Alt restriction on dropping GBU12s?

[rrohde]

Hi,

 

just a quick question - yesterday I flew the awesome Viper mission "Dawn Raiders", and I selected to drop one pair of GBU12s on the first target at WP3, and another pair at WP4 using CCRP.

 

I was at FL250.

 

However, both pairs missed their targets, even though the TGP was correctly slewed to their respective targets, and I was lasing right after bomb release until the TPG could no longer see the target.

 

No joy.

 

Should I have flown lower with GBU12s? Something else?

 

That said, redoing the same mission with 2x GBU10s instead, with the same parameters applied as above, I was able to hit both targets just fine.

 

Thanks.

[will-]

check ur ins. steerpoint on hud vs tgp.

 

the only alt restriction is the ability to get the bomb to track to target. so best results would be higher the better.

Edited November 5, 2019 by will-

[rrohde]

Good to know - I will check.

[sobek]

The laser designator usually has a max range depending on attenuation, which depends on atmospheric conditions. Above that range, too little laser energy is reflected by the target for the bomb to pick up. Not sure if DCS models a max range for the laser designator though.

[Harker]

The laser designator usually has a max range depending on attenuation, which depends on atmospheric conditions. Above that range, too little laser energy is reflected by the target for the bomb to pick up. Not sure if DCS models a max range for the laser designator though.

It's 8 NM in DCS, IIRC. With the difference that the laser spot will float in mid-air if the laser beam doesn't intersect a target or the ground within 8 NM. This should be kept in mind when deploying weaponry, as it can obviously cause very weird behavior with laser guided weapons.

[Oceandar]

Hi,

 

just a quick question - yesterday I flew the awesome Viper mission "Dawn Raiders", and I selected to drop one pair of GBU12s on the first target at WP3, and another pair at WP4 using CCRP.

 

I was at FL250.

 

However, both pairs missed their targets, even though the TGP was correctly slewed to their respective targets, and I was lasing right after bomb release until the TPG could no longer see the target.

 

No joy.

 

Should I have flown lower with GBU12s? Something else?

 

That said, redoing the same mission with 2x GBU10s instead, with the same parameters applied as above, I was able to hit both targets just fine.

 

Thanks.

Just happened to me yesterday on 104th server. First lgb dropped below 20k hit its mark with delay lasing around 5 sec. Second LGB dropped above 20k missed. So I tried again, this time with same alt but with delay lasing 2 sec and it hit the target.

[rrohde]

So, I flew the mission again yesterday, with the original loadout. This time, both targets were destroyed.

 

What changed? Well, the first time around when I missed both targets I let the TGP slew itself onto steerpoint 3 and 4 respectively, but I didn't touch the TGP crosshair any further, and I didn't go TMS right to area-stabilize it. I didn't slew it, I just let it sit there and started lasing.

 

Yesterday, I pretty much did the same except for manually slewing the TGP crosshairs a little - and now all the bombs hit.

 

Question about that - when the TGP slews itself onto a steerpoint that already shows the correct targets and there really isn't any need to move the crosshair at all, would that leave the TGP in a caged state and I have to move it to uncage it? Or would simply point- or area-stabilizing do the trick here?

 

Thanks.

[Frederf]

The difference is if the laser is inhibited or not. I'm not exactly sure if it's a realistic requirement to be in inertial area or point when lasing. The A-10C module is this way. Overall it's very odd to not be from a practical point of view.

 

 

 

There is positive visual feedback of laser emission and this should be the first point of troubleshooting

[SkipperSMG]

Laser is not intended to be fired right after release. AFAIK gbu12 guidance consists only of "point head to laser". This will disturb flight and can lead to a miss. Let the bomb go balistic until 15-8 seconds (depends on alt and conditions) before impact. Right now we have no time to impact counter. so we can only guess. Maybe thats the reason you missed. Or as @Harker already said.

[Mover]

Have you guys/gals ever heard of "bang-bang" guidance?

[Dee-Jay]

Hi!

 

Laser is not intended to be fired right after release. AFAIK gbu12 guidance consists only of "point head to laser". This will disturb flight and can lead to a miss. Let the bomb go balistic until 15-8 seconds (depends on alt and conditions) before impact.

 

For GBU-12.

For GBU-24 (lets rather say : for PIII) it is another story.

 

Regards.

[rrohde]

Have you guys/gals ever heard of "bang-bang" guidance?

 

Can’t say I Have. Could you share some insights?

[rrohde]

So after releasing the bomb, I usually maintain a turn 30 degs left or right to allow the TGP to maintain line-of-sight until impact; is that what this means?

 

Thanks.

[rrohde]

Also, interesting notes on the GBU12 and time of lasing. Wasn't aware.

[Frederf]

High altitude delivery means that continuous lasing is perfectly adequate. If you are flying at 1,000' at 550 knots like an F-111 then yes continuous lasing for PII bomb can be a problem. From 20,000' accuracy is essentially the same. Only for real world weaponeering effects where bomb impact velocity of 650 knots v 500 knots is of importance is it of any worth to avoid early guidance. From level delivery the first several seconds of lasing don't produce guidance anyway because the bomb is looking at the horizon and not the laser.

 

Leaning away during lase is supposed to keep the illuminated laser spot on the same side of the building at the bomb. Flying directly over the target such as a building means the laser spot goes from the front wall to the roof to the back wall very shortly before bomb impact. From the bomb's point of view the laser spot hides in the backyard and tracking is lost. DCS has never demonstrated this effect and so it can be ignored.

 

Drop your bomb and look at it with F6 external view. PII under laser guidance is distinctive. Don't worry about such advanced topics is it's obvious bomb never guides. A bomb miss can be caused by so many things. Confirming that guiding is happening at all must be analyzed before one becomes preoccupied with how it's guiding.

[rrohde]

This is very useful info, Frederf - thank you.

 

 

The below is a key learning point for me, so thank you for the write-up! :thumbup:

 

Leaning away during lase is supposed to keep the illuminated laser spot on the same side of the building at the bomb. Flying directly over the target such as a building means the laser spot goes from the front wall to the roof to the back wall very shortly before bomb impact. From the bomb's point of view the laser spot hides in the backyard and tracking is lost. DCS has never demonstrated this effect and so it can be ignored.

[rrohde]

@Frederf "PII under laser guidance is distinctive." <<< could you clarify this a little?

[Dee-Jay]

Hi!

 

@Frederf "PII under laser guidance is distinctive." <<< could you clarify this a little?

 

He means this:

Have you guys/gals ever heard of "bang-bang" guidance?

 

... control surfaces are not proportional ... they are behaving "all or nothing". This is why lasing too early will bleed its energy and could (will) make it falling short.

 

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

 

"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."

 

 

Regards.

Edited November 7, 2019 by Dee-Jay

[rrohde]

@Dee-Jay: Thank you - this is very useful as well. Didn't consider that lasing too early can affect the bomb itself that way.

[Dee-Jay]

When Fred says "distinctive" :

 

@

 

${1}

[rrohde]

Thanks for the visualization.

[rrohde]

Have you guys/gals ever heard of "bang-bang" guidance?

 

Ok, found some info on it - thanks for the pointer:

 

"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."

 

Source

[sobek]

... control surfaces are not proportional ... they are behaving "all or nothing". This is why lasing too early will bleed its energy and could (will) make it falling short.

 

 

Well the issue is less that the guidance is bang-bang, but that it doesn't guide on a ballistic path. Instead it guides on a straight collision course, which is a problem when the line of sight is less steep than the bombs best achievable glide angle (which, owing to its small wings, isn't stellar to begin with). It wastes a lot of energy if it is allowed to guide immediately. The Paveway III dealt with both of these issues (it has proportional guidance and it guides onto a much more optimal flight path).

Edited November 7, 2019 by sobek

[greenmamba]

Running into similar issues with LGB on the Persian Gulf map only.

 

I wait 8 to 10 seconds before lasing and the bomb falls short or long from the target.

 

Booted up the training mission on the Nevada map for LGB, and i did hit the target everytime.

 

I fly to the target with the target steering line centerd, pickle, wait 8 to 10 seconds before lasing, once overhead the target i make a left turn and continue lasing. No interruption in the lasing and the bomb fall off target everytime. This is only happening since the latest update to the F-16 module. In the Nevada map it works like a charm.

[Notso]

Laser is not intended to be fired right after release. AFAIK gbu12 guidance consists only of "point head to laser". This will disturb flight and can lead to a miss. Let the bomb go balistic until 15-8 seconds (depends on alt and conditions) before impact. Right now we have no time to impact counter. so we can only guess. Maybe thats the reason you missed. Or as @Harker already said.

 

Not entirely true. For Paveway II weapons, there is always a constant debate about Continuous vs Delayed Lasing. Both work fine, as long as you are in the correct parameters. The absolute min lase time is 8 sec before impact, but most will pad that to 10-12 sec to impact to account for some slop in the timing countdown and to account for the eye to brain to finger delay of seeing the time on the screen and then commanding the finger to push the laser fire button.

 

The debate centers solely around weapon energy. The conventional wisdom is ALWAYS delay lase if releasing from low altitude such as a dive toss or loft. Because if the laser is on at release and the seeker sees the laser energy, the weapon will immediately maneuver to attain a direct flight path to the target. If already at a low energy state, this will bleed energy even more and most likely cause a miss short.

 

However, if dropping from Medium altitude and above (usually defined as around 15K HAT to about 25K HAT, IIRC) - the the PWII can be continuous lased as the weapon ballistic profile is usually energy gaining anyway. On top of that, the PWII seeker is not usually able to see the laser spot from that distance (~ 4.5-5.5nm slant range) until it gets within its acquisition range anyway, depending on atmospheric conditions, so its a moot point if the laser is on at release or not.

 

Another factor to consider is winds. The jet's computer will account for winds at release altitude and then do a standard algorithm to "model" the winds from release down to the surface, but unless there is a wind model that can be manually programmed or captured - if there is any kind of windsheer, the bomb might be pushed out of the ballistic "basket" to the point where it might not see the laser spot when its turned on by the pilot because it's no longer looking at the correct area.

 

Bottom line is from higher altitudes (15K HAT and up) - delay or continuous should both work fine. But most will use 10-12 sec delay lase to stick with one habit pattern for all cases and then adjust for special circumstances like strong wind sheers and such. Especially with GBU-10s as they are MUCH more energy sensitive than GBU-12s, delay lase is usually always recommended.

 

GBU-24s are an entirely different animal.

 

Speaking of which, is there going to be a TTI counter added to the F-16 module?