CAA NZ AME Piston Engines flashcards

32 cards. Read the term and the definition here. The deck at the top of this page is optional.

Otto cycle efficiency

For an ideal constant-volume cycle, efficiency equals 1 minus 1 divided by the compression ratio raised to the power gamma minus one, where gamma is about 1.4 for air.

Brake mean effective pressure

A size-independent measure of an engine's power output, calculated from brake power, engine speed, swept volume and the number of cycles per revolution.

Detonation versus pre-ignition

Detonation is explosive after-burning of the end gas following normal spark ignition; pre-ignition is ignition before the spark, usually caused by a hot spot such as a glowing plug or valve.

Master and link rods

In a radial engine, the master rod carries the piston on the crankpin directly, while articulated link rods attach around its big end for the remaining cylinders.

Crankcase line boring

Machining of the assembled crankcase halves so the main bearing bores are perfectly aligned; it restores bearing alignment after wear or repair.

Firing order purpose

The sequence in which cylinders fire, chosen to spread power impulses evenly, balance crankshaft loads and give uniform cooling across the engine.

Ring end gap

The clearance between the ends of a piston ring when fitted in its cylinder bore; too small causes scuffing and breakage, too large allows blow-by and oil consumption.

Valve lash

The cold or hot clearance between the valve stem tip and the rocker or tappet, allowing for thermal expansion; it is set to the maintenance manual figure.

Valve seat contact width

The width of the sealing band between valve face and seat; too narrow causes overheating and burning, too wide promotes carbon build-up and poor sealing.

Venturi icing

Ice forming in the carburettor venturi as fuel vaporisation and pressure drop cool moist air below freezing; it can occur at outside temperatures well above zero.

Idle mixture adjustment

Turning the idle mixture screw to give the specified RPM rise when the throttle is closed; too lean causes a stumble, too rich causes rough running and plug fouling.

Best power mixture

A fuel-air mixture roughly 100 to 150 degrees Fahrenheit rich of peak exhaust gas temperature, giving maximum power with detonation margin.

Condenser function

A capacitor across the magneto contact points that suppresses arcing, speeds the collapse of the primary magnetic field and protects the points from burning.

Impulse coupling

A spring-loaded device that retards magneto timing and delivers a strong spark for starting, then disengages above a set engine speed.

Magneto dead-cut check

A test confirming the ignition switch grounds both magnetos when selected off; it verifies the engine cannot fire during propeller handling.

Dry-sump lubrication

A system where a pressure pump feeds oil to the engine and a separate scavenge pump returns it to an external tank, allowing inverted flight and a smaller crankcase.

Cowl flap function

Adjustable outlets that control cooling airflow through the engine compartment; closed flaps raise cylinder head temperature, open flaps increase cooling and drag.

Shock cooling

Rapid reduction of cylinder temperature from sudden power reduction or flap opening, which can cause unequal contraction and cylinder or exhaust cracking.

Wastegate function

A valve that bypasses exhaust gas around the turbine to regulate boost pressure, preventing overboost and holding the selected manifold pressure.

Critical altitude

The highest altitude at which the engine can maintain its rated manifold pressure; above it, power decreases with density altitude.

Turbo cool-down

A period of reduced power before shutdown so oil continues to cool the turbine bearings and does not coke in the hot housing.

Propeller governor

A flyweight and speeder-spring device that senses engine RPM and ports oil to the propeller hub to change blade angle and hold the selected speed.

Feathering

Rotating the propeller blades to the flight position to minimise drag from a failed engine, usually achieved by releasing hub oil pressure or using an accumulator.

Propeller strike inspection

After a blade strike, the engine needs teardown checks of crankshaft runout, counterweights, gear train and bearings because shock loads can cause hidden damage.

Manifold pressure gauge

An absolute-pressure gauge reading intake pressure; it is the primary power indication for a constant-speed propeller and reads low at idle.

Exhaust gas temperature use

A thermocouple indication used mainly for leaning the mixture, with peak EGT as the reference point for best economy or best power settings.

Engine fire warning response

Shut off fuel, mixture and ignition, stop electrical supply, discharge the fire bottle, and land as soon as possible while monitoring for return of the warning.

Differential compression check

A test applying regulated air to the cylinder at TDC; leakage heard at the breather indicates rings, at the intake indicates an intake valve, at the exhaust an exhaust valve.

Borescope inspection

Visual examination of cylinder bores, piston crowns, valves and seats through the spark plug hole, used to detect scoring, burning and carbon without disassembly.

Magneto drop check

During run-up, switching each magneto off in turn and recording the RPM drop; an excessive drop indicates fouling, weak spark or incorrect timing.

Engine preservation

Preparing a stored engine by fogging cylinders with oil, sealing openings, fitting dehydrating plugs and inhibiting fuel and oil systems per the manual.

Volumetric efficiency

The ratio of air mass actually inducted to the theoretical swept-volume air mass; it falls with throttle restriction and improves with tuned intake and exhaust effects.