carburetor heat recommendation for 912 ULS?

[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
88057145-F1AA-445E-BD4A-44C9760A3D44.jpg