Powerplant: Reciprocating and Turbine Engines
Reciprocating engines
The four-stroke cycle is induction, compression, power and exhaust. Compression ratio CR = (swept + clearance)/clearance. Detonation is uncontrolled rapid burning after spark; pre-ignition is ignition before spark, often from a hot spot. Both raise CHT and can damage. Mixture must be set for density altitude; carburettor ice can form at moderate temperatures and high humidity. Magnetos are independent ignition sources; a dead mag check is a no-go.
Turbine engines
Turbines use the Brayton cycle: intake, compression, combustion, exhaust. Compressor stall is local flow breakdown; surge is a global reversal with bang and EGT rise. Hot starts exceed limits because fuel is too rich or rpm too low. FADEC controls fuel and limits; EGT and rpm are key indicators. Turbine fuel must be clean and biocontamination controlled.
Worked example
A four-cylinder engine displaces 360 in³. Swept volume per cylinder = 360/4 = 90 in³. With CR = 8.5:1, clearance volume = swept/(CR − 1) = 90/7.5 = 12 in³. Total cylinder volume at bottom dead centre = 102 in³. If the clearance volume is reduced to 10 in³, CR becomes (90 + 10)/10 = 10:1 - higher CR raises thermal efficiency but also detonation risk.
Traps
Do not confuse detonation with pre-ignition; do not lean aggressively at high power without monitoring; do not treat a turbine 'hot start' as normal; and do not assume a magneto check is optional because the engine runs smoothly.