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Old 05-09-2018, 04:43 PM   #1
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Default R27R and how it works

So how the R27R works is pretty simple in explanation, but something still confuses me.
Namely, semi-active radar guided, which is explained as "guided by launcher's radar" to the target. So what I have seen many times in the simulator, is what made me question how does it really work.
In the simulator, after the R27R is launched, it then flies to the target, but if the target dispenses chaffs and flanks avoid the missile, then the missile gives up prior to flying past the target and flies straight. (It doesn't fly straight from the start, it does try to intercept the target). If it is guided by the radar, then the radar should also be tricked by the chaffs and the maneuver and it should brake the lock. The question is - If the missiles is guided by the radar, how comes it gets lured by chaffs while the radar still keeps the target locked?

That's if it works like this. I would like to know how exactly to these SARH missiles work and communicate with the launcher's radar.
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Old 05-09-2018, 05:05 PM   #2
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Originally Posted by FistofZen View Post
So how the R27R works is pretty simple in explanation, but something still confuses me.
Namely, semi-active radar guided, which is explained as "guided by launcher's radar" to the target. So what I have seen many times in the simulator, is what made me question how does it really work.
In the simulator, after the R27R is launched, it then flies to the target, but if the target dispenses chaffs and flanks avoid the missile, then the missile gives up prior to flying past the target and flies straight. (It doesn't fly straight from the start, it does try to intercept the target). If it is guided by the radar, then the radar should also be tricked by the chaffs and the maneuver and it should brake the lock. The question is - If the missiles is guided by the radar, how comes it gets lured by chaffs while the radar still keeps the target locked?

That's if it works like this. I would like to know how exactly to these SARH missiles work and communicate with the launcher's radar.
The R-27R has an inertial navigation system(INS) with radio-correction(datalink) for the initial stage of flight and semi-active radar homing(SARH) for terminal stage.

At initial stage of flight the missile is steered towards the target by its onboard INS, which receives target updates from the launching radar(aircraft) via datalink. At this point the missile itself cannot be fooled by chaff, as its seeker is not yet within range of the target.

At terminal stage the missile's onboard seeker acquires the target by picking up the target returns of the radar energy emitted by the aircraft radar....if these are reflecting off chaff, the missile seeker might get decoyed.
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Old 05-09-2018, 05:28 PM   #3
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Yes the launchers radar should actually be picking up on the chaff, but this is not modeled in DCS. There is hud footage on youtube somewhere of a mock dogfight that shows the radar tracking being spoofed the chaff of his target. Its been explained that in game each countermeasure release basically initiates a "dice roll" that effects probability of the missile being spoofed.
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Old 05-09-2018, 09:29 PM   #4
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At terminal stage the missile's onboard seeker acquires the target by picking up the target returns of the radar energy emitted by the aircraft radar....if these are reflecting off chaff, the missile seeker might get decoyed.
What do you mean by "missile's onboard seeker acquires the target by picking up the target returns of the radar energy emitted by the aircraft radar"?
So, the R27R is picking up the energy emitted by the Su27 which is then reflected by the target?
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Old 05-09-2018, 09:40 PM   #5
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What do you mean by "missile's onboard seeker acquires the target by picking up the target returns of the radar energy emitted by the aircraft radar"?
So, the R27R is picking up the energy emitted by the Su27 which is then reflected by the target?
Yes. This is how all semi-active radar homing (SARH) missiles work, so in terms of DCS, the R-27R /ER, the AIM-7 and Magic 530 (?) on the M-2000.
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Old 05-09-2018, 11:40 PM   #6
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Thank you guys.
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Old 05-10-2018, 01:46 PM   #7
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What do you mean by "missile's onboard seeker acquires the target by picking up the target returns of the radar energy emitted by the aircraft radar"?
Heh yeah that was a rather clumsy sentence on my part

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So, the R27R is picking up the energy emitted by the Su27 which is then reflected by the target?
The aircraft radar "illuminates" the target and the returns of this are picked up by the missile seeker, which in turn processes these, generates its own target coordinates and feeds the INS.

At this point they(own target coordinates) override the "ready-made" ones transmitted directly from aircraft radar to missile INS via datalink.
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Old 05-10-2018, 04:10 PM   #8
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The question is - If the missiles is guided by the radar, how comes it gets lured by chaffs while the radar still keeps the target locked?

r.
it shouldn't get lured, at least not as they currently are.

the missiles heads to where the radar is illuminating, but because DCS radar are quite simplified about their interaction with ECM / Chaffs, the SARH missiles currently behave like all aspect IR guided missiles which require a radar lock on ( but doesn't guide on it ), while the radar never get lured by chaff.
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Old 05-13-2018, 02:49 PM   #9
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it shouldn't get lured, at least not as they currently are.

the missiles heads to where the radar is illuminating, but because DCS radar are quite simplified about their interaction with ECM / Chaffs, the SARH missiles currently behave like all aspect IR guided missiles which require a radar lock on ( but doesn't guide on it ), while the radar never get lured by chaff.
So the simulation is not accurate at all. Yeah, if the radar is tracking a plane and illuminating only it, then how is the SARH supposed to see chaff if chaff isn't illuminated....dang it, thats why R27R's suck.
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Old 05-13-2018, 03:35 PM   #10
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So the simulation is not accurate at all. Yeah, if the radar is tracking a plane and illuminating only it, then how is the SARH supposed to see chaff if chaff isn't illuminated....dang it, thats why R27R's suck.
The radar will be illuminating the chaff as well as the target airplane. The radar illuminates a volume more or less centered on the target, and unless the plane has moved a significant distance from the chaff it has deployed, the chaff will also be within that volume.

The reason the radar has to illuminate a volume is that the target is moving, and can change direction unpredictably. So radar has to illuminate a large enough area so that no matter how the target maneuvers the target will still be well within the area of illumination, otherwise it would be very easy for targets to evade all radar locks by maneuvering a bit.


The inaccuracies in the sim have to do with how seeker vs countermeasure situations are resolved.

In real life there are a large number of factors of signal strength, signal characteristics, and sensor limitations that determine if the real target or the countermeasure is more attractive to the missile seeker.

A lot of that information about that is not publicly available, so DCS uses a simple probability test where each countermeasure has a 0.x chance to fool the seeker, modified by a few parameters.

It leads to missiles sometimes hitting when they should miss, sometime missing when they should hit, and it rewards pumping out large volumes of chaff and flares more than it really should.

The community consensus seems to be overall that missiles should be a bit more deadly, a bit longer range at high altitude, but that with professional quality piloting there's a high probability that most A2A battles are likely to resolve in the WVR arena.


The general advice is to practice flying like a real combat pilot, as the trend in DCS is toward increasing realism. The real techniques generally work well even against the not quite realistic elements of the game, and when those elements are revised to be more realistic, you don't want to have a collection of bad habits that only work against unrealistic game features. Practicing techniques that are game oriented has given a lot of people nasty surprises in the past when a patch has increased realism and what used to "work" is suddenly suicidal.

I'd recommend hanging out with some of the Multiplayer realism oriented groups that work on realistic combat flying. There's a lot to learn, and having skilled teachers really helps a lot.
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