Question on GBU-32 drops (TOO and PP)

[Recluse]

Dear Harrier Drivers,

 

This is marked RESOLVED/USER ERROR over in the other section:

 

Just wanted to get a sense of how many folks might be seeing this to figure out if it is a bug or machine specific thing.

 

I can drop GBU-38 all day long and get hits from either TOO or PP (F10 ATHS) modes so I think I have the switchology and procedure right. However, with the GBU-32, it ALMOST always drops way short. In TOO mode, I can OCCASIONALLY get a hit waiting for the countdown to go to ~95-97 into the LAR, but in PP mode, I cannot seem to hit no matter what. By contrast, I usually drop GBU-38 at about 65 on the LAR counter.

 

Just wanted to get a sense of whether this was widespread or not.

 

Thanks!

 

[Longiron]

From my experience it seems to be an issue with the default flight profile of the JDAM.

They appear to favor a top attack 90deg dive onto the target, with the dive starting about 6000ft or so.

Picture a funnel, so basically you release, and the bomb tries to conserve its altitude to the top of the funnel, and this is where it also bleeds a lot of speed trying to hold its altitude. The results are it then loses lift and never makes it into the funnel and falls short, never going into its terminal dive phase.

 

I have battled with this for some time, seems to be a limitation until we can define terminal and heading parameters for the bomb.

Rule of thumb for me now is to release when the range cue is at 7oclock to 5oclock.

[Alighierian]

Having had Elmo show me how it's done, and some more practice regarding it, I think it's partially user error, and partially terminal impact behaviour to blame. The lighter JDAM's are either more lenient in their funnel, as Longiron phrased it, or they simply have more energy to spare compared to the GBU-32's.

Given normal approaches are used, I never had an issue with the lighter JDAM's when dropped at the first instance of 100 LAR percentage number on the HUD. They basically behaved as if I was dropping normal dumb bombs via CCIP, with a relatively minor deviations based on target location, especially noticeable when doing Pre-planned multi target drops.

That said, I don't think it's directly a bad idea to drop them long, even more so when using the LJDAM's against targets moving in the same direction as you are, so the bomb has enough energy to get a proper angle. It just requires mentally setting a different value to drop at, rather than the first time it ticks to 100.

 

It would still be optimal if we could change terminal impact properties, though. I wouldn't be surprised at all if that would also solve this.

[Recluse]

32 minutes ago, Alighierian said:

Having had Elmo show me how it's done, and some more practice regarding it, I think it's partially user error, and partially terminal impact behaviour to blame. The lighter JDAM's are either more lenient in their funnel, as Longiron phrased it, or they simply have more energy to spare compared to the GBU-32's.

Given normal approaches are used, I never had an issue with the lighter JDAM's when dropped at the first instance of 100 LAR percentage number on the HUD. They basically behaved as if I was dropping normal dumb bombs via CCIP, with a relatively minor deviations based on target location, especially noticeable when doing Pre-planned multi target drops.

That said, I don't think it's directly a bad idea to drop them long, even more so when using the LJDAM's against targets moving in the same direction as you are, so the bomb has enough energy to get a proper angle. It just requires mentally setting a different value to drop at, rather than the first time it ticks to 100.

 

It would still be optimal if we could change terminal impact properties, though. I wouldn't be surprised at all if that would also solve this.

Thanks! Care to share Elmo's tips for GBU-32 and the Proper "Funnel" aspect? I have had little success at ~65 which seems to work for GBU-38 and variable success at ~97-100.

 

I seem to have SLIGHTLY better success doing TOO drops vs. F10 ATHS PP drops (maybe because DMT/FLIR is more precise than than the map markers).

 

Also interestingly, I found that dropping 4 PP GBU-38 from F10 CAS points in the current STABLE version worked much better than the current Open Beta, but GBU-38 were the opposite.

[Alighierian]

From the top of my head, as I haven't flown for a while now (new 1440p monitor and old GTX970 do not agree about DCS, still waiting for new GPU to actually be available):
- take a long enough approach, so you're not cutting things short with last ditch drops

- steady flying

- ~400kts so you can impart enough energy

- not sure about altitude, but 10-15k is fine for level flight JDAM dropping (lofting is also very possible, but a different ballpark)

- go through the appropriate targeting setup steps (MA on, AG mode, JDAM's selected, fuses on, target(s) selected (depending on PP/TOO)

- let the LAR% tick up to 100, and then a bit beyond (for a long drop), pickle around the 70-ish (not entirely sure on the value anymore, as, again, I haven't flown in a while)

- repeat as necessary

 

In regards to LJDAMing moving targets (very fun), it's basically the same as TOO, but for terminal guidance the TPOD laser (or other source) is used instead. Do note: the laser always overrules the GPS guidance from what I've noticed, so whilst you can do a multi-drop in TOO given you're nimble enough with the controls, that's not an option with laser designating a target, be it a normal GBU or a LJDAM.

I had the most success dropping whilst flying on the same trajectory as the moving target, so I had the longest amount of time to keep the laser on target. In that situation, you have to drop long, as the normal GPS TOO marker will be outdated pretty much as soon as you drop, resulting in not enough energy to catch up to a moving target if you drop on 100 LAR%.

 

As for lofting GBU-38's, something I've done quite a bit to deal with pesky long range sam systems, I basically follow the following method:
- approach on ~the same level as the target if possible, so generally on the deck

- once closed in to 15-10nm, kick the engine into just shy under full throttle (as to avoid the 15s engine burnout)

- around the 5-4.5, start a rapid 45° climb, and pickle around the 3nm to target on HUD

- turn, chaff/flare, and hit the deck again to avoid AA/SAM's

- admire the explosions

 

Obviously it only works with PP mode on known targets, but given you know the location(s), it's a fun way to hunt sams.

[Recluse]

OK, so you are saying for GBU-32 drop against stationary targets, GO LONG? i.e. let the LAR counter pass 100 and count back down to 70?

 

I honestly haven't messed with the LJDAM or moving targets, just want to get the 1000 pounder on targets that are too tough for the GBU-38's.

 

Edit: SWEET! That worked just fine. 4/4 hits with GBU-32. Two PP and Two TOO. I waited till the initial 100 counted back down to between 60 and 70, so the "5 -7 o'clock" that Longiron mentioned looks about right.  One of these days we will figure out what those numbers really mean w/re to LAR. Maybe they have more meaning when we get Terminal guidance settings. This time I paid attention to the LAR circles on the EHSD as well. and noted that it was still well between MAX and MIN ranges.  Thanks to both of you. I am a happy JDAMer now!

Edited December 22, 2020 by Recluse

[Vakarian]

1 hour ago, Recluse said:

... One of these days we will figure out what those numbers really mean w/re to LAR. ...

 

 

Only god knows that. That countdown goes like this. 0 (outer circle) -> 100 -> 0 (center of the zone in EHSD) -> 100 -> 0 (inner circle)

 

I tend to disregard those numbers as there isn't documented what does that represent so I just use the unwinding thingy on HUD and release bombs from between 9 and 6 o'clock which seems to yield best results.

 

There really is a need for a manual, depicting exactly what RB have implemented. A bunch of stuff is lost in translation what works on a plane and what the thing is supposed to be doing on real aircraft.

[LastRifleRound]

18 hours ago, Vakarian said:

 

Only god knows that. That countdown goes like this. 0 (outer circle) -> 100 -> 0 (center of the zone in EHSD) -> 100 -> 0 (inner circle)

 

I tend to disregard those numbers as there isn't documented what does that represent so I just use the unwinding thingy on HUD and release bombs from between 9 and 6 o'clock which seems to yield best results.

 

There really is a need for a manual, depicting exactly what RB have implemented. A bunch of stuff is lost in translation what works on a plane and what the thing is supposed to be doing on real aircraft.

The countdown is bugged. It's just supposed to be 0-100-0. Represents how close to LAR center you are. Therefore, the bug could in the calculation, or the LAR itself.