Chaff and R27(E)R

[apocom]

Ok, I think here are numerous bugs or implementation problems.

 

1. Chaff is not like flare

You can't simply say flare is an IR and chaff a radar decoy. Flare is an IR decoy, but chaff is not a radar decoy.

There are so many sources how chaff works, here is an example: http://www.dtic.mil/dtic/tr/fulltext/u2/a135928.pdf

 

Basicly:

Chaff consists of many small particles that should reflect as much energy back to the radar as possible. What happens, is that the radar can no longer track the target, because the energy reflected back by the target is too small in comparision, and can't be distinguished from the chaff cloud.

 

Therefore the radar looses lock of the target (not implemented in DCS or bug).

 

2. SARH missiles are just following the radar

As long as the missile "sees" the illuminated target, it follows it.

https://web.archive.org/web/20070109230625/http://www.army.mod.uk/linkedfiles/royalartillery/units/royal_school_of_artillery/bst_handout_f02.pdf

 

http://www.ausairpower.net/TE-Radar-AAMs.html

 

So, in order to hit a target, the missiles sensor has to lock on onto the radar beam reflected by the target. Two conditions must be fullfilled, the target must be illuminated and the sensor has to be able to see the target. So if a SARH can't see the illumination anymore, it goes ballistic.

 

In conclusion, chaff is not only very effective against the missile itself, but also against the hostile fighters radar.

 

3. SU27 IRL features

To overcome the problems with chaff the russians have at least two ways to increase the missiles hit chance."(I dont understand russian and I hope I've copied the correct parts ;))

 

a) "расчет условий пуска ракет, формирование и выдачу разовых команд в СУО-27Э2, а также подсвет атакуемой цели и передачу команд управления на пущенную ракету в РГС по линии радиокоррекции;"

 

So a link to the missile for controlling it

 

b) "выдачу угловых координат визуально видимой цели в РЛПК и в управляемые ракеты с ТГС при прицеливании с помощью кнюпеля в режиме ОПТ и от НСЦ в режиме ШЛЕМ;

 

So giving the radar the IRST target information. So, as long as IRST has a stable lock, the radar illuminates the target and the missile is homing it. Because IRST is immune to chaff, the whole process makes the missile more or less (proximity fuse may cause problems) immune to chaff.

 

Source: САМОЛЕТ СУ-27СК РУКОВОДСТВО ПО ЛЕТНОЙ ЭКСПЛУАТАЦИИ Книга 1

 

 

4. BUG

 

So, but what happens really often, is that my missiles are chasing chaff. This cannot happen because chaff is not a decoy, but by no means it is possible that 2 missiles are chasing 2 different chaff-decoys. My radar can only lock 1 thing.

 

Ok, I'm rewatching some of my tacview files because I wanted to add some screenshots, but there is so much unlogic behaviour, that I don't think a screenshot can transport all the problems.

 

5. Conclusion

Overall I think that chaff is implemented like flare, as a decoy, and that my passive missiles behave, like they have an active radar that locks on chaff.

 

EDIT: Some spelling, shouln't make such topics that late.

Edited November 15, 2015 by apocom

[Ragnarok]

You want to say, if I do fire 4 missiles, you throw chaff, can not happen that the two go to the bait and two on target? Or all of the bait or all of the target?

[Sweep]

a) "расчет условий пуска ракет, формирование и выдачу разовых команд в СУО-27Э2, а также подсвет атакуемой цели и передачу команд управления на пущенную ракету в РГС по линии радиокоррекции;"

 

So a link to the missile for controlling it I -think- thats the M-link, used for midcourse guidance (assumption here -->) until the seeker is within range (\end assumptions) (Sparrow does that AFAIK, so why wouldn't R-27?)

 

b) "выдачу угловых координат визуально видимой цели в РЛПК и в управляемые ракеты с ТГС при прицеливании с помощью кнюпеля в режиме ОПТ и от НСЦ в режиме ШЛЕМ;

 

So giving the radar the IRST target information. So, as long as IRST has a stable lock, the radar illuminates the target and the missile is homing it. Because IRST is immune to chaff, the whole process makes the missile more or less (proximity fuse may cause problems) immune to chaff.

 

I'd like to know more about this, I think the launching fighter's angle off tail comes into play here, if you're near-rear aspect the missile might see chaff, and if you're side aspect the radar/missile might not.

 

What I'd really love to know is if the radar actually tracks the target in this mode, or is it more of a F-15 Flood mode setup where the energy is emitted (in this case down the bearing and elevation of the target)without the radar locking/tracking anything

 

 

Replying in the quoted text in Red. Interesting ideas there...

[Santi871]

So, but what happens really often, is that my missiles are chasing chaff. This cannot happen because chaff is not a decoy, but by no means it is possible that 2 missiles are chasing 2 different chaff-decoys. My radar can only lock 1 thing.

 

I think you have a misconception on what "locking" means. "Locking" simply means the host radar focuses its energy on a target. Depending on the width of the beam and the aspect, it may be able to illuminate two different sets of chaff. SARH missiles are simply guiding off the return of the radar (without counting datalink), and since they are sensitive, its possible they see chaff as the target.

 

I'm not saying you're wrong, though.

[apocom]

Thanks for the replies. I'm aware that I might be mistaken, thats why I try to use as many sources as possible to support my points. If anybody find something different, plz let me know.

 

You want to say, if I do fire 4 missiles, you throw chaff, can not happen that the two go to the bait and two on target? Or all of the bait or all of the target?

 

The first thing I say is, that it's not even possible to be baited by chaff, because that's not how it works. But even if someone would think so, it's not possbile to be having different targets.

 

Replying in the quoted text in Red. Interesting ideas there...

 

The russians have a lot of interesting ideas how to hit with their missiles. Unfortunatly none of them seems to be implemented in this game.

But to answer your second part, the way I understand this, is that the radar is slaved to the IRST, so it illuminates simply the target the IRST is locking.

 

I think you have a misconception on what "locking" means. "Locking" simply means the host radar focuses its energy on a target. Depending on the width of the beam and the aspect, it may be able to illuminate two different sets of chaff. SARH missiles are simply guiding off the return of the radar (without counting datalink), and since they are sensitive, its possible they see chaff as the target.

I'm not saying you're wrong, though.

 

Yeah, but my point is, that chaff is not a target like flare. Just assume it would work like that. Every radar with simple logic could identify the real target (its the fastest object and its always the first object along the moving vector). The next problem is, that the distance to the aircraft is fast too huge for getting cought in the radar beam.

 

I added a picture to show that point. Look how far away the target is from the chaff. My radar will not illuminate it, so it is invisible for my missiles. But for some reason they chase it. The fourth missile however, kills the target. I can't see any logic in this behaviour.

Edited November 15, 2015 by apocom

[Tello]

So would that mean that the bug lies in the HUD symbolic ? It sounds to me then, that when the radar picks up the chaff then the HUD/radar would as well show/follow that you have locked on to a new source ? i'm just trying to understand basic stuff here. :helpsmilie:

 

 

I think you have a misconception on what "locking" means. "Locking" simply means the host radar focuses its energy on a target. Depending on the width of the beam and the aspect, it may be able to illuminate two different sets of chaff. SARH missiles are simply guiding off the return of the radar (without counting datalink), and since they are sensitive, its possible they see chaff as the target.

 

I'm not saying you're wrong, though.

[*Rage*]

The way it works in DCS now is that the chaff act as flares do. Enough of them within the seekers FOV will tip the guidance equation into a 'miss-track' and the missile will guide to the first chaff it sees regardless if radar lock is maintained on the target or not. Infact the chaff it miss-tracks to is often way outside the radar beam since its relatively stationary on release so far behind the target aircraft.

[apocom]

So would that mean that the bug lies in the HUD symbolic ? It sounds to me then, that when the radar picks up the chaff then the HUD/radar would as well show/follow that you have locked on to a new source ? i'm just trying to understand basic stuff here. :helpsmilie:

 

No, the radar does not pick up the chaff. I say it again, its not a decoy.

 

Your radar will also not pick up a mountain, even if the mountain will interfere with your radar. Chaff blinds your radar so you can't have a lock on the target anymore. It's a little bit like a target flying behind a mountain (this example is not really true, because your radar will still reach your target, but you can't distinguish the reflected waves. Basicly your target is invisible for your radar, like behind a mountain).

 

EDIT:

The way it works in DCS now is that the chaff act as flares do. Enough of them within the seekers FOV will tip the guidance equation into a 'miss-track' and the missile will guide to the first chaff it sees regardless if radar lock is maintained on the target or not. Infact the chaff it miss-tracks to is often way outside the radar beam since its relatively stationary on release so far behind the target aircraft.

 

Like I said, I have the feeling that chaff is implemented like flare, and the R27(E)R like they have an active seeker that chases it.

Edited November 15, 2015 by apocom

[Tello]

Thank you! And what a great explanation.

 

Have a nice day o7

 

 

No, the radar does not pick up the chaff. I say it again, its not a decoy.

 

Your radar will also not pick up a mountain, even if the mountain will interfere with your radar. Chaff blinds your radar so you can't have a lock on the target anymore. It's a little bit like a target flying behind a mountain (this example is not really true, because your radar will still reach your target, but you can't distinguish the reflected waves. Basicly your target is invisible for your radar, like behind a mountain).

 

EDIT:

 

 

Like I said, I have the feeling that chaff is implemented like flare, and the R27(E)R like they have an active seeker that chases it.

[GGTharos]

The way it works in DCS now is a probabilistic process, which is how it is modeled in literature. Regardless of implementation details being either too simple or incorrect, the model is essentially what real air forces used to use for a chaff model.

 

And yes, chaff is a target like a flare as far as the sensor is concerned.

[*Rage*]

The way it works in DCS now is a probabilistic process, which is how it is modeled in literature. Regardless of implementation details being either too simple or incorrect, the model is essentially what real air forces used to use for a chaff model.

 

Thats not to say its modelled wrong (or the numbers in the equation are wrong). 100% effective chaff regardless of radar lock in a look up situation?

 

And yes, chaff is a target like a flare as far as the sensor is concerned.

Right now chaff works as a target for the missile not the sensor which is much more easily spoofed than the radar in the sim. Its still wrong.
Edited November 15, 2015 by ///Rage

[Ragnarok]

The first thing I say is, that it's not even possible to be baited by chaff, because that's not how it works. But even if someone would think so, it's not possbile to be having different targets.

 

See the picture. If is target and chaff in fighters strobe and chaff only in field of view, SARH go to chaff. Four missiles have different angles field of view in relation to a real target. You're wrong.

 

The question is, as a seeker of SARH gives priority chaff, especially if there is a secondary radio channel. What is important, is not a reflection from chaff, than dopler puls element. At the time of ejection, chaff always has the same direction (3-9 position like target), and lower Doppler effect because it lags in speed. What confuses me is bad encodedness in DCS when it comes to frequency ejection. If you throw 50 chaff per sec. it is better than 2-3 per sec. Vector between separate fixation points must exist. In reality, if you go chaff has consistently much, it can make the target even more visible. In DCS, spam with chaff pays off.

[GGTharos]

Spam with chaff pays off in RL too, up to a point - again, according to literature.

 

In any case, the game models a probabilistic process, it doesn't worry about vectors in general, though it does take target aspect, look up/down into effect.

[Ragnarok]

On "look up" condition, there must be rapidly progressive speed reduction, like hot aspect + chaff + 3-9 position, barrel roll (speed reduction). With large distance between attacker and bandit + small distance between SARH and bandit like on the picture, exist condition.

Edited November 15, 2015 by Ragnarok

[apocom]

And yes, chaff is a target like a flare as far as the sensor is concerned.

 

Could you plz provide a source for that, because I can't find anything that chaff acts like flare in A2A combat.

 

There exist chaff systems that acts like that, for example intercontinental missiles can release baloons that act as additional targets.

 

See the picture. If is target and chaff in fighters strobe and chaff only in field of view, SARH go to chaff. Four missiles have different angles field of view in relation to a real target. You're wrong.

 

 

Of course the missiles a differente FOV, but they can't see the chaff if the chaff is not illuminated by my radar. Either I illuminate a target in their FOV or not.

[Ragnarok]

Of course the missiles a differente FOV, but they can't see the chaff if the chaff is not illuminated by my radar. Either I illuminate a target in their FOV or not.

Dude, your radar illuminates both, and target and chaff. If is distance large, of course. This is not point illuminates. you understand? Look picture!

[GGTharos]

Any military literature treats it as such. I don't have time to go looking up specific sources for you. You can try dtic.MIL if it is accessible from your location. There are other sources but they are in journals that you have to pay money for.

 

While the specific mechanisms of how chaff can decoy a missile math be different from that of a flare, the end result is the same: an increase in miss distance.

 

Could you plz provide a source for that, because I can't find anything that chaff acts like flare in A2A combat.

 

There exist chaff systems that acts like that, for example intercontinental missiles can release baloons that act as additional targets.

[apocom]

Dude, your radar illuminates both, and target and chaff. If is distance large, of course. This is not point illuminates. you understand? Look picture!

 

This depends on the distance between chaff and target. If you look at my picture there is a really big distance inbetween. And the illuminated area is not that big, because it is impossible for the missile to distinguish targets in that area.

 

Any military literature treats it as such. I don't have time to go looking up specific sources for you. You can try dtic.MIL if it is accessible from your location. There are other sources but they are in journals that you have to pay money for.

 

While the specific mechanisms of how chaff can decoy a missile math be different from that of a flare, the end result is the same: an increase in miss distance.

 

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.

[Ragnarok]

This depends on the distance between chaff and target. If you look at my picture there is a really big distance inbetween. And the illuminated area is not that big, because it is impossible for the missile to distinguish targets in that area.

 

I did not see that ED plans to swear by currently in behavior. It will be good. No one wishes to convert the simulator in "chaff combat", or that chaff there is no function.

[Santi871]

Could you plz provide a source for that, because I can't find anything that chaff acts like flare in A2A combat.

 

There exist chaff systems that acts like that, for example intercontinental missiles can release baloons that act as additional targets.

 

 

 

Of course the missiles a differente FOV, but they can't see the chaff if the chaff is not illuminated by my radar. Either I illuminate a target in their FOV or not.

 

Depending on how strongly the chaff produces clutter, the missile can "think" it is the target.

 

The difference between chaff and a mountain is that chaff returns noise in a very small concentrated spot, whereas a mountain will return noise in a much wider area. Depending on processing techniques, the missile's avionics might determine that a small concentrated spot of noise = target. Remember that we have old radars in DCS, even in FC3 planes, nowadays radars are much more advanced.

Edited November 15, 2015 by Santi871

[apocom]

I did not see that ED plans to swear by currently in behavior. It will be good. No one wishes to convert the simulator in "chaff combat", or that chaff there is no function.

 

I agree, but this is not my point.

 

Depending on how strongly the chaff produces clutter, the missile can "think" it is the target.

 

The difference between chaff and a mountain is that chaff returns noise in a very small concentrated spot, whereas a mountain will return noise in a much wider area. Depending on processing techniques, the missile's avionics might determine that a small concentrated spot of noise = target. Remember that we have old radars in DCS, even in FC3 planes, nowadays radars are much more advanced.

 

Of course there is a difference between a mountain and chaff. I've never stated otherwise.

 

Ok, here is another great document, that also explains the math behind the chaffs radar cross section

http://www.dtic.mil/dtic/tr/fulltext/u2/a133967.pdf

 

I seriously don't know what to add. That's simply how it works, and again, for me the whole thing how the missile behave in DCS makes no sense.

[ShuRugal]

And yes, chaff is a target like a flare as far as the sensor is concerned.

 

But only if the chaff is illuminated by the radar. If you look at the picture Apocom posted on the first page of the thread, you can see a scenario from Tacview where the F-15 and its chaff were so far apart (relative to how close the Su-27 was) that the radar on the flanker was looking to its right to see the F-15, but the chaff was to the left side of the flanker. Nevertheless, his first three missiles took off after the chaff. This is, clearly, impossible behavior: That chaff burst was no longer within the radar illumination cone, and would therefore be completely invisible to the chaff.

 

Dude, your radar illuminates both, and target and chaff. If is distance large, of course. This is not point illuminates. you understand? Look picture!

 

While this is true as you said, at long ranges, when fighting a WVR engagement, a flanking target won't stay close to its chaff long enough for the radar to keep the chaff illuminated.

[Teknetinium]

But only if the chaff is illuminated by the radar. If you look at the picture Apocom posted on the first page of the thread, you can see a scenario from Tacview where the F-15 and its chaff were so far apart (relative to how close the Su-27 was) that the radar on the flanker was looking to its right to see the F-15, but the chaff was to the left side of the flanker. Nevertheless, his first three missiles took off after the chaff. This is, clearly, impossible behavior: That chaff burst was no longer within the radar illumination cone, and would therefore be completely invisible to the chaff.

 

 

 

While this is true as you said, at long ranges, when fighting a WVR engagement, a flanking target won't stay close to its chaff long enough for the radar to keep the chaff illuminated.

 

Lets hope ED gets it sorted as soon as possible since this is getting exploited big time in MP, SARH missiles are not a threat at all.

Edited November 15, 2015 by Teknetinium

[Beamscanner]

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).

 

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)

 

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.

 

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.)

[apocom]

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).

 

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)

 

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.

 

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.)

 

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.

Edited November 15, 2015 by apocom