Just what is the recommendation on using carb heat? My old 172 required it to be used all the time when under 2000 rpm. My old Commanche had no recommendations at all and I never pulled the knob except to check it out at run up.
On the carbon cub should we be pulling the knob every time we land, or every time we cut power to slow down, or when we feel the engine starting to run a little rough (which might be a little too late)?
Rick-
My two cents worth: I'll start out with the standard FAA statement of, " Carb ice is possible at any time".
But in reality, we have a few things going for use. First the CC-340 ( Lycoming) engine has the carb bolted
right to the hot oil pan. Unlike the low slung Continental C-65,75,85 style that doesn't get as much heat
transfered to it. This helps (a bit) to keep it warmer. Second we are lucky to have a carb temp gauge,
( Exec. Glass) which adds to the heads up on just what the freezing temps might be in the carb. Third we
can monitor the OAT and Dew Point, to give us a better picture of carb ice potential.
I have a little cheat sheet that shows the temp and dew point. If the Dew Point is at or less for any given
temp (on the cheat sheet), than carb ice is highly unlikely. If the Dew point is Higher for any given temp.,
than carb ice becomes more probable. Note these Temps and Dew points on the (colored graph), and you
will see that these numbers are way outside of probable icing conditions. Since most Metars, ATIS, AWOS
etc report Temp/Dew Point, I made the cheat sheet for Dew point and not Relative Humidity. Do not confuse
Humidity with Dew Point,( refer to the colored graph for Humidity and ice potential ).
So for me, I would answer- NO, I don't Always use the carb heat. In my area, and ref the Carb Ice graph,
I would say my carb heat gets used almost never in the CC. But if I was in SEA today the temp/Dew is 12/08 or
53.6/46.4 , so YES I would use carb heat and consider it to be moderate to sever carb ice potential.
Your miles may vary...
Steve
Last edited by Steve Y; 10-16-2013 at 03:21 PM.
XCub: CCX-2300-0011
SPOT X TRACKING: https://maps.findmespot.com/s/09SL
I seem to be getting carb ice on every first takeoff of the day lately. Once the engine is warmed up I don't get it but before then I am.
Outside temperatures have been in the teens and 20's and there is some moisture in the air. But it seems much worse this winter. I'm wondering if setting the mixture at full rich might contribute? If there is more cold fuel going through the carburetor and vaporizing maybe that leads to more ice if the conditions are right? I often lean some for take off but haven't been lately.
Any thoughts on full rich contributing?
Flying Carbon Cub EX #11 since 2011
I found a contributor to my recent and consistent carb ice problem. The cable clamp on the air box holding the carb heat control had allowed the cable to slip slightly in the clamp. This in turn was leaving the butterfly partially open when it should have been closed. So I was getting some warmed air into the carb along with normal air and the combination must have been creating air that was prime for icing.
Readjusting the cable has cured the problem. And twisting a piece of safety wire around the cable sheath on both sides of the clamp will hopefully keep it from ever slipping again.
Flying Carbon Cub EX #11 since 2011