I have one of these
In flight one rarely looks at it, but it was noticed during partial panel flight when training for the JAA IR that the compass exhibits dynamic errors (during turns) which are way bigger than a normal liquid compass shows.
Is that to be expected?
I would never go back to the old style compass because this one is actually usable 
but this is worth knowing if it is typical.
I fly with one of these on a PA28 Arrow - will have to take note of its behavior. So intuitive compared with the 'liquid' thing.
However, on the conventional liquid one, once somebody told me to mentally turn the aircraft (and self) round the the 'card' and consider the 'card' as 'sitting' stationary over the earth, things made more sense.
This, in effect, is what actually happens anyway.
I don't remember the last time I've looked at my liquid compass. I have a slaved EHSI and my check is comparing it to the runway heading.
When I bought the aircraft, it had a 1979 directional gyro and that thing was so worn out, that it used to show 10-20 degrees of error every half hour. I was looking at the liquid compass all the time and adjusting the gyro. That is easy in smooth air but absolutely impossible in turbulent IMC.
I also have a vertical card compass in the TB.
As it is driven by magnets it leads and lags but in my installation/experience a lot less than the previously installed normal liquid compass.
I have one in my Falco. It wanders all over the place during turns but then stabilises once the new track is established. I fretted over it quite a lot and went to quite some lengths to eliminate it by installing Mu metal and swinging the compass. In the end I gave up as I rarely look at it in flight anyway but for IMC one should really expect better.
My experience with the vertical card compass is that it is not usable during steeper turns. I can not tell if it is worse than a traditional compass. What makes it difficult is that it somehow looks similar to a gyro so one is tempted to assume it will operate in a similar fashion during turns.
Thinking about fitting one into my permit aeroplane has anyone got any experience of them?
I have one. Works fine. I use it regularly – for about three minutes every couple of years on my IRR renewal/revalidation flight.
It’s quite a bit lighter, cheaper, and occupies less panel space than my iPad or GTN 650Xi. As (if) I get older, I may become more attached to it, as one does to paper and fountain pen, wind-up watches, and similar relics of a bygone civilisation.
’Had one in my 150 for 33 years, very happy with it.
Make sure it’s correctly mounted. We had problems with the vertical compasses in our fleet, as the shop incorrectly mounted three of them on the old, free swinging mount. Wrong. The vertical ones need to have a rigid mount as they need the vibrations of the airplane to move freely.
