Overview
This lecture explains how a carburetor mixes air and fuel in aircraft engines, describes the causes and dangers of carburetor ice, and outlines preventive measures using carburetor heat.
Carburetor Function and Placement
- The carburetor mixes air and fuel in the correct ratio for engine combustion.
- Air enters through a filter and passes through the venturi, a narrow section in the carburetor.
- In the venturi, static air pressure drops, drawing fuel into the airstream for combustion.
- Aircraft carburetors are mounted upside down and below the engine to prevent flooding and improve pilot visibility.
- Excess fuel drains away when the carburetor is mounted below the engine.
Carburetor Ice Formation
- Carburetor ice can form in the venturi, restricting airflow and risking engine failure.
- Ice may form even in warm, moist air due to dramatic temperature drops in the venturi from pressure decrease and fuel evaporation.
- Low engine power settings and closed butterfly valves increase the risk of ice formation due to significant temperature drops and cooler carburetor temperatures.
- Symptoms of carburetor ice include rough engine running, reduced power, and possible engine failure.
Carburetor Heat and Prevention
- Carburetor heat redirects air through a heat exchanger to warm it before entering the venturi.
- Warm air prevents ice formation or melts existing ice, but reduces engine power due to lower air density.
- After applying carburetor heat, engine power may drop briefly, then increase as ice melts.
- Melting ice ingestion may cause temporary rough engine running.
- Use carburetor heat only as instructed in the pilot's handbook; avoid using it on or near the ground because bypass air is unfiltered.
- Extended use of carburetor heat can overheat the engine or damage the exhaust.
Key Terms & Definitions
- Carburetor — A device that mixes air and fuel for internal combustion engines.
- Venturi — A narrow section in the carburetor where air pressure drops, drawing fuel into the airflow.
- Carburetor Ice — Ice accumulation in the carburetor, restricting airflow and affecting engine performance.
- Carburetor Heat — A system that warms incoming air to prevent or remove carburetor ice.
Action Items / Next Steps
- Follow the pilot's operating handbook for correct carburetor heat usage.
- Avoid using carburetor heat during low flight or near the ground.
- Do not use carburetor heat for extended periods to prevent engine or exhaust damage.