alt air/carb heat, Lyc 0320 with MA4SPA carb
FWIW: For a long time, I flew with an alt air capability, but not carb heat. The carb placement (on the hot oil pan of the 0320) is in my case particularly resistant to carb ice. I fly in the Northwest where it gets cold/damp/wet often, and I've only noted the effect of carb ice twice, on the ground during run-up on wet days. The alt air would induce a 50RPM drop. Good enough, I thought.
Then I installed a temperature sensor in the carb throat, just below the butterfly valve.
In winter, carb throat temp is often in the teens (degF); in summer, in the 20's. The alt air (which was just engine-side air) produced very little temp rise. A bit worrysome, even if I had not experienced in-air carb ice. But even once would be too much! So I put a small muff on an exhaust pipe (stacks and muff from Vetterman). Now when I apply alt air, the carb throat temp zooms from the teens to over 60-degF, with a 100RPM drop. If the primary filtered intake clogs or gets frozen over (hasn't happened yet), the heated alt-air source will always work, since it delivers air directly to the carb, bypassing the filter.
- Steven
700+ RV hours
(another hour last Sunday!)