HSI indicator knobs - why 2

[Gabe777]

I don't fully understand what the lower left knob is for next to the heading bug.

Help ?

Thnx

[LZ-WIL]

Hello Gabe777,

Do you mean the Course Select Knob? Like shown here. HSI combines a Heading Indicator with a VHF omnidirectional range-instrument.

Cheerz,
Vladimir

[Gabe777]

No, the 172 hasn't got that instrument.

The left knob says "Push", but also turns if you scroll the mousewheel. It turns the entire dial. Never seen one before.

https://www.simshack.net/images/a2a-ces ... -p3d-4.jpg

[Oracle427]

That is necessary to align the gyro with the magnetic compass.

[LZ-WIL]

No, it doesn't, the C182 does

It corrects the precession of the DI instrument. It tends to lose correctness as the aircraft changes it's position in space.

Cheerz,
Vladimir

[Gabe777]

???

[Oracle427]

The directional gyro does not sense magnetic north. It is just a gyroscope. Or must be manually adjusted periodically and certaintly right before take off to ensure it is displaying the correct heading.

Typically one would adjust it every 15 minutes in flight.

[Gabe777]

So what does the Push function do on the A2A 172 ?

No one actually seems to know.

[Tomas Linnet]

I think you will have to push it in, while you adjust the DI, but this is not simulated.

[Oracle427]

Correct.

[Gabe777]

Ok. Thnx. So we are getting there.

How do I adjust it ? Do I set it the same heading as the compass, i.e. is it the same as pressing "D"

[LZ-WIL]

Correct,

"D" will set it up instantly, while with the knob you will do it more realistically.

Cheerz,
Vladi

[Gabe777]

Got it. Thank you ....

[Hook]

You can turn off Gyro Drift in the simulator settings, but you'll still have to do the correction occasionally on long flights. This one has caught me out a few times.

Hook

[Oracle427]

That is because the non-precessing gyro will still fail to compensate for magnetic variation. Damn those pesky isogonic lines!