carburetor heat recommendation for 912 ULS?

[hallschuch]

Does anyone have any recommendations for adding carb heat to a 912 ULS? thanks in advance

[jiott]

If you really think you need it, I think the best and easiest to install is the coolant collar kit that installs on the carb inlets using hot engine coolant to heat the carb throats. It is ON all the time heating only the carb throat, not the air so there is no loss of power. Sold by most of the Rotax parts dealers, ACS, Lockwood, CPS, etc.

[Dave S]

In my opinion, Jim is spot on.

There is probably a good reason why Rotax providers use that system.

I am a bit hesitant about the original carb heat on the IV . Aside from unfiltered air, the fabricated heat muff is potentially a source of loose parts/rivets/etc that could potentially mess up the carbs operation or get sucked onto the the engine due to the design/construction of that particular part - you want to inspect it frequently enough to assure that vibration has not worn and dislodged the spacers/rivets between the outer tube and the exhaust pipe.

[hallschuch]

thanks both of you - Jim, you said "if I think I need it"... so I'm new to the kitfox world and my build is almost complete, but is it the case that many do NOT install carb heat? , I ask because all the other small craft I've flown have had it. I'd rather not install it if its not necessary...?

[Dave S]

HC,

I don't know how many do vs how may don't; however, I suspect that a lot of 912 operators do not have carb heat.

I studied the issue quite a bit when our kitfox was built and decided against it. I don't know that the 912 is immune to carb ice, but it certainly is resistant to the problem. A rotax is designed differently compared to traditional aircraft carbureted gasoline engines. A C150 with a continental will find 12 molecules of water within a 5 KM radius, put it in the carb and make ice; but, the carb is under the engine and completely insulated from the engine heat, except for the carb heat. A 912 has the carbs on top and a certain amount of heat will be conducted and radiated upward - then you have two carbs so the temp drop due to fuel vaporization is split between two places with each carb evaporating only half of the fuel and consequently each carb makes only half of the "cold" necessary to make ice. The 912 engine has variable venturi carbs rather than a butterfly system which behaves a bit differently too.

At any rate, over the time we have flown our kitfox, never a hint of carb ice, admittedly it is not flown through clouds with lots of moisture - but I think each builder needs to figure it out for themselves.

It would be nice if there was some sort of survey to find out how prevalent the use of carb heat is with the 912 carbureted engines.

[jrevens]

Drawing air from the warmer rear, upper area of the engine compartment, as opposed to your average Lycoming or Continental that draws air directly from outside (when carb heat is "off") is a big difference in my mind. I'd like to instrument that area with a thermocouple some day and measure what the temperature is compared to the outside air temp. It would be useful to do that several different times under various ambient conditions. For the record, I don't have carb heat for my 912 ULS either.

[HighWing]

Much of my flying has been alongside a bunch of Model IVs. My kit came with the carb heat box and like the vast majority of others the carb heat box eventually went into the recycle bin. Lots of talk about in the early e-mail lists and experience resulted in very few installations and virtually no reports if issues. Of course, these were mostly the 912 UL version.

[jiott]

Hallschuch, you can do a search on this forum for carb heat and find a lot of reading. I, like the other responders to your post do not have carb heat, nor never found a need for it, but like Dave said, I don't fly thru moist clouds for any length of time. Seems to me like most of the folks installing it live in Canada where I think it is required by law.

[Dusty]

I use a temperature guage by the firewall on my 4. The temp is generally 10c above ambient in flight.
A smooth cowl installation may see a bigger differential. I removed my airbox assembly and use hot water directly to the throttle spindle as there wasn't enough room to use the carb intake heaters. Carb icing is is sometimes a problem in our environment.

[jrevens]

That's good information, Dusty.

[atosrider]

yes for mandatory carb heat systems for Canadian home builts,
so I put 600 hours on a Rans 912uls and twice the engine stumbled, the only explanation being carb ice must have been starting, they're cheap compared to being scared or damaging your plane. you/ll feel wonderful about that $ still in your bank account as the engine struggles to breath .... both times the rough running was almost hard to detect (like could have been missed by a passenger not tuned in to mechanics) and short lived, but what would it have been without the hot water jackets?
and this reminds me, there is a new system with electric heat, improved from the earlier failure version that used a probe, and they are only 40 miles away, so I'll update when I confirm there service record - good timing for my K3 912ul rebuild project

[chipjumper]

I’ve seen the electric kits on the internets. I’m guessing they work off of the thermoelectric Peltier principal. Note that any carb’d motor is subject to carb ice this includes any Lycoming. I was nearly killed in a C-150 that iced up on takeoff (Continental O-200). Per the NTSB my Mooney went down in NM in the 70’s due to the O-360-A1D icing up and they were unable to restart the engine in the air. I suppose it is a factor of the temperature, humidity, AND induction system. There is no way I would run without some sort of carb ice detection and mitigation system. Note that even the snowmobiles have carb ice mitigation systems built in (electric).

[jrevens]

... Note that even the snowmobiles have carb ice mitigation systems built in (electric).

I can imagine that snowmobiles might potentially be sucking up as much snow as air on occasion. Seems like "carb ice mitigation systems" would be standard equipment on them alright.

[sturdee]

Does anyone have any recommendations for adding carb heat to a 912 ULS? thanks in advance
Hi, well for those who don’t think you get carb ice on the 912 instalation on a Kitfox. I have to say are wrong because you do!
I have a standard instillation where the heat is drawn from the exhaust shroud And directed to the carbs by selection. Now before I fitted a carb temperature probe too the carbs I would get rough running during selection of hot air ie top of descent or in cruise. I was suspicious of ice but couldn’t be sure as the hangar chat was oh it’s probably running richer when carb heat applied.
So with that uncertainty I installed a carb temperature probe. Ahaa guess what carb ice, big time
No more rough running keep that sucker warm, so as I said I have the old selection system however have fitted too other kitfoxes, the electrical heaters and water jacket type.

The electrical version does draw a high load when selecting the highest setting watch you don’t pull to many amps from the generator. Found strobes non essentials needed switching off when on high.

2 the water jacket type does move the carbs further back which can cause the air filters to contact the fire wall so ensure your filters don’t rub. Heat wise when the engines up to temp the carbs stay warm period so you can’t select it on or off, this doesn’t appear to effect performance.
we operate in a rather wet environment in Scotland, moist air.
Stay safe, Mike

[Dorsal]

When you say "standard installation" where is the air drawn from when heat is not selected?

[sturdee]

Sorry should have mentioned that the filter is left of the gearbox
at the front of the engine as per installation Manuel fitted to the carb heat box!
scat tube to each carb.

[jrevens]

Sturdee,

So, you are drawing air directly from outside the engine compartment when not using carb heat. It is a very different situation when the air is drawn from the relatively warmer top rear area of the engine compartment.

[Dorsal]

As John mentions, for many "standard installation" is filters directly on the back of the carbs or on an airbox located inside the top rear of the engine compartment. I believe this is a bit like running medium carb-heat all the time. I have not heard of anyone having carb-ice with this setup. If I were drawing outside air directly to the carbs I would include a heat option.

[sturdee]

Sturdee,

So, you are drawing air directly from outside the engine compartment when not using carb heat. It is a very different situation when the air is drawn from the relatively warmer top rear area of the engine compartment.
Morning jrevens,
the air box and filter are inside the top cowl as per the build Manuel Mk4 912 1993.
Believe me ice is forming inside the carb. Have had manifold drop due too it before carb temp probe installed.
the amount of air flowing through the round cowl in principal you would expect to be warmer after flowing over the engine however someone should measure that. As we know the carb temperature will be colder due to the mechanics of fuel vaporizing.
I think most of the airflow travels down and out the bottom cowl as there is no baffles inside the cowl or need for them as water cooled heads, only air cooled barrels.
I was sceptical until I had seen the probe temps so believe carb heat is nessecary especially in this climate.
I can select on or off. Stay safe
Sturdee

[jrevens]

Morning jrevens,
the air box and filter are inside the top cowl as per the build Manuel Mk4 912 1993.
Believe me ice is forming inside the carb. Have had manifold drop due too it before carb temp probe installed.
the amount of air flowing through the round cowl in principal you would expect to be warmer after flowing over the engine however someone should measure that. As we know the carb temperature will be colder due to the mechanics of fuel vaporizing.
I think most of the airflow travels down and out the bottom cowl as there is no baffles inside the cowl or need for them as water cooled heads, only air cooled barrels.
I was sceptical until I had seen the probe temps so believe carb heat is nessecary especially in this climate.
I can select on or off. Stay safe
Sturdee

Thanks, Sturdee. Just to clarify, I believe that you have said that your outside air intake is adjacent to the gearbox, basically right at the front opening of the cowl. Your points are all well taken, but people have measured the air temp (as per a previous post on this thread) at the back of the engine near the firewall, and an increase in temperature of 10 deg. C over ambient was mentioned. I think it may be, & probably is higher with the smooth cowls that many of us are using now. However, many builder/owners with round cowls and carburetors with air filters directly mounted on them have never experienced carb ice over many thousands of hours of combined experience. I have a friend who has flown his Kitfox Mod. IV to every state in the United States except Hawaii, and almost every province in Canada, in all types of weather, and I don't think that he's encountered carb ice. I believe he is approaching 3,000 hrs. flight time in that airplane. He doesn't have carb heat. I have no doubt that you experience carb ice with your situation. Kitfox owners need to do what they feel is safe, all things being considered, and I respect your need for carb heat.

[hallschuch]

Thanks everyone, your inputs are appreciated!

[sturdee]

Thanks everyone, your inputs are appreciated!
Just added a picture of the temp in the carb whilst coming home from Ireland last summer, glorious day as you can see, the temperatures and too the left of throttle the carb heat knob pulled half way out too maintain that temp. Stay safe I was hotter than the engine as wearing an emersion suit so stopped off at Bute too de robe
24109

[Auster]

Just to make the point once again, the point that John Evens was making. The big difference between needing or not needing a carburettor heat system on a Kitfox with a Rotax is usually determined by whether you are drawing intake air from the front of the cowl or from the rear, underneath the cowl with the carbs facing the firewall. Accumulated experience with both Rotax and the Kitfox would (I think) lead to the conclusion that a system drawing intake air from the front (outside) of the cowl requires a carburettor heat system while one drawing warm air from the rear inside of the cowl does not.

I am flying with the latter system, i.e. no carburettor heat device or system because I am using a smooth cowl and the Rotax 912 ULS carburettors draw warm air from the rear, that is they face the firewall. The one concern I have is that in winter the motor runs rather cool and I have worried that it might be too cool under that cowling to provide the necessary warm (temperature differential) air. To address this, in winter I partially cover both the oil cooler and radiator with aluminium tape and bring the temperatures closer to those I would see in summer. I hasten to add that I have never experienced carburettor ice despite flying in low temps and moist conditions. Ground testing with cowls removed in ideal icing conditions also failed to produce a problem. However keeping those engine temps up to normal gives me a warm feeling in winter so that I fly without worrying about carburettor icing.

[sturdee]

Just to make the point once again, the point that John Evens was making. The big difference between needing or not needing a carburettor heat system on a Kitfox with a Rotax is usually determined by whether you are drawing intake air from the front of the cowl or from the rear, underneath the cowl with the carbs facing the firewall. Accumulated experience with both Rotax and the Kitfox would (I think) lead to the conclusion that a system drawing intake air from the front (outside) of the cowl requires a carburettor heat system while one drawing warm air from the rear inside of the cowl does not.

I am flying with the latter system, i.e. no carburettor heat device or system because I am using a smooth cowl and the Rotax 912 ULS carburettors draw warm air from the rear, that is they face the firewall. The one concern I have is that in winter the motor runs rather cool and I have worried that it might be too cool under that cowling to provide the necessary warm (temperature differential) air. To address this, in winter I partially cover both the oil cooler and radiator with aluminium tape and bring the temperatures closer to those I would see in summer. I hasten to add that I have never experienced carburettor ice despite flying in low temps and moist conditions. Ground testing with cowls removed in ideal icing conditions also failed to produce a problem. However keeping those engine temps up to normal gives me a warm feeling in winter so that I fly without worrying about carburettor icing.
Hi Auster,
if you take a look at my pic, you will see a T handle 2nd left of throttle, locks with quarter turn. This controls a hinged door in the radiator scoop and varies the amount of air passing through my radiator. Fail safe too fully open the good part I can close off the radiator or fully open subject to how cold or hot I want my engine. Wasn’t happy with guessing how much too blank of. Also during long descent can close the cowl and keep the engine warm great for winter starts and quick warm up.
as for carb ice well you take your chances it’s a known killer and after the accident the evidence melts away,
if you know the temps in the carb your good if you assume thier temp good luck!
Stay safe,
sturdee.