JDAM alignment

So...

When you align the JDAM's and switch to any other weapon or mode and switch back you basically have to start-over on the alignment. Is that actually accurate? Seems like it would a rather serious tactical liability.

IRL you can box it on deck in NAV mode and it’ll stay aligned.

Yea should be investigated

Not a bug per last time this was reported

Pretty sure it happened to me a day or two ago switching to harms and then back.

It was marked as NO BUG and the argument was that the JDAM needs constant power supply in order to remain aligned. Furthermore it was said that the hornet does only power the active pylon.

Proof?

IRL you can box it on deck in NAV mode and it’ll stay aligned.

If you can prove this with relevant documentation, I am sure ED will be happy to revisit this.

It was marked as NO BUG and the argument was that the JDAM needs constant power supply in order to remain aligned. Furthermore it was said that the hornet does only power the active pylon.

If this is true (not that I don't believe you) that would indeed be a giant tactical liability, as Harlikwin already said. I also noticed it before, but I assumed I did something wrong.

Seems incredibly strange that such an expensive weapon would not stay aligned.

It is not that I am necessarily correct, i recall reading it somewhere. I think you can find the discussion about it in the big section

I thought this had previously been confirmed as correct, but according to JDAM Tactical Manual for the F/A-18C/D (rule 1.16, look it up for yourself), the current way it functions is not realistic, or perhaps I am just misinterpreting the document. It states that boxing a JDAM on the STORES format powers on all JDAMs loaded on the aircraft and begins alignment. Power continues to be applied to all JDAMs until they are all deselected. They are only deselected when they are explicitly unboxed, selecting a different weapons station or changing the master mode will make the JDAMs background-selected. While background-selected, power is still applied and transfer alignment continues to all JDAMs. Hopefully there is an unclassified source that can confirm this so that ED can implement the background-select functionality.

What you quote mu110 actually confirms the OP‘s observation to be correct, doesn’t it? When you switch from JDAMs to another weapon (i.e. you deselect/unbox the JDAM), the JDAMs lose power so they have to align again once selected again. I would say that is the correct behavior as per the doc you mentioned.

Furthermore (but I think that wasn‘t questioned yet), when you select/box JDAM, ALL stations that carry a JDAM will be powered and all JDAMs on these stations will start alignment simultaneously, not only the one on the priority station. Which also appears to be correct per the above mentioned document.

What you quote mu110 actually confirms the OP‘s observation to be correct, doesn’t it? When you switch from JDAMs to another weapon (i.e. you deselect/unbox the JDAM), the JDAMs lose power so they have to align again once selected again. I would say that is the correct behavior as per the doc you mentioned.

there's a comma between "unboxed" and "selecting", which, to me, means that selecting another weapon, and not explicitly unboxing the JDAM, will put it into the background-power mode and not deselect it.

From what info I have (all publicly available so hopefully 1.16 compliant, and I'm not copy pastaing anything) on jdam integration in other aircraft, the weapon is powered on, pulls GPS alignment data from the aircraft GPS/INS, aligns its own inertial nav system. The plane supplies 28VDC/115VAC via MIL-STD-1760 and GPS data continuously to the bomb via MIL-STD-1553 data bus. During the initial release phase the bomb uses its INS while searching for the GPS constellation. The JDAM initiates a GPS search at 3 seconds after release, and using the aircraft provided GPS handoff information it attempts to achieve full GPS aided guidance by 28 seconds post-release. The handoff of high quality GPS information to the bomb, allows the JDAM to achieve full position and velocity acquisition within a maximum of 27 seconds and full GPS navigation within 28 seconds after release.

The sources I have don't specifically pertain to the hornet, nor do they mention anything like battery life of the weapon, though presumably its powered from the aircraft until release. I guess its plausible that the hornet can't power more than 1 pylon at a time, though that would imply I could only release 1 or 2 weapons at a time. Then have to wait for the other pylon to power on/align. Which seems really really dumb IRL. And it isn't the way DCS is doing it either.

It also begs the question of if its pulling the GPS data from the plane, and the figure of merit (1-10) displays are tied to GPS why is it taking so long to move that data? I get that whatever INS gyros have to spin up too, but I wonder on the time that actually takes.

As I understand it the 1-10 FOM value we see pertains to the quality of the aircraft GPS/INS alignment. The best being 1 with the correct GPS crypto keys and pulling in PPS mode. Anything greater than 4 indicates that SPS mode is being used (no/wrong crypto keys)

Given that the JDAM isn't trying to use its own GPS until after release it should be pretty much instant or at least equal to whatever the aircraft GPS is reading at any given moment?

I thought this had previously been confirmed as correct, but according to JDAM Tactical Manual for the F/A-18C/D (rule 1.16, look it up for yourself), this is not realistic, or perhaps I am just misinterpreting the document. It states that boxing a JDAM on the STORES format powers on all JDAMs loaded on the aircraft and begins alignment. Power continues to be applied to all JDAMs until they are all deselected. They are only deselected when they are explicitly unboxed, selecting a different weapons station or changing the master mode will make the JDAMs background-selected. While background-selected, power is still applied and transfer alignment continues to all JDAMs. Hopefully there is an unclassified source that can confirm this so that ED can implement the background-select functionality.

That makes much more actual sense. And would be quick/easy fix for ED hopefully.

there's a comma between "unboxed" and "selecting", which, to me, means that selecting another weapon, and not explicitly unboxing the JDAM, will put it into the background-power mode and not deselect it.

That would make the most sense.

Alignment is implemented basically at the moment and will be improved in the future.

Thanks NEWY

How about the power-on behavior? I.e. staying aligned if I select a different AG weapon or AA weapon?

Interesting that it is different for JDAM and JSOW. Deselecting JSOW depowers it and you have to do the whole en-route statup from scratch, but that doesn't seem to require a realignment (which is in the post start, not en-route) which would make sense based on what I've read elsewhere.

What you quote mu110 actually confirms the OP‘s observation to be correct, doesn’t it? When you switch from JDAMs to another weapon (i.e. you deselect/unbox the JDAM), the JDAMs lose power so they have to align again once selected again. I would say that is the correct behavior as per the doc you mentioned.

 

Furthermore (but I think that wasn‘t questioned yet), when you select/box JDAM, ALL stations that carry a JDAM will be powered and all JDAMs on these stations will start alignment simultaneously, not only the one on the priority station. Which also appears to be correct per the above mentioned document.

I just edited my post to make it more clear, but yeah I do think the OP is correct in saying the current state of this function is not accurate.

I just edited my post to make it more clear, but yeah I do think the OP is correct in saying the current state of this function is not accurate.

Yeah it looks like you can leave the JDAM's powered on in the background. However for whatever reason the JSOW is different and if deselected it depowers. But it might not require the 2min realigment?

there's a comma between "unboxed" and "selecting", which, to me, means that selecting another weapon, and not explicitly unboxing the JDAM, will put it into the background-power mode and not deselect it.

:doh: Took me a while to read what it actually says, I completely overlooked the comma indeed (probably the byproduct of an 11h working day). Thanks for making that clear!

Yeah it looks like you can leave the JDAM's powered on in the background. However for whatever reason the JSOW is different and if deselected it depowers. But it might not require the 2min realigment?

I think you're correct regarding JDAM's... even if you select A/A accidentally or otherwise, all JDAM's remain powered in the background. Selected station(s) remain in memory too.

The 2 min you mentioned in JSOW mech. might be related to something else... I can only speculate... I can't find this stuff anywhere now... then there's this DCS UCMJ paragraph 1.16 yea, I know... extreme caution has to be exercised.:matrix:

I think you're correct regarding JDAM's... even if you select A/A accidentally or otherwise, all JDAM's remain powered in the background. Selected station(s) remain in memory too.

The 2 min you mentioned in JSOW mech. might be related to something else... I can only speculate... I can't find this stuff anywhere now... then there's this DCS UCMJ paragraph 1.16 yea, I know... extreme caution has to be exercised.:matrix:

Well, I think we can discuss it, just not post links/pics etc.

At any rate, the 2-3min mechanic is some sort of power on/BIT/gyro deal. in the case of JDAM it should happen once if you leave them powered on in the background you shouldn't need to do it again.

In the case of the JDAM it seems like if you deselect them you have to go through en route mech, but maybe not on start mech with the 2 min alignment either.

At any rate I'm pretty sure the GPS data pull is near instant I mean its like less than this post worth of data. Plane is at XYZ, spd, angle etc.

There is a warning in there about if there are issues, and you need to do the BIT/realign 3 min before drop, that you are probably hosed for the JDAM's but that seems like a "warning" and not normal SOP.

IRL you can box it on deck in NAV mode and it’ll stay aligned.

Pretty sure that's how it works now - you can box JDAM/JSOW on the ground as soon as it's equipped and it'll start aligning. You can then select AG mode without losing the selection on the stores page.

:doh: Took me a while to read what it actually says, I completely overlooked the comma indeed (probably the byproduct of an 11h working day). Thanks for making that clear!

I often wonder why legal documents appear to contain so little punctuation, as it can totally change the meaning of the text. I guess they must use really clear and easy-to-understand language? ;)