wrote in message
...


There's a shroud around some part of the exhaust system, and air
is forced through it to accumulate heat from the hot exhaust. If the
throttle is closed or nearly so and the aircraft is gliding, the
exhaust system cools off quickly because it's made from very light
material of little mass and large area. If ice forms in the carb, less
fuel and air reach the cylinders, things cool off more, and soon
enough, if the pilot isn't paying attention or doesn't understand,
it's all over.
There have been numerous accidents because the engine began to
lose power so carb heat was applied, it ran rougher so the pilots shut
the heat off, and after the thing died altogether they pulled the heat
on again but it was too late. It reflects a lack of training: the
engine will run rougher both because the mixture gets richer and it's
getting liquid water into the cylinders, which tends to annoy it some.
Applying the heat and leave it until the thing sorts itself out is the
only solution. And go to a higher power setting; partial power might
just get more ice forming. There have been cases where the throttle
froze solid and would not move.
Lycomings have the carb bolted to the oil sump and the hot
oil warms the carb body so that the carb heat system around the
exhaust is really small. In cooler weather the oil may not do the job
and ice will form, especially early in the flight when the oil isn't
too hot. Continentals don't have the carb bolted to such warm stuff
and they'll ice up much quicker.


I don't care if you write a novel and include cad drawing. It's still not
true. YMMV