GBU-24 Kinematics/CCRP Calculations Issue
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I noticed some new behavior with GBU-24s that is causing them to overshoot by quite a bit. It appears (to my layman eyes) that the CCRP drop parameters do not match the kinematics of the bombs. I discovered this first in a campaign flight, but reproduced the issue in a controlled TE.
To preface, I am aware that LGB CCRP drop cues factor in some additional energy to keep the bomb from falling short when you lase. The behavior I’m seeing is specific to the GBU-24, where the bomb drastically overshoots the target enough that the seeker can no longer see the lased target by the time lasing begins.
Version: BMS 4.34
Description Overview: GBU-24 bombs travel significantly farther than SPI when released in CCRP auto-drop mode.
Picture:
Test Conditions:
Test-specific LGB TE (see download below), Sunny conditions, reduced clouds from default.
Target unit is ACRV on the far northwest corner of the enemy battalion.
Straight and level at ~25,600 ASL, ~340-350kts.
CCRP auto-drop (hold pickle before drop cue and let the computer release the bomb).
Units are stationary.Expected Behavior:
Bombs fall with enough extra energy to slightly overshoot the target SPI.
Lasing the target at 8-16 seconds is seen by the bomb seeker, bomb trajectory changes as seeker “captures” the laser.
Bomb hits target.Observed Behavior:
Bomb falls with enough additional energy to impact just over 3nm from the target.
By the time lasing begins, the bomb is past the target and the seeker cannot see the lased target to adjust the bomb trajectory.Please see the TE and ACMI download links below:
LGB Test TE Download
Test ACMI DownloadI tested with GBU-10s and verified that they do not suffer from the same issue. I have been told that LGTRs do suffer from this problem, however I have not tested those.
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Hi!
Bomb falls with enough additional energy to impact just over 3nm from the target.
Normal.
By the time lasing begins, the bomb is past the target and the seeker cannot see the lased target to adjust the bomb trajectory.
Lase earlier.
I need to check , bit if I remember corectly PIII “shall” be continuously lased.
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Paveway III should almost always be lased as long as possible since it uses that info well. It’s normal for PII to be kinematically long by some amount so extra energy can be used to maneuver. I’m sure real F-16 has a toggle option so in emergency cases can be dropped ballistic (vice energy surplus) trajectory if used without laser. PIII has some sophistication like barometric altimeter and digital autopilot but I don’t know how much BMS models. PIII has pretty good FOV scanning laser detector so it should see things well off axis but you actually have to have laser on.
I think possible PIII should have energy positive release disabled because PIII already performs well enough with ballistic release to not need it. But if I remember right it is normal for no-laser PIII to fly some kind of energy optimized profile which explains the long miss excess distance. I wonder how it performs with continuous lasing.
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IIRC I used ~20 - 25 seconds lasing time with PIII and it was always working. 8 - 16 seconds may be too close and the bomb may already overshot the point where it can spot the laser spot.
Also, do not count on auto lasing, AFAIK in real the pilot is always lasing manually, in all cases. -
IIRC I used ~20 - 25 seconds lasing time with PIII and it was always working. 8 - 16 seconds may be too close and the bomb may already overshot the point where it can spot the laser spot.
Also, do not count on auto lasing, AFAIK in real the pilot is always lasing manually, in all cases.Sorry for the slight off topic, but it’s a laser related question regarding the GBU-54 LJDAM. With the bomb set from CTNL page 2 to AFTER, can you give position updates before the auto lase time? Say you drop a -54 on a static, and it moves from A to B 1/3 of the way of the bombs flight path; can you ‘blip’ the laser to update the INS/GPS guidance data before the auto lase has started?
Or once it’s in the laser ‘stage’, is it still essentially a GBU that requires constant lasing?
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I think auto lase time controls F-16 emission with no change to bomb logic. If for example someone else were to lase then bomb would use it. If question is are you allowed to emit laser manually when auto lase is enabled I think you can.
From what I heard LJDAM is using laser to update target position at any time with any amount of starting and stopping. INS and laser logics are not mutually exclusive.
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Yes for laser JDAM there is special code that handles it. Because the way that the bomb is working, once a laser spot is detected, the coordinates are extracted out of it and the bomb then follow those updated coords. Means that once you fire the laser and the bomb detects that laser spot, it’ll follow the new coords even if laser isn’t detected anymore afterwards (That’s in opposite to LGB which has no “memory” of target position and must sense laser all the time).
Also, Auto lasing isn’t relevant here, so if you fire manually or using the auto laser, the bomb will aim to the updated position on any laser “blip”.
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PIII has pretty good FOV scanning laser detector so it should see things well off axis but you actually have to have laser on.
Actually, and according to the figures I have, PIII’s seeker FOV is about 1/3 less FOV (seeker) than PII, while their gimbals are roughly the same. So PIII total FOV is less than PII.
Another difference between PII and PIII is also that PII total (seeker + gimbals) FOV is tied to airflow which is not the case on PIII.On PII the entire seeker is going into bomb’s airflow (trajectory axis).
On PIII, there is the seeker FOV (less than PII) , plus gimbals (roughly the same than PII but not dependent on airflow => reference is bomb’s axis whatever its actual trajectory)
If PIII is blind, it enters into a gliding mode.
… in other words,
PII’s seeker will “always” roughly points to the target whenever it has been release in correct parameter.
PIII (gliding with a slight aoa) has “less” look down angle and could more likely loose the laser spot if it is gliding for a too long period of time.So … “typical” lasing in BMS is about 8s - 30s for PII
Continuous lasing for PIIITry this …
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I think auto lase time controls F-16 emission with no change to bomb logic. If for example someone else were to lase then bomb would use it. If question is are you allowed to emit laser manually when auto lase is enabled I think you can.
From what I heard LJDAM is using laser to update target position at any time with any amount of starting and stopping. INS and laser logics are not mutually exclusive.
Yeah I’m aware of that, I wasn’t sure how the LJDAM was designed to react. Like, does it follow the initial INS/GPS guidance soley until the bomb programmed (not talking jet lase time here) ‘switchover’ to ‘laser mode’.
Yes for laser JDAM there is special code that handles it. Because the way that the bomb is working, once a laser spot is detected, the coordinates are extracted out of it and the bomb then follow those updated coords. Means that once you fire the laser and the bomb detects that laser spot, it’ll follow the new coords even if laser isn’t detected anymore afterwards (That’s in opposite to LGB which has no “memory” of target position and must sense laser all the time).
Also, Auto lasing isn’t relevant here, so if you fire manually or using the auto laser, the bomb will aim to the updated position on any laser “blip”.
Thanks, this is how I thought/hoped it worked. Makes lasing targets through a cumulus layer a little bit more successful
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Thanks for the follow up, Dee-Jay!
Some limited research on my end shows that the Paveway III was designed specifically as a low level LGB for better standoff at lower levels, to counter capable enemy AD and low-ceiling weather limitations.
Not that it’s “official” documentation, but here’s what I’m looking at:
http://www.designation-systems.net/dusrm/app5/paveway-3.html
https://fas.org/man/dod-101/sys/smart/gbu-24.htmWhat you say matches up with these sites regarding bomb trajectory. The Paveway III kit acts like a glide bomb initially to maximize range, and will continue to glide well past the target if no lase is detected.
So the problem is that I’ve been using these munitions out of intended parameters. They’re meant to be delivered from low altitude and lased for a long time before impact. I will relegate them to this duty from now on.
Consider this issue closed
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They’re meant to be delivered from low altitude
But rarely are. They can be also used in HA (or course).
EDIT: Even if it has been designed for low level delivery, we can understand that a loft increases the risk of never being able to get the laser spot and then, increase the risk of collateral damages. This makes that kind of delivery very tricky and restrictive since there must be no potential civilian infrastructures way behind the TGT on the launch axis since the bomb will fall very long in case of no guidance.
To be used with extra care, even if in BMS, collateral damages are not implemented … (yet).
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I’m really naive to USAF SOPs and doctrines. Are LGBs even used nowadays, or like Dos Gringos say, is everything just droppin’ JDAMs?
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I’m really naive to USAF SOPs and doctrines. Are LGBs even used nowadays, or like Dos Gringos say, is everything just droppin’ JDAMs?
Don’t know about USAF SOP / doctrine, but LGB are still used.
Target area may have GPS jammers, you may want to keep positive control over your bomb in case something happens (e.g. civilians entering the blast radius), LGB is cheaper than JDAM (I think?), … -
Don’t know about USAF SOP / doctrine, but LGB are still used.
Target area may have GPS jammers, you may want to keep positive control over your bomb in case something happens (e.g. civilians entering the blast radius), LGB is cheaper than JDAM (I think?), …Would they then not be better with LJDAM? I think the USAF doesn’t have Paveway IV stuff. Surely for static a JDAM would be best, but as you say, the laser element would allow them to deflect the bomb away before impact if needed.
Like I say, my in my naive eyes, I feel to see the necessity of a true LGB (12/24/27 etc.) when an LJDAM can do everything of both worlds. The loiter time of a INS/GPS guided weapon is much less than that of a laser guided munition even with buddy or ground based lasing.
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but LGB are still used…
A lot.
GPS is not 100% immune to GPS signal loss and do not allow moving targets. And of course, less expensive.
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I’m really naive to USAF SOPs and doctrines. Are LGBs even used nowadays, or like Dos Gringos say, is everything just droppin’ JDAMs?
They are still in the AF’s inventory, but the are not being manufactured any more and have gone out of favor with target planners as of today just because they take the aircraft over or near the target. This is where JTAC’s come into the picture IRL, to laze for the attacking aircraft so the LGB’s become more of a fire-&-forget weapon and keeps the aircraft/pilot in a relative safe environment. And why glide bombs like JDAMs & SBD’s are the norm now.
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Actually, and according to the figures I have, PIII’s seeker FOV is about 1/3 less FOV (seeker) than PII, while their gimbals are roughly the same. So PIII total FOV is less than PII.
I do not know much about PIII and would like to know more but I have info. PII FOV is staring seeing all at once with four overlappng zones for steering but PIII is scanning like a radar with a movable seeker. So be careful what value for FOV for PIII you are looking at because it has two: the instantaneous picture and the total angle the seeker can see over the pattern of scanning.
"Furthermore, the scanning laser seeker has a larger field of view, and the tailfins have been enlarged for higher manoeuverability and aerodynamic efficiency. The improvements enable a Paveway III LGB to maintain level flight at low altitude for effective ranges of more than 18 km (10 nm). Other delivery options include high-altitude drops (with a range of about 30 km (16 nm) from 10000 m (33000 ft) altitude) or long-range low-altitude launches using a lofted trajectory. "
“The resulting Paveway III weapon used an agile gimbaled laser detector under a glass dome, in an arrangement very similar to that used in heatseeking missiles. This allowed the detector to track the aimpoint at very high angular rates and high off-boresight angles independently of the bomb’s immediate orientation and motion – within the gimbal limits of the seeker.”
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So be careful what value for FOV for PIII you are looking at because it has two: the instantaneous picture and the total angle the seeker can see over the pattern of scanning."
This is what I was trying to said with my poor English. … Mechanical scanning => FOV + IFOV.
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The GBU 24 weapon is designed for low altitude delivery and with a capability for improved standoff ranges to reduce exposure:The improvements enable a Paveway III LGB to maintain level flight at low altitude for effective ranges of more than 18 km (10 nm) but I didn’t see that in game …it is pity!
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