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Rotax Carb Ice

H

HDDAHL

Active Member
Just curious; the RV-12 has no provision for dealing with carb ice. I am assuming that airflow past the coolant radiator heats the input air to the carbs enough so that ice will not form. Anybody have any info on this?

Doug Dahl RV-12 flying, waiting for the gear SB fix kit
RV-9A for sale
 
Carb Heat!

The 912 can be installed in many configurations. As a pusher on an ultralight with no cowl or as in the RV12 in a tightly cowled configuration. Although not impossible Vans decided that it was not necessary to use carb heat in the RV12. IMHO because of the tightly cowled configuration ambient heat coming from the engine and exhaust would provide enough heat around the carbs to prevent icing to occurs. See some of the other banter on the subject on this thread link.;)

http://www.vansairforce.com/community/showthread.php?t=51935&highlight=Carb+heat
 
Keep in mind....should you have the very rare incident of carb ice (you have two!), what better plane for an off field landing. The glide ratio is so high you must teach yourself exactly how far you really can glide..most often to a real runway. The glide ratio is one of the primary reasons everyone should take transition training (with Jetguy, **** yes). Your sense of security will improve dramatically when you actually discover the amazing distance you can cover with no power. Should any ice melt, your rotating prop would start the engine again automatically.
 
912 carb ice

I've got a dozen or so hours flying a Gobosh LSA, which sports the Rotax 912 UL 100hp. Probably a 2009 model or so.

I was on a night cross country returning from Palm Springs to San Diego, from about the Julian VOR I was cleared direct through the class bravo on into Gillespie KSEE. I was on a throttled back decent for probably twenty miles. Decided on a couple touch n go's upon my return for night currency. Once I throttled up and lifted off the engine started spitten and sputtering making about half power. I threw on the fuel pump and carb heat and the engine made a recovery and started running smooth again by downwind. Next time around was a full stop:eek: probably should have had the carb heat on in the decent but had got out of the habit because it had been rumored to be "not needed" or of no benefit.

So, that particular setup had some carb issue, not sure exactly what it was. Haven't flown one since;). I do recall there was never a noticeable drop in RPM with carb heat but you could see the carb temp rise.
 
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carby heat

I used a spare temp input to the skyview and installed a thermocouple next to the carby airfilter and it generaly reads about 100f so it is like flying with the carby heat on all the time
 
Peterk said:
Keep in mind....should you have the very rare incident of carb ice (you have two!), what better plane for an off field landing. The glide ratio is so high you must teach yourself exactly how far you really can glide..most often to a real runway. The glide ratio is one of the primary reasons everyone should take transition training (with Jetguy, **** yes). Your sense of security will improve dramatically when you actually discover the amazing distance you can cover with no power. Should any ice melt, your rotating prop would start the engine again automatically.
Click to expand...

The above is slightly misleading. The glide ratio at idle power is completely different than the glide ratio with NO power. That's because the Rotax is actually producing quite a bit of power at idle. To develop a feel for how far one can glide after an engine failure, the engine has to be shut off. I have done this high over an airport, and made the classic spiral-to-land maneuver, and the glide ratio is way different from just an idling engine. This is not for the faint hearted, and I am not advocating everyone do this, just keep in mind that in the unlikely event of a complete engine stoppage you will need to plan for a much shorter approach.

Additional information - when I performed my engine off glide test, the prop stopped immediately when the ignition was killed, and slowed no signs of windmilling during the glide at best glide speed. Due I believe, to the high compression and geared prop. IMHO an air start would require using the starter.
 
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Thanks Tony - -

It will turn if you have enough speed. I had to slow down to about 60 kts to keep it from turning, Hard to imagine such a case, but if decending at 70 or up, it would start the engine. The thing to keep in mind. If you try what I did, make sure you do slow down enough to stop the engine from turning over. With the mags off, it would build up gas in the engine.

John Bender
478.3 hrs
 
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