reported JDAM taking to long to align when not in AG mode.

[Furiz]

When not in AG mode and SMS page is not selected JDAM takes more than 5 min to align, in other case when in AG mode and SMS page is selected it takes less time to align, 2 - 3 min.

tracks:

Slow align - JDAM slow .trk

 

Fast align - JDAM fast .trk

 

Don't know which one is correct but I guess one of them needs tweaking.

[BIGNEWY]

Hi, 

what makes you think it is incorrect, do you have some public evidence I could check. 

thank you

[Moonshine]

what makes us think is wrong? the fact that upon pressing "power on" to start aligning the JDAM  should not make ANY difference at all which master mode, which other MFD pages or whatever is selected that would affect the duration of the alignment process.

when starting the alignment of the JDAM while in AG mode and then swichting master mode back to nav for example completely stops (or slows down the alignment process) until the next time you get back to AG mode and check the SMS page, then it picks up where it "left off" when switching from AG to NAV. this can not be correct 

Edited February 9, 2023 by Moonshine

[Furiz]

41 minutes ago, BIGNEWY said:

Hi, 

what makes you think it is incorrect, do you have some public evidence I could check. 

thank you

JDAM has Inertial Navigation System, while aligning it transfers navigation data from the aircraft to the onboard system. When the bomb in turned ON on the SMS page it starts the alignment. Therefore it doesn't matter if the AG mode is selected or if the SMS page is selected as long as it is turned ON it should continue aligning at the same pace.

Currently we have 2 different align duration times, 5+ min if in Nav mode and SMS page not selected and 2-3 min if in AG mode and SMS selected. Both times should match each other.

I only don't know which time is correct. Maybe an SME could help.

[Moonshine]

this by the way has already been part of a discussion and raised by other people, including track replays: 

then there is this:

„The navigation system is initialized by transfer alignment from the aircraft that provides position and velocity vectors from the aircraft systems.“ source  https://www.af.mil/About-Us/Fact-Sheets/Display/Article/104572/joint-direct-attack-munition-gbu-313238/

so that leaves us with this: when the INS data is transferred from the jet to the bomb, why would the currently selected master mode make a diffence in the speed at which this is done?

Edited February 9, 2023 by Moonshine

[Furiz]

Also this article, long read, states that  -

The JDAM employs the US standard Mil-Std-1760 umbilical interface, incorporating the Mil-Std-1553B digital multiplex bus. Before launch the JDAM's embedded software communicates with the launch aircraft's stores management processor, no differently than a computer peripheral. Prior to release the JDAM is powered up using an umbilical feed from the launch aircraft. The JDAM executes an internal self test, warms up and aligns the HG1700 inertial unit. Once the JDAM is ready, it communicates status information to the launch aircraft, which then downloads GPS timing, GPS Almanac (ie nav message), GPS Ephemeris (constellation) and the GPS PPS crypto key. This information is used to initialise the GEM-III receiver.

https://www.ausairpower.net/TE-JDAMPt1.html

 

So if the alignment is happening on the prosessor inside the bomb, there should be no difference in the alignment time whatever the mode the aircraft is in as long as the bomb is powered ON,

we currently have 2 different alignment timings, depending on which mode is selected and what is displayed on MFD.

Edited February 10, 2023 by Furiz

[Lord Vader]

Hi @Furiz

Thank you for bringing this up. There's an actual discrepancy here, for sure. Thank you for those references and we'll also review our own.

For now, it's been reported and the team will look into it. 

[RogueRunner]

The CBU-105 will not align if you are not in A2G mode and the weapon is not selected. It will stop at whatever it was when you deselect the weapon or exit A2G mode.

This might be as it is IRL but seems odd.

Edited May 4, 2023 by RogueRunner
grammar

[BIGNEWY]

Hi, 

please include a track replay example and any public evidence to support your claim. 

Feel free to PM me. 

thank you

[_SteelFalcon_]

This was already reported and affects all IAMs including gbu 38 @BIGNEWY

[_SteelFalcon_]

 

[BIGNEWY]

thank you I will merge