Given that 'cold' and 'warm' are vague terms the Rotax engine runs on a warm air mix and so generally avoids carburettor icing but they are not immune from it. The cylinder heads are liquid cooled maintaining temperatures. Engine failure, of some Rotax engine installations, owing to carburetor icing is not uncommon. Rotax subsequently introduced what is placarded as Carburetor heat although it does not add hot air. The Rotax carb. ht. control shuts off the cold air part of the intake air mixture therefore causing the intake air temperature to rise, hopefully, out of the icing range. The Rotax engine is altitude limited, presumably due to its limitations to cope with the range of temperatures and the needle and float carburettor mixture control limitations for air density.
For power the densest of air possible is required. The colder the air the better and rammed in (even without a turbo) is preferable. Most light engines are not altitude limited other than by performance. Hot air is reserved for when it is required to prevent or dispel icing. The range of temperatures an aircraft regularly experiences is far greater than the automatic systems a car is expected to deal with. Regarding the mixture, an aircraft passes through a vast range of air density and therefore a large range of mixture control is required. There are automatic systems for both of these issues but obviously adding weight, complexity and cost.
Last edited by Fl1ingfrog; 23rd Nov 2021 at 23:34.