GBU-38's inaccurate or is it me?

[JayPee]

GBU-38's inaccurate or is it me?

 

(I haven't dropped one in a couple of months)

 

Do they miss, do they hit some other point, or do they show decreased accuracy?

 

 

Bombs are fine. Its the creation of mark points by TGP SPI thats the issue.

Edited February 11, 2014 by JayPee

[kontiuka]

Forgive my ignance. I know how to make markpoints but is there a way to make a markpoint the SPI, similar to making a steerpoint a SPI?

[Eddie]

Forgive my ignance. I know how to make markpoints but is there a way to make a markpoint the SPI, similar to making a steerpoint a SPI?

 

 

Make it your steer point, then set steer point as SPI.

[kontiuka]

Make it your steer point, then set steer point as SPI.

Sanka. Now I have to look up how to do that. :)

[Supersheep]

Flip your CDU steer point dial to Mark mode, then select them as you would switch through waypoints :)

Edit: See below. I didn't remember that the Mrk Point has to be made Spi...

Edited February 11, 2014 by Supersheep

[PFunk1606688187]

Sanka. Now I have to look up how to do that. :)

 

On the Auxiliary Avionics Panel (AAP), set the STEER PT dial to 'Mark', set your chosen Mark point as the steer point by scrolling through them with either the UFC Steer Rocker or the Steer toggle switch on the AAP, then set your Steer Point to SPI by pressing TMS Aft Long.

 

I think I got that all correct. ;)

[kontiuka]

^

cool. thanks.

[PFunk1606688187]

Np.

 

FYI, you can also set STEER PT to MARK on the UFC by pressing the FUNC button then the '8' button.

[ApoNOOB]

Np.

 

FYI, you can also set STEER PT to MARK on the UFC by pressing the FUNC button then the '8' button.

 

WTF! Why didn't I know that, right in front of my face all the time too. I need to look into the manual again. Thank you! :)

 

 

Btw: you can also hook up your most recent mark point on the TAD. When you switch your STEERPT Dial to MARK you can also see them on the TAD.

[JayPee]

UFC shift functions allow access to all CDU pages regardless of the rotary switch.

 

Btw, when deploying weapons, is Mark Z created at the jet's coordinates or is it created at the current SPI (target in this case)? Most of the times it is going so fast by the time I think of checking Mark Z I'm not sure anymore whether it was a target or possibly my position.

[Supersheep]

Mark Z stores the IFFCC-generated SPI at the point in time the trigger/pickle was pressed.

In other words, the impact's location.

 

 

Edit: That doesn't hold all water. What if the release is in CCRP? Then the IFFCC doesn't compute a point on the ground (I think).

[JayPee]

GBU-38's inaccurate or is it me?

 

Time I start making use of MK Z because it's easy to re-engage if (hardly ever happens, duh! ;) ) I miss...

[Supersheep]

That's possible, but I think not the most efficient way.

[JayPee]

Most efficient way is not missing, obvsly.

[Supersheep]

Wrong wording. Efficient, if the target is static. Dangerous, because you're likely well within range of something and spend time manipulating your avionics. If the target moves I'd prefer to pick it up again visually. But that's now, finally, really off topic.

[PFunk1606688187]

I believe that Mark Z is merely the computed target point at pickle/trigger regardless of current SPI.

 

What I would like to know is when using consent to release is Mark Z the point you had under the hashed pipper when you initially press Weapon Release, or is it the point that is actually under the assumed CCIP pipper at actual weapon release?

[NoCarrier]

Edit: That doesn't hold all water. What if the release is in CCRP? Then the IFFCC doesn't compute a point on the ground (I think).

Why wouldn't it? A CCRP solution is calculated on the basis of a SPI (i.e., a point on the ground) anyway.

[camsr]

High winds can affect JDAM accuracy. If you can, avoid heavy crosswinds from high altitude.

[JayPee]

GBU-38's inaccurate or is it me?

 

I'm sure you have a reason for this statement but I can't find the logic in it.. The bomb knows the target L/L and the bomb knows its own position in 3D space at all times as it is continuously (?) communicating with four GPS satellites. So whatever external factors are in play like the position of the launch platform and wind, the bomb knows where it is and where it should go. If wind pushes the bomb off its own defined track, the GPS would notice that and simply correct for it?

[Flagrum]

I'm sure you have a reason for this statement but I can't find the logic in it.. The bomb knows the target L/L and the bomb knows its own position in 3D space at all times as it is continuously (?) communicating with four GPS satellites. So whatever external factors are in play like the position of the launch platform and wind, the bomb knows where it is and where it should go. If wind pushes the bomb off its own defined track, the GPS would notice that and simply correct for it?

I am just guessing here: the steering signals that the weapons nav system generates to get it back on track might be "calibrated" for "normal wind" conditions and might perhaps not be sufficient for too strong winds.

 

Like, the bomb knows that it needs the amount X of steering input to correct a deviation of Y of it's planned flight path. X would normally be enough (X-Y=0), but with too strong winds, it is not (X-Y > 0). The next time the bomb is already futher off track (X1-Y1+X2)

[JayPee]

GBU-38's inaccurate or is it me?

 

Hmm, possibly. Yet that would indicate the bomb is continuously referencing its release point and comparing its own position along the line between release point and target. While the ultimate purpose of a GPS system is knowing one's own actual position with great accuracy, instead of something predefined or compunted, to know where you are in relation to your target destination.

 

I see it like this, whether I'm driving my car, it is towed, it is on the back of a trailer, or if a hurricane is throwing it around, the navigation unit inside knows my current location at all times. Hence it can tell me the heading, distance, and preferred route to my target destination. If I take a wrong turn (wind pushes the bomb significantly off course) I will recieve a correction immediately. So ultimately I will always arrive at my target, except when I run out of time, that is, when the bomb's about to hit the Earth's surface.

 

If for some reason it is correct in what you say that although the bomb's GPS module is aware of the situation but it can't correct any more, than what about these comments on JDAMs traveling around objects and hitting targets from behind? I'd say that requires a great deal more corrections and manoeuvrability than fighting cross winds..

Edited February 12, 2014 by JayPee

[Flagrum]

Hmm, possibly. Yet that would indicate the bomb is continuously referencing its release point and comparing its own position along the line between release point and target. While the ultimate purpose of a GPS system is knowing one's own actual position with great accuracy, instead of something predefined or compunted, to know where you are in relation to your target destination.

 

I see it like this, whether I'm driving my car, it is towed, it is on the back of a trailer, or if a hurricane is throwing it around, the navigation unit inside knows my current location at all times. Hence it can tell me the heading, distance, and preferred route to my target destination. If I take a wrong turn (wind pushes the bomb significantly off course) I will recieve a correction immediately. So ultimately I will always arrive at my target, except when I run out of time, that is, when the bomb's about to hit the Earth's surface.

 

If for some reason it is correct in what you say that although the bomb's GPS module is aware of the situation but it can't correct any more, than what about these comments on JDAMs traveling around objects and hitting targets from behind? I'd say that requires a great deal more corrections and manoeuvrability than fighting cross winds..

Well, ofc I might be totally wrong. And perhaps the situation I described might only be relevant if you drop JDAMs in hurricanes where it gets totally blown off target (but that would be rather a total miss than "affected accuracy" that camsr mentioned).

 

edit:

just thinking "loud" ...: having the weapon impact from a different, even opposite direction - I guess that is all depending on respecting the weapons flight envelope. If you release the bomb immediately at max range it might be difficult for it to get onto a glide path that lets it impact from the opposite side. And if then some head wind comes into play ...

But if you release it well within the envelope (i.e. half way between max and min) it might have plenty enough energy to maneuver wherever you want it to - even with some winds.

Edited February 12, 2014 by Flagrum

[camsr]

I'm sure you have a reason for this statement but I can't find the logic in it.. The bomb knows the target L/L and the bomb knows its own position in 3D space at all times as it is continuously (?) communicating with four GPS satellites. So whatever external factors are in play like the position of the launch platform and wind, the bomb knows where it is and where it should go. If wind pushes the bomb off its own defined track, the GPS would notice that and simply correct for it?

 

I have seen it happen. My JDAMs missed at 16000 and I checked STR info after the fact and the windage was 18 across at least. The target was a ammo bunker (the big one) so it's safe to say the bomb was off.

The bomb's nose is always aiming for the target point, but the wind is constantly pushing it away. It is also building velocity in the dive, so less room for correction closer to the ground. It doesn't "fly sideways" like the hog does :)

 

It could also have been different tiers of wind velocity.

Edited February 12, 2014 by camsr

[JayPee]

GBU-38's inaccurate or is it me?

 

OK. This would indicate that the bomb's flight control surfaces cannot counteract the wind's forces and gravity sufficiently. Or that the body in general is still suffering from bare model as it is built to free-fall and not to actually fly. However, I'm still sure the GPS module is aware of the fact that the bomb is off course and headed for the wrong coords.

[camsr]

But if you release it well within the envelope (i.e. half way between max and min) it might have plenty enough energy to maneuver wherever you want it to - even with some winds.

 

I suppose so, I noobingly dropped them early