GBU-12's are missing target

Question 2 - are you lasing prior to releasing the weapon, or immediately upon release? If so, good practice is to release the weapon and then fire the laser. From higher altitude, sometimes up to 5 seconds after release.

This! And I would recommend waiting with lasing untill 10-15 seconds time to impact (TTI). The reason for this is the rather old guidance system of the Paveway II series, the so called bang-bang guidance. This causes the bomb to loose a lot of energy once it starts guiding on a laser and if it starts guiding too early it can happen that it falls short as it looses too much energy.

Paveway II laser-guided bombs use what is known as "bang bang" guidance. This means the bomb's fins deflect fully, rather than proportionally when it is attempting to guide to the laser spot. For example, if it sees the laser spot and determines that it should make a change it deflects its fins until it has over-corrected and then it deflects back the opposite direction, creating a sinusoidal type of flight path. This type of guidance may be less efficient at times, however is more cost effective and allows the use of simpler electronics in the guidance system.

https://en.wikipedia.org/wiki/GBU-12_Paveway_II

Hi,

To answer those question first :

- The waypoint is not designated (not boxed), not necessary for LGW,

- I am first release the weapon and then lase the target 15 seconds TTI (I have tried also 20, 25 and 30 seconds)

- I have tried to spot the base and the middle of the vehicle

Here's a track with the stable version, giving the same result : https://drive.google.com/open?id=16gqV7866KOeG3aBYSzlpxdFvyvXuKe5X

This is not caused by the wind because the bomb always falling on the left and slightly after the target, independently of the attack direction.

Hi,

I don't know if you can see that on tracks, but I observed the bomb maneuvering to the target.

15 seconds TTI, I set the laser ON and the bomb attempt to capture the laser point, but still not flying to the target.

The bomb try to correct the impact point in the last few hundred feet, 2-3 seconds before impact, and obviously unable to hit the target.

I hope this help.

Hi,

 

I don't know if you can see that on tracks, but I observed the bomb maneuvering to the target.

 

15 seconds TTI, I set the laser ON and the bomb attempt to capture the laser point, but still not flying to the target.

 

The bomb try to correct the impact point in the last few hundred feet, 2-3 seconds before impact, and obviously unable to hit the target.

 

I hope this help.

Is your release type set to AUTO (stores page, select desired LGB, left column of OSB's, top option)?

Cheers,

Don (callsign Ziptie)

Yes.

By the way, I posted some tracks to check.

I tried also with GBU-16 and -10, and those bombs have the same flight path.

So, i tried with no wind, and the bomb is hitting the target.

The wind seems to be the problem.

When is the bomb supposed to correct for the wind ? Seems that the LGB bombs are not able to correct for the wind component.

Is there a wind limitations for those kind of bombs ?

That is correct, for my mission, I used real weather condition from archive :

201810112358 METAR KLSV 112358Z 01019KT 10SM CLR 24/09 A2979 RMK AO2A PK WND 01029/01 SLPNO T02430087 10260 20239 53002=

6000ft 220/57

FL240 260/97

The ME give automatically 190°/41kts at 1600ft, which is a quite high component.

When I fly a heading of 280 to align the FPV with the fall line, the LGB is influence more by lower layer wind at 1600ft.

I try again with a heading of 010°, so I have to correct my heading for the wind component and anticipate the moment I have to drop the bomb (which is indicated by the fall line and the timing), but the bomb have a better correction on the lower layer and fall very close to the target, enought to destroy it.

I am always surprised how DCS can be so realistic.

I am still curious to know if there is a wind limitations for LGB ?

Thanks for all suggestions and have a good day;

vctpil,

It's not surprising that you're not hitting the target on a run-in heading of 280 with those winds. You're dropping the weapons with a 41 knot crosswind.

I can't speak to wind limitations on the LGB, but I can confirm that LGBs do "weather vane" naturally during their fall. While in flight, winds will blow them downwind off target, and when the laser spot is on (and acquired by the guidance package), they'll compensate by steering back upwind. This results in a curved trajectory when viewed from top down. The stronger the winds, the greater the distance the weapon will be blown off target. Likewise, the longer the time from release to impact, the greater the effect of the wind.

For this reason, it's recommended that the lasing aircraft come off the target on the downwind side, thus reducing the chance that the spot will be masked by the target itself as the weapon comes in from the downwind side.

I understood that during those flights test.

Like a lot of people, including myself, using LGB assure a target destroyed. This is not always the case.

Too much realistic... lol (for a real pilot like me)

This! And I would recommend waiting with lasing untill 10-15 seconds time to impact (TTI). The reason for this is the rather old guidance system of the Paveway II series, the so called bang-bang guidance. This causes the bomb to loose a lot of energy once it starts guiding on a laser and if it starts guiding too early it can happen that it falls short as it looses too much energy.

 

 

 

https://en.wikipedia.org/wiki/GBU-12_Paveway_II

True, but is it confirmed that this is simulated?

Question 1 - are you placing the laser spot at the base of the vehicle, or directly on the vehicle (say the turret of the tank)?

There is, and has been an issue of weapons not hitting the target due to the laser actually passing through the target (vehicle/building).

 

Question 2 - are you lasing prior to releasing the weapon, or immediately upon release? If so, good practice is to release the weapon and then fire the laser. From higher altitude, sometimes up to 5 seconds after release.

 

 

Trying to assist, as currently the LGB's are working as intended for me on the Hornet (among others).

 

 

Cheers,

 

Don (callsign Ziptie)

Hey Ziptie, to your Q1 - I have not seen any issues so far with lasing the top of a tank turret or the roof of a building. That is the preferred technique with a horizontally developed target and I've had very good success tank plinking that way with GBU-12s.

On your Q2 comment - I disagree with your statement about lasing 5 sec after release from a higher altitude drop. A 5 Sec delay after release is (from the bomb's POV) continuous lasing. Typical Time of Fall (TOF) from say 20K is around 35 sec. So if you are delaying only 5 sec - then you are getting a full 30 sec of lase time which is essentially continuous lasing. If you truly want to delay lase, then you want to to wait until no earlier than 15" Time to Impact (TTI). Ideally, you would want start lasing around 8-12" TTI for a true delay lase attack. Anything over 16 Sec of lasing time is considered Continuous lase for practical purposes.

As I said on in earlier post - there are two schools of thought on the Continuous Lase vs Delay Lase technique when we are doing Medium Altitude or higher deliveries, i.e. 15K HAT or higher. The Continuous Lase camp correctly says that the bomb will be in an energy gaining maneuver due to the ballistics and long TOF and that it will have more than enough energy to overcome the bang bang guidance issues. The Delay Lase guys say that more energy is always mo better, so delay lasing is the way to go. Plus it keeps you in one habit pattern because Low Altitude deliveries are almost always delay lase, so just do it one way always for muscle memory.

There are some caveats however. The accepted technique is that if there are known strong winds at the surface and your jets wind model will account for it, then delay lase to make sure the bomb has more than sufficient energy to overcome the wind. If however you have unknown winds or a suspected wind shear where it changes directions from release altitude to the surface, then continuous lase to make sure the bomb doesn't get blown out of the seeker FOV before the laser is turned on and live with some lower energy and takes your chances that it hits.

So, i tried with no wind, and the bomb is hitting the target.

 

The wind seems to be the problem.

 

When is the bomb supposed to correct for the wind ? Seems that the LGB bombs are not able to correct for the wind component.

 

Is there a wind limitations for those kind of bombs ?

It has nothing to do with the bomb's wind limitation, it likely has to do with the jet's inability to calculate the winds at other than the release altitude and therefore adjust the release point correctly. If the release point is accounted for correctly and you delay lase - the bomb should (in theory) have sufficient energy to hit the target.

I posted a question to the Mod's about wind modelling that might explain some of what you're seeing: https://forums.eagle.ru/showthread.php?t=257983

The reality is that despite your best efforts and even if you do the attack perfectly - sometimes the bomb just misses. No weapon is 100% perfect, even JDAMs, although they are close. Barring a seeker failure (which does sometimes happen), the culprit for most misses is either too much spot motion - moving the crosshair around in the last critical 10 sec or so - or strong winds at the surface. If the jet's bombing computer can't account for that wind and adjust the release point upwind accordingly, then the bomb will struggle to hit the target. Sometimes "sh*t happens. That is why most weapons accuracies are expressed as CE90 or CE50. I don't remember the exact numbers, but let's say the CE90 of a GBU-12 is 5 meters and the CE50 is 5m. That means that 90% of all weapons dropped will hit within 5m of the aimpoint and 50% will hit within 3m. Which obviously means that 10% & 50% don't hit within those parameters.

To mitigate some of these wind issues - if tactics, threats and the target orientation allows - always try to drop with a Tailwind.

vctpil,

 

It's not surprising that you're not hitting the target on a run-in heading of 280 with those winds. You're dropping the weapons with a 41 knot crosswind.

 

I can't speak to wind limitations on the LGB, but I can confirm that LGBs do "weather vane" naturally during their fall. While in flight, winds will blow them downwind off target, and when the laser spot is on (and acquired by the guidance package), they'll compensate by steering back upwind. This results in a curved trajectory when viewed from top down. The stronger the winds, the greater the distance the weapon will be blown off target. Likewise, the longer the time from release to impact, the greater the effect of the wind.

 

For this reason, it's recommended that the lasing aircraft come off the target on the downwind side, thus reducing the chance that the spot will be masked by the target itself as the weapon comes in from the downwind side.

To your bolded statement above, that is not exactly correct. The bomb doesn't "weathervane" when its released because both the jet and the bomb are flying in the same air mass. For instance if you are dropping in a 41kt crosswind, at the instant the bomb is ejected off the pylon, it doesn't suddenly cock into the wind because its already travelling in the same air mass and drifting downwind with the jet. You are correct, however, that when the bomb sees the laser spot, it will then Point at the laser spot on a direct LOS path.

Ideally though, the jet's bombing computer has already accounted for the wind and moved the release point well upwind. So once the laser is turned on, the bomb is already upwind of the target and it doesn't have to "fight" the wind to get there. The easy way to tell this is to look at the TD box on the ground and the Bomb Fall Line (BFL). If you are dropping with no wind or a pure HW or TW - the BFL will be coincident with the TD box. i.e. it will run right through the box or diamond on the ground. However, if you're dropping in a crosswind, the BFL should be upwind of the TD box or diamond on the ground. If you line up early, you will be able to see the TD box in your HUD and compare the BFL to it. The stronger the wind, the more the BFL is upwind of the box/diamond on the ground.

It appears that DCS is modelling winds because I've noted the TD Box upwind of the target on XW attacks. But I suspect it's only accounting for the wind at the release altitude. I don't know what the DCS wind model does after that. The worst case scenario is if the winds are relatively light at altitude but strong on the surface, the jet won't account for enough wind correction at release and the bomb will most likely miss because it then has to fight its way back upwind. The reverse is true as well such as a honking wind at altitude but very light halfway down to the surface. But this usually isn't as catastrophic unless the bomb is too far upwind for the target to be out of the relatively narrow seeker FOV.

The simple answer is, if possible, try to avoid dropping in a crosswind at all costs.

Great few post Notso,

Thanks for the intel...

Makes total sense :)

Sound logical, thanks a lot for the post.

Great few post Notso,

 

Thanks for the intel...

 

Makes total sense :)

Thanks, happy to help out. I'm always worried I'm overdoing it and getting into TL;DR. But its a complex subject.

I think the DCS wind model (or lack of one) is at the key to a lot (but not all) of these LGB miss issues being reported. Almost all tactical jets since at least about the mid-2000s will have some sort of wind model that will not only calculate the release point based on the release alt winds, but will then extrapolate those winds down to the surface using a set of pre-programmed assumptions so it can adjust the 3D release point taking all of that into account. As tapes got more sophisticated and features were added based on real world lessons learned - the wind models got much more detailed and user configurable. For instance, through the MPD in flight or through the DTC after mission planning back in the Sq - the pilot could preselect several wind bands to either manually input the winds based off the forecast or more ideally capture the winds in the target area in real time. The latter being the prefered method for obvious reasons. That works fantastic if you're doing a low level ingress and then will pop up to med altitude to drop the weapons, because you capture the winds on the climb and they are then used by the bombing computer to massage the release point. But that's not always practical if you're doing a med or high altitude ingress to the target.

If the three main jets we are discussing (Hornet, Viper and A-10C) do not have this and rather have the single wind model that adjusts for winds at release only - that's not a slam on DCS or the ED team. But it may just be reflective of the tape loads at the time of the block jet they are modeling. And if so, it means there is still a lot of knowledge of how the LGBs work and a lot of technique to account for those variables. That's real life. The one thing most people need to understand is a GBU-12 and certainly not a GBU-10 is a 100% death ray from above. PWII is a finicky weapon that requires lots of love and understanding to make work well. :smilewink: If you think the PWII is difficult - try a PWIII, which I hope we will be getting soon. Yeah a GBU-24 can handle winds FAR better than a GBU-10 and is far more accurate. But it is a very difficult weapon to understand and employ, depending on the mode used. There were LOTS and lots of GBU-24 misses in the early days of both OIF and OEF due mainly to just plain misunderstanding of the weapon, especially when trying to get them inside cave entrances in Tora Bora.

Notso,

My apologies for not being entirely clear. I was attempting to use illustrative language to simplify what happens, and OF COURSE the weapon doesn't SUDDENLY "cock into the wind", it will respond to the forces acting upon it. In the absence of a guidance package, the weapon will follow a ballistic flight path as established by the launch parameters, and will be affected by the wind over the time of flight. As you correctly point out, the wind's effects are not constant. The guidance will attempt to compensate for those varying environmental conditions, directing the weapon back upwind as needed, and resulting in a flight path which is curved when viewed from above. The guidance package absolutely will "fight the wind"; that's the entire point. The guidance package exists because of the uncertainty inherent in the exterior ballistics.

I'm not entirely sure what means you believe would be available to an aircraft weapons computer to measure the winds at every level between the aircraft and the target. It makes perfect sense to me that the weapons computer would automatically compensate only for the winds affecting the aircraft itself; that's the information that is readily available through onboard sensors. As for surface winds, I would expect the JTAC to advise the pilot if he feels the surface winds will be a factor in delivery. Environmental factors in between are simply unknown without additional measurements not commonly available in a tactical situation, and it's the function of the guidance package to minimize the effect of the environmental factors during the bomb's fall. No amount of assumption or extrapolation can change the fact that without actually measuring the wind data, those winds not in the immediate vicinity of the jet are an unknown.

Launch it in 300kts airspeed. Try to mantain iluminated the target, adjust the velocity. If you launch it fast, sure you miss.

Notso,

 

My apologies for not being entirely clear. I was attempting to use illustrative language to simplify what happens, and OF COURSE the weapon doesn't SUDDENLY "cock into the wind", it will respond to the forces acting upon it. In the absence of a guidance package, the weapon will follow a ballistic flight path as established by the launch parameters, and will be affected by the wind over the time of flight. As you correctly point out, the wind's effects are not constant. The guidance will attempt to compensate for those varying environmental conditions, directing the weapon back upwind as needed, and resulting in a flight path which is curved when viewed from above. The guidance package absolutely will "fight the wind"; that's the entire point. The guidance package exists because of the uncertainty inherent in the exterior ballistics.

 

I'm not entirely sure what means you believe would be available to an aircraft weapons computer to measure the winds at every level between the aircraft and the target. It makes perfect sense to me that the weapons computer would automatically compensate only for the winds affecting the aircraft itself; that's the information that is readily available through onboard sensors. As for surface winds, I would expect the JTAC to advise the pilot if he feels the surface winds will be a factor in delivery. Environmental factors in between are simply unknown without additional measurements not commonly available in a tactical situation, and it's the function of the guidance package to minimize the effect of the environmental factors during the bomb's fall. No amount of assumption or extrapolation can change the fact that without actually measuring the wind data, those winds not in the immediate vicinity of the jet are an unknown.

Hi Yoda, no worries. All good on the weathervane definition.

However, it is incorrect that modern tactical jets from about 2005ish don't have a means to measure or input the winds for other than release altitude so it can give the weapons computer better data to adjust the release point. See my thread over on the DCS 2.5 forum for a discussion on wind models. https://forums.eagle.ru/showthread.php?t=257983

Yes, very early bombing computers with early INS could only measure the wind at release - so the bomb solution assumes a constant 40 kt wind for instance from release all the way to the surface, which is not ever going to happen. Then later they added algorithms to measure the winds at release and then extrapolate those winds to the surface using a wind decay formula of some sort - as the norm is the winds typically decrease as you get lower in altitude. But even that was found to be seriously lacking - as the winds never follow some standard pattern. You can have light winds at 15K and 30kts on the surface. You can have winds 90-180 deg different directions between release and the ground. So the engineers built better wind model programs to attempt to account for this either through the ability of the pilot to manually input the forecast winds in the TGT area or have the computer auto capture them as it flies through various altitudes. Or both. Usually both.

Again, I cannot say with certainty that the Hornet or the Viper has the ability to either manually input winds at various altitudes or have the jets computer auto capture them as it climbs or descends - but other contemporary jets such as the A-10C and the Strike Eagle absolutely have that ability. So it would greatly surprise me if either of the aforementioned jets did not have the same capability.

And I still somewhat disagree that in all cases the bomb is having to fight its way upwind the entire way. If the bombing computer is doing its job, the jet is going to release upwind of the target and the bomb will fall downwind towards the TGT - either ballistically if the laser is off, or on a direct LOS path to the target if the laser is on and the seeker head sees it. But in both cases the bomb is already UPWIND of the target. Unless something is really screwed up at release, the bomb doesn't cross over the target to the other side and then have to swim back upstream. It just doesn't work that way. Even if you drop the weapon in a direct HW, yes in this case it will have to fight its way upwind - but the jet should compensate for that by dropping it much closer to the target than in a no wind situation and the combo of vectors will still have the weapon arrive at the target. So yes in this one case its fighting its way upwind, but that release point has already (in theory) been compensated for in the release point IF it has good wind data and the GBU won't have to expend as much energy as it would if the wind was not accounted for correctly.

But even despite all these Gucci advanced wind models - nothing is ever perfect or steady. So the mantra is: "IF POSSIBLE, NEVER DROP WITH A HW OR XW". Its the "if possible" that always bites you.

Launch it in 300kts airspeed. Try to mantain iluminated the target, adjust the velocity. If you launch it fast, sure you miss.

That is exactly the opposite of how its supposed to be done. Faster is better, up the weapon carriage limits.