Originally Posted by
Step Turn
I gathered a little data today. O-200 in C150M, at 2500 RPM, 58F OAT.
Carb air temp cold air = 42F, apply full carb heat = 62F carb air temp, RPM now 2425. Lean to peak 74F carb air temp, and RPM 2425. I did it three times this way, and in all cases, temps within 2F of those values. If I needed to deice the carb, I would like to have those additional 12 degrees F, which i get just for leaning the mixture.
It would seem to me that blowing 62F air on the frosted parts of the carb would be more than enough to melt the obstruction quickly. I base this observation on carb icing I have experienced in a C 150 shortly after start. At idle RPM on a Coastal winter day the engine will ice very quickly yet applying carb heat only resulted in a modest rise in carb temp, certainly not as high as 62 deg, but the ice clears in seconds. While the carb temp will be hotter when leaned does the extra heat really make a difference ? My personal opinion is not really
However operating an engine for prolonged periods very over rich can be almost as bad as too lean. The broader issue of understanding the effect of carb heat and carb icing on the mixture is an important one and IMO not well understood by many pilots
In conclusion I continue to believe that the most important pilot action is to apply carb heat at the first sign of icing. Adjusting the mixture is much less important than getting that heat on early. I am distressed that there is still a constant drip drip drip of accidents where pilots let carb ice develop to such and extent that the engine stops.