Chaff and R27(E)R

[*Rage*]

A plane flying at 900km/h (M0.7) moves 250 metres away from the chaff it releases every second

[Santi871]

Awesome post :thumbup:

 

But I really doubt that this happens in the most cases I encounter that problem. Just make an example with light, just another electromagnetic wave, so the physic is the same.

 

If I point with a lasberpointer on a plane, how can an object a noteable distance away emit a stronger light in my direction, based on the reflection of the laserpointer? There might exist scenarios where this behaviour might occur, but I really doubt that this is not negligible. I try to do some calculations, just because it's a great example.

 

That's a different scenario really, a laser pointer is much sharper than a radar antenna, and anything from the ground to birds to clouds returns noise.

 

You shouldn't picture the radar beam like a beam but rather a diffuse cone with "spillage" to the sides, where chaff can get caught. This picture will help:

 

 

As you can see from that rough diagram, it's not perfect.

[ShuRugal]

to play devils advocate.. not that anyone here is the devil :)

 

Radar beams are not perfect. The advertised beam widths usually represent the majority of the the directional gain, but depending on the antenna type and frequency side lobes of various shapes and gains exist(on both transmit and receive).

 

The signal to noise ratios of the missile's receiver and the aircraft radar are likely not of similar values.

1. The seekers antenna is smaller then the radars antenna(less sensitivity / larger beam width)(hence the use of a powerful CW emission for target illumination)

 

2. There is likely less clutter rejection processes and filters on the missile then on the radar (due to power consumption, size restrictions, and costs associated with consumables).

 

While side-lobes are a factor to consider, at any range outside a few hundred meters (if the minimum AGL to operate radar is any indicator), side-lobe emissions are inconsequential in comparison to the main-lobe.

 

Points 1 and 2 both carry a degree of merit, but only when the chaff is illuminated. in WVR combat against a flanking bandit locked in STT, the chaff is simply not going to stay in the illumination cone long enough to be a factor, unless the target begins to release a continuous stream of chaff. As ///Rage points out, even at a relative sedate mach 0.7, the target will be outdistancing his chaff release by over 200 m/s

 

Another factor when considering the signal to noise ratio is the targets RCS. By design, Chaff is shaped and sized to match the target emissions wavelength so that it not only reflects RF energy, but re transmits the energy out in the form of a dipole antenna.

Because of this, the RCS of a small cloud of chaff is significantly greater than that of and aircraft (whose return is mostly that from the optical reflectivity of the air frame and not so much a matched resonating frequency)

 

Assuming that the resonant-dipole behavior you describe is correct (I'm not fully prepared to believe that it is, but feel free to show me your source if I'm wrong), this may not be as useful as you might expect. The chaff cannot radiate/reflect more energy than what strikes it from the radar. If the chaff is perfectly tuned to collect and re-transmit the radar energy as a dipole antenna, it will be doing so in a nearly spherical pattern. While this spreads the energy out to make it visible evenly from all directions, it reduces gain on the reflection to zero. This would result in the reflected energy being much more diffuse than the energy input to the chaff.

 

Now, whether that is significant when compared against the total area/volume over which the chaff is absorbing and returning radar energy, I cannot say.

 

 

 

That being said, a cloud of chaff outside the radar's illumination cone will still be illuminated to a certain degree (sure, much less then inside the cone). But the RCS of the chaff is greater than that of the target aircraft, so conversely more energy may be seen off the beams axis depending on the angle and range between these objects in space.

Unless the chaff burst is within a few hundred meters of the radar, side lobe illumination would be negligible. Dipole resonator or not, the chaff cannot return more energy than it receives.

 

 

The aircraft's radar may not be effected during this process(even if the missile is), because it's superior signal to noise ratio, smaller beam width, robust clutter rejection techniques, (Doppler filters, side lobe suppression, etc.)

Side lobe suppression applies to the transmitting end: the goal is to reduce undirected emissions so as to avoid detection by hostile E-War equipment not being directly illuminated. Smaller beam width also works in favor of the missile, as the launching/directing aircraft focuses much greater energy onto the target than any spillage which might be picked up by chaff. Clutter rejection and signal:noise ratio really only comes into play for the radar tracking side of the house. A SARH missile is fairly dumb, it will go for the brightest radar return it can see. The bottom line is, if it's not in the primary focused zone of the radar beam, the missile won't be able to see it, because that beam is (at a conservative estimate) an order of magnitude brighter than any of the side-lobes.
Edited November 15, 2015 by ShuRugal

[GGTharos]

Then I commend you for starting with the good stuff :)

 

As for the beam illumination width:

 

The radar beam (what we call x degrees) is mathematically defined to be the half power point (IIRC about 0.72 power). Chaff itself is cut/made to resonate at the frequencies of the typical attacking radars, so even if it's out of the main beam it can produce a very powerful reflection.

 

IIRC creating a 50m^2 RCS isn't that difficult with chaff (and it is also about the limit of chaff usefulness for track-breaking. This is probably part of why very large aircraft don't carry chaff).

 

 

Regarding your question: This is a long-time behavior in this sim, and while the result isn't necessarily incorrect (the missile misses), the details of how the result is presented may well be.

 

As for actual effectiveness, I'll just say again that the code is rolling dice, with some modifications for the probability of the missile being seduced by chaff. Some of the factors are:

 

Aspect

Ground clutter

Number of chaff bundles

 

It is always possible to make the simulation more complex, but it is not necessarily easy to design a complex RF guidance simulation that is also more realistic than the simple one.

 

I'd like to see more complex handling, but for now we make do with what we have.

 

If you read my original post, you will see that I use dtic.MIL as a source.

 

And yes, the end result is the same, I completly agree with you, the missle will very likely miss the aircraft and I'm surprised about the effectivness of chaff in that regard. But if you read my original post, that is not my problem.

[GGTharos]

Assuming that the resonant-dipole behavior you describe is correct (I'm not fully prepared to believe that it is, but feel free to show me your source if I'm wrong), this may not be as useful as you might expect. The chaff cannot radiate/reflect more energy than what strikes it from the radar. If the chaff is perfectly tuned to collect and re-transmit the radar energy as a dipole antenna, it will be doing so in a nearly spherical pattern. While this spreads the energy out to make it visible evenly from all directions, it reduces gain on the reflection to zero. This would result in the reflected energy being much more diffuse than the energy input to the chaff.

 

Break out your radar/RF bible and read all about it. Chaff RCS can and will exceed that of the mothership easily in the main beam, and it'll be a while before it drops off.

 

Unless the chaff burst is within a few hundred meters of the radar, side lobe illumination would be negligible. Dipole resonator or not, the chaff cannot return more energy than it receives.

 

But it can return more energy than the actual target ;)

 

 

A SARH missile is fairly dumb, it will go for the brightest radar return it can see.

 

Then what DCS is doing now with SARH would be totally realistic, aside from the far-away chaff.

 

The bottom line is, if it's not in the primary focused zone of the radar beam, the missile won't be able to see it, because that beam is (at a conservative estimate) an order of magnitude brighter than any of the side-lobes.

 

Don't need the side-lobes. The size of the beam itself is mathematically defined, but illumination by this beam exists well outside of that number.

 

Now, seeing chaff 1km away laterally at a 10km shooting distance is pretty iffy, and this is pretty old behavior of this game. That should tell you something about the in-code relationship of target, countermeasures and illumination.

[apocom]

Regarding your question: This is a long-time behavior in this sim, and while the result isn't necessarily incorrect (the missile misses), the details of how the result is presented may well be.

 

It's important to know why a missile misses, so I can find away around this.

 

If my missiles just show a complete unrealistic behaviour, I have problems to use them. And it's not only unrealistic, it just makes no sense (Problem: far away chaff)

 

On a side note: I've read other sources and it seems to be possible that old radars (not lookdown/shootdown capable radars) can actually lock on a chaff. I've stated this different. And no, my missile will not chase this chaff if I illuminate a target kilometers away.

[Santi871]

It's important to know why a missile misses, so I can find away around this.

 

If my missiles just show a complete unrealistic behaviour, I have problems to use them. And it's not only unrealistic, it just makes no sense (Problem: far away chaff)

 

On a side note: I've read other sources and it seems to be possible that old radars (not lookdown/shootdown capable radars) can actually lock on a chaff. I've stated this different. And no, my missile will not chase this chaff if I illuminate a target kilometers away.

 

He did say the factors that affect whether it'll miss.

[apocom]

He did say the factors that affect whether it'll miss.

 

You mean this?

 

Aspect

Ground clutter

Number of chaff bundles

 

Aspect? So my target is on a 3-9 line. It moves away from its chaff the fastest way possible relative to my postion. It's impossible that he will generate a higher angle for me.

 

Ground clutter? 5000m above the sea?

 

Number of chaff bundles? Thats why my R27 starts chasing the very first chaff?

 

 

Of course that are reasons, but all the stuff seems not to be implemented.

 

 

EDIT:

We are talking a lot about side effects (groud clutter, the radar beam is diffuse etc.) but the main effects of chaff are not implemented, mainly that the attackers radar will loose the target and is uable to track or find it anywhere near a chaff cloud.

Edited November 16, 2015 by apocom

[*Rage*]

And the way its modeled in game leaves it open to exploitation in a way that im assuming the devs did not intend to simulate.

[red_coreSix]

And the way its modeled in game leaves it open to exploitation in a way that im assuming the devs did not intend to simulate.

 

True, I've seen players somehow putting out 20 or more chaffs per second instantly trashing any radar missile launched at them.

[Falcon_S]

Perhaps an interesting source: http://www.dtic.mil/dtic/tr/fulltext/u2/a164106.pdf

[Ragnarok]

True, I've seen players somehow putting out 20 or more chaffs per second instantly trashing any radar missile launched at them.

 

Like me. 40/s :lol:

 

It's important to know why a missile misses, so I can find away around this.

 

If my missiles just show a complete unrealistic behaviour, I have problems to use them. And it's not only unrealistic, it just makes no sense (Problem: far away chaff)

 

 

For you of me. (Chaff logic - ZIP). But I prefer the official version, even if it was bad and illogical

 

http://forums.eagle.ru/showthread.php?t=152429

example.rar

Edited November 16, 2015 by Ragnarok

[Tello]

Do we know ED's sources on the matter ? What are they aiming for - surely it must be realism, regardless if it is "just" FC3 the sandbox/world that we all fly in should have proper working mechanics so we all can enjoy the best realistic experience. I do not care if that means if missile A or B don't stand a chance vs one another. As long as it is implemented correctly with out bugs or anything like that.

 

Then we have something to point at, or aim for (^^) every time these posts are popping up on the forum.

 

Or do we have to wait for F/A-18 release before we can have a guarantee that weapon systems are not "FC3" :) either it is game mechanics or it is the formulation(simulation?) that need to be adjusted :)

[ShuRugal]

Break out your radar/RF bible and read all about it. Chaff RCS can and will exceed that of the mothership easily in the main beam, and it'll be a while before it drops off.

 

Have just done some skim-reading, and it does seem that the dipole behavior makes the most sense after all for providing an efficient reflector. I suppose that the energy a non-dipole fails to reflect (or even absorb) is so much greater than what is lost due to being a zero-gain radiator that it does make sense in hindsight.

 

 

 

But it can return more energy than the actual target ;)

 

 

Then what DCS is doing now with SARH would be totally realistic, aside from the far-away chaff.

 

 

Don't need the side-lobes. The size of the beam itself is mathematically defined, but illumination by this beam exists well outside of that number.

 

So, i guess the real question for solving this problem is going to be what does the actual radiation pattern of your typical fighter radar set look like? How sharply does the intensity drop off from the center of the main lobe?

 

 

Now, seeing chaff 1km away laterally at a 10km shooting distance is pretty iffy, and this is pretty old behavior of this game. That should tell you something about the in-code relationship of target, countermeasures and illumination.

 

So, it is a known issue, it just hasn't been touched since LOMAC because it wasn't a significant problem before we started getting fancy with missile flight models?

 

As for actual effectiveness, I'll just say again that the code is rolling dice, with some modifications for the probability of the missile being seduced by chaff. Some of the factors are:

 

Aspect

Ground clutter

Number of chaff bundles

 

It is always possible to make the simulation more complex, but it is not necessarily easy to design a complex RF guidance simulation that is also more realistic than the simple one.

 

So, it sounds like a good intermediate solution (since ED presumably won't have time in the near future to draft a full-blown radar simulator, not to mention the damage running it would do to my wallet in terms of hardware upgrades) would be to add one more variable to that equation: angle of offset between the chaff bundle and the locked target. If this variable was applied to the chaff "seduction factor" after all the rest, it would solve the problem of close-range shots going right instead of left, while leaving medium to long range shots relative unaffected.

[GGTharos]

Aspect? So my target is on a 3-9 line. It moves away from its chaff the fastest way possible relative to my postion. It's impossible that he will generate a higher angle for me.

 

It's also the worst possible scenario for the offending radar and missile.

 

Of course that are reasons, but all the stuff seems not to be implemented.

 

It's implemented.

 

We are talking a lot about side effects (groud clutter, the radar beam is diffuse etc.) but the main effects of chaff are not implemented, mainly that the attackers radar will loose the target and is uable to track or find it anywhere near a chaff cloud.

 

The results are implemented and that's what matters: The missile misses. Maybe one day we'll get track-breaking for your radar in the cockpit, who knows.

[apocom]

It's also the worst possible scenario for the offending radar and missile.

 

Care to explain? Like I said it's the best way to make sure the enemy radar can pick you up again.

 

 

It's implemented.

 

Any source for this? The main effects that chaff has are not implemented, but GC? Besides everytime I'm reading something about unrealistic behaviour it's groundclutter.

 

 

The results are implemented and that's what matters: The missile misses. Maybe one day we'll get track-breaking for your radar in the cockpit, who knows.

 

So by this logic it would be ok that if the enemy chaffs, my missile will start to go 90° up into the sky, because the result is the same. I miss.

[Ironhand]

Care to explain? Like I said it's the best way to make sure the enemy radar can pick you up again.

Not if you're notching him. :)

[Capn kamikaze]

Of course it's a decoy, it's just not an active one like a flare is, a flare emits IR, but chaff needs to be illuminated by a radar to produce a return, and that return gives the seeker a second target to guide to, whether that is an active or SARH seeker, the effect is the same, a second target appears to it.

 

Considering chaff will consist of thousands of little strips of metal, then its RCS will be huge, so as far as a radar is concerned that will give a stronger return, and the missile if it's not too smart, ie it doesn't ignore the slower returns, afterall the chaff will slow down a lot more than the aircraft that ejected it, then it is likely to track to that.

[Capn kamikaze]

So by this logic it would be ok that if the enemy chaffs, my missile will start to go 90° up into the sky, because the result is the same. I miss.

 

Theoretically if the missile goes completely unguided, ie ballistic, then if the last command to the control surfaces is held then yes it could do that.

[blkspade]

Something I know would be a long way off for any desktop sim but could be interesting to have, would be real time ray tracing, but for Radar. Documents can be found going back to at least 1996 about its use for radar simulations. This would probably the best and most realistic way to handle modeling of radar and effects of chaff.

[Capn kamikaze]

It's not a long time off, I'm nearly certain that Janes F/A-18 had that.

[blkspade]

It's not a long time off' date=' I'm nearly certain that Janes F/A-18 had that.[/quote']

 

LOL, the computational resources needed to do it, make it highly unlikely to have been done in a Janes sim. Particularly since not only was MT/MC not much of a thing at the consumer level, nor was GPGPU compute which would do this 1000x times better than CPU.

[Capn kamikaze]

Depends on the fidelity they went to.

[Capn kamikaze]

SPIKE14 mentions it here...

 

http://www.combatsim.com/cgi-bin/ubbcgi/ultimatebb.cgi?ubb=get_topic&f=31&t=004080

[blkspade]

SPIKE14 mentions it here...

 

http://www.combatsim.com/cgi-bin/ubbcgi/ultimatebb.cgi?ubb=get_topic&f=31&t=004080

 

Who is this Spike14 in relation to the sim? I haven't come across anything official to indicate ray tracing was in fact used in real time for the Radar model. Considering 1999 hardware, I'd be amazed if that was the case. Even more so in how no other sim since has done such it seems. I could imagine maybe a model built from ray traced data. Wags was apparently involved with the Janes F-18 development in some capacity.