What does carb heat do in C172?
Applying carburetor heat moves the air box valve closing the intake air from the air filter (cold air) and opening the intake from the carburetor heat shroud (hot air). This heated air will melt any ice formed in the carburetor. When carburetor heat is applied, the heated air that enters the carburetor is less dense. This causes the air/fuel mixture to become enriched, and this in turn decreases engine output (less engine horsepower) and increases engine operating temperatures.Use of carburetor heat reduces available power and changes your air/fuel ratio due to reduced density of the heated air.The carburetor heat is operated by a push-pull control in the flight deck. When the carburetor heat air door is closed, warm ducted air from around the exhaust is directed into the carburetor. This raises the intake air temperature.
When should carb heat be turned on?
Pre-Flight Check: Always verify the carb heat system is functional during your engine run-up by observing the RPM drop. Low Power: Apply full carb heat whenever the throttle is below 2,000 RPM (for fixed-pitch props) or 15 inches of manifold pressure (for constant-speed props). RPM Drop: Because warm air is less dense than cold air, applying carb heat disrupts the optimal fuel-air ratio and causes a slight, expected drop in RPM. Engine Roughness: When the heat begins melting ice, a temporary introduction of water into the engine may cause brief, temporary roughness.It recommends that after applying carb heat we may have to reduce power slightly and lean until the engine roughness starts to lessen. RPM should start to increase after a period of 30 seconds to several minutes. Leave the carb heat on until environmental conditions improve.
Does carburetor heat increase engine performance?
Pulling on the carb heat brings hot air into the engine’s intake. Hot air is less dense that colder air. Adding less dense air to a fixed flow of fuel results in a richer mixture flowing into the combustion chambers, hence, an increase in RPMs. Application of carburetor heat will decrease air density, causing the RPM to drop even lower. Then, as the carburetor ice melts, the RPM will rise gradually.