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AIM-120 and R-27 homing


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I know this has been discussed before (can't seem to find the thread now) but are we sure that the PRF actually changes in STT mode when the toggle PRF command is given to the radar? Does the actual Flanker manual have anything to say on this specific situation?


Edited by DarkFire

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This has been discussed before and AFAIK there was nothing conclusive about this.

But try this:

 

TWS bug a target at max range in HPRF and then change to MPRF. Bug is dropped.

 

STT lock a target at max range in HPRF and then change to MPRF. Lock should be lost, but nothing happens.

 

So either STT doesn't follow the same logic as TWS or we can't change PRF in STT. Or it's a bug.

 

At least that how it plays out in the F-15.

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It is the same in the F15! Under 30nm, you should always be scanning, locking stuff up in MED. The effect on STT lock is also the same, but less noticeable given that F15 can keep a more stable lock to further distances in a multitude of different PRF settings.

 

Guys this has nothing to do with ERs going for chaff in head on situations. Even if it's a recent revelation to some... Let's not derail the topic!

 

 

 

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I know this has been discussed before (can't seem to find the thread now) but are we sure that the PRF actually changes in STT mode when the toggle PRF command is given to the radar? Does the actual Flanker manual have anything to say on this specific situation?

 

No idea in RL although I'd assume real STT mode would take care of PRF tweaking automatically. In-game though, I'm sure adjusting PRF in STT helps. Now whether this is a bug or intended, I don't know.

Sometimes, you would swear you still have a nice solid STT lock where in fact M-link is gone and probably EOS has taken over automatically rendering all airborne semi actives useless, chaff or no chaff.

 

This has been discussed before and AFAIK there was nothing conclusive about this.

But try this:

 

TWS bug a target at max range in HPRF and then change to MPRF. Bug is dropped.

 

STT lock a target at max range in HPRF and then change to MPRF. Lock should be lost, but nothing happens.

 

So either STT doesn't follow the same logic as TWS or we can't change PRF in STT. Or it's a bug.

 

At least that how it plays out in the F-15.

 

No idea in the Eagle, I suspect this could be a Russian radar thing.

 

Anyway, OP said he wants to understand why 120 reacquires but not R-27 so this PRF thing is very relevant. Getting so fixated on chaff is misleading: make sure first that R27 is actually tracking then start worrying about chaffs.

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No idea in RL although I'd assume real STT mode would take care of PRF tweaking automatically. In-game though, I'm sure adjusting PRF in STT helps. Now whether this is a bug or intended, I don't know.

Sometimes, you would swear you still have a nice solid STT lock where in fact M-link is gone and probably EOS has taken over automatically rendering all airborne semi actives useless, chaff or no chaff.

 

 

 

No idea in the Eagle, I suspect this could be a Russian radar thing.

 

Anyway, OP said he wants to understand why 120 reacquires but not R-27 so this PRF thing is very relevant. Getting so fixated on chaff is misleading: make sure first that R27 is actually tracking then start worrying about chaffs.

 

51st pilots have been doing it for over a year now, SARH is not tracking better when I change PRF. The main issue is chaff resistance. Or that SARH reacts to chaff when it is not in its field of view, No matter PRF. Aim-7 is not doing better when guided by F-15.


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No idea in RL although I'd assume real STT mode would take care of PRF tweaking automatically...

 

That's what I would imagine happens. Given that in STT mode the radar is clearly able to determine target aspect it would be logical for it to be able to adjust PRF on the fly to suit. Somewhat frustratingly the Su-27 flight manual is silent on the subject, hence my wondering if the real Su-27 manual mentions what happens.

 

With regards to the missile tracking problem, and the susceptibility to being decoyed by expendables, the problem is and has always been the '%decoy' mechanic that controls how chaff effects missile lock. Until the system is re-modelled to be a more sophisticated EM-centroid tracking model with all that goes with it, the issue will persist.

 

Hopefully the missile guidance review that ED is or will be conducting will make things more realistic. Maybe in the mean time the CM susceptibility figures for missiles can be tweaked a bit so that they better reflect what little evidence there is in the public domain for actual combat-conditions SARH missile performance.

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Last night i noticed that the countermeasure probability factor is missing from the R and ER but is there for the AIM-7.

Anybody knows why?

 

EDIT: In the missile_data.lua


Edited by Svend_Dellepude

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Guidance is done in HPRF for SARH. Lose HPRF for whatever reason, you probably lose the missile.

 

That's why you have backup modes like FLOOD on the F-15 and EOS-slaved radar antenna on the flanker.

 

That's what I would imagine happens. Given that in STT mode the radar is clearly able to determine target aspect it would be logical for it to be able to adjust PRF on the fly to suit. Somewhat frustratingly the Su-27 flight manual is silent on the subject, hence my wondering if the real Su-27 manual mentions what happens.

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Guidance is done in HPRF for SARH. Lose HPRF for whatever reason, you probably lose the missile.

 

That's why you have backup modes like FLOOD on the F-15 and EOS-slaved radar antenna on the flanker.

 

So in reality the whole 'change PRF while in STT mode' is a red herring? That would explain why the HUD doesn't show the PRF mode in STT: because in reality it's fixed to high PRF for missile guidance.

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So in reality the whole 'change PRF while in STT mode' is a red herring? That would explain why the HUD doesn't show the PRF mode in STT: because in reality it's fixed to high PRF for missile guidance.

The reason to change it is so that, when you lose the target in the notch, you can automatically reacquire it when it exits...assuming EOS still has it locked: https://forums.eagle.ru/showpost.php?p=3170743&postcount=8. When the lock is dropped, the Radar Complex is waiting for an opportunity to reacquire. Changing the PRF gives it a better chance of doing that. That may not be how the real system works from what I've read so far in the manual. But that's how it's working in the sim.

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The PRF should be shown, the F-15 manual 34-1-1-1 states that when a contact is locked up in HPRF the set immediately transfers to MPRF track, when Rmax is achieved it switches to HPRF unless the contact is low, beaming etc. where it will remain in MPRF track. It then advises the pilot to change heading to achieve HPRF track before launching the weapon.

 

Added interest it also states that at 10nm radar search range the radar automatically goes into MPRF.


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The reason to change it is so that, when you lose the target in the notch, you can automatically reacquire it when it exits...assuming EOS still has it locked: https://forums.eagle.ru/showpost.php?p=3170743&postcount=8. When the lock is dropped, the Radar Complex is waiting for an opportunity to reacquire. Changing the PRF gives it a better chance of doing that. That may not be how the real system works from what I've read so far in the manual. But that's how it's working in the sim.

 

Thanks, I just read your other thread. That clears that up then as far as our Flanker goes.

 

At 1.35 and 2.00 in this video you can see what I think is a similar thing happening where it takes time during lock for HPRF to be achieved. But HPRF does show during lock.

 

Very interesting, thanks for posting that video. Provided that HUD cam footage is from an Su-27S and not a more modern version, ours appears to be missing quite a few HUD elements that the real one features. Hopefully these might be added at some point.

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Either you misread or I did:

 

What happens before launching a weapon is no big deal, but it's all 'attempts to transfer', meaning it will attempt to use whatever PRF works to keep the target. MPRF is preferred for clutter rejection.

 

The ability of the AIM-7 to track the target is represented by the DSR cue, and is the main range limiting factor in a bunch of conditions (here is where the R-27 is superior)

 

When you launch, the radar will attempt to transfer to HSTT+ straight away. There's nothign for the pilot to do. If this fails, or if the radar transfers out of HSTT+ and times out the memory with a weapon in fight, it will switch to FLOOD (or if you launch without a lock whatsoever).

 

At VSD settings of 20nm or less (IIRC) the radar will switch to MPRF and the beamwidth is reset to 3.4 deg or so, so the scan zones become larger. Likewise, the dish is driven at 90deg/s instead of 70deg/s - most of this stuff N/A in DCS at this time.

 

The PRF should be shown, the F-15 manual 34-1-1-1 states that when a contact is locked up in HPRF the set immediately transfers to MPRF track, when Rmax is achieved it switches to HPRF unless the contact is low, beaming etc. where it will remain in MPRF track. It then advises the pilot to change heading to achieve HPRF track before launching the weapon.

 

Added interest it also states that at 10nm radar search range the radar automatically goes into MPRF.

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I think it's safe to say everyone knows by now the SIM does not model the PRF stuff correctly as in RL, hence we must improvise and set PRFs manually during STT locks. Perhaps Mirage comes closest to having a RL representation by only allowing Fox 1 launch in HPRF.

 

Anyway, clearly the major issue is CM effectiveness because that's what causes SARH to miss in ridiculous 'perfect' condition shots.

 

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