912S - Carb Heat or Not??

[jrevens]

I had an issue with the statement earlier in this thread stating that carb ice - "...has killed people in Kitfoxes before. https://aviation-safety.net/wikibase/wiki.php?id=138373" Jumping to conclusions and using that link to imply something that is certainly not stated in that accident report didn't seem right. I'm not at all adverse to anyone using carb heat either... of course not. You're right Jim... it is required in Canada. I would not dare to question the necessity of a regulation imposed by bureaucrats, requiring compliance in all circumstances. No potential variance allowed.



I'm just having a little fun here... no insults intended.

[Ronin]

Those of us without carb heat and speaking for myself are certainly not averse to it at all. We are only disagreeing with the comments that imply we are idiots and that there is no difference between a 912 Kitfox and other Lyc/Cont aircraft that all require carb heat. Even though many of us have never found the need for it, I would be the last person to discourage someone from installing it if they feel a need for it. After all, it has no down side other than a little cost and complexity.

If I lived in Canada, especially the northern parts, I think I would install it. Correct me if I am wrong, but I believe it is required by the equivalent to the FAA to be on all aircraft in Canada and most European countries.

Sounds good but it can happen anywhere. In the Rans S-6 it was around 1,500 feet while crossing the Mississippi river somewhere in Arkansas in April. In the Europa it was at 10,500 over Jacksonville Florida in April. The Europa one I had to shut it down it started shaking so bad I thought it might come off the mount. Dead sticked it into St Augustine and pulled the cowl immediately after landing. The left carb was hot & dry but the right carb was cold to the touch and wet like condensation. I also found water in the airbox. Had no throttle loss or indication what was going on until the engine must have ingested a chunk of the ice, it sounded like we had hit a bird on the lower fuselage.

[atosrider]

does anyone with a model III have the hot water extension sleeves installed on a 912? Those skydrive water jackets must put the carbs about an inch closer to the firewall, and I question if there is still enough room against the firewall for an air filter ...
the other carb heat system of using probes that are electric heaters received bad reviews a decade ago when I was choosing which way to go to add carb heat to the 912, on an imported experimental registered Rans S6 ... does anyone have experience with the heater probes

[Hockeystud87]

I wan't to add to this to give another data point in case there is someone out there debating on heat or not.

I have concluded that flying last week I did experience carb icing. Engine showed all signs of it. Gradual increase in roughness, carb air temp sensor showing in the yellow. As I pulled heat engine increased in smoothness with an occasional large bump as a chunk of water/ice breaks off and enters the engine.

I also live in the Pacific Northwest. Humidity and rain is kind of our thing here. I think it's important to know where people are flying that do and don't have issues.

My setup

94 Model 4 Speedster
Round cowl
912 UL (stock)
Bing carbs
Carb heat/cool rammed air box (the box that sits on top your engine)

Weather and conditions

outside temp was 32F +/- 2F degrees
Low ceiling (thick overcast) ~2000+ of airport
High humidity
dew point and temp spread less than 10 degrees.
carb air temp sensor showing anywhere between -2C up to 8C

I will be installing the hot coolant carb heaters on my plane plus keeping my carb heater box. The way I look at it is I have no loss for adding the coolant heater except maybe a pound of weight and I get the additional increased safety of having the hot air if needed. Also get cool air provided to the engine.

I think the combination of the two makes my plane able to counteract even a larger amount if icing scenarios if they are to occur. Gives me more options and tools to tackle tasks in case of a Xcountry where I get in a pinch.

[jiott]

Al, I am not surprised at all that you may have had carb icing with your airbox setup that brings in cold outside air; with that kind of installation you certainly need a carb heat option. But that doesn't mean that the common setup that most of us have (warm undercowl air with no airbox) is at all likely to experience carb icing in your same climate location. Certainly do what makes you feel comfortable, but you may be going overboard with belts and suspenders.

[Hockeystud87]

I agree I think my data point shows more evidence that the carb box does create a increased icing situation. I just want to make sure that if someone is researching them selves they understand the differences in the two carb setups. I don't want anyone getting "tricked" into a false sense of security if they have a similar carb setup to mine or believing they have a un trusty motor with a different setup.

My setup may be a little over kill but I consider my self a happy paranoid pilot haha!

I had a engine out while solo, during my long cross country, with only 32 hours under my belt. So I might be a little more sensitive/paranoid about my motor than most. Whether that's good or bad IDK!

[Slyfox]

Al, I am not surprised at all that you may have had carb icing with your airbox setup that brings in cold outside air; with that kind of installation you certainly need a carb heat option. But that doesn't mean that the common setup that most of us have (warm undercowl air with no airbox) is at all likely to experience carb icing in your same climate location. Certainly do what makes you feel comfortable, but you may be going overboard with belts and suspenders.

to add to the description of my setup like mentioned by others. I have an oil cooler right up front under the gear box, a good size one at that. plus I have the oil cooler thermostat. which insures the oil is 180+ so I'm sure my carb are in the warmest air in the back with ru2700 filters which is the smallest you can get for the bing carb. moving to the water system, I incorporate a heater off my radiator (redneck type with funnel off the back and scat tube into the cockpit) I also cover up most the radiator to insure 180+ on the water. so my engine doesn't run cool. might also add to warmer area for the carbs.

[Hockeystud87]

I want to add that when I was using the carb heated air from the carb box I was not impressed with the rise in temperature I saw. I have a carb temp prob that sticks into the inlet air stream of the carb. The rise I saw was only maybe 15F. I can't confirm if this is 100% accurate and not being effected by the carb housing but at lest would have expected a larger rise over all. This was even after having the carb heat on for a few minutes. Not impressive =/.

[DesertFox4]

When I purchased my first Kitfox (model 3/912 ul) back in 1998, it came with the carb heat box with a K&N cold ram air filter mounted atop the pilot’s side of the engine. My playground is the desert southwest. Our local Kitfox pilots with the same Rotax engines never encountered carb ice so I removed that from my engine. Also there was an incident reported where a nut and washer came loose inside a carb heat box and got down on top of one of the pistons and severly damaged the engine. That really was the icing on the cake, no pun intended, to remove that system.

Flash ahead to my model 4 with 912uls and no carb heat system-
While returning from a Priest Lake, Idaho flight with 4 other Kitfox’ all Rotax equipped, we had a fuel stop scheduled for an airport in central Idaho. The day was one with high humidity and overcast with very intermittent sprinkles on our windshields and outside temps in the 60’s. We made a fairly quick decent from altitude all the way down to landing. A couple of us, including myself, had a couple of short bursts of rough running engines in that long low powered decent.
Our combined conclusions, likely carb icing. I believe it was all of our’s first encounter with minor carb ice. None of us had a carb heat system installed.

So what do I think I understand about carb icing on carbureted Rotax equipped Kitfoxs?
1. Yes it can occure with the right conditions even on a Kitfox pulling warm air from the back of both the bump cowls and smooth cowls, however it is rare.
2. The standard carb heat system that was used on many early 912 equipped Kitfox aircraft with the cold air intake will induce carb icing much quicker and in less severe ice forming conditions than those engine installs pulling warmer air at the back of the cowls. Most reported incidents of carb ice come from owners flying with the carb heating system installed that have cold air intake locations.
3. The original carb heat diverter boxes could offcast small parts that could translocate into a running engine thereby ruining a pilot’s day very quickly.

Would I intall a carb heating system? Yes. If I flew in a high humidity level area frequently and ever encountered suspected carb ice even once.
Or if the governing body in charge said install one or stay on the ground.
What system would I install? Certainly not the cold air intake box.
I would install the engine coolant carb heating system mentioned previously in this and other threads. Or just go with the fuel injected engines and then no worries.

[Slyfox]

so please explain why fuel injection doesn't have a problem. they still have a throttle body with a filter into the airstream. just curious. I have an io360 that doesn't have carb heat. but never thought much about it.