GBU12 missing targets by a few meters

[amalahama]

Are you sure AUTO doesn't perform wind correction?

[Fri13]

some of this makes sense, but then why is the bomb missing the target if lased onto it in presence of strong winds?[/Quote]

 

First need to make correction that bombs some use proportional navigation but pursuit navigation, so the laser spot is kept at center, simply pointing bomb at it and then let the bomb aerodynamics get it there.

 

But if you do not have lift to get there, you don't get there.

 

 

The study on Deliberate Force in Bosnia posted earlier says that real military pilots back then had issues in dropping LGB in high winds and had to change their delivery parameters to record better hits[/Quote]

 

Delivery parameters are that what gets bomb to drop near the target.

 

So when you have high wind, you drop upwind so the bomb will drop with The wind on target.

 

If you look at my post #40 I tried to change the release technique and lasing-timing reproducing what was discovered in that study and I was able to hit the target without lasing upwind. You need however a low altitude and high speed plus continuous-lasing to give the bomb the energy and time needed to maneuver itself, and this may not be possible during some deliveries (e.g. low-level threats, a/c type, etc)[/Quote]

 

Laser just adds a bomb to know what direction to point itself.

It does not make bomb kinematic properties different. No extra lift, no extra drag, no extra speed or anything like that.

 

So if you know a object ballistic properties, and you know wind properties, you can alter your delivery parameters so that bomb ballistic is such that wind properties affects it so that it will drop where you want.

 

It is simple as shooting a rifle. You know that gravity pulls bullet down specific manner when shooting level. You know that at given range the bullet drag causes it to slow down and drop even more.

So if you shoot indoor range, it becomes very easy to learn specific cartridge and rifle combination so that you are accurate with it.

 

But now if you go outdoors, you get moisture, temperature, wind etc that affects your bullet. Rain makes your bullet fly straighter as there is less drag, moisture changes drag properties etc. And then wind makes your bullet fly longer or shorter or sideways depending direction.

So if you know wind, you can compensate for it and adjust your sights or you adjust your aiming so that bullet hits where you want.

 

If we now would add a laser to that, where bullet has a sensor in front and fins so that bullet can be made pointing wanted direction, we get guidance. But the bullet still has limited capabilities to guide itself. So you can't shoot 45 degree off and expect it to turn on target even if it sees laser. If you increase bullet lift capabilities so it has greater turn capabilities, you can make it so.

 

 

Does it sound similar as example Hornet with VVI on HUD showing you where it actually flies, compared to where your nose truly is pointing?

 

The laser guided bomb has same problem, nose is made to point at laser target, but there is no aerodynamic capabilities to get it drop toward the laser spot. It is same as your nose points upward when landing and your VVI points on the landing strip. Unless you change some kinematic properties, you are going to touch ground and not get up. Why if you give more thrust, you start moving where you point yourself, up in the sky.

 

The GBU like GBU-12 doesn't have any extra in it. Simple fins with controlled ones so the nose can be pointed at the laser spot. And as long the it has kinematic energy (thrust) with the aerodynamic lift (fins size and AoA) it can change its trajectory toward laser spot and meet with it.

 

But if those ain't met, it will drop and drop in wrong trajectory and all it can do is keep pointing its nose toward laser and it just falls sideways even, if it just can turn itself around so much. But without lift it can't change trajectory.

 

So I think that the lasing upwind technique is more relevant to high altitude, "slow" speed release like for example if you drop it with the A-10C and that's why this technique is mentioned in that training mission.

 

I don't think they would insert such a statement if this wouldn't be accurate and the initial release of that campaign was around 2015. It would be interesting to know where they sourced that information, maybe the original designers of that campaign can chime in?

 

I know DCS has an history of long-lasting bugs but I don't think this is a bug at all. There are also a couple of other threads discussing this where they mention this upwind correction, they are quite old but they exists:

 

• What are the wind speed limitations of LGB ordinance?
   
  
• LGB help
  

 

I'm not saying that lasing upwind is the only technique to be used in case of LGB releases in high-winds, but in some cases it is needed if you don't give or you can't give the bomb enough energy and/or time to correct itself onto the target.[/Quote]

 

You should change the bomb drop parameters based the wind, not targeting.

 

So if flying upwind, then you drop later as the bomb speed will slow down from horizontal and then it start to get pushed in vertical fall by the wind back to way you came.

 

If wind is behind you, you drop sooner, as bomb will get extra push to move toward your heading and then pushed by wind even further forward.

 

If wind comes from sidewaysz you drop by flying on target from the side of wind direction.

 

And that is ballistic release point correction. Regardless do you have laser or not, you would hit target.

But with laser you can adjust your changes to hit target as your release precision doesn't need to be so exact, higher you are, less exact and closer you are more exact, as bomb has time-lift requirements to get falling toward laser spot.

 

And if aerodynamic properties don't allow, bomb will fall off.

It is same thing as shooting with rifle in high side wind or upwards/downwards same settings as indoor and at level.

Same thing with or without laser guidance when dropping bombs.

Or same thing as shooting missiles against high maneuvering target, missile aerodynamic properties with it's kinematic energy rules can missile intercept target. Missiles just has more complex guidance systems while bombs has some basic like the pure pursuit navigation, as you are not suppose to fight in unsuitable weather.

 

The new TPOD features might be there to help. As it added the Off-Set marker for lazing. So you can have TPOD tracking a target and then move Off-Set from it where laser points.

 

But Harrier ARBS system was made to calculate this in, and A-10C has the ballistic computer to correct the release point for the wind. But all those can work only so well as parameters are known. And if bomb needs to drop through multiple levels etc, it becomes challenging.

 

Now, what is odd is the auto-set windshear at 1600ft that DCS imposes based on the surface wind which again, in my opinion is somewhat unrealistic.

 

For a surface wind of 30kts, DCS auto-sets a 64kts wind at 1600ft, that is a lot. But this is OT

 

Yes it is. 12 m/s surface and 500 m is already a hurricane speed. You almost hover above the target with hornet when flying upwind.

[Fri13]

I don't know if DCS simulate this.

But IRL, Paveway II control surfaces are all or nothing.

Each time the guidance kit make a correction, the guidance kit control surfaces go full deflection, so each correction produce drag which depletes bomb's energy, and it may fall short.

This is way the preferred method is to delay the illumination, guiding the bomb only in termi:smilewink:nal phase preserves the bomb energy and maneuvering capacity.[/Quote]

 

That ain't modeled. We have Paveway III kind proportional guidance fins, so the bomb fins deflects only as much needed.

 

There are although situations that I have seen GBU-12 start very fast rapid oscillation at the final. The bomb literally points in one axis 45 degree opposite directions couple times a second, yet it falls perfectly straight.

 

So bombs might not have got AFM modeling like AGM-65 and others did.

 

The aircraft release system should compensate for the wind.

But if there are wind shears in various level of altitude, the bomb may drift outside of guiding parameters and miss.[/Quote]

 

Yes, too early or too late guidance and bomb flies itself outside it's capabilities to hit.

 

IMHO, with strong winds, releasing down wind makes more sense.

 

At the end, GBU-12 may not be the best suited weapon for moving targets. You have AGM-65 for that purpose.

 

GBU-49 was brought for F-35 for that reason, as GBU-12 is not suitable for moving targets. The GBU-49 has guidance kit with detection where target will be in X time, and it will guide itself there instead directly on target in pure pursuit mode.

 

So there ain't problems in laser guidance, but possible in bombs aerodynamic properties and still in Hornet/Viper possible missing features in targeting computer to calculate proper release point.

 

But as in reality GBU-49 was made to fix moving target problem, so should be in DCS that GBU-12 ain't suitable for moving targets or high wind scenarios.

[Fri13]

Actually I am going to change my opinion, don't yet get the math done in my head as I am doing something else, but it is about the bomb pure pursuit navigation system. Where it is guiding itself constantly to keep pointing at the laser point, but if you have enough force moving you laterally, then you might not generate enough lift by pointing on the laser spot so you will move laterally and bomb just keeps correcting itself toward pointing the laser spot so in otherwords, dropping down sideways.

 

So moving the laser spot upwind forces bomb to turn further toward wind than if lazing target, so the bomb should get just enough more lift generated to move toward upwind, but still "fall short" from the new laser spot position.

 

And this might be the reason why there is this offset tracking capability in the targeting pods as fighters like F-16 and F/A-18 doesn't have the A-10C wind calculation for firing computer, so you can keep tracking target by using offset on it, while the targeting pod is ponting a head of the target, and bomb is trying to hit that laser spot front of the moving target (or in the upwind side) while it is dropping toward the tracked target.

 

But does it work if you are rotating around the target, that offset would be angular stabilized?

[Fri13]

Not necessarily.

 

From the bomb point of view going against the wind is just like chasing a moving target.

 

So on my picture in trajectory A you aim your laser at the tank and let the bomb chase it.

On trajectory B you aim laser at the point where the tank will be at the impact point.

Clearly, trajectory B is much more energy efficient.

 

Now, to go back to the wind, if you aim upwind it's just like choosing trajectory b in the picture.

 

 

My only question is, should the Hornet take the wind into account when calculating release point or not?

 

The problem is in the bomb guidance and lift generation for the required speed.

As what the GBU-49 does is explained as:

 

The Enhanced Paveway II EGBU-12 is a dual-mode guided bomb designed to effectively operate in all-weather conditions. Laser-guided GBU-12s can only operate in optimal weather conditions endangers the laser beam which guides the bomb through its intended target. EGBU-12s, which were introduced in 2001 during operation Enduring Freedom in Afghanistan, relies on semi-active laser guidance and Global Positioning System (GPS) aided inertial guidance system to seamlessly hit the target. The GPS guides the bomb in poor weather conditions and laser guidance aides engaging mobile targets of opportunity.

 

The EGBU-12 was employed successfully during military operations in Afghanistan (Enduring Freedom 2001) and Iraq (Iraqi Freedom 2003) by the US Air Force and the armed forces of the United Kingdom. The same weapon was selected by the armed forces of Denmark and Spain as well as other international customers not disclosed yet (France?). As of May 2005, the EGBU-12 has been integrated onto the Tornado, Harrier and Super Etendard aircraft. Integration is under way on the F-16, F/A-18, AMX fighter/bomber, F-35 and Eurofighter aircraft. In May 2005, the Enhanced Paveway II bomb was undergoing integration on the F/A-18 aircraft on behalf of the US Navy at China Lake Test Range, California.

 

The GBU-49 was designed with built-in "lead laser capability" that allows the bomb to calculate how far a target will move, an ability the F-35’s suite of weapons doesn’t have in its 3i configuration, or the current software that has been in use since the aircraft hit initial operational capability last year.

 

Integrating GBU-49 with the F-35 can be done within the "single digital months" because much of the necessary activities have already taken place. GBU-49’s interfaces are very similar to the dual-mode Paveway 4 — which has already been integrated on the joint strike fighter for the U.K. — and its size and flight characteristics are comparable to the GBU-12 that’s part of the F-35’s 3i weapons load. Much of the ground-based testing has already been completed by Raytheon and F-35 prime contractor Lockheed Martin, Jarrett explained.

 

So the bomb should get uploaded with target coordinates (or movement vector and speed) before release, and then it tracks the laser spot, but it knows by using GPS that when it is not going to hit the target and will correct itself to higher angle so it get more lift to move upwind/direction of movement?

[Dagger71]

No, not in point, but in manual tracking of course.

 

 

 

 

Do you have a track of you "manually tracking" a moving target with an LGB? And where did you get this "procedure" from? Are you referring to the F18 or A10c?

[AW139]

Anyone else have this issue with JDAMs? Whenever I put drop JDAMS even in moderate winds, they don't hit on target and get blown downwind. I was bombing from 20,000 feet and they were hitting 50 feet away, entirely missing their targets. Removing the wind, and they hit dead center of the target.

[Drac]

Anyone else have this issue with JDAMs? Whenever I put drop JDAMS even in moderate winds, they don't hit on target and get blown downwind. I was bombing from 20,000 feet and they were hitting 50 feet away, entirely missing their targets. Removing the wind, and they hit dead center of the target.

 

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