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

G'Day,
Actually there is now carby heat available on the Rotax 912 S. It consiosts of an alloy casting with a tube cast into it to circulate coolant sandwiched between manifold and carby, it appears to be effective enough, although it may not meet the stringent requirements of the CASA in Oz as the temperature of the required hot air is is specified.

Years ago I was having a consultation with a Post Office worker, who like myself was a biker, he was complaining that on his way to work in the very early morning his new Yamaha Virago would snuff as  he descended a certain hill, the dealer was of no help. I explained that he was getting carby ice. He was pretty skeptical, but some months later told me that Yamaha was belatedly fitting an electric heater, this had been deleted from the models sold in Oz.

A couple of years ago a group of 912 powered MT03 Gyros flew around Australia, while not admitted at the time some of them complained of the usual symptoms of icing under moist conditions. They were not fitted with the heaters described above, but all new ones now have it.

John Evans