Autopilot CPL mode problem in CASE III

[FrostLaufeyson]

Why does selecting CPL mode in A/P mode enter CPL HDG instead of CPL TCN when establishing a Link 4 connection? (I do boxed TCN in HSI every time) Although I am able to manually correct and maintain the heading, when I try to use A/P to take a rest, it always causes me to deviate further from the course line due to entering CPL HDG.

I can provide a trk file if necessary

[Foka]

Because Link 4 is ACLS system and if you're connected with the system plane "thinks" you're landing.

If you're on penetration part of recovery don't use A/P when you don't have to. When you're in flight, don't turn on Link 4, it's only for ACLS recovery.

[FrostLaufeyson]

2023/4/19 PM6点32分，Foka说：

When you're in flight, don't turn on Link 4, it's only for ACLS recovery.

I know I shouldn't. But I still don't understand the logic, why ACLS will change CPL TCN to CPL HDG

[norman99]

Because, the ACLS system is in Traffic Control mode, indicated by T/C on the link 4 display.

Technically, the T/C mode provides data link heading commands to aid the pilot in reaching the marshal point and/or it may be used for azimuth alignment from marshal until ACL acquisition. These heading commands can be coupled to the flight control computer for automatic lateral axis control or can be used for manual steering aids.

In practice, DCS’s version of T/C seem to always direct you to a place on BRC, about 30-35nm from the boat. There is no real variation to this.

[FrostLaufeyson]

20小时前，norman99说：

Because, the ACLS system is in Traffic Control mode, indicated by T/C on the link 4 display.

Technically, the T/C mode provides data link heading commands to aid the pilot in reaching the marshal point and/or it may be used for azimuth alignment from marshal until ACL acquisition. These heading commands can be coupled to the flight control computer for automatic lateral axis control or can be used for manual steering aids.

In practice, DCS’s version of T/C seem to always direct you to a place on BRC, about 30-35nm from the boat. There is no real variation to this.

That make sense, thanks a lot

[CBStu]

That may be true for this instance but CPL has some idiosyncrasies. Flying to an airfield I get the tacan for it, cancel SEQ1 and CPL to the TCN. Cool working fine. Now I check the runway heading and want to set a CRS so I have a better visual idea of my approach. I know, if I just hit the CRS toggle the CPL will suddenly turn the plane to that heading. Ok so I unclick CPL, set the CRS, but I know if I hit CPL the same thing will happen. So I unclick TCN on the HSI screen, wait 10 seconds (no idea why but, what the he11, latest experiment), hit TCN, but now the CRS line is gone from the HSI screen. So I hit the CRS toggle once and the CRS line reappears but 1 degree off. No biggy, I hit CRS again w/ the other mouse button to get the correct CRS. Now maybe...I can hit CPL again. Nope, plane goes ape sh-t again, so I kill CPL and just fly to the symbol on the HSI screen. I guess a lot of this is just that the FA-18 was in the infancy of computer controls but this entire plane does a lot of stuff on it's own that I wish it wouldn't.

[norman99]

Yep. You can have a course line selected, and couple the AP to fly that specific course, or you can hide the course line, and have the AP fly straight to the TCN. You just can’t do both.

The simple answer, change to HSEL before you select the runway course.

In this regard, it’s exactly the same as coupling the AP to a VOR NAV receiver in any civilian aircraft. Want to fly straight to the station but have a different radial selected on the OBS, then you’ll need to use HDG hold to make it work.

[CBStu]

I'd be happy if it would fly to the TCN and KEEP flying to TCN when I put a CRS line on the HSI. But it doesn't. It immediately turns the plane to fly that CRS from where ever I am when I hit CPL. I will try HSEL. Yes HDG hold might work OK if there isn't much crosswind. I wish the code writers would quit trying to think for us. Their idea of something that might be helpful when it is done automatically often creates a lot more work than if reduces.

[norman99]

Accurately tracking to a TCN with a significant crosswind can very easily be done in HSEL. Simple adjust the HSEL bug until the ground track pointer, (small diamond at the top of the HSI, is perfectly in line with the TCN bearing pointer (triangle on the outside of the HSI compass rose).

Even easier, engage the AP in TCN CPL mode. Then just move the HSEL bug to match the aircraft heading, under the lubber line at the top of the HSI. Then select HSEL.