Quote:Any pilots on the board who can give us the technical answer to carb icing, I know small plane pilots dread carb or wing icing as it has caused many an unplanned landing in a less than favorable spot. If you've flown in the winter, they de-ice commercial planes to prevent wing icing on take off preventing such event. Ruins the lift of the wing and the pilot has an " o nuts" moment.
Actually, carb and wing icing are two completely different things.
Well, except the ice part.
Carb icing occurs due to water vapor in the air cooling while being sucked through the carb (Boyle's law) and solidifying as ice on the walls of the venturi or on the butterfly valve (or equivalent - in this case it would be a slide valve, I guess) - the key is that the ice gums up the works and causes a reduction of air to the engine (i.e. richer mixture) and thereby a reduction in power.
Note that carb ice (as was previously stated) is a function of temperature, but also of altitude and most importantly, humidity. I'm sorry to say that we lose people here in Florida every year due to that. ("It's 70, it can't be carb ice...") I think I read somewhere (Continental or Marvel manual - one of the two) that you can get carb ice as warm as 90 degrees F given the right humidity.
In wing icing, on the other hand, the concern is that formation of ice or rime on the surface of the wing disrupts the flow of air over the leading edge by turbulating the laminar boundary layer. This leads to a lower C
Lmax and resultant lower critical AOA or higher speed stall or both..... uh...... It makes the plane lift less, m'kay? WAYYY off topic.
Anyway, the way cars and airplanes solve carb ice is by use of a manual (typical in airplanes) or automatic (typical in cars - called a diverter valve) valve that typically sucks some inlet air past the hot exhaust headers to prewarm it or mixes in a little exhaust gas (how and what depends on your setup). Either way, there's less O
2 to work with (both because it's warmer=less dense, and because it may actually be exhaust) so it's actually a lot less efficent, but it's so much warmer that it eliminates the ice.
How do you keep this from happening in a M/C carb without such a system? Well, you could theoretically rig something like what an airplane has (a manual carb ice diverter) by running some of the inlet air....over the exhaust would be easiest, I think. and using a valve with a plunger...but practically, leaning it out seems a much better idea to me.