This is a multi-part message in MIME format.
----[Please read http://ercoupers.com/disclaimer.htm before following any advice in this forum.]----
Humidity, in simple terms, is moisture or dampness. The relative humidity of air is the ratio of the amount of moisture which the air does have to what it could contain, usually expressed as percent of relative humidity. For example, if we have saturated air at 20*F (-6.67*C)and the temperature is increased to 40*F (4.44*C), the relative humidity would drop to 43%, if the barometric pressure has remained unchanged. If this same air is heated farther without removing or adding moisture, its capacity for holding water vapor will increase and its relative humidity will be less. Some pilots erroneously believe that carburetor icing does not take place when the free air temperature is above the freezing point. Ice can be formed when the inlet-air temperature is above the freezing point and relative humidity is below 100%. Water condensation takes place,and since heat is absorbed from the air-vapor mixture by the evaporating fuel, the mixture drops below 32*F, then freezing the condensed water vapor. The mos sever carburetor icing conditions may occur with the outside air temperatures between 50 and 60*F (15.56*C) with a humidity above 60%. Under these conditions, the moisture in the air is frozen and deposited in the carburetor, where the ice deposites continue to grow in size until it may lock the throttle valve, or restrict the amount of air entering the system to a degree that will cause engine failure. When the fuel is vaporized in the carburetor as the fuel sprays out of the nozzle, the temperature of the incoming air usually drops at least 30*F (-1.11*C) and may drop as much as 70*F (21.11*C) depending on several factors. As the throttle is opened, the temperature of the incoming air drops even farther.
