Barometric setting change during autopilot in HÖJD mode

[TOViper]

When flying the Viggen in HÖJD mode:

 

Does the autopilot follow barometric changes (done by hand for e.g. changing QFE setting for the next target) while autopilot is active or not?

 

Answer: In 1.5.8 it DOES follow changes

Answer: In 2.5.x it DOESN'T follow changes

 

See Video:

 

But what was the behaviour IRL?

[TOViper]

Hm ... no one knowing? Not even RagnarDa, Cobra? :noexpression:

[MYSE1234]

From what I've understood from the manual, the current behaviour is the correct one.

The altimeter has nothing to do with the reference height/ pressure used in "Höjd".

[RagnarDa]

Yes I don’t know what is correct actually. But our QA kept asking me to change it so I changed it into having standard barometric altitude as reference, which is what introduced the bug (now fixed) that the HUD would align to a different altitude reference (standard but in reference with indicated).

[MYSE1234]

HÖJD uses the static pressure from the pitot tube (Ps).

When you click the the button to engage HÖJD, the static pressure gets saved as "Ps-ref". That is then gets continuously compared to Ps to get a height difference. If there is a difference, the resulting error signal get directly sent to the outer rudder servos, to get the aircraft back to the the correct altitude.

[RagnarDa]

Barometric setting change during autopilot in HÖJD mode

 

It’s a lot more complex than that :P but I understand what you mean

[MYSE1234]

Well yeah, of course. Just didn't feel the need to write a 5 page essay about it. :smilewink:

[TOViper]

HÖJD uses the static pressure from the pitot tube (Ps).

When you click the the button to engage HÖJD, the static pressure gets saved as "Ps-ref". That is then gets continuously compared to Ps to get a height difference. If there is a difference, the resulting error signal get directly sent to the outer rudder servos, to get the aircraft back to the the correct altitude.

 

 

Thanks for clearing this up!

 

 

In fact, there were only these two options in my head: yours (above), and another one: having the current barometric setting as reference, which is then continuously polled when the HÖJD mode is active (which would explain the "old" 1.5.8 behaviour of the module).