developing would probly be super helpful, list all of the features you are implementing or are intending to eventually implement, and then prior to each update explain in full what that feature does in a tagged form that can easily be linked to and read. That way everyone knows how exactly to determine if its a bug or a not implemented feature.

Let me put it in a way that hopefully makes this painfully obvious, right now only ED knows how the missile and its seeker and guidance and all of this actually works, and what is planned. By putting it on the open beta without explicitly having all of that available, you are enabling so many spurious bug reports that do not know how or why things are working that is increasing your workload and leading to all of these off the rails conversations about intent. Tell us how it works and what is intended with each update, tell us what we should be looking for to see if things are implemented correctly or not. Obscuring these details are making ours and your lives in this harder. You will absolutely get questioned if you put up a feature change that's intent does not seem to match how the community thinks it should work, but at least we know what is correct as is.


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On 6/10/2022 at 9:08 AM, Маэстро said:

That all well known. At the moment very low S/N chosen(2 dB only) for target detection assuming effect of PDI. Regarding sigma values - now its some averaged value depending on incidence angle.

I saw this earlier. it assumes unambiguous range.

That's correct value(you may estimate it knowing antenna diameter and carrier frequency). You can't obtain narrow beam with small dish. Also 15 degrees circle you can see on F-18s HUD in amraam visual mode. For AIM-7 it will be 12 degrees.

  

 

After some research, I'm pretty sure I've found THE solution to the problem (no, it's not clickbait lol):

2 patents (now in the PUBLIC DOMAIN), deposited by Hughes (manufacturer of the AIM-120 at the time), in 1995 and 1996 (the AIM-120C deliveries began in 1996!). I join the patents PDF files. The patent EP0747723A2 was deposited first, then the following year the patent US5748140A was deposited, and uses the 1st one to refine the method.
Both patents explain how to specifically track a target beaming the missile to hide in the ground clutter. Here is how they describe the situation they claim to solve:

2022-06-11 19.27.06 patentimages.storage.googleapis.com 21804df7efd1.png7

 

That picture at the bottom reminds you something, no?

 

Here are just a few highlights of the system and algorithms, and the differences with the new missile API by ED:

- the new ED's API uses what is called "constant false alarm rate" (CFAR), which means detection occurs when the signal/noise ratio is high enough. Problems arise when the target signal has not enough range/Doppler separation with the ground clutter (as we see in DCS currently). In these patents, it is claimed that:

2022-06-11 19.23.04 patentimages.storage.googleapis.com 8a03157df350.png

That means the radar can determine the angles from which the signals (target and clutter) come from! That also means that this angle information can be used to help discriminate the target (the whole process is describes in the patents, way too long and complicated to write here). Basically, that huge ground patch producing an enormous noise and described by Маэстро earlier, with this system the vast, vast majority would not hamper target detection as the angle of the returns are different enough from angle the target returns.

- here are the results they obtain:

2022-06-11 19.38.50 patentimages.storage.googleapis.com 9d212affd79d.png

These results show that when the beaming target has a return that is barely superior to the clutter return, and the clutter comes from an angle with 3° difference compared to the target return, with the old method (used by ED) the detection probability was almost 0%, while with the new method it's already 15%. At signal/noise ratio where the old method has a probability of detection of just 50%, they now obtain between 65% and 90% of detection.

IMPORTANT: Keep in mind, those results are for when the clutter comes from a single big source, with an angle slightly different from the angle of the target return. In most DCS situations, the clutter comes from a way bigger area, moderately reflective. In those situations, almost all the clutter will be filtered out by the new method, since most of the clutter will come from angles very different from the angle of the target return.

in the US5748140A patent, it is explained that if the missile seeker has a lock on the target, but loses the target fort a short period, the lock gates will continue to follow, for a period of time, along the predicted target angle, Doppler and range. That allows the missile to not break lock immediately when the target isn't detected anymore, and to continue to fly toward the predicted intercept point. If the target is lost for too long (a few seconds?), the lock is lost and the radar enters search mode again

I'll also add some personal remarks on the modelling as explained by ED and Маэстро:

- to your remark "it assumes unambiguous range" I quoted at the top, it seems you don't model blind Doppler and blind ranges. Now, most MPRF radars indeed use several frequencies (generally 8 ) to avoid those blind regions, but also to solve range and Doppler ambiguities. I don't quite understand why you assume target range is ambiguous, when most MPRF radars solve that problem.

- target detection probability should be a thing for all radars in DCS. The Mirage, and in the last update the JF-17, implement this now, and we see how it's way more realistic than "5sqm RCS = detection at 26 miles exactly", like in all other modules.

- We see how important it is in real life that the target RCS is way bigger when seen from the sides and from above/bellow. Jets RCS are tens or hundreds of time bigger than when seen from front aspect, and that plays a huge role in being able to still detect them while they're beaming a radar. That's not modelled in DCS, except for the new missile API. Stores increasing the RCS would be really nice too.

- the patents authors here mainly refer to a missile, but you can be sure that means that similar systems are used on the most recent radar jets (F-16, F-18, JF-17), and that beaming those radars should probably be really quite hard (most probably VERY hard).

EP0747723A2.pdf US5748140.pdf


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10 hours ago, KlarSnow said:

I am afraid that it may exacerbate the disconnect between what players are expecting to see and what your (ED's) intent is.

Well that is one of the issues right, many players have many expectations, not always agreeing with each other, but our goal isn't to meet everyone's expectations, its to do the very best simulation of these missiles that we can with given info and of course some creative thinking. The idea behind the white paper is to give you an idea of how we came to our conclusions, and like many of your conclusions, its based on what is available to us, and how it is interpreted. 

What that will probably mean, even after the white paper and final wrap on any one missile is someone somewhere will not be happy with something. I would hope that at the end of the day there is some trust in our work, and that we will take any and all input and information we can find to do the very best we can. Sure someone will invoke the GUA-8 or something else, but even after all that, once good hard evidence is produced we can and will adjust. The same here with missiles, we have very experienced and knowledgeable people working on this, and there is a lot of assumption being thrown around that may or may not be right, we have to filter all this and do what we think is best for the missiles. 

A roadmap wont work here, I am sorry but its not that simple when you are trying to tune these things, its not like a module and adding different systems and weapons. We wont do a roadmap on each and every individual missile, this is what the white paper is about.

Again, we appreciate all the feedback and input being conveyed here, we really do. The final say on the missiles will be from our weapons team though, its not just for DCS but our commercial products as well. That is not to say new information won't come to light later on and changes are needed, but we have to draw a line in the sand somewhere and say this is where the missiles are right now, otherwise it will be a new game each update trying to chase some fantasy/hypothetical/assumption based missile.

At the end of the day, this will be DCS World AIM-120, it might not match any other game out there (which isn't the goal) but it will be something that our weapons team will be proud of, and deem they did their very best. Some of you will not agree, or not be happy, but at some point we will need to say this is the best it can be, and move forward. 

Thanks.

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11 minutes ago, NineLine said:

Well that is one of the issues right, many players have many expectations, not always agreeing with each other, but our goal isn't to meet everyone's expectations, its to do the very best simulation of these missiles that we can with given info and of course some creative thinking. The idea behind the white paper is to give you an idea of how we came to our conclusions, and like many of your conclusions, its based on what is available to us, and how it is interpreted. 

What that will probably mean, even after the white paper and final wrap on any one missile is someone somewhere will not be happy with something. I would hope that at the end of the day there is some trust in our work, and that we will take any and all input and information we can find to do the very best we can. Sure someone will invoke the GUA-8 or something else, but even after all that, once good hard evidence is produced we can and will adjust. The same here with missiles, we have very experienced and knowledgeable people working on this, and there is a lot of assumption being thrown around that may or may not be right, we have to filter all this and do what we think is best for the missiles. 

A roadmap wont work here, I am sorry but its not that simple when you are trying to tune these things, its not like a module and adding different systems and weapons. We wont do a roadmap on each and every individual missile, this is what the white paper is about.

Again, we appreciate all the feedback and input being conveyed here, we really do. The final say on the missiles will be from our weapons team though, its not just for DCS but our commercial products as well. That is not to say new information won't come to light later on and changes are needed, but we have to draw a line in the sand somewhere and say this is where the missiles are right now, otherwise it will be a new game each update trying to chase some fantasy/hypothetical/assumption based missile.

At the end of the day, this will be DCS World AIM-120, it might not match any other game out there (which isn't the goal) but it will be something that our weapons team will be proud of, and deem they did their very best. Some of you will not agree, or not be happy, but at some point we will need to say this is the best it can be, and move forward. 

Thanks.

While I agree with what you say, I hope the elements I provide above, which given the context of the publications are almost certainly describing how the AIM-120C deals with target beaming, will be considered.

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I'm locking to let Маэстро catch up. Will unlock when he says so. Thanks all.

15 minutes ago, Mad_Shell said:

While I agree with what you say, I hope the elements I provide above, which given the context of the publications are almost certainly describing how the AIM-120C deals with target beaming, will be considered.

Маэстро will take a look I am sure, just give him a chance to catch up.

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On 6/10/2022 at 5:33 PM, KlarSnow said:

No they wont because they are range bins... why would they have any of the main lobe ground return in them. IF they are sorted by range and in the situation presented at the start of this thread. There is no Main Lobe or side lobe clutter in the 2.5 Nautical mile range bin. So if you sort it by range and receive the unambiguous range benefits of MPRF with PRF Jitter, how is the Main lobe or side lobe doppler that is 20 miles away getting into the 2.5 nautical mile range bin. And if it is, how is it of such magnitude that it is overwhelming the target return.

I’m sorry, but that shows you misunderstood how range bins really work and how range ambiguities may be resolved. I highly recommend you to read chapter 12 of Introduction to Airborne Radar by Stimson. It very clearly describes these things.

For ones who have no access to this book I will try to briefly explain it right here.

To measure range, pulsed radars may use pulse delay ranging. The idea is simple – you just need to measure time between pulse transmission and target echo receiving. Then knowing that pulse travels with speed of light you may calculate range (by simple multiplying of measured time by speed of light).

However, any pulsed radar has its own unambiguous range(s) which equal to

Ru = SpeedOfLight * T / 2, where T = 1/PRF – inter-pulse period, dividing by 2 means that pulse should make two-way travel – to target and back.  For 10KHz PRF this equation gives Ru = 15km. Why there is Ru? Because radar should use identical pulses (for several reasons) and cannot differ one from another, so it should start new time measurement after each transmitted pulse. Suppose we have two targets, one at 5km and another one at 22km and Ru equals to 15km. Radar transmit first pulse and measures time of echo returns. Echo from 5km target comes back within one inter-pulse period, so distance measured correct. When second impulse transmitted, first impulse echo from second target is still on the way and had covered 30km distance (SpeedOfLight * T), so it still needs to travel 22 * 2 – 30 = 14km. Second impulse should travel to first target forth and back only 10km, so radar receives it first and only after this receives first impulse echo from second target (which left to travel 14km).  So radar see two targets now – one at 5km(where it really is) and second at 14/2 = 7km. Note, when PRF is changed Ru changes too, so “visible” range of second target will also change(visible range of first target will be unchanged until it within Ru). Thus, second target has unambiguous range.

About range bins. In modern digital radar range bins is a set of memory cells. Each cell stores signal from radar receiver, which come in corresponding moment of inter-pulse period. For example, if PRF is 10KHz (T = 100 microseconds) and radar have 10 range bins, then each range bin should store 1/10 part of inter-pulse period (10 microseconds). So, first range bin stores signal for 0-10mcs interval, second for interval from 10 to 20mcs, and so on up to 100mcs. Each 10mcs corresponds to 1.5k range. If such radar will look at two targets from example above targets will fall in 4th and 5th bins correspondingly. In other words, range bins just filled with signal received during inter-pulse period and can contain range-unambiguous signal. Range bins do not do any ambiguity resolving themselves, just store signals. Range resolving can be made by signal processor. For this purpose, you need to save signal from each range bin (after Doppler filtering), change PRF and see how targets jumps from one range bin to another with respect to previously saved data. As was stated posts above, to calculate real range to such jumping targets Chines reminder theorem may be used.

Now imagine that radar sees very extended target which length exceeds Ru (as ground clutter may be in certain conditions). In this case range of such extended target cannot be resolved. Switching of PRF gives nothing because all range bins stay filled with target signal and radar does not see any target jumps between bins.

On 6/10/2022 at 5:33 PM, KlarSnow said:

The side of this as well is that by sorting the entire return into range bins the total clutter level in each bin is lowered. Think instead of the massive MLC spike you get in HPRF, you instead have as many little MLC spikes as you have range and velocity bins. Makes it much much easier to see the target which will have all of its return in one bin, vs the entire spread out clutter spectrum.

 

Yes, and exactly this way it works in DCS. The power of ground return spreads over range bins making target detection more possible. But range gating helps a lot to contend with side lobe clutter(the main reason of using range gating) and may not help in case of strong mainlobe return(which usually simply cuts off by clutter cancellers in fighter radars).

On 6/10/2022 at 5:33 PM, KlarSnow said:

If you are doing a single PRF MPRF radar as is apparently being implemented, then yeah, none of this works because you cant solve any of the ambiguity problems and there will totally be doppler in every single range bin no matter what you do.

No. As it already was stated above by Beamscanner ADAPTIVE single PRF gives you some advantages in case of STT. And there is no any problem with tracking while target is outside of mainlobe CENTRAL LINE clutter. All issues with eclipsing and notching by clutter harmonics easily solved by adaptive PRF change when target get close to such problem regions. The only region where this does not work is central line mainlobe clutter. Please try to understand that we talk about different parts of clutter. You talk about clutter harmonics which doppler frequencies changes with PRF switching (so regions previously obscured by clutter may be cleared even in case of range ambiguous mainlobe clutter) and I talking about clutter central line frequency, which stays unchanged with PRF switching. The central line clutter is the only clutter which can make you some troubles in DCS.

 

On 6/11/2022 at 3:10 AM, Beamscanner said:

The only way the AIM-120 could re-acquire / track the target through a look-down and doppler notch would be with a LPRF mode precisely for this purpose. Who knows if its actually capable of this.  MPRF would likely succeed in tracking the target if the target went into the notch in a 'look-up' condition.

Theoretically it possible and some fighter radars do that, but for missile system it may be a bad solution. In LPRF mode radar can track in range and angle, but cant perform robust velocity tracking, so radar became very sensitive to chaff. Properly designed extrapolation (inertial tracking) more robust in that case.

On 6/11/2022 at 3:10 AM, Beamscanner said:

What about dogfights?

With a Fighter radar in "MPRF", the Main Beam is much tighter, and has reduced sidelobes because it can afford to taper the antenna. This means the SNR would be much better than with the AIM-120's radar. Also, a fighter radar may have the capability to lower the PRF into the "LPRF" regime during a lock. There's room to argue that a fighter radar could have decent performance in tracking through a look-down + notch. At least at close range.

Yep. Fighters have bigger dishes, consequently narrower beams, this gives them an advantage of narrower doppler frequencies band (each harmonic will be narrower) of mainlobe clutter return and smaller beam footprint (smaller power of ground return).

 

On 6/11/2022 at 3:38 AM, KlarSnow said:

My issue right now is less the range gating vs clutter issue, its more the assumptions that are going into this "advanced missile API" and the follow on effects because they betray an utter misunderstanding of what should be some very basic MPRF concepts. 

My other issue is that the dev working on this is not engaging with any of the research, he is dismissing it and literally cherry picking the setup that is describing the problems in the first part of the paper and then ignoring the solution provided at the end because he has "seen it all before". 

And how do you know how many research I did? Aren't too much accusations?

There was no any cherry picking. You are mixing different things. This paper not about clutter ambiguity resolving. Author just uses simplest clutter model and trying to improve performance of matched filtering in presence of clutter, but with POSITIVE SCR. There is no clutter separating or range gating. Moreover, calculating SCR in this paper looks not clear for me (looks wrong to be precise). Equation 4.14 assumes that target and clutter located at the same distance, but MATLAB code uses this one

SCR=(sigma_target*4*altitude)/(10^(sigma0_surface/10)*pi*(altitude^2+distance^2)*deg2rad(beamwidth))

And that’s not equivalent of 4.14 with 4.12 substitution. Its equivalent of 4.14 multiplied by [sqrt(altitude^2+distance^2) * deg2rad(beamwidth)]. Such equation gives SCR for clutter at range Rc = sqrt(altitude^2+distance^2) and target at much closer range which equals to Rc / quadroot(Rc * deg2rad(beamwidth)). Of course, that’s much better SCR than eq.4.14 gives. All this looks weird to me. Thoughts?

Also note that missile have much wider beamwidth than fighter. 15deg vs ~3deg, five times wider. This results in SCR 25 times worser (because footprint area 25 times bigger) at the same circumstances.

 

 

Guys, in my opinion there are no major issues with notching itself. Of course, there may be some tweaks on normalized rcs of surface or we make different values for different surface types, but this will not change situation drastically.

BUT

In this particular case (see first post of topic) the problem is that INS data does not updated by seeker measurements, so without datalink updates missile performance after losing track of maneuvering target is degraded. We know about that and missile development in part of merging seeker data, datalink and INS data is not finished. Such systems may be built in several ways and I have some thoughts on that, but it is not as simple as it may looks like and good solution requires additional research.

 

 

 

On 6/10/2022 at 10:01 PM, KenobiOrder said:

No it does not. I am looking at it right now in two separate documents. It specifically states that maintaining datalink has no affect on missile Pk after the missile goes Pitbull UNLESS the missile loses track. 

On 6/11/2022 at 12:35 AM, KlarSnow said:

89401B73-DF7C-4829-A756-C4EE3E42DCD8.pngA paper that explicitly says the opposite, and has data later on to back up why (seeker accuracy and SnR at close range is better than supporting radars,especially in a degraded environment) and as GGTharos said there are ample manuals that match this paper as well. How old are your documents.

https://trace.tennessee.edu/cgi/viewcontent.cgi?article=6680&context=utk_gradthes

There is no any contradiction if we suppose that range at wich missile stops to incorparate data links is less then Pitbull range.

The paper is a very useful, thanks.

 

On 6/11/2022 at 7:32 PM, Mad_Shell said:

  

 

After some research, I'm pretty sure I've found THE solution to the problem (no, it's not clickbait lol):

2 patents (now in the PUBLIC DOMAIN), deposited by Hughes (manufacturer of the AIM-120 at the time), in 1995 and 1996 (the AIM-120C deliveries began in 1996!). I join the patents PDF files. The patent EP0747723A2 was deposited first, then the following year the patent US5748140A was deposited, and uses the 1st one to refine the method.
Both patents explain how to specifically track a target beaming the missile to hide in the ground clutter. Here is how they describe the situation they claim to solve:

2022-06-11 19.27.06 patentimages.storage.googleapis.com 21804df7efd1.png7

 

That picture at the bottom reminds you something, no?

 

Here are just a few highlights of the system and algorithms, and the differences with the new missile API by ED:

- the new ED's API uses what is called "constant false alarm rate" (CFAR), which means detection occurs when the signal/noise ratio is high enough. Problems arise when the target signal has not enough range/Doppler separation with the ground clutter (as we see in DCS currently). In these patents, it is claimed that:

2022-06-11 19.23.04 patentimages.storage.googleapis.com 8a03157df350.png

That means the radar can determine the angles from which the signals (target and clutter) come from! That also means that this angle information can be used to help discriminate the target (the whole process is describes in the patents, way too long and complicated to write here). Basically, that huge ground patch producing an enormous noise and described by Маэстро earlier, with this system the vast, vast majority would not hamper target detection as the angle of the returns are different enough from angle the target returns.

- here are the results they obtain:

2022-06-11 19.38.50 patentimages.storage.googleapis.com 9d212affd79d.png

 

EP0747723A2.pdf 512.89 kB · 8 downloads US5748140.pdf 948.62 kB · 9 downloads

Thank you! These patents are really interesting, but I’m afraid that’s not a solution. Not a full at least. See explanations below.

On 6/11/2022 at 7:32 PM, Mad_Shell said:

These results show that when the beaming target has a return that is barely superior to the clutter return, and the clutter comes from an angle with 3° difference compared to the target return, with the old method (used by ED) the detection probability was almost 0%, while with the new method it's already 15%. At signal/noise ratio where the old method has a probability of detection of just 50%, they now obtain between 65% and 90% of detection.

Admit right now we have 100% probability of detection (and lock) for 2dB SCR, and 1.5dB for detecting at all (extremely low values!). Of course, if I’ll try to implement this thing missile tracking capabilities will grow up to 15 or maybe 30% at 1dB SNR. But practically you wont notice any difference because in most of cases SNR is much lower that 1dB. It could easily be -10dB or worse! So, even this new method will provide very low detecting probability in such circumstances.

Additionally, there will be troubles for radar if beaming target will use chaff

On 6/11/2022 at 7:32 PM, Mad_Shell said:

IMPORTANT: Keep in mind, those results are for when the clutter comes from a single big source, with an angle slightly different from the angle of the target return. In most DCS situations, the clutter comes from a way bigger area, moderately reflective. In those situations, almost all the clutter will be filtered out by the new method, since most of the clutter will come from angles very different from the angle of the target return.

That’s not quite true. First of all, angle difference limited by beamwidth. If you track a target seeker LOS is pointed at the target and difference limited by half of beamwidth. Practically it will be even less than half because you need to put some ground surface inside of beam to have significant return. In case of ambiguous clutter return when patches of clutter superimposed in range bins angle difference may be small(signal from several patches located at different angels for radar will look like signal from one bigger patch located at some average angle). Also, it’s hard to say what average angle of clutter will be in most DCS situations.

On 6/11/2022 at 7:32 PM, Mad_Shell said:

in the US5748140A patent, it is explained that if the missile seeker has a lock on the target, but loses the target fort a short period, the lock gates will continue to follow, for a period of time, along the predicted target angle, Doppler and range. That allows the missile to not break lock immediately when the target isn't detected anymore, and to continue to fly toward the predicted intercept point. If the target is lost for too long (a few seconds?), the lock is lost and the radar enters search mode again

As I said the missile has such extrapolations, but there is a problem with updating data for extrapolation. It will be solved.

On 6/11/2022 at 7:32 PM, Mad_Shell said:

- to your remark "it assumes unambiguous range" I quoted at the top, it seems you don't model blind Doppler and blind ranges. Now, most MPRF radars indeed use several frequencies (generally 8 ) to avoid those blind regions, but also to solve range and Doppler ambiguities. I don't quite understand why you assume target range is ambiguous, when most MPRF radars solve that problem.

 

I did not say exactly that. There is no any problem with resolving range ambiguity for ordinary target. I was talking about extended target (about ground clutter in particular). Please see explanations above.

On 6/11/2022 at 7:32 PM, Mad_Shell said:

- the patents authors here mainly refer to a missile, but you can be sure that means that similar systems are used on the most recent radar jets (F-16, F-18, JF-17), and that beaming those radars should probably be really quite hard (most probably VERY hard).

 

Be assured modern PD radars still have problems with beaming targets tracking and try to contend with this generally by inertial tracking(extrapolation) or LPRF using. If it’s the ESA radar there are several additional methods to contend with this issue.

BTW. Proposed method does not look as good improvement for fighter radars because they usually have narrow beam 3 deg circa. (so only 1.5 deg halfwidth…)

On 6/11/2022 at 7:32 PM, Mad_Shell said:

- target detection probability should be a thing for all radars in DCS. The Mirage, and in the last update the JF-17, implement this now, and we see how it's way more realistic than "5sqm RCS = detection at 26 miles exactly", like in all other modules.

- We see how important it is in real life that the target RCS is way bigger when seen from the sides and from above/bellow. Jets RCS are tens or hundreds of time bigger than when seen from front aspect, and that plays a huge role in being able to still detect them while they're beaming a radar. That's not modelled in DCS, except for the new missile API. Stores increasing the RCS would be really nice too.

Yep, but we have lots of different high-priority tasks, so can’t promise such features soon. Will add to wishlist.

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6 hours ago, Маэстро said:

In this particular case (see first post of topic) the problem is that INS data does not updated by seeker measurements, so without datalink updates missile performance after losing track of maneuvering target is degraded. We know about that and missile development in part of merging seeker data, datalink and INS data is not finished. Such systems may be built in several ways and I have some thoughts on that, but it is not as simple as it may looks like and good solution requires additional research.

 

Maestro, If you had said this at the beginning instead of correct as is. I think this would have alleviated a lot of the concerns. This entire thread was instigated by you dismissing that complaint as realistic and not acknowledging that there was any further work that needed to be done. Maybe be honest with the flaws and what needs to be done with your modelling as this goes forward instead of every single question is correct as is. Maybe Correct as implemented, but improvements are coming would be a better way to answer that.

As for the rest. You are correct on much of the theory. However you are consistently making assumptions that lead to these results regarding the seeker. And ignoring anything that could potentially make these issues better. An MPRF Monopulse seeker should have a notch in the 10's of knots, not 100's. Especially once it has found and is tracking the target. Angle gating is something I think you should look into, because yeah if it has a 15 degree beamwidth all of that clutter can get illuminated, doesn't mean it cant digitally cut what its looking at down to only a couple of degrees once it has the target acquired. As a monopulse seeker that should be inconsequential.

It should be able to as well as measuring range and velocity, measure angle of return, and can then use that to filter out much of this 15 degree beamwidth noise. once it has an angle and range track on the target, Why is it still competing with the entire 15 degree beamwidth of clutter, once it knows where the target is all returns that are not in that tiny window and angle should be disregarded. Yes there will still be MLC in that window due to aliasing, and yes its not a completely clean picture, but you are treating it like no matter what the target is always competing with the 15 degree beamwidth of clutter, and that is not at all a requirement. It should be completely able to gate that down to a couple of degrees around the target, and then the tiny range gate around the target, and finally the velocity. None of this would remove the notch, but it would make it much much smaller than you have currently implemented it. 

Again the issue here isn't really the modelling. The issue is where this years long process is going and what the end result will look like. You cannot have it both ways. You cannot claim to be making the missile "realistic" and maintain the current gameplay mechanics that have been essentially the same for the past 20 years. If you are making the system more realistic then you are going to at some point have to deal with that.


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First and foremost, thanks for this insightful and open discussion. Highly appreciated and very educational.

 

That said, from a much less brainy caveman perspective of a man with no degree of any sorts in radar physics, but with a huge passion for organized online play in DCS:

I'm simply concerned with what is now well over 2 years of having the game's primary missile in flux on both the Stable and Open Beta branches. From the looks of this thread, DCS might well be simulating the most physically accurate missile seeker ever created. Yet as a player all I notice is that it still fails to capture a clear, transparent representation of how a missile should seemingly function.

Simply put: Missile behaviour does not convey its mechanics to the player transparently, consistently or logically. This is not exclusive to the AIM-120, but SARH missiles are equally affected, if not worse. The simple fact is that there is no consistent way to tell from the virtual cockpit whether a missile is going to have a high probability of kill. Everyone flying frequently will be able to throw examples on the pile of missiles exhibiting weird behaviours causing them to miss. Whether from chaff they shouldn't be able to see, hard turns away from target on split-second notches, energy-draining intercept geometry or any other reasons that seem to defy intuitive logic.

This could be hugely alleviated by a number of heavily abstracted, non-fidelitious solutions

  • simulating aforementioned angle/range/magical fairy gates by simply narrowing down the notch width value
  • making RWR's less accurate
  • reworking chaff diceroll parameters (just shortening effective time per particle to 0.5-1 seconds instead of 6 would already go a huge way)
  • giving STT/TWS locks an equal dice-roll chance to break lock as missiles currently do, while making the missile near-immune to chaff (Mirage 2000 approach)

All of these could be implemented in a fraction of the time-span we've experienced now with the AIM-120 development. All of these would hugely improve clarity of "game systems" and the reflection of real world function and therefore enhance the immersive simulation experience for us players.

 

While I hugely appreciate the mind-blowing depths you seem to go to for an accurate simulation, all that really counts at the end of the day is whether the simulation captures the essence of the real world, no matter how abstracted, as that is all players will ultimately experience.

The way this thread is looking, I fear we're still years out from a satisfying, stable result on achieving this for the various core parts of this combat simulator.


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The other concern is that you are putting all of this effort into constantly adding features that make the missile the same or worse than it was previously. 

We currently have so many filters that every missile has to get through to make it to the target. Random chaff rolls, notching, support from the radar, whatever effects jamming have, finally terminal glint effects. And this is all assuming the supporting radar doesn't bite off on a missile that was launched by yourself or the target on the way and completely defeat your own shot.

When are you going to add features that make missiles more effective, because right now it seems you have worked for years to make them exactly the same or less effective.

Someone could have left the game in 2019 and come back and found the EXACT same mechanics at play as they have been for the past twenty years. This makes me question what the point of all of this in depth modeling is if ED can't make a decision on changing any mechanics and are just modeling the same mechanics "more realistically".


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10 hours ago, Маэстро said:

I was talking about extended target (about ground clutter in particular).

So earlier you mentioned that in some "certain conditions" ground clutter can extend past the ambiguous range; what are these "certain conditions". And what conditions would the ground clutter not be spread out enough in range, and thus is not filling every range bin?

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10 hours ago, Маэстро said:

I’m sorry, but that shows you misunderstood how range bins really work and how range ambiguities may be resolved. I highly recommend you to read chapter 12 of Introduction to Airborne Radar by Stimson. It very clearly describes these things.

For ones who have no access to this book I will try to briefly explain it right here.

To measure range, pulsed radars may use pulse delay ranging. The idea is simple – you just need to measure time between pulse transmission and target echo receiving. Then knowing that pulse travels with speed of light you may calculate range (by simple multiplying of measured time by speed of light).

However, any pulsed radar has its own unambiguous range(s) which equal to

Ru = SpeedOfLight * T / 2, where T = 1/PRF – inter-pulse period, dividing by 2 means that pulse should make two-way travel – to target and back.  For 10KHz PRF this equation gives Ru = 15km. Why there is Ru? Because radar should use identical pulses (for several reasons) and cannot differ one from another, so it should start new time measurement after each transmitted pulse. Suppose we have two targets, one at 5km and another one at 22km and Ru equals to 15km. Radar transmit first pulse and measures time of echo returns. Echo from 5km target comes back within one inter-pulse period, so distance measured correct. When second impulse transmitted, first impulse echo from second target is still on the way and had covered 30km distance (SpeedOfLight * T), so it still needs to travel 22 * 2 – 30 = 14km. Second impulse should travel to first target forth and back only 10km, so radar receives it first and only after this receives first impulse echo from second target (which left to travel 14km).  So radar see two targets now – one at 5km(where it really is) and second at 14/2 = 7km. Note, when PRF is changed Ru changes too, so “visible” range of second target will also change(visible range of first target will be unchanged until it within Ru). Thus, second target has unambiguous range.

About range bins. In modern digital radar range bins is a set of memory cells. Each cell stores signal from radar receiver, which come in corresponding moment of inter-pulse period. For example, if PRF is 10KHz (T = 100 microseconds) and radar have 10 range bins, then each range bin should store 1/10 part of inter-pulse period (10 microseconds). So, first range bin stores signal for 0-10mcs interval, second for interval from 10 to 20mcs, and so on up to 100mcs. Each 10mcs corresponds to 1.5k range. If such radar will look at two targets from example above targets will fall in 4th and 5th bins correspondingly. In other words, range bins just filled with signal received during inter-pulse period and can contain range-unambiguous signal. Range bins do not do any ambiguity resolving themselves, just store signals. Range resolving can be made by signal processor. For this purpose, you need to save signal from each range bin (after Doppler filtering), change PRF and see how targets jumps from one range bin to another with respect to previously saved data. As was stated posts above, to calculate real range to such jumping targets Chines reminder theorem may be used.

Now imagine that radar sees very extended target which length exceeds Ru (as ground clutter may be in certain conditions). In this case range of such extended target cannot be resolved. Switching of PRF gives nothing because all range bins stay filled with target signal and radar does not see any target jumps between bins.

 

Yes, and exactly this way it works in DCS. The power of ground return spreads over range bins making target detection more possible. But range gating helps a lot to contend with side lobe clutter(the main reason of using range gating) and may not help in case of strong mainlobe return(which usually simply cuts off by clutter cancellers in fighter radars).

No. As it already was stated above by Beamscanner ADAPTIVE single PRF gives you some advantages in case of STT. And there is no any problem with tracking while target is outside of mainlobe CENTRAL LINE clutter. All issues with eclipsing and notching by clutter harmonics easily solved by adaptive PRF change when target get close to such problem regions. The only region where this does not work is central line mainlobe clutter. Please try to understand that we talk about different parts of clutter. You talk about clutter harmonics which doppler frequencies changes with PRF switching (so regions previously obscured by clutter may be cleared even in case of range ambiguous mainlobe clutter) and I talking about clutter central line frequency, which stays unchanged with PRF switching. The central line clutter is the only clutter which can make you some troubles in DCS.

 

Theoretically it possible and some fighter radars do that, but for missile system it may be a bad solution. In LPRF mode radar can track in range and angle, but cant perform robust velocity tracking, so radar became very sensitive to chaff. Properly designed extrapolation (inertial tracking) more robust in that case.

Yep. Fighters have bigger dishes, consequently narrower beams, this gives them an advantage of narrower doppler frequencies band (each harmonic will be narrower) of mainlobe clutter return and smaller beam footprint (smaller power of ground return).

 

And how do you know how many research I did? Aren't too much accusations?

There was no any cherry picking. You are mixing different things. This paper not about clutter ambiguity resolving. Author just uses simplest clutter model and trying to improve performance of matched filtering in presence of clutter, but with POSITIVE SCR. There is no clutter separating or range gating. Moreover, calculating SCR in this paper looks not clear for me (looks wrong to be precise). Equation 4.14 assumes that target and clutter located at the same distance, but MATLAB code uses this one

SCR=(sigma_target*4*altitude)/(10^(sigma0_surface/10)*pi*(altitude^2+distance^2)*deg2rad(beamwidth))

And that’s not equivalent of 4.14 with 4.12 substitution. Its equivalent of 4.14 multiplied by [sqrt(altitude^2+distance^2) * deg2rad(beamwidth)]. Such equation gives SCR for clutter at range Rc = sqrt(altitude^2+distance^2) and target at much closer range which equals to Rc / quadroot(Rc * deg2rad(beamwidth)). Of course, that’s much better SCR than eq.4.14 gives. All this looks weird to me. Thoughts?

Also note that missile have much wider beamwidth than fighter. 15deg vs ~3deg, five times wider. This results in SCR 25 times worser (because footprint area 25 times bigger) at the same circumstances.

 

 

Guys, in my opinion there are no major issues with notching itself. Of course, there may be some tweaks on normalized rcs of surface or we make different values for different surface types, but this will not change situation drastically.

BUT

In this particular case (see first post of topic) the problem is that INS data does not updated by seeker measurements, so without datalink updates missile performance after losing track of maneuvering target is degraded. We know about that and missile development in part of merging seeker data, datalink and INS data is not finished. Such systems may be built in several ways and I have some thoughts on that, but it is not as simple as it may looks like and good solution requires additional research.

 

 

 

There is no any contradiction if we suppose that range at wich missile stops to incorparate data links is less then Pitbull range.

The paper is a very useful, thanks.

 

Thank you! These patents are really interesting, but I’m afraid that’s not a solution. Not a full at least. See explanations below.

Admit right now we have 100% probability of detection (and lock) for 2dB SCR, and 1.5dB for detecting at all (extremely low values!). Of course, if I’ll try to implement this thing missile tracking capabilities will grow up to 15 or maybe 30% at 1dB SNR. But practically you wont notice any difference because in most of cases SNR is much lower that 1dB. It could easily be -10dB or worse! So, even this new method will provide very low detecting probability in such circumstances.

Additionally, there will be troubles for radar if beaming target will use chaff

That’s not quite true. First of all, angle difference limited by beamwidth. If you track a target seeker LOS is pointed at the target and difference limited by half of beamwidth. Practically it will be even less than half because you need to put some ground surface inside of beam to have significant return. In case of ambiguous clutter return when patches of clutter superimposed in range bins angle difference may be small(signal from several patches located at different angels for radar will look like signal from one bigger patch located at some average angle). Also, it’s hard to say what average angle of clutter will be in most DCS situations.

As I said the missile has such extrapolations, but there is a problem with updating data for extrapolation. It will be solved.

 

I did not say exactly that. There is no any problem with resolving range ambiguity for ordinary target. I was talking about extended target (about ground clutter in particular). Please see explanations above.

 

Be assured modern PD radars still have problems with beaming targets tracking and try to contend with this generally by inertial tracking(extrapolation) or LPRF using. If it’s the ESA radar there are several additional methods to contend with this issue.

BTW. Proposed method does not look as good improvement for fighter radars because they usually have narrow beam 3 deg circa. (so only 1.5 deg halfwidth…)

Yep, but we have lots of different high-priority tasks, so can’t promise such features soon. Will add to wishlist.

The issue here is that in MPRF when you feed the returns into the associated apparent range bins then feed that into the attached doppler bins a good portion of that clutter will fall into another doppler bin whereas the target will be in one range bin.  This will reduce the amount of energy that the target return has to compete against to whatever happens to fall into the same doppler bin.  The MLC is not all at the same doppler as the target and the larger the look angle and the larger the velocity of the missile the more that energy is distributed.  Were in STT not search as well, currently it seems that the notch is 100kts'ish hopefully you can give the exact number.  But In STT your tracking gates are going to be much much smaller then this.  Typical values I see referenced are 15m/s in total width.  And the missile should really only loose the tracking gate if the target is not competing with clutter.  But that would mean that you could get a lot closer to the central MLC return (especially at close range and for high RCS say being side on or given your belly to the target) without loosing track.  If not right on it if the noise is low such as in only very low look angles or low return clutter like calm seas.

Spoiler

image.png

Also we can't ignore factors like integration time and PDI for S/N.


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1 hour ago, KlarSnow said:

When are you going to add features that make missiles more effective, because right now it seems you have worked for years to make them exactly the same or less effective.

Someone could have left the game in 2019 and come back and found the EXACT same mechanics at play as they have been for the past twenty years. This makes me question what the point of all of this in depth modeling is if ED can't make a decision on changing any mechanics and are just modeling the same mechanics "more realistically".

What if that happens? I mean if we do all this for the AIM-120 and it operates the same, or maybe worse, but we feel it is more accurate and the work done will help all other missiles in the game for good/bad/or not. At the end of the day, we will take all we know about missiles, apply that and see where we end up, whose to say they are not accurate, I don't think saying because the are the same or worse (IF THAT IS WHERE THEY END UP... IF) than 3/5/10 years ago means they are less accurate. That is not a good bar to aim for, only make improvements to the modeling where it improves the performance of the missile.

This is a subject that is going to be very open to opinion, but not a lot of strong data to be able to say how accurate they truly are. These are Gray Subjects that are simply not going to have all the info needed to make them 1:1, no one should expect that out of a sim/game either. 

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2 hours ago, KlarSnow said:

Другая проблема заключается в том, что вы тратите все эти усилия на постоянное добавление функций, которые делают ракету такой же или даже хуже, чем она была раньше. 

Сейчас у нас так много фильтров, что каждая ракета должна пройти, чтобы добраться до цели. Случайные броски мякины, надрезы, поддержка радара, какие бы эффекты ни вызывали помехи, наконец, эффекты терминального блеска. И это все при условии, что вспомогательный радар не откусит ракету, запущенную вами или цель на пути, и полностью поразит собственный выстрел.

Когда вы собираетесь добавить функции, которые сделают ракеты более эффективными, потому что сейчас кажется, что вы работали годами, чтобы сделать их точно такими же или менее эффективными.

Кто-то мог покинуть игру в 2019 году, вернуться и обнаружить ТОЧНО ту же механику, что и последние двадцать лет. Это заставляет меня задаться вопросом, в чем смысл всего этого глубокого моделирования, если ED не может принять решение об изменении какой-либо механики и просто моделирует ту же механику «более реалистично».

 

Yes, we try to make it realistic. We do not have a goal to just stupidly increase efficiency.
Currently, AMRAAM missiles show an worldwide effectiveness in multiplayer at the level of 0.5 ... 0.6 hits per launch, approximately the same as the real combat score.

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22 minutes ago, Chizh said:

Yes, we try to make it realistic. We do not have a goal to just stupidly increase efficiency.
Currently, AMRAAM missiles show an worldwide effectiveness in multiplayer at the level of 0.5 ... 0.6 hits per launch, approximately the same as the real combat score.

And how much of that Pk is due to short range terminal notches or kinematically dragging and defeating the missile. You should be aware that these are two very different things. I sincerely doubt improving the missiles capabilities in this regard will change the Pk all that much. All it will do is remove the ability to completely negate missiles up until extreme short range. And move the gameplay into kinematic defeat and away from sensor defeat. Players will still kinematically defeat the missiles they will just pay for trying something as high risk as pushing inside where they can kinematically defeat it.


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1 hour ago, Chizh said:

Yes, we try to make it realistic. We do not have a goal to just stupidly increase efficiency.
Currently, AMRAAM missiles show an worldwide effectiveness in multiplayer at the level of 0.5 ... 0.6 hits per launch, approximately the same as the real combat score.

DCS does not heavily model ECM, mechanical reliability, or any additional number of factors that are likely to reduce PK of a real world missile but are not present in the DCS environment (unless you know exactly how the IRL missiles failed to reach their target and can precisely replicate that within the simulator, then that would be a fairer argument). 

In DCS the aircraft and weapons have been generally assumed to be on their best day without incorporating the above factors so assuming launch parameters and defensive techniques are comparable to IRL... DCS should see a marginally (debatable as to how much higher) higher PK. 

Lastly, there is the unknown standard of pilot training in DCS. Should we account for shots that were not in range in the PK when this is less likely of an occurrence IRL? 

I think without additional data and controlled parameters it is unwise to argue on that stance alone. 


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If we are pulling out the stat sheet what is the current effectiveness of the AMRAAM within it's NEZ in MP? It just doesn't seem like that stat sheet is an accurate way to assume something is correct.

40 minutes ago, Chizh said:

Yes, we try to make it realistic. We do not have a goal to just stupidly increase efficiency.
Currently, AMRAAM missiles show an worldwide effectiveness in multiplayer at the level of 0.5 ... 0.6 hits per launch, approximately the same as the real combat score.

 

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14 hours ago, Маэстро said:

 

That’s not quite true. First of all, angle difference limited by beamwidth. If you track a target seeker LOS is pointed at the target and difference limited by half of beamwidth. Practically it will be even less than half because you need to put some ground surface inside of beam to have significant return. In case of ambiguous clutter return when patches of clutter superimposed in range bins angle difference may be small(signal from several patches located at different angels for radar will look like signal from one bigger patch located at some average angle). Also, it’s hard to say what average angle of clutter will be in most DCS situations.

 

The radar has a monopulse seeker, it should be resolving the target and any return in angles, otherwise it would not be able to tell two targets in its field of view from each other. I don't know what kind of angle resolution you have it capable of but the target should not be competing with the entire field of view of clutter in front of it, just what is directly along its line of sight. It can see and measure the angles to all of the large clutter returns using the monopulse seeker so should be able to ignore it by simply not looking there unless the target begins to overlap it in clutter. Yes by your calculations the radar has a 15 degree beamwidth but once it has found the target, its effective beamwidth (what it is considering for tracking purposes) should be incredibly small.

Some very basic googling on monopulse multi target resolution is showing roughly 3 degrees, so even if that's a horrible estimate, once it has found the target, it can now disregard ( and should disregard) all returns that are outside of a very tight window around the target. Reducing the clutter that is directly competing with the target to just what is in that narrow field of regard.

if the seeker cannot resolve angular resolution then it would have zero capability to tell one aircraft from another if both are in the field of view, or which is closest to the cue the INS is providing when it goes active. Yes it is sorting by range and velocity, but it also should be able to sort by angles as well.

The Main lobe clutter is not going to be spread out evenly across the field of view of the seeker and if it can see where the target is via angles it can also see where the largest MLC returns are by angles and ignore them, reducing the total clutter that is competing with the target to just what is in the direct line of sight that it can resolve.


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Cleaned out a couple posts...

Guys lets keep the topic on track, everyone has an opinion of what missiles should look like, at the end of the day it will be Eagle Dynamics version of the AIM-120, we are always open to opinions and thoughts, but lets not go off the rails. Thanks.

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1 hour ago, Chizh said:

Yes, we try to make it realistic. We do not have a goal to just stupidly increase efficiency.
Currently, AMRAAM missiles show an worldwide effectiveness in multiplayer at the level of 0.5 ... 0.6 hits per launch, approximately the same as the real combat score.

Could we ask truthfully how important that stat really is?

AMRAAMs IRL are employed by trained pilots, much more familiar with the weapon and how to best employ it.
And in some cases constrained by the context of the operation.

Some shots could've been defensive flows to delay pursuit from enemy fighters.

The absolute myriad of different skill levels and shot context in DCS MP and SP should easily prove to ED this 'stat' is kind of worthless.


Should I spam out of parameter AMRAAM shots on the deck at mach .6 on MiG-31s in space at mach 2 at 66 miles until EDs stats finally fallw below the much vaunted .6 pk to have the AMRAAM fixed according to known documentation?

 

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The point Chizh has made is that our implementation on the AIM-120 is seeing stats similar to real life, that is another indication we are on the right track but not the only one. 

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4 minutes ago, BIGNEWY said:

The point Chizh has made is that our implementation on the AIM-120 is seeing stats similar to real life, that is another indication we are on the right track but not the only one. 

I'm sorry but his response was a deflection and has very little to do with what we have been discussing. Nowhere in this entire discussion was the total Pk of the Amraam in DCS brought up, nor is it really relevant. We have discussed the design philosophy and decisions that seem to be going into the new missile API and the frustrations that are inherent to the percieved modeling. We have also discussed specifics about how the seeker is being modeled and tried to determine what assumptions and possibilities could go into it. Nowhere in there was the missiles Pk or relation to the real world brought up. I'm sorry but that is obvious deflectionary tactics and is not addressing what we are discussing.


Edited by KlarSnow
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Dont derail this thread with talk of stats we will just close it down. 

Try to stay on topic

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No problem, 

I think we can all agree Маэстро post was a good one that shows the level of work that is being put into the AIM-120. The DCS AIM-120 will be the best we can make it with the information we have. As mentioned we will always welcome new information that does not break our 1.16 rule. 

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Forum rules - DCS Crashing? Try this first - Cleanup and Repair - Discord BIGNEWY#8703 - Youtube - Patch Status

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