GBU-12 guidance affected by winds?

[Nealius]

Flying online, Sinai, area track, point track, stationary targets, moving targets, black hot, white hot, something seems wierd with the GBU-12s as they frequently miss by a couple of meters. At first I thought this matched with the advertised CEP of 4m, however note where the bombs land in reference to the target and the North arrow: every miss is to the East. This isn't a random CEP error, this is consistently missing to the east. In this particular mission, winds are from 280. Perhaps the GBU-12 is having issues compensating for wind? Or is this an F-15E specific issue that should go in the Razbam section?

F-15E tracks don't work reliably on my system so I'll try to reproduce with something more robust like the Hornet or Viper when I get a chance. This particular instance was duing a 3-hour flight so the track is probably useless. 

 

[Hobel]

vor 4 Stunden schrieb Nealius:

Flying online, Sinai, area track, point track, stationary targets, moving targets, black hot, white hot, something seems wierd with the GBU-12s as they frequently miss by a couple of meters. At first I thought this matched with the advertised CEP of 4m, however note where the bombs land in reference to the target and the North arrow: every miss is to the East. This isn't a random CEP error, this is consistently missing to the east. In this particular mission, winds are from 280. Perhaps the GBU-12 is having issues compensating for wind? Or is this an F-15E specific issue that should go in the Razbam section?

F-15E tracks don't work reliably on my system so I'll try to reproduce with something more robust like the Hornet or Viper when I get a chance. This particular instance was duing a 3-hour flight so the track is probably useless. 

 

best would be a track to see what exactly is happening.

but basically, if you know which direction the wind is coming from and especially when it is a bit stronger, you should offset accordingly

 

[Nealius]

I can try to get a track but this is over extremely long sessions, possibly caused by refuel/rearming. I don't recall any of my bombs missing like this prior to a rearm.

8 minutes ago, Hobel said:

if you know which direction the wind is coming from and especially when it is a bit stronger, you should offset accordingly

Requiring Kentucky windage for precision guided munitions defeats the entire reason PGMs exist in the first place, though.

[Hobel]

vor 14 Minuten schrieb Nealius:

I can try to get a track but this is over extremely long sessions, possibly caused by refuel/rearming. I don't recall any of my bombs missing like this prior to a rearm.

okay do i understand correctly that you achieve 2 different results with the same wind force?

vor 14 Minuten schrieb Nealius:

Requiring Kentucky windage for precision guided munitions defeats the entire reason PGMs exist in the first place, though.

Not really, if you know the wind direction and then laser a few feet in that direction you still have a pinpoint weapon.

10knots wind 3,7 CEP for GBU12 should still be possible

[Nealius]

4 minutes ago, Hobel said:

okay do i understand correctly that you achieve 2 different results with the same wind force?

Partially. Of the first 8 drops most were accurate, only one or two fell downwind. After rearming and refueling the second set of 8 drops had a much higher miss frequency.

To-do list today is to test with the Viper to see if the behavior is a weapon issue or a module issue.

[Nealius]

Confirmed in the Viper from a cold start. All four drops about 4m downind from crosshairs. Next step is to get an airstart debug track for you. In the meantime, three questions:

1. Shouldn't CEP be a random error, not the same error every single drop?

2. Shouldn't CCRP (Viper and Mudhen, in this case) calculate for wind? My understanding is that it should, though IIRC the Mudhen's isn't fully fleshed out at the moment. I thought the Viper's had been finished? 

3. Shouldn't a GBU have sufficient ballistic energy to overcome a 10kt wind? Release in the low 20s at 350-400kts.

My understanding from real-world reading is that laser guided weapons should have enough precision to go through a window, hence being preferred over JDAMs in certain situations. Currently with this 4m downwind error a laser guided munition has no precision advantage over a JDAM on static targets. 

Edited September 1, 2023 by Nealius

[Hobel]

vor einer Stunde schrieb Nealius:

1. Shouldn't CEP be a random error, not the same error every single drop?

well, DCS is just software at the end of the day. (for GPS bombs it is currently the case in DCS)
and especially LG bombs(in DCS) are very accurate in terms of the hit pattern (not tested for a long time, could be different again).

 

vor einer Stunde schrieb Nealius:

2. Shouldn't CCRP (Viper and Mudhen, in this case) calculate for wind? My understanding is that it should, though IIRC the Mudhen's isn't fully fleshed out at the moment. I thought the Viper's had been finished? 

well they are laser bombs which are quite simple compared to GPS bombs and if you laser directly on the target the bomb will try to steer there and wind can affect it if you don't compensate for it. Even if the aircraft calculates a perfect drop, the "control logic" of the bomb after detection of the laser would nullify this.

@Iron_physik

vor einer Stunde schrieb Nealius:

3. Shouldn't a GBU have sufficient ballistic energy to overcome a 10kt wind? Release in the low 20s at 350-400kts.

in 10 knot winds, the bomb will deviate 3-4 meters in a drop from 20,000 feet, I would consider plausible.

but since nothing is set in stone, it would of course be cool to see how it ultimately performs IRL, taking a  shot in 10-20 knots of wind and holding the laser directly on the target.

vor einer Stunde schrieb Nealius:

My understanding from real-world reading is that laser guided weapons should have enough precision to go through a window, hence being preferred over JDAMs in certain situations. Currently with this 4m downwind error a laser guided munition has no precision advantage over a JDAM on static targets. 

 that is also the case in DCS without wind the bomb is very very accurate.

 

here you can see the effect of 10 knots of wind, dropped from 20,000feet.
if i were to equalize the wind and laser 3 meters next to the APC, i would still have a pinpoint hit.

Edited September 1, 2023 by Hobel

[Nealius]

18 minutes ago, Hobel said:

in 10 knot winds, the bomb will deviate 3-4 meters in a drop from 20,000 feet, I would consider plausible.

I dug through the Viper's -34. Under flightpath characteristics for Paveway I/II it says that winds (among other factors) "would be fully compensated for." It goes on to mention that errors near or outside CEP only result from improper deliveries. Don't want to copy word-for-word due to forum rules.

Is our GBU-12 a Paveway II class weapon? I assume my delivery is sound since I'm wings level and on the ASL. 

Edited September 1, 2023 by Nealius

[Magoote]

I experienced the same problem of lack of precision with wind greater than 10 knots. Now, it is strange that without wind and a vehicle moving at 15 or 20 knots the bombs are very precise, wouldn't it be the same level of compensation that the bomb must do?

[Nealius]

Just adding some thoughts for the sake of discussion:

42 minutes ago, Hobel said:

that is also the case in DCS without wind the bomb is very very accurate.

42 minutes ago, Hobel said:

but since nothing is set in stone, it would of course be cool to see how it ultimately performs IRL, taking a  shot in 10-20 knots of wind and holding the laser directly on the target.

Real world is rarely 0 winds. I doubt the testing done to determine accuracy and CEP would only be in 0 or less than 10kt conditions. I also doubt real world deliveries were all done in sub-10kt winds, especially considering varying winds aloft between release point and surface winds. Realistically speaking I'm not sure it would even be possible for weaponeering testers to control the environment so much as to minimize winds during their ballistic testing.

EDIT Adding more info from -34 reading and Tacview:

Documentation says deliveries at >500KTAS should give >35deg terminal angle and thus excess energy in the terminal phase. Excess energy=energy to overcome winds. Looking at my Tacviews, my deliveries were on the slow side varying 475-500KTAS, but the bomb's terminal angle was usually around 60, meaning it should have excess energy.

Now the weird part is that the bomb is bullseying the laser spot until about 1,000~2,000ft AGL, at which point it suddenly shifts off target. This 1,000-2,000ft range is right around where the DCS hard-coded 1600ft wind sheer is. No idea if it's related but I'm throwing stuff at the wall here.

Edited September 1, 2023 by Nealius

[Hobel]

Hm could you create track of the situations so that we all see the same? 

 

And I see the point from the hints you give, you can otherwise contact @BIGNEWY via pm with it.

 

Zitat

Real world is rarely 0 winds. I doubt the testing done to determine accuracy and CEP

Yes and that is also the case, there are reports that talk about 10 knots of wind and a 3.7 cep is reached. However, it is not specified whether the pilots compensate the wind with an offset.

Edited September 1, 2023 by Hobel

[Nealius]

Contacted Bignewy but also found additional information in the -34 about wind corrections. It looks like we're both right, in a sense. Real-world doc says that laser spot should be offset upwind 1ft per 1kt of wind, but never more than 20ft. This seems to match the bomb errors I see in DCS. However it also says that wind offset shouldn't be necessary when dropping with a tailwind, whereas in DCS this error still occurs when releasing in a tailwind. I don't get why the manual contradicts itself by saying wind is compensated for then saying laser spot needs to be adjusted.

 

Track attached. Winds 10kts from the south. Tire markers 10ft upwind and downwind from the tank. First drop from the south (tailwind) should not need an offset laser spot per -34, however in this pass the bomb lands 15ft long, which also does not follow the 1ft per 1kt wind rule of thumb. Second pass from the north (headwind) should require laser offset but doesn't, as the bomb lands with 2~3ft accuracy. 

GBU12wind.trk

Edited September 1, 2023 by Nealius

[IrLED]

Reported similar problem ~1 year ago.
GBU-12 + wind on AV8B (i assume there is no wind correction for the laser spot on harrier targeting pod)
Tracks replays were unreliable back then.

General observation - zero wind and moving T-90 (50kmh ~=25kt) receives significant damage (but not direct hit)
stationary T-90 in 20kt(36kmh) wind doesn't get any damage because the miss is much greater.
I assume the tracking of stationary target + X kmh wind should be equivalent as X kmh moving target with zero wind for the GBU going through the airmass. But still air conditions give much better results.
Edge case for target moving directly downwind with the speed of wind should be equivalent to stationary target in still air (airmass moves with the target)