Harrier's JDAM

[Kappa]

Hi everyone, I was wondering if the harrier's JDAMs are modeled correctly or if there are any known bugs.

 

I tried to use both 38 and 54 (without laser illumination) and both were not very accurate, sometimes they hit the target with a direct hit, other times they miss 10 meters or more ...

 

I do not understand if the mistake is mine, if it is normal that they are so inaccurate or if they are bugged ...

 

In addition to the imprecision I also notice a very strange flight path that often brings the bomb above the target (sometimes beyond it), shouldn't it hit at an angle of about 45 °?

 

Thanks

[Gunnar81]

Sounds like it could be an INS issue? Sorry I can't be of more help, I prefer to use the more legacy ord on the Harrier.

[F1GHTS-ON]

I've just got back into flying the AV-8B after 6 months +. So have relearnt how to use the JDAMs. I am lazy, and rarely use the terminal phase options (direction/angle that bomb arrives at etc) and cheat by just loading up positions from the F10 map (when the Multiplayer shows where the targets are). I ONLY drop when the numbers are > 70%.

 

So I offer the following as an observation, When I attack targets within 5 - 10 mins of re-spawning, I am hitting 90+ % of the time. Yesterday, I had managed to remain "alive" for 90 mins +, several landings, refuels etc (plus SAM evasion) and my hit rate seemed to drop right down. I just assumed I was making errors, but reading Gunnar81's comment above, I wonder if I had INS drift? 

 

Except don't GBU-38s & 54s take their "update" from GPS rather than INS? So even if my INS was out by several meters, this should NOT effect target accuracy??

 

Awaiting incoming to correct my naivety..

[cw4ogden]

10 hours ago, Kappa said:

Hi everyone, I was wondering if the harrier's JDAMs are modeled correctly or if there are any known bugs.

 

I tried to use both 38 and 54 (without laser illumination) and both were not very accurate, sometimes they hit the target with a direct hit, other times they miss 10 meters or more ...

 

I do not understand if the mistake is mine, if it is normal that they are so inaccurate or if they are bugged ...

 

In addition to the imprecision I also notice a very strange flight path that often brings the bomb above the target (sometimes beyond it), shouldn't it hit at an angle of about 45 °?

 

Thanks

One recent update you can now input desired heading for the bomb to track to target.  If you leave it unset, I believe it defaults to 000, so if you're attacking from north to south, bomb has to fly over and turn back around.  Possible your bombs are maneuvering to get on course.

You select heading by toggling bomb pushbutton on MFD, then two push buttons on the data input panel thing, then set the course via up front controller.  

[Shmegegge 1-1 Aero]

3 hours ago, cw4ogden said:

If you leave it unset, I believe it defaults to 000, so if you're attacking from north to south

I'm pretty sure that heading is relative to your release heading and not compass heading, though I could be wrong.

[cw4ogden]

15 hours ago, [TF-108] Aero said:

I'm pretty sure that heading is relative to your release heading and not compass heading, though I could be wrong.

I don't think it's a relative heading, but I can't find anything definitive on the web.  Might have to test it out.  

Give what the original poster wrote, "a very strange flight path that often brings the bomb above the target (sometimes beyond it)" it sounds like his bomb is seeking a particular heading which led me to believe it's jdam terminal parameters getting him.

[Kappa]

I also recall that bomb heading was realative, don't remember how i know.

Anyway bomb heading is ok, the strange thing is the vertical angle that sometimes is fine and sometimes you see the bomb overfly the target and then point down at 90 degreees...

 

In my first post i forgot to specify that i find JDAM inaccurate only in TOO mode, if I input coordinatest (UTM) into CAS page they are a sniper round.

 

My guess is that aiming with TGP is subject to error, but i can't be sure because i always try to aim to the ground where the target is but the result can change..

[Wisky]

use Terminal Params for your release (WPN button on UFC)

You will want an angle of ~60-85°

activate Terminal Params by pressing the uncage button

The Release line color will change from red to green (this is your cue you are in Terminal Params now, also the HUD will change from N0 to T0)

shortly after you are in Range just let it go, it will be a perfect hit

Edited July 2, 2021 by Wisky

[Recluse]

The other JDAM TOO caveat is to make sure your TOO spot is not directly on top of the target but at the intersection of the target and the ground as JDAM only seeks a ground position not any kind of lock.  As I understand it, setting TOO right on top of a target will actually target a spot on the ground somewhat beyond it based on slant angle (unless, I guess, if your sensor is pointing STRAIGHT down when you make the designation which is almost never the case). 

 

EDIT: Oops... you already knew that. Sorry!

 

My guess is that aiming with TGP is subject to error, but i can't be sure because i always try to aim to the ground where the target is but the result can change..

Edited July 3, 2021 by Recluse

[Fri13]

On 7/1/2021 at 12:42 AM, F1GHTS-ON said:

Except don't GBU-38s & 54s take their "update" from GPS rather than INS? So even if my INS was out by several meters, this should NOT effect target accuracy??

 

The standard operation is that you fly 4 hours with NAV computer set to IFA and then fifth hour so it is in INS. This so that you can find out INS errors.

 

When you have it in IFA you have tightly coupled INS+GPS and basically NAV computer is constantly updating INS with GPS.

 

this means you can't have error in release because INS drifting. Why you hold release button for long with JDAM is that mission computer uploads aircraft GPS coordinates to bombs for initial position information. There is as well almanac sent in.

 

So immediately bomb knows where it is on the moment of release, where it needs to be, and where it isn't.

 

So stay in IFA all the time, don't go through GYRO as it will reset INS system.