The way this works is that the gyro is biased to self-erect.
So if you give it about 5 minutes, it will return to showing level flight.
This means that if you were to hang around in a turn for a long time, the artificial horizon would gradually return to level flight despite the fact that the turn was still continuing.
The other thing to remember is that these old instruments don't seem to have failure flags. If the suction or electrical power source driving the gyro dies then obviously the second law will take its course, and the gyro will slow down.
The first you'll know of this is when it starts to nutate (ie wobble like a spinning top that's about to fall over). Then it'll topple, and you'll have false indications. Without failure flags, the only way to work out that the artificial horizon has failed is to cross-check it against the other instruments; hence the requirement for a good instrument scan.
This really makes instrument flying difficult. You can still proceed partial panel with the turn & slip (assuming that it has an independent power source), but it's not fun. You have to make a real effort to ignore the failed instrument, and you also have to infer what it would normally tell you from the remaining good instruments. In fact, IRL it's a really good idea to carry some scrap paper and tape around just in case; that way, if an instrument does quit on you then you can at least cover it over with a bit of paper so that the false indication doesn't distract you.
This might be quite a nice little easter-egg type feature if somebody could code it up. So you'd right-click an instrument and get the option to cover it. Then you'd suffer anthropromorphic pain for a few seconds before the dead instrument was obscured...
[During my PPL I had to do some sim time, and since the sim was IFR only I found myself very much out of my comfort zone flying blind. The instructor was bored and feeling evil, so he tried to "kill" me. First I lost an engine, and then when I survived that he started failing my instruments. I ended up trying to shoot an ILS partial panel with one engine and 25 knots of crosswind, and I can tell you that somewhere along the line that sortie I started to sweat...]
In addition to the Artificial Horizon toppling, you will probably also topple the turn & slip and the DG if you chuck the aeroplane about. The magnetic compass will also be spinning all over the place for a while. So after aerobatics or combat you're back to pure VFR for probably 5-10 minutes until you work out where you are and what you're doing. This can make you very vulnerable if you're not careful.
It also means that it's sensible to work out alternative means of navigation, especially over the channel. I suggest using the sun and a wrist watch to work out which way is North. Then you can at least head for the correct coastline.
Once you get there you can then switch to visual navigation.
Also note that IRL you get static port position errors on the ASI and altimeter. These can make life really difficult. For example the Merlin Spitfires have VNE of 450 mph EAS; the position error is about 20 mph at this speed, and therefore the acceptance tests involved diving to 470 mph IAS, which is a slightly unnerving concept.
The other classic, post war, was that the English Electric Lightning would tend to under estimate altitude at transonic speed. This meant that low level intercepts over the sea were routinely flown at negative indicated altitude. And they did this at night. Balls Of Steel!
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