I'm thinking about very different types such as fixed wing and rotary, or fixed wing and flexwing, or such things as airships if anyone here flies them; not flying a PA38 and a PA28. But I tried explaining that in the thread title and it got ridiculously long!
Anyway, when I first started learning to fly helicopters, I got a bit confused. I remember being halfway down the runway in a C152, and thinking: "Oops, this isn't a helicopter; I'd better go around".
Some people told me that flying both wasn't safe, and for a while I didn't fly f/w alone. But after a bit, things seemed to sort themselves out, and I didn't get confused any more. In fact the two appeared to complement each other.
Recently, when I started learning to fly a flexwing microlight, people prophecied similarly - how would I ever remember which type of control system it was and so on. Well, it was hell learning to fly flexwings initially, but now I've got it sorted, it's fine (the control system anyway; landing the damn thing is still... well, that's another story). And how can I possibly mix up a bar and a control column? And a helicopter is so so so different from everything. And I do get the feeling that they all complement each other; eg I'm more aware of weather and thermals and possible forced landings since I've been flying flexwings; better at doing loads of things at once since flying helos, etc.
So, especially (but not exclusively) all you readers of these forums with many many more hours than me on many more different types of aircraft - what have you found? And is there a limit - at which point it does become unsafe?
I'm only asking out of interest - I have no intention of learning to fly something else new at the moment!!!!!!!