G'Day Paul,

   From what I can recall opinion seems fairly evenly divided on the merits
  of
  carburettors and fuel injection, however the importance of carby heat
  seems to
  get ignored and I haven't noticed any provision for it on any of the
  installations I have seen here. Are rotaries immune from carby ice, or
  have i
  missed something?

  John Evans
  The FAA will not sign off on a AC carb here in the U.S. unless it has
  carb heat.

  I have never brothered to draw something up as it is quite simple
  to copy certified aircraft carb heat designs. God knows we have plenty
  of exhaust heat to work with :)

  Paul Lamar

  Not sure that is true. Just looked at an RV-12 -- no carb heat on the
  Rotax 912S.

  Joe Spelz

  That is dangerous. I am not familiar with that engine.
  It could be hidden. Due to evaporation of fuel the AC intake
  manifolds generally run ice cold.

  Paul Lamar

 In my experience with Rotax 912/912S (about 3000hrs) the only time ice was
 an issue was in the first five minutes of running, on the first flight of
 the day, in temperatures slightly above freezing. Once the engine had
 warmed
 up, the heat rising up off the engine into the manifold and carbs seemed
 to
 stop the carbs from icing. I can not recall ever experiencing icing with
 these engines in the air. Of course I am not advocating not having carb
 heat
 and not testing for its correct operation before every flight.

 John

 I assume the carb is on top of the engine while the typical
 ac engine the carb is on the bottom. Heat rises.

 Paul Lamar

Correct, twin carbs on top.

John

In that case we may not need carb heat with this design.

I still doubt however the FAA inspector will accept it with
out what looks like carb heat.

Paul Lamar