Engine Systems: Fuel, Ignition, Lubrication, Cooling, and Starting
Core concepts
For fuel systems, know carburetion versus fuel injection, mixture control, fuel/air ratio, and the purpose of the fuel control unit or hydro-mechanical unit. For ignition, understand magnetos, spark plugs, ignition timing, and the difference between reciprocating and turbine ignition systems (turbines often use exciters and igniter plugs). For lubrication, know wet-sump versus dry-sump, oil grades, oil pressure and temperature limits, and the function of oil coolers. For cooling, understand air cooling with baffles, cowl flaps, and cylinder head temperature limits. For starting, know starter types, starter-generators, and the sequence for turbine start.
Traps to expect
A common trap is mixture: full rich at high power, leaned at cruise, and never lean aggressively at high power. Another is ignition: a magneto check that shows a large drop on one magneto indicates a problem, while a small drop is normal. For lubrication, remember that oil does more than lubricate; it cools and cleans. For cooling, cowl flaps open increase airflow and drag. For starting, know that a turbine start requires monitoring EGT and N2, and that a failure to light off or a hot start requires aborting the start.
Worked example
If an engine burns 12 gallons per hour and fuel weighs 6 pounds per gallon, fuel flow is 72 pounds per hour. At a fuel/air ratio of 1:15, air mass flow is 72 × 15 = 1,080 pounds per hour. Rule of thumb: stoichiometric gasoline is about 15:1 by mass.
Study habit
Build a one-page system diagram for each system showing source, control, and indicator. Most questions reduce to identifying which component controls which variable.