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Purpose of the different HARM modes?


Fred00

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So I'm studying the HARM at the moment, trying to get a firm grip of when to use which mode. Unfortunately there seems to be few descriptions detailing when to use each mode. Tell me if I'm right or wrong:

EOM: The most exact mode. Primarily used when we have a steerpoint on the exact location of the SAM. HARM missile lofts for greater range.

PB: A little less exact than EOM. Primarily used when we have a steerpoint in the vicinity of the SAM. HARM missile lofts for greater range. Lofting cues are also shown on HUD in this mode to increase range by aircraft pitch up.

RUK: Used when we only know the general direction of the SAM and not the range. HARM does not loft, and goes active shortly after launch to search for targets with a 120 degree FOV.

A few questions arise:

1) Is there any real benfit of using EOM over PB? PB seems to do the same thing just fine.

2) Even though lacking HUD lofting cues, lofting before launch seems to work fine in EOM too. Just pitch up 25 degrees and pickle. What is the advantage of lofting in PB mode? Also, lofting does not work like in the Hornet, where you hold the pickle button, pitch up and the missile is launched when the flight path marker passes the lofting cues. In the F-16C the missile is launched immediately when pressing the pickle button, even if the flight path marker is still behind the lofting cues. Therefore, exactly the same thing can be achieved in EOM as in PB (it seems)

Thankful for some input from more experienced Viper pilots. 🙂

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2 hours ago, Fred00 said:

1) Is there any real benfit of using EOM over PB? PB seems to do the same thing just fine.

Yes, EOM mode is very useful when you are trying to get inactive radar to activate and start pinging you, you can pas the site close, for example on your left side, ready to bank and run, and fire the missile at the same time, you don't have to point your nose at the radar.

 

PB has greater range (range depends on altitude and speed of the aircraft that fires the missile) but nose needs to be pointed towards the radar, it is great to use against radars that are already emitting and you don't want to get close and risk getting shot.

 

2 hours ago, Fred00 said:

2) Even though lacking HUD lofting cues, lofting before launch seems to work fine in EOM too. Just pitch up 25 degrees and pickle. What is the advantage of lofting in PB mode? Also, lofting does not work like in the Hornet, where you hold the pickle button, pitch up and the missile is launched when the flight path marker passes the lofting cues. In the F-16C the missile is launched immediately when pressing the pickle button, even if the flight path marker is still behind the lofting cues. Therefore, exactly the same thing can be achieved in EOM as in PB (it seems)

Yes Viper has slightly different launch rules than Hornet, as for lofting, you can loft any missile, or bomb all of them will have benefit from vertical velocity.


Edited by Furiz
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PB is prebriefed mode and has the longest range, because it assumes that the coordinates that were entered are very close to where the SAM's radar actually is. You will have to follow the cue on the HUD for the missile to be able to reach the target if you're firing at maximum range.

RUK is range unknown mode, works pretty much like prebriefed, but due to the larger search area, the indicated range is smaller than with PB.

EOM is equations of motion mode and allows you to fire off-boresight (e.g. you can fire while flanking the SAM site), and the range indicated is calculated depending on your aircraft's attitude, and obviously even less than in range-unknown mode if you're e.g. flanking the SAM site, because the missile will have to turn towards the site first, which costs energy, and as a result, reduces range.

Hope that helps.

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Thanks for the replies guys. Good info about EOM off boresight shots. I just tested and it works like charm. One question though:

Why does PB have longer range? If I'm flying straight towards a SAM and launch, both EOM and PB will loft. Why is the range in PB longer? Shouldn't they be about the same in that case? I have to confess that I haven't tested in the game, but I will tomorrow.

Also, another question. In the Nevada instant action mission with HARM and russian SAMs the briefing says "SAM target 2 and 3 are tactical mobile SAMs. As such, only their general position can be determined. SP2 and SP3 are in the general location of these SAMs. POS RUK mode is not viable for these targets. HAS is the recommended mode".

Isn't POS RUK actually a good fit for the scenario above?

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19 minutes ago, Fred00 said:

Thanks for the replies guys. Good info about EOM off boresight shots. I just tested and it works like charm. One question though:

Why does PB have longer range? If I'm flying straight towards a SAM and launch, both EOM and PB will loft. Why is the range in PB longer? Shouldn't they be about the same in that case? I have to confess that I haven't tested in the game, but I will tomorrow.

Also, another question. In the Nevada instant action mission with HARM and russian SAMs the briefing says "SAM target 2 and 3 are tactical mobile SAMs. As such, only their general position can be determined. SP2 and SP3 are in the general location of these SAMs. POS RUK mode is not viable for these targets. HAS is the recommended mode".

Isn't POS RUK actually a good fit for the scenario above?

Maybe the waypoints aren't reliable, so HAS should be employed.

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EOM and PB are similar in a lot of ways. Historically PB was a mode of launch in the F-4 (and other planes) involving a loft. The PB mode in the F-16 is the only one which inhibits launch outside of a certain azimuth of bearing directly to the target point. It has a relatively early and wide search program which is good for making sure it hits something. The downside is you can hit the wrong thing is a busy environment and off-axis attacks aren't supported.

EOM has a precise footprint for when you know exactly where the emitter is and you don't want it to home in outside this area. For absolute standoff range I don't expect that EOM is dramatically worse than PB. Maybe the math going on in EOM is harder which taxes the processor more, I don't know.

RUK is a degraded mode with the widest footprint which is terrible for being selective and worse energy management than PB. It is the true "to whom it may concern."

 

No reason for RUK to be not viable for targets with the exception that they are probably not emitting all the time as required for a POS attack. A HAS attack is different in that you genuinely detect threat emissions before firing. Lofting POS shots at a SA-19 or similar probably won't kill one because they aren't constantly emitting like a strategic SAM might (and even then strategic SAMs tend to rely on other radars for alerts.) A big part of the SEAD mission is firing HARMs which never kill a target because the SAM radars never switched on which was the few minutes the striker airplanes needed to get in and out of the target area unmolested.

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Thanks Frederf, what a great reply! What I get is that it is not always obvious what mode is best to use, and sometimes two different modes could do basically the same job. With your description and more testing I believe I will get a hang of it. With some experience one will probably know instinctively which mode is best in different situations.

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Adding to what's mentioned about EOM being more precise, it has a narrower seeker field of view once activated, so the steerpoint must be extremely close to the target. PB has a wider seeker field of view, so the steerpoint doesn't have to be as precise. IIRC PB mode also has a 120-second self-destruct timer that must be taken into account. No idea if this is in DCS but it was in "that other" Viper sim. 

  

On 11/8/2021 at 6:09 AM, Fred00 said:

SP2 and SP3 are in the general location of these SAMs. POS RUK mode is not viable for these targets. HAS is the recommended mode".

Isn't POS RUK actually a good fit for the scenario above?

 

I would be inclined to say you could even use PB mode here, but that all depends on what the mission creator's personal definition of "general location" is. 


Edited by Nealius
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On 11/8/2021 at 3:37 AM, Fred00 said:

So I'm studying the HARM at the moment, trying to get a firm grip of when to use which mode. Unfortunately there seems to be few descriptions detailing when to use each mode. Tell me if I'm right or wrong:

EOM: The most exact mode. Primarily used when we have a steerpoint on the exact location of the SAM. HARM missile lofts for greater range.

PB: A little less exact than EOM. Primarily used when we have a steerpoint in the vicinity of the SAM. HARM missile lofts for greater range. Lofting cues are also shown on HUD in this mode to increase range by aircraft pitch up.

RUK: Used when we only know the general direction of the SAM and not the range. HARM does not loft, and goes active shortly after launch to search for targets with a 120 degree FOV.

A few questions arise:

1) Is there any real benfit of using EOM over PB? PB seems to do the same thing just fine.

2) Even though lacking HUD lofting cues, lofting before launch seems to work fine in EOM too. Just pitch up 25 degrees and pickle. What is the advantage of lofting in PB mode? Also, lofting does not work like in the Hornet, where you hold the pickle button, pitch up and the missile is launched when the flight path marker passes the lofting cues. In the F-16C the missile is launched immediately when pressing the pickle button, even if the flight path marker is still behind the lofting cues. Therefore, exactly the same thing can be achieved in EOM as in PB (it seems)

Thankful for some input from more experienced Viper pilots. 🙂

 

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On 11/11/2021 at 7:17 AM, pete_auau said:

1) Is there any real benfit of using EOM over PB? PB seems to do the same thing just fine.

2) Even though lacking HUD lofting cues, lofting before launch seems to work fine in EOM too. Just pitch up 25 degrees and pickle. What is the advantage of lofting in PB mode? Also, lofting does not work like in the Hornet, where you hold the pickle button, pitch up and the missile is launched when the flight path marker passes the lofting cues. In the F-16C the missile is launched immediately when pressing the pickle button, even if the flight path marker is still behind the lofting cues. Therefore, exactly the same thing can be achieved in EOM as in PB (it seems)

For 1), EOM allows you to fire while not pointed at the target, while PB would inhibit firing from more than 5 degrees off-target laterally (not sure if it actually does in DCS). Same for RUK, but with even less range, due to allowing for a greater search area of the missile. RUK is a degraded EOM mode.

For 2), The advantage of lofting in PB mode is that when the missile is fired at the indicated ideal loft angle, you will be able to engage the target from further away, meaning, it optimizes the missile's range.

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9 hours ago, Aquorys said:

For 1), EOM allows you to fire while not pointed at the target, while PB would inhibit firing from more than 5 degrees off-target laterally (not sure if it actually does in DCS). Same for RUK, but with even less range, due to allowing for a greater search area of the missile. RUK is a degraded EOM mode.

For 2), The advantage of lofting in PB mode is that when the missile is fired at the indicated ideal loft angle, you will be able to engage the target from further away, meaning, it optimizes the missile's range.

yep knew  this already only posted  the link  for  others

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HAD (HTS) shots are not POS shots, they aren't EOM/PB/RUK but their own thing. I think they're closest to EOM but it probably depends on the FOM of the target location. It should be relatively narrow compared to some of the wider POS shots.

In DCS all of the POS modes are fully wide search for the entire flight. A POS-EOM will find something a good 90 degrees off axis a few seconds after shooting and ignore its assigned target area.  I think realistically EOM is a late-game search of maybe a 1nm patch, PB a mid-game search of ~5nm patch, RUK an early-game lane of about +-10nm either side of axis.

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HAD (HTS) shots are not POS shots, they aren't EOM/PB/RUK but their own thing. I think they're closest to EOM but it probably depends on the FOM of the target location. It should be relatively narrow compared to some of the wider POS shots.
In DCS all of the POS modes are fully wide search for the entire flight. A POS-EOM will find something a good 90 degrees off axis a few seconds after shooting and ignore its assigned target area.  I think realistically EOM is a late-game search of maybe a 1nm patch, PB a mid-game search of ~5nm patch, RUK an early-game lane of about +-10nm either side of axis.
How do you know that in DCS all POS shots are seeking right off the rail? You're saying that as implemented in game now, the only changes are pre-launch symbology and flight path, but not post launch seeker behavior? Woof.

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2 hours ago, Frederf said:

HAD (HTS) shots are not POS shots, they aren't EOM/PB/RUK but their own thing. I think they're closest to EOM but it probably depends on the FOM of the target location. It should be relatively narrow compared to some of the wider POS shots.

Wait if they're not POS shots then why does switching between POS modes in Wags' video change the HARM footprint displayed in the HAD (and also the POS mode is displayed in the bottom right corner of the HAD page)? 

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12 hours ago, CybrSlydr said:

The mode I use the most is RUK.  Allows me to just specify the steerpoint and the SAM to look for, fire it, and get on with life.

Especially since HAS mode doesn't have any range information.

 

Once I made simulation. I created a mission with steerpoint (as HARM designated steerpoint) and placed radars in different distances from steerpoint (radius). Sorry for visualization in CAD but it's only what have in workplace 🙂

image.png

So I placed SA-19 in 25nm radius from steerpoint (one emitter for each test), then launched HARM in RUK/PB/EOM (one after another).

My conclusion was that:

  • Every HARM RUK/PB/EOM tracked every target and tried to fly to the target,
  • Every PB/EOM HARM tracked and striked every target (notice that steerpoint in center of the circle is beyond SA-19 radar range),
  • RUK HARM flies to target but fall short due to lack of kinetics or battery life,
  • Every HARM, after lunch, flies straight. Then turns to detected threat [turns earlier on bigger emitter (S) and later for smaller (SA-19)].

So honestly I don't see any difference of footprints for RUK/PB/EOM. (For my test max. radius was 25nm, next I tried 27nm but it was too much and rockets do not track).

34 minutes ago, Mustang25 said:

Wait if they're not POS shots then why does switching between POS modes in Wags' video change the HARM footprint displayed in the HAD (and also the POS mode is displayed in the bottom right corner of the HAD page)? 

In HAD we can see difference in range between RUK and PB/EOM, and difference between launch parameters between EOM/PB (PB have narrow launch angle). I don't think so it is exactly mode footprint but rather like range coupled with launch parameters.


Edited by Bricux
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9 hours ago, Mustang25 said:

Wait if they're not POS shots then why does switching between POS modes in Wags' video change the HARM footprint displayed in the HAD (and also the POS mode is displayed in the bottom right corner of the HAD page)? 

My understanding is if you have HAD and WPN up at the same time (left/right MFDs) the WPN page will be forced to the HAS-POS-DL menu because HAD is overriding all other modes. I see in the video HAD and WPN are open at the same time and WPN isn't forced to menu. According to the latest video HAD is acting like just another SPI source (with TGP even slaved to SPI). I don't know which is correct but obviously use the DCS reference for DCS behavior.

There is a confusion about "footprint". Footprint can refer to the area the missile can maneuver to. This maneuver footprint is what is shown as the white bordered area on the HAD format. The search footprint is the region which is searched when the missile seeker is activated and is not displayed in any mode as far as I know. The shape of the maneuver footprint and search footprint are quite different. It makes sense that the maneuver footprint

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10 hours ago, TheBigTatanka said:

How do you know that in DCS all POS shots are seeking right off the rail?
 

Because I've tested it. Put a waypoint that's your EOM target and an emitter many miles away but within detection region of the HARM. Firing an EOM shot against the waypoint (without an emitter there to track) will show the missile very quickly finding the distant emitter and flying to that. I'm not saying that all modes are identical (although I haven't seen any particular post-launch difference in seeker behavior) but in a crowded environment missiles aren't waiting to search or narrowing their search to the vicinity of the assigned target point.

 

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4 hours ago, Frederf said:

My understanding is if you have HAD and WPN up at the same time (left/right MFDs) the WPN page will be forced to the HAS-POS-DL menu

Ah, that's interesting, good to know!

 

4 hours ago, Frederf said:

There is a confusion about "footprint". Footprint can refer to the area the missile can maneuver to.

And yeah, I guess we got a bit off track. My initial question was about the seeker search area but then we drifted to the maneuver footprint in following posts.

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Can someone tell me what's the technical difference between PB and EOM on the HARMs?

If it's just the launch window and HUD symbology i would assume that they were called PB1 and PB2 or PBX or whatever.
Also the german wikipedia article on the HARM says that EOM is very much dependant on the aircraft's avionics and only available on SEAD platforms. The article does not go into detail though, so i somehow doubt that it is super accurate.

Does anyone know a bit more about EOM and if there are more differences between PB and EOM under the hood?

Thanks!

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