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Rotax Carb Heat

gblwy

Well Known Member
Any thoughts on carb heating for a 912? I'm assuming the engine as delivered doesn't include anything. There appear to be a couple of options, and some folks in the UK have recommended considering something.
 
Most of the SLSAs that I have done use it for the Jabiru (same basic type of carb). Both American Legend and Indus use a firewall mounted box.
 
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My experience with the 2 kitfoxes I built with 912's and 1200 hours of flight time between them was that they are not prone to icing. I even flew the Speedster IFR in the clouds and rain, along with 7 years in the high humidity of Atlanta. I never experienced any carb icing at any power setting. That doesn't mean it couldn't happen. Just my experience.

vic
 
CAUTIOUS NOTE

I have flown behind a 912S for years. At least in a tractor installation, with a cowl, this engine does not seem prone to icing. I am NOT recommending anything, but I have tried to ice one of these, and just can't seem to do it. I have flown it with ZERO difference between dew point and temp. Tried various things within gliding distance from the field. I think there is enough heat generated within the cowl, that it warms the air enough to prevent icing. If others have had different results, I would really like to hear them.

John Bender
 
You are correct in that these carbs are not "prone" to icing in this configuration. Primarily because they typically receive warm air most of the time. However, they still use a "butterfly" throttle valve and CAN ice. Let's be careful out there.
 
My first flight in a Rans S-12 with a 912S had a little ice on it when we landed. The PIC said the engine stumbled on final, but kept running. This is very rare, but as Mel said it certainly can happen. The S-12 is a pusher with the engine in the open. The RV-12 is a tractor configuration and has a coweling to trap and hold direct heat and radiated heat from the engine. IMHO it should not be a problem.
 
Some S-LSA have "real" carb heat with a muff over the exhaust somewhere. Probably overkill for the 912 in most installations.

Another solution is to use coolant to heat the carb bodies - there are commercial kits to do just that (photo below). Ice is a problem in the UK where is always cold and wet except for high summer (no offense to my Brit friends, God Save the Queen) and this solution seems to work very well there.

sd_img_ch.jpg


My LSA has not so much "carb heat" as "alternate induction" with a flapper door that then takes intake air from inside the cowling. It's not as good as some real kind of heat, but it's better than nothing. I rarely use it unless the dewpoint spread is small.

The exhaust from the 912 gives of a lot of heat inside the cowling and probably contributes to the cowling air being warm. Some 912 operators actually use an insulation wrap on the exhaust header to keep cowling temps down.

TODR
 
My RANS S-7 had carb heat, and although I put 275 hours on the airplane in 3 years, I never felt the need or occasion to use it. The engine installation in the S-7 was very much like that in the RV-12. Steve
 
Carb Heat

My 912ULS came with factory installed with Carb Heat. Coolant circulates continuously thur rings mounted between carb and manifold. I have chosen not to use it as it robs HP at cruise. If I lived in the UK I would definitely consider the factory Carb Heat System.
Gerry
Threepeat Builder
RV-12, N6GC
Cub, NC88583
 
Hey Keith

I would not bother installing carb heat. I have several hundred hours with the 912S, and I have not been able to make it ice. I have intentionally tried to ice the carbs going in circles above the airport on days when there was no difference between temps and dew points. In this type installation, there seems to be enough heat in the engine compartment to prevent icing. Maybe others have had different experiences. I don't know anyone that has reported ice when the engine is enclosed.

John Bender
 
Reassurance

Just reopening this topic after a while to see if anyone has, indeed, had experience of carb icing in an RV-12.

Previous comments ranged from:

- I tried to make this happen, it didn't

to

- UK pilots should install it!

Cheers...Keith (in the UK)
 
Hi Keith

On my 12, I'm going to fit the Sky Drive (ConAir) coolant fed carb heating sytem. The theory is you don't lose performance as you are heating the carbs not the induction air.

We have 250hrs on our Tecnam P2006T with a pair of 912S. It does suffer from carb ice but normally only when the engine is cold at low rpm and high humidity conditions (damp, misty, rain etc). It has suffered a bit inside cold wet clouds as well.

The P2006T uses hot air from the muffler piped into the airbox and gets rid of it fine. Our P2002-JF single soesn't seem to suffer very much at all and also uses the same hot air system (the coolant heater system isn't certified).
 
Carb Heat

I have an HKS700 on one of my homebuilts, and it uses the Bing Carburetor like the 912. They offer an electric heating element that screws into the carburetor throat for about $125 per carburetor. Google the HKS engine to order a couple.
 
I am measuring the air temp at the air filter and it is 130 degrees f so it is like having carby heat on all the time
 
If the engine is cowled it is pretty rare to have a Rotax 912 experience carb icing. I've flown the RV-12 in just about every temp and humidity configuration and condition with nothing adverse happening.

I've seen carb icing on the Rotax 912 with an open engine pusher configuration in very high humidity situations and when pulling the throttle back on approach for landing. The engine coughed a little, but kept running. Upon landing we found water on the outside of the carbs indicating (to us) some icing.

Your mileage may very. ;)
 
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