[NO BUG] Jester INS alignment on a moving carrier - problems

[MobiSev]

Is anyone else having problems with Jester aligning on a carrier that's moving?

 

The start up procedure seems to work like normal (i.e Jester goes through the alignment process like normal, everything seems to be correct). However, the INS seems to be off slightly upon further inspection (for example, I am showing heading 150 but the player in the GCI/tactical commander slot tells me that I have a heading of 170 a while after launch). Jester might be aligning like we are on the ground, not on a moving carrier?

Edited July 11, 2019 by MobiSev

[IronMike]

Check for the MV acronym. The Magnetic Variation can be as strong as +/- 30° on the carrier due to the ship hull. The MV will disappear a while after launch, alternatively you can press and hold the HDG button for about 1 minute in level flight at constant speed on your COMP panel. This is intended.

[MobiSev]

Check for the MV acronym. The Magnetic Variation can be as strong as +/- 30° on the carrier due to the ship hull. The MV will disappear a while after launch, alternatively you can press and hold the HDG button for about 1 minute in level flight at constant speed on your COMP panel. This is intended.

 

So, you're saying that it's supposed to be misaligned for a little bit after launch, then correct itself? If so, how long are we talking about before it fixes itself on it's own after launch?

Edited July 9, 2019 by MobiSev

[MobiSev]

Because this has yet to correct itself like, 20 minutes after launch if it's supposed to work that way

Edited July 11, 2019 by MobiSev

[Home Fries]

When they spin up, the first thing inertials do is determine true north. An INS knows true headings, and magnetic headings are abstracted. I'm not a tomcat guy, so I don't know exactly how the Tomcat INS works, but the LTN-72 I used had magvar in its database and applied it based on present position. You can also manually apply magvar in the CAP based on the number present on the kneeboard.

 

Bottom line: magnetic deviation does not affect the inertial's recognition of true north, nor degrade its accuracy.

[sLYFa]

An INS knows true headings

 

Does it though? Assuming the Tomcat does have a magvar database, it would determine true north by adding/substracting the local magvar from the magneting heading recieved from the AHRS. If the AHRS magnetic heading is off for whatever reason, the true north computed by the INS would be off too, resulting in large position errors once the aircraft starts moving. Or is there some other method of determining true north I am not aware of (perhaps SINS?)

I also wonder if INS heading should be linked to AHRS heading. Right now it seems that it is, since the carrier's magnetic field will throw off both VDI/HUD and BDHI heading once you get back to the boat.

In any case, right now, you have to resync the compass after taking off from the carrier or you will have large heading errors, which seems rather unpractical and I wonder if this was the case IRL.

[Super Grover]

The F-14 doesn't have any magvar database. It uses the AHRS magnetic heading together with the INS true heading to compute the magnetic variation.

 

The INS knows how to draw true north during alignment from observing the gyros drift.

[MobiSev]

The F-14 doesn't have any magvar database. It uses the AHRS magnetic heading together with the INS true heading to compute the magnetic variation.

 

The INS knows how to draw true north during alignment from observing the gyros drift.

 

all in all, is it supposed to be misaligned for a little bit after launch, then correct itself? If so, how long are we talking about before it fixes itself on it's own after launch? If it's supposed to correct itself fairly quickly after launch, then this topic should be reclassified as [bUG], since it was significantly misaligned for 20-30 min since launch.

 

I haven't had this problem before, and I wasn't the only one on the server having the problem.

[sLYFa]

 

The INS knows how to draw true north during alignment from observing the gyros drift.

 

Very interesting, I didn't know the Tomcat had that!

So position calculations are not influenced by local magvar.

Just one question: How is manual magvar initialized? Does jester enter it on startup or does it use some pre stored value?

[Super Grover]

If so, how long are we talking about before it fixes itself on it's own after launch?

 

 

It depends on how you fly the aircraft as an acceleration greater than 75 knots/minute disables slaving the directional gyro of the AHRS to the magnetic field from the magnetic azimuth detector (MAD). This means that it's very easy to never let your AHRS resync. You have to fly level and constant speed, and this is often a challenging task when those two engines are just waiting to give you more power and more speed, and when the pilot is looking for the opportunities to fight and keeps maneuvering.

 

 

 

 

@sLYFa

 

Jester knows the mag var from the kneeboard :) and he enters it on startup, after switching the NAV mode to INS.

Edited July 12, 2019 by Super Grover

[Home Fries]

If the AHRS magnetic heading is off for whatever reason, the true north computed by the INS would be off too, resulting in large position errors once the aircraft starts moving. Or is there some other method of determining true north I am not aware of (perhaps SINS?)

I also wonder if INS heading should be linked to AHRS heading. Right now it seems that it is, since the carrier's magnetic field will throw off both VDI/HUD and BDHI heading once you get back to the boat.

In any case, right now, you have to resync the compass after taking off from the carrier or you will have large heading errors, which seems rather unpractical and I wonder if this was the case IRL.

 

The way inertials work (assuming ground start; SINS alignment is a different animal) is that you input your present position. Then when they first spin up, they can detect the direction of the earth's rotation. From this direction, they take a 90 degree offset to calculate True North. In fact, some inertials can detect the amount of rotation and determine your latitude, and will tell you if you have input your latitude incorrectly!

 

True North is the basis for INS navigation, and no magnetic source will change this. The only reason magnetic headings are calculated by the INS is for the pilot when dealing with systems, sources and procedures that use magnetic headings (e.g. navaids, ATC, approaches/departures). For over water navigation, we always used true heading and switched back to magnetic when in coastal range.

 

Regarding your second paragraph, since the AHRS is the magnetic source for the Tomcat INS, any inaccuracies (magnetic deviation) will affect the INS calculated magnetic heading. However, the true heading remains consistent.

Edited July 12, 2019 by Home Fries