912S - Carb Heat or Not??

[N82HB]

My airplane does not have carb heat. It has been that way for 350 hours, but that doesn't make it right. Should it have it? I would love some opinions...
Kelly

[Dorsal]

I asked the same question while I was building and my research suggested carb heat was not necessary if your intake is drawing from inside the cowl. This is, of course, only what I found and chose to do and at 70 hours I have significantly less time on my plane than you do. I sometimes contemplate moving my air intake to the scoop (possibly a skosh more HP) in which case I would implement CH.

[Av8r3400]

I took off the ducted carb heat system from my yellow plane. In doing so, I gained 200 static rpm from the loss of restrictions.

The anecdotal information that I have heard, and believe, is that the only planes which have ice issues are the ones with the ducted carb heat setup on them. This is due to the intake just behind the prop taking in the colder air. With the intakes by the firewall the air is preheated by the ambient temp inside the cowling lessening the likelihood of ice.

I have no scientific evidence to support this, but it does make logical sense.

The liquid heating type of carb ice prevention does seem to be interesting, though.

[Dorsal]

I took off the ducted carb heat system

Good to know, I can leave mine the way it is without the feeling there might be an extra fraction of a HP left on the table.

[kitfox2009]

G`day Kelly
For Canadian homebuilts it is mandatory according to Transport Canada to have some approved form of carb heat regardless of where the carbs are located. In order to meet this requirement (and also for my own piece of mind) I installed the small hot water manifolds that mount between the intake and the carbs. I have no operating experience prior to installation so are not able to comment on power loss,etc. They are always "on" therefore I just do not worry about icing.These units are available from Bob at Light Engine Service (780-418-4164) or possibly directly from Sky-Drive in UK.Supposedly the carb throat body maintains enough heat to prevent ice build up without preheating the intake air resulting in a noticeable power loss.

Have fun

Don

KF5 Vixen C-FOXK
912UL

[DesertFox4]

Kitfox2009- Good point. Required North of the border. I'd also go with the hot water manifold type if I felt the need. No issues with carb. ice yet with the intakes by the firewall. I do spend most my time in the desert so moisture usually isn't a problem. Unusual for dew points and temps to get within 10 degrees of each other.
I'll deffer to the guys that fly in moister climates for their experiences in this matter.

[Ken Birchard]

I put the Bing 64/32 electrodes that screw into the vacuum port on the carbs in my 912uls. Easy to install, hook to a switch on the panel and shouldn't affect HP. Look like they should work. Haven't tied them out yet...Ken

[brjohnso]

I don't know why anyone would remove a carb heat system. Carb ice happens. It happens on Kitfoxes, I happens with the 912, and it has killed people in Kitfoxes before. https://aviation-safety.net/wikibase/wiki.php?id=138373

Rotax also has a fuel circulation feature to prevent vapor lock, but for some reason, not everybody connects that up either.

[brjohnso]

There is nothing special about the 912 or the Kitfox when it comes to carb ice. It is as vulnerable as anything else. Ice is uncommon but not rare, and it's also unpredictable. It can form as fast as a minute or two. https://aviation-safety.net/wikibase/wiki.php?id=138373

I had it happen to me once in a Cessna. It took less than a minute to form and my engine stalled during my takeoff roll.

[jiott]

Sorry to totally disagree, but the Rotax Bing carb is different than other aircraft carbs in that it is a constant depression altitude compensating carb whose throat design is NOT as susceptible to icing. I will not try to describe the design reasons this is true because its been quite a while since I read up on it. Go do a search yourself and read about it. Also the position the carbs are mounted in the Kitfox tight cowl gives it an icing advantage compared to many other aircraft.

Mind you I am certainly not saying that the 912 in a Kitfox will never ice up, but I am disagreeing withe your blanket statement that "there is nothing special about the 912 or Kitfox when it comes to carb ice". There are probably thousands of us who have been flying 912 Kitfoxes without carb heat for hundreds of hours without a single icing incident.