NCAA CPL Aircraft General Knowledge cheat sheet
NCAA CPL Aircraft General Knowledge · Keep the key ideas within reach.
Aircraft General Knowledge
Four-stroke cycle order: intake, compression, power (combustion), exhaust; the crankshaft completes two revolutions per cycle, so a four-cylinder four-stroke engine produces two power strokes per revolution.
Engine displacement = bore area × stroke × number of cylinders; compression ratio = (swept volume + clearance volume) ÷ clearance volume, and higher ratios raise thermal efficiency but demand higher octane.
Air density falls with altitude and rising temperature; since power output tracks mass airflow, a normally aspirated engine loses roughly 3% of sea-level power per 1,000 ft, and density altitude, not pressure altitude, governs takeoff and climb performance.
Fuel/air mixture ratio is expressed by mass; chemically correct (stoichiometric) ratio for gasoline is about 15:1, best power is near 12.5:1 to 13.5:1, and best economy leans toward 15:1 to 16:1 within detonation limits.
Detonation is uncontrolled explosive combustion after normal ignition, driven by high manifold pressure, high inlet temperature, or too lean a mixture; pre-ignition is ignition before the spark, usually from a hot spot such as a glowing deposit or plug.
Carburetor icing risk is highest at ambient temperatures between about -7 °C and +21 °C with high humidity; the venturi and throttle plate can drop temperature 15-20 °C, so carb heat is applied before reducing power.
Magneto ignition is independent of the aircraft electrical system; a magneto generates its own current by electromagnetic induction, and the two magnetos fire separate plugs so the engine keeps running after one magneto or plug fails.
Fixed-pitch propellers trade blade angle for RPM: a climb propeller has a low blade angle for high RPM and static thrust, a cruise propeller has a higher blade angle for speed, and constant-speed units vary blade angle to hold a selected RPM.
Load factor n = lift ÷ weight; in a level turn n = 1 ÷ cos(bank angle), so a 60° bank doubles load factor and raises the stall speed by the square root of n (about 41%).