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TACAN/HSI heading on catapult launch?


Topper81
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Steps to reproduce:

- Activate TACAN before catapult launch

- Enter for the TACAN course the heading of the aircraft (214°)

 

grafik.png

- Note that there is a straight line in the HSI as expected

grafik.png

- Activate the catapult launch

- As soon as the aircraft moves, press pause

 

Observed behaviour

- Note that the line is not straight anymore, even if the heading of the aircraft has not changed?

grafik.png

 

grafik.png

HSI_CRS_HEADING.trk


Edited by Topper81
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  • Topper81 changed the title to TACAN/HSI heading on catapult launch?

What I see is that after you start moving, the little diamond indicator (which is your ground track pointer -- i.e. the direction you're moving relative to the earth) changes to match your actual movement.  Since the cat run is offset slightly from the direction of travel of the carrier (i.e. it's not perfectly parallel to the course the carrier is traveling), once you start moving the diamond changes from 214 deg (where the ship is heading) to your actual course (which looks like about 210).  In the first pics, since you're stationary, you are traveling exactly the same course as the carrier (it only cares about your actual motion, not where your nose is pointed), so it matches up with the 214 deg that the carrier is traveling at.

Not sure what the ribbon across the bottom takes it data from, but I would say the HSI is more likely correct than it.


Edited by rob10
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The airplane magnetic heading is not 214°. That is the airplane true heading. Since almost all of the airplane systems are referencing magnetic North the relationship between true heading and TACAN magnetic course is meaningless. A vertical orientation for the CSEL on the HSI in my test mission is 350° despite my airplane true heading of 352°. That's because vertical on the HSI is the ground track of 350°M (CV track is 356°T). The #1 catapult is angled to the left about 4 degrees.

 

I think there is an issue with HSI display. The lubber line should always be at the 12 o'clock position and the airplane heading read against it. The ground track should vary in angle on the display, not heading. A constant heading launch should not rotate the displayed compass rose on the HSI and by extension the orientation angle of the CSEL line should also not change. There is a bug but it has nothing to do with TACAN directly.

 

Since the HSI is oriented "track up" that means the 12 o'clock position on the HSI is where you're going, not pointed. During catapult launch your track will change and it's normal for your HSI orientation (and thus CSEL line orientation) to change. Makes you wonder why they have a "track pointer" in track up orientation since that's always just going to be 12 o'clock on the display.


Edited by Frederf
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3 hours ago, Topper81 said:

Enter for the TACAN course the heading of the aircraft (214°)

This is not the heading of the aircraft.

 

Syria, 2016 MagVar = +5°E [from HSI>Data>A/C]

 

• The Super Carrier is travelling 220°T (215°M) [from F10 map, external info bar]

• On the catapult, the aircraft heading is 214°T (209°M), this is also the heading shown by the info bar.

 

209°M is confirmed by the HUD's heading tape when in the catapult.

 

Screen_210821_174034.jpg

 

Your programmed TACAN course is 214°M i.e. to the right of your current heading.

 

This is how it looks diagrammatically

 

FA-18C HSI TACAN Syria.png


Edited by Ramsay
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Since HSI orientation is track-up then HSI orientation should change as track azimuth changes regardless of heading (constant or otherwise). I assume when at zero/small velocity (track azimuth undefined) that system switches over to using heading as a substitute.

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Ok I haven't known that it's track up orientated. I guess this should be the case in flight but not on the deck and it switches to be "heading orientated" on the deck because you don't want to know the direction where the carrier is moving to when you are moving on the deck. So the behaviour makes sence.

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