A spark plug for model aircraft engines is an ignition device used in small internal combustion engine-powered model aircraft. Its function is to ignite the fuel mixture (such as methanol or gasoline) through an electric spark, driving the engine. It is similar to a full-size aviation spark plug, but smaller and designed specifically for model engines.
Center Electrode: Conducts high-voltage current, generating the spark.
Ground Electrode: Forms a gap with the center electrode where the spark ignites.
Insulating Ceramic Body: Prevents current leakage and is resistant to high temperatures (usually alumina ceramic).
Metal Housing: Secures the spark plug and dissipates heat, usually made of copper or steel.
Sealing Gasket: Ensures airtightness within the cylinder.
High-voltage Input: The ignition system (such as a CDI or magneto) generates high voltage (over 10,000V). Sparkover: Current flows from the center electrode across the gap to the ground electrode, igniting the fuel mixture.
Continuous Combustion: Fuel explodes within the cylinder, moving the piston and driving the propeller.
Factors |
Recommended Selection |
Engine Type |
Methanol engines use short threads; gasoline engines use long threads |
Operating Conditions |
High RPM: cold type; low RPM: hot type |
Fuel Mixture Ratio |
Rich fuel operation: hot type; lean fuel operation: cold type |
Brand Compatibility |
Refer to engine manufacturer's recommended models |
Engine Starting Difficulty
Possible Causes:
Severe Carbon Deposits on Spark Plugs
Abnormal Electrode Gap
Insufficient Ignition System Power
Solutions:
Clean or Replace Spark Plugs
Adjust Gap to 0.3-0.5mm
Check Battery Voltage and High Voltage Transformer Output
Sudden Stalling During Operation
Possible Causes:
Spark Plug Electrode Burnout
Fuel Contamination Leading to Carbon Deposits
Poor Heat Dissipation Leading to Overheating
Solutions:
Replace Spark Plugs
Clean Oil Circuit and Use High-Quality Fuel
Improve Engine Cooling
Unstable Power Output
Possible Causes:
Spark Plug Heat Value Mismatch
Electrode Excessive gap between electrodes
Improper mixture ratio
Solution:
Replace spark plugs with appropriate calorific value
Readjust gap
Optimize fuel needle setting
Cleaning and Maintenance
Inspect after every 5-10 flights
Remove carbon deposits using a dedicated spark plug cleaning brush
Stubborn carbon deposits can be cleaned by soaking in acetone
Gap Adjustment
Use a feeler gauge for accurate measurement
Standard gap:
Methanol engine: 0.3-0.4mm
Gasoline engine: 0.5-0.7mm
Use a special tool to bend the ground electrode
Installation Precautions
Insert by hand first, then use a spark plug wrench
Torque should be maintained between 5-10 N·m
A copper gasket must be installed to ensure a tight seal