Carb heat 912ULS

[rainbird]

I live on the coast of Oregon where it's common to have 45* temps and humidity around 80 to 95%. Is carb heat needed with the Bing 64 carb?

[Dave S]

Rainbird,

Overall, it seems that people have little trouble with the Bing 64s and carb icing. Its even hard to find a 912ULS powered factory light sport of any brand with carb heat in the US. Quite different than the small continentals I once flew behind that could pick out two molecules of water from within a 5 nautical mile radius and use them to put ice in the carb.

The early Kitfoxes with the 80 hp Rotax came with a carb heat kit - although I am not sure that is without problems as there have been cases of the carb heat exhaust spacers wearing and shedding parts into the induction system - no idea if that is due to inadequate maintenance or poor assembly - If I had one of these I would have a screen in the induction system before the carbs - but that is just me. I don't think you will find many 912 powered Kitfoxes with carb heat (not mine either)

Here is one situation where a rotax powered airplane reportedly had carb ice with the Bing 64's. The link below was referenced by FAA FAAST (safety team) recently. Might be worth a look.

https://spark.adobe.com/page/tkWvPqGXK0OVl/

I should say that this link does not help a lot with specifics other than it seems to show a photo of a Bing 64 with some frost in it.....much of the text is stuff we already know. I wish they were more specific.

I don't have carb heat on our 912 ULS and have not had any hic-ups but our conditions are mostly not as conducive to carb icing as the conditions you indicated. I believe most do not have carb heat.

[Av8r3400]

I would agree totally with Dave S.

I do understand that some people and non US governments want to have carb heat. IMO, if I needed to add a system I would go with the coolant heated spacers on the carbs. It keeps the body of the carb warm to prevent icing, but does little to heat the air passing through.

This is one example of this design. (http://www.skydrive.co.uk/proddetail.asp?prod=CH-912-3)

I had the hot air system on my old plane when I first got it. When I removed the system, I gained nearly 300 static RPM. It was quite draggy and power robbing.

[av8rps]

My 80 hp Kitfox also had carb heat when I bought it. I found the exact same thing, it robbed about 300 rpm, so I took it off. I've never had the engine quit because of carb ice, but I have had it run poorly a few times when carb icing would be the most probable cause. So given my druthers I would always install a airbox that gives one the option of turning on carb heat, or I would put on coolant heated carb heaters like av8r3400 suggested.

But using an airbox will have another benefit besides just providing carb heat. Because you will now have cold air coming into the engine, your 95 hp Rotax will now be 100 hp (cold air works better than hot air, which is what the engine mostly gets when it is sucking in engine compartment air). So in my opinion, an airbox is still the best approach. They tend to be pricey but not really when you recognize the horsepower gain. And it is always nice to have the option of turning on carb heat when you need it, vs having no option when your engine is running rough.

[kitfox2009]

Hi guys
I have used the small coolant manifolds on the 912UL on a Vixen,now for over 500 hours. Carb heat is mandatory for "homebuilts" in Canada. I have disconnected the coolant lines in the summer but could see no difference in performance. Thought it might improve the hot start issues.
Never had carb ice that I know of.
Cheers
Don

[rainbird]

Thanks that's the kind of info I was looking for I didn't know about the coolent heated carb spacers which are interesting. The air box was also interesting I had been wondering how a piece of pipe could be worth an extra 5 hp I had overlooked the denser cooler air. So now comes decision time go with the coolent heated carb heatedcarb heater spend more and get 5 more hp.

[Paul Z]

I live in Texas, and I had a carb icing issue once on landing. Since I fly a SLSA I pulled the Carb heat and it was resolved. I usually don't have an issue with icing but I was sure glad I had it available. Here is a photo of the set up. Pretty simple mounted to the end of the Co-Pilots side Exhaust

[rainbird]

Ahh that's the missing part of the air of system that I was t seeing Is there also a hot air dump to get rid of the excess heat from the heat box when not using carb heat? I once had an instructor who once told me that not using carb heat here on the Coast was going to kill me. I have watched a carb ice up till the engine stopped, not a Rotax but with a slide carb. Thanks Paul I'm starting to see my solution.

[Dave S]

Paul,

On your light sport, Where is the non-heated air intake located? Can't see that from the photo.

[Paul Z]

The air cleaner is on the air plenum, hangs down from the center between the carbs just behind the engine. I could go take a photo.

If you zoom up on the photo the scat tube is hooked to a flange that is attached to the exhaust. The bracket has 3 attachment legs, and the actual flange is about 1/2 inch from the exhaust. Air flow frount to rear not much goes up the scat tube as long as the butterfly valve is closed off. I'll see if I have a photo of the air intake manifold air box.

[Dave S]

Hi Paul,

Your explanation makes it perfectly clear. Our Kitfox is an E-AB, not a LS; however, we do have the Rotax Airbox so your comments ring true to as to how how it would be hooked up. Currently we have an alternate air (no carb heat) with a screen over the tube stub on the airbox with the primary air intake plumbed to a flange on the side of the NACA vent - so the filter is in the air duct just ahead of the radiator.

With some time on the KF, one of the things we observed with regard to the airbox is the rubber carb flanges have no wear or cracks....I replaced them @ the 5 year recommended time - but, I feel that I replaced perfectly good parts as the only way to tell the old from the new is the old ones smelled like gasoline and the new ones did not:rolleyes:

Thanks for the info - I do like the carb heat setup you have compared to the somewhat complicated earlier version. Think I need to talk to John McB. when I get the time.

[Dusty]

Here is some photos of a home grown carb heat system that is simple and works well

[brjohnso]

Rainbird,

Overall, it seems that people have little trouble with the Bing 64s and carb icing.

Well, there is this one....https://aviation-safety.net/wikibase/wiki.php?id=138373

[Ronin]

I have had carb icing with two different 912s powered birds, once a Europa that was bad enough to require an emergency landing and once in a Rans S-6.


My 4 will have a carb heat system.

[Esser]

You don't have trouble with carb ice until you do. You can buy a water jacket style that has a valve on it so it's not always on. Lots of hot water on a Rotax.

[sturdee]

I have the carb heat box that came with the kit hot air from around exhaust re directed to carbs the old fashioned way.
Last year I fitted a carb temp. Probe and oh boy was amazed at how quickly I get carb ice. Before the temp probe I would wait for the manifold pressure to drop, then when carb heat was applied the engine ran rough and appeared too be over rich, however I now know it was severe carb ice, what I do now is as soon as the needle on the gauge enters the yellow area I apply carb heat and no rough running . So those who believe the Rotax 912ul doesn’t suffer from carb ice because the carbs are in warm area of the cowling are going too get a shock
Bam engine stop!
There are several ideas out there , electric/ water jacket and what I have .
The electric does pull a fair amperage,so be careful you don’t exceed the generator limit.
The water system obviously only works when the water is hot you can’t switch it on or off so whether that effects the performance of the carb would be interesting to know.
Stay safe

[jiott]

The water system carb heat suppliers say it does not affect engine performance and can be left on all the time. It only heats the carb intake body to prevent ice forming, but does not measurably heat the intake air which would affect air density/performance. Sounds like the simplest best system to me if you think you need it.

[Dusty]

I did some trials a while ago by clamping off the water supply to the carb heat blocks I had made.If there was a difference in performance it wasn't obvious.

[Ronin]

The water system carb heat suppliers say it does not affect engine performance and can be left on all the time. It only heats the carb intake body to prevent ice forming, but does not measurably heat the intake air which would affect air density/performance. Sounds like the simplest best system to me if you think you need it.
This was the kit I had mounted in the Europa I flew

http://skydrive.co.uk/proddetail.asp?prod=CH-912-3

Left it on at all times and it didn't hurt performance in a measurable way.