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JDAMS are really inaccurate now from longer range?


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Did ED change something with the GPS logic?  seems that JDAMS miss a lot now...at least the larger ones (GBU-31)


Edited by MobiSev

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  • MobiSev changed the title to JDAMS are really inaccurate now from longer range?
34 minutes ago, Tholozor said:

Are you releasing when you hit IN RNG, or IN ZONE?

 

Both

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I only launch when IN ZONE and make sure the weapons have aligned to good quality - JDAM accuracy has decreased substantially since the last big stable update. It almost feels like a RNG has been built in as there is no consistency either. Before the patch I could reliably kill tanks with GBU38's from 10K and up; now at even lower altitudes it would miss entirely. It is hard to work out whether it is a problem with the GPS or the new zero alpha terminal mode to avoid 'slapping' the target. 

I would rather have it slap the target than miss by 20m altogether.

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I've had issues the last couple times I used JDAMS against SAM sites.  Staying low-level and then popping around 10nm and releasing once I get an In Zone indication, but they impact well short.  It's like the In Zone indication is appearing before the bomb really has the range.  I'd wondered if I was doing something wrong. 

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Are you using the HMD to designate your targets perchance? There's a reported bug with the TDC drifting. If you designate using a WP, or VVSLV or snowplow, it works fine.

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1 hour ago, Zyll said:

Are you using the HMD to designate your targets perchance? There's a reported bug with the TDC drifting. If you designate using a WP, or VVSLV or snowplow, it works fine.

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Can't speak for OP, but not in my case. I'm using waypoint designate, and verify with the pod that the TD is on the target.  GBU 38s in my case. 

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5 hours ago, Stearmandriver said:

I've had issues the last couple times I used JDAMS against SAM sites.  Staying low-level and then popping around 10nm and releasing once I get an In Zone indication, but they impact well short.  It's like the In Zone indication is appearing before the bomb really has the range.  I'd wondered if I was doing something wrong. 

I’ve had a few instances where I had similar experiences doing pop-up attacks, but I also don’t know how realistic/acceptable that method is. 
 

When high altitude loiter bombing I have zero issues with the JDAMs

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Well, considering that the JDAM has a CEP of ~13 meters (which means that 50% of bombs will fall within a ~13 meter circle radius, with the rest 50% falling outside of it (https://en.wikipedia.org/wiki/Circular_error_probable), you shouldn't expect it to hit head-on every time. Far from it, actually.

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JDMA is NOT a very accurate weapon,but in DCS, due to the damage model ,if you can't hit the head of the target,the damage is very limited

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50813874592_d56b9b44e3_b.jpg

ALSO,this why you feel inaccurate from longer range


Edited by flankerjun

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1 hour ago, flankerjun said:

 

ALSO,this why you feel inaccurate from longer range

 

 

If and only if the user targets the object directly. Most JDAM users know however to target the ground under the object and not the object itself to avoid slant inaccuracies.

 

Sadly I am getting more direct hits with CCIP Mk-82's than with GB-38's at the moment. For high-altitude work I started carrying a mix of GBU-38's and GBU-12's again; JDAM for soft skin vehicles that doesn't mind a miss with a few meters, and then LGB for tanks. I was always under the impression that GPS weapons had premium GPS accuracy?

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The thing about GPS is that it's not perfect, there tons of factors that come into play. GPS weapons normally can't acquire satellite signals while carried, as they're blocked by the aircraft itself, meaning that the first phase of the flight profile is usually INS-only for the first 30 seconds or so until the signal is acquired. After that you've got all the issues of inaccuracy that GPS itself comes with, including but not limited to (which can also affect the aircraft itself as well):

In DCS this isn't much of an issue, everything is perfectly ranged and coordinates are pretty much spot-on, but in reality a factor to consider is Target Location Error. Due to this inherent uncertainty in the aircraft's ability to calculate accurate coordinates, JDAM missions are more likely to be flown against PP targets, or programmed for such with support from the ground to obtain those coordinates.


Edited by Tholozor

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2 hours ago, Tholozor said:

The thing about GPS is that it's not perfect, there tons of factors that come into play. GPS weapons normally can't acquire satellite signals while carried, as they're blocked by the aircraft itself, meaning that the first phase of the flight profile is usually INS-only for the first 30 seconds or so until the signal is acquired.

 

The GPS signal can be received, but the problem is that the weapon own battery doesn't last than just seconds or few minutes. That is a limiting factor for huge amount of weapons from MANPADS to glide bombs etc.

 

When a bomb like JDAM is to be released, it knows nothing about its location. It own INS is initialized (warmed up) and on the release moment the aircraft will energize the weapon to use it own battery, upload aircraft known GPS almanac (GPS satellite exact position on the sky) and specific set of GPS satellites for bomb to use, as well the coordinates of the bomb in release moment and the target coordinates.

On the physical release the umbilical cable is disconnected that provided data connection and start power.

 

AFAIK This is how when you are programming the weapon for the coordinates etc, it is just in the aircraft own weapon system but not in the bomb. So as long you do not release the bomb, it will maintain its service life (but shorten anyways, why you can't keep attaching same weapons all the time if not going to use them).

 

Point is, on the moment the bomb is released, it knows where it is and where it needs to be. It knows what satellites are visible to it and what are told satellites to use and it connects to them in seconds. And this is why you can't load the bomb with target data and load it to some old aircraft that is capable carry Mk.82/84 bombs and just drop it in estimated range as the aircraft weapons systems and programmed mission data is the critical part.

So then it just comes to mechanical guidance system to maintain the trajectory to the impact.

 

2 hours ago, Tholozor said:

After that you've got all the issues of inaccuracy that GPS itself comes with, including but not limited to (which can also affect the aircraft itself as well):

 

Those are likely the major factors for it. But I don't even now recall that what guidance mode did the JDAM have, like did it have same bang-bang control system as the GBU-12 does have. So with GPS updates and possible guidance errors the bomb itself generates it might be just the limitation.

 

2 hours ago, Tholozor said:

In DCS this isn't much of an issue, everything is perfectly ranged and coordinates are pretty much spot-on, but in reality a factor to consider is Target Location Error. Due to this inherent uncertainty in the aircraft's ability to calculate accurate coordinates, JDAM missions are more likely to be flown against PP targets, or programmed for such with support from the ground to obtain those coordinates.

 

JDAM, JSOW etc are almost by default used in scenarios where you can not have laser guidance, so you can not have optical targeting capability and you get the coordinates in mission planning phase and you input those coordinates to waypoints and you just fly there to release the weapon and fly away. The intelligence accuracy is limiting factor, why you are not going to use these on targets that are mobile as intelligence can not provide such a accuracy unless it is just really confirmed and nothing changes between planning and explosion.

 

If you can use optical targeting or laser guidance, it is cheaper and easier to put something else on target.

 

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9 hours ago, Harker said:

Well, considering that the JDAM has a CEP of ~13 meters (which means that 50% of bombs will fall within a ~13 meter circle radius, with the rest 50% falling outside of it (https://en.wikipedia.org/wiki/Circular_error_probable), you shouldn't expect it to hit head-on every time. Far from it, actually.

That's the specification, but it seems in the real world JDAMs are more accurate than they were designed to be - achieving a CEP of about 7 meters. 

 

The point is still completely valid, JDAMs in the real world do not seem to be accurate enough to reliably score direct hits on tank sized objects. That, and cost, is probably why the GBU-12 still seems to be the preferred US weapon for "tank plinking." GBU-54 and DM-SDB may be changing that now though. 

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Demonstrated CEP, last I recall, was under 5m with GPS, and within 30m for up to 100 sec of flight time if GPS was not available for any reason.

 

17 minutes ago, Fri13 said:

Those are likely the major factors for it. But I don't even now recall that what guidance mode did the JDAM have, like did it have same bang-bang control system as the GBU-12 does have. So with GPS updates and possible guidance errors the bomb itself generates it might be just the limitation.

 

I don't know the guidance algorithm but it's probably not Bang-Bang, and probably not proportional either.  The package uses strakes for lift and IIRC a single moveable fin for course changes.


Edited by GGTharos

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I really think there is something with JDAMs, and it's not a GPS/INS problem but game problem. Look at my screen shot - near upper hangar there is a hole after bomb. the one falling hit exactly this same point. Target was placed on the runway crossing, left on picture.

 

qufnSoC.jpg

 

I noticed sometimes (not always) map coordinates changes with map zoom - for example I zomm map, so I can view whole airbase, I write down coords in format DD MM SS.ss, then I make maximum avaible zoom for target point and coords are different. The differenc is greater, the greater was zoom difference.

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