The Four-Stroke Piston Engine
How the typical aircraft engine makes power, and the basics of mixture, carburettor heat and detonation.
Most training aircraft are powered by an air-cooled, horizontally-opposed four-stroke piston engine. Understanding its cycle makes mixture, carb heat and engine-management decisions intuitive.
The four strokes
1. Intake — the piston draws in a fuel/air mixture. 2. Compression — the piston compresses it. 3. Power — the spark plugs ignite it and the expanding gases drive the piston down. 4. Exhaust — the burnt gases are pushed out.
Two magnetos (engine-driven and independent of the battery) fire two spark plugs per cylinder for redundancy and more complete combustion — which is why you check each mag during the run-up.
Managing it
- Mixture — at altitude the air thins, so you lean the fuel to match, for efficiency and to avoid a rough, rich engine; enrich for takeoff and descent per the POH.
- Carburettor heat — diverts warm air to melt or prevent carburettor icing, common at reduced power in humid air.
- Detonation and pre-ignition — uncontrolled or early combustion (from low-grade fuel, excessive heat or over-leaning) that can destroy an engine; manage power, mixture and cowl flaps to keep temperatures in range.
Common pitfalls
- Forgetting to enrich the mixture before a go-around at altitude.
- Running over-square or over-lean beyond POH limits.
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*Reference and training only — not for navigation. Always consult the current AIM, FAR/AIM, your aircraft’s POH/AFM and a certificated flight instructor.*