didn't the RAF permanently wire-lock the carb-heat on all their Chipmunks to hot?
Brooklands,
They did... but on the Chipmunk it's not really "hot, it's more like "warm" - all that happens is that the engine starts breathing warm(-ish) air from within the cowling rather than the chillier stuff outside. So the power loss is much less significant. It's still a loss though, but the RAF operated its Chippies from HUGE long airfields, so didn't really need the power.
With the carb heat being less effective it takes a lot longer to clear any ice.
Similar set-up on the Yak-52 where the external air scoop retracts into the cowling for warm air. The Yak is more prone to carb-ice on the ground than in the air, but I got a touch of it the other day, in a spinning exercise, so it's still possible.