Carburettor heat in Spits and Hurri

[Sutts]

Is it true that the merlin had inbuilt and continuous carb heating? Any period refs you can point me to please?

The reason I doubt this point is the same reason carb heat is usually controlled by a switch/lever in the cockpit - heating the air going into the carb reduces engine power as warm air is less dense than cold air so you get less air going into the cylinders to burn with the fuel. This is the same reason compressed air from the supercharger is often cooled before it gets to the carb (to remove the heat created during compression).

Now I can't see the designers of the merlin permanently reducing engine performance by continuously heating the air entering the carb.

On the other hand, if just the carb body is heated then I suppose the effect on the air might be insignificant. Would be nice to see some docs on the subject.

Cheers