Reciprocating Engine Systems: Ignition, Induction, Cooling, Lubrication, and Starting
Domain 3 tests the support systems that make a reciprocating engine start, run, and stay cool.
Ignition
- Magnetos are self-contained: rotating magnet, coil, breaker points, capacitor, and distributor.
- An impulse coupling gives a retarded, strong spark for starting.
- Spark plug fouling, breaker-point gap, and timing affect drop; a typical magneto check allows a limited drop and a small left/right difference.
Induction, cooling, lubrication, starting
- Induction includes air filter, throttle/mixture, carburetor heat or alternate air; carb heat reduces charge density.
- Cooling uses baffles and cowl flaps to force air through fin passages; the oil cooler is part of the cooling system.
- Dry-sump lubrication uses a pressure pump and scavenge pump; oil is checked after shutdown.
- Starters may be direct-cranking or geared; starter duty cycle prevents overheating.
Worked example
During a magneto check, left drop is 75 rpm and right drop is 120 rpm. Both are within a 150 rpm maximum, and the 45 rpm difference is within a 50 rpm limit. The reasoning is to check both absolute drop and difference; a large difference suggests timing or plug issues.
Traps
Assuming magnetos need the aircraft battery; running a magneto check with the engine lean; using carb heat as a cruise mixture control; overpriming; ignoring oil temperature before run-up.