Ice Flashcards
Why do we need ice protection?
A great deal of heat is required to change liquid fuel into fuel vapors. This heat comes from the metal of the carburetor and incoming air. This causes the float type to act as a very effective refrigerator. Depending on atmospheric conditions, this may result in carburetor icing.
Carburetor icing
This is caused when the temperature of the incoming air is decreased enough to condense and freeze. Ice builds up in the Venturi of the carburetor around the throttle valve blocking the air passage and causing. A loss of power, airspeed, and flight shutdown.
Condensation
The change of the physical state of matter from gaseous phase into a liquid phase.
Three types of carburetor icing
Fuel evaporation ice, throttle ice, impact ice
Fuel Evaporation Ice
Ice or refrigeration that is formed because of the decrease in air temperature resulting from the evaporation of fuel after it is introduced into the airstream. As the fuel evaporates, the temperature is lowered in the area this takes place. Any moisture in the area can form ice. This type of ice tends to accumulate on the discharge nozzle and may even occur at carburetor temp as high as 100 Fahrenheit.
Fuel evaporation ice
Ice builds up on the discharge nozzle, manifold pressure decreases, fuel flow is obstructed, mixture distributions is affected.
Throttle ice
Formed on the rear side of the throttle, usually when the throttle is in a partially “closed” position. Temps less than 38 Fahrenheit. The rush of air across and around the throttle valve causes a low pressure on the rear side. This sets up a pressure differential which has a cooling effect on the fuel/air charge. Moisture freezes in this low pressure area and collects as ice on the low pressure side.
Throttle ice effects
The effect depends on the size/amount of ice formed. A small amount of ice may cause a large reduction in airflow and manifold pressure. A large accumulation may jam the throttles and cause them to become inoperable
Impact ice
Formed from water present in the atmosphere as snow, sleet, or from liquid water which effects surfaces that are at temperatures below 32 Fahrenheit.
Impact ice effects
Due to inertia effects, impact ice collects on or near a surface that changes the direction of airflow. This builds up on carburetor elbow, screen, and metering elements.
The most dangerous is when the impact ice collects in the carburetor screen and causes a very rapid reduction of airflow and power.
How can ice be prevented?
Ice build up can be compensated for, or avoided entirely, by the use of “alternate air systems” known as: carburetor heat and alternate air valve (fuel injected engines)
