NCAA AME Powerplant Exam Practice Test & Question Bank key terms

Bore is the inside diameter of an engine cylinder; stroke is the distance the piston travels from top dead center to bottom dead center. Together they determine piston displacement for each cylinder.

The ratio of cylinder volume with the piston at bottom dead center to the volume with the piston at top dead center. Higher ratios raise thermal efficiency but increase detonation tendency and require higher octane fuel.

The position of the piston at the highest point of its travel in the cylinder. Ignition timing and valve events are commonly referenced to this position, measured in degrees before or after it.

An operating cycle in which the piston makes four strokes (intake, compression, power, exhaust) and the crankshaft turns twice per power event. Most aircraft reciprocating engines use this cycle.

The sequence in which cylinders deliver power, chosen to distribute loads evenly on the crankshaft and reduce vibration. It is determined by crankshaft throw arrangement and must be respected when installing ignition leads.

Uncontrolled explosive combustion of the fuel-air charge after normal ignition, producing a sharp pressure spike, high cylinder temperatures, and possible piston damage. Causes include low octane fuel, excessive manifold pressure, high intake temperature, and over-advanced timing.

Ignition of the fuel-air charge before the spark occurs, usually caused by a glowing spark plug electrode, carbon deposit, or overheated exhaust valve. It can rapidly destroy pistons and is often confused with detonation.

The crankshaft angle, in degrees before top dead center, at which the spark occurs. Correct timing varies with engine speed; excessively advanced timing promotes detonation and excessively retarded timing reduces power and raises exhaust temperature.

A self-contained engine-driven generator that produces high-voltage pulses for the spark plugs without relying on the aircraft battery. Most light aircraft have two independent magnetos so that one failed unit still provides ignition.

A spring-loaded device on a magneto that retards spark timing and accelerates the rotating magnet at low cranking speed, producing a strong spark for starting. It disengages by centrifugal action once the engine reaches operating speed.

A threaded device that carries high voltage into the combustion chamber and forms a spark gap across which ignition occurs. Electrode wear, fouling, and incorrect heat range all affect engine operation and must be checked at inspection.

Ice that forms in a carburetor from fuel vaporization and pressure drop cooling, obstructing the venturi or throttle. It can occur at outside air temperatures well above freezing and is countered with carburetor heat.

A system that routes heated air from a shroud around the exhaust or a heat muff into the carburetor to melt or prevent ice. Applying heat enriches the mixture and typically causes a slight power loss.

A carburetor in which a float chamber maintains a constant fuel level that is metered into the venturi airstream. It is sensitive to unusual attitudes and to ice, unlike a pressure carburetor.

A metering system that delivers fuel under pressure to each cylinder's intake port or directly into the cylinder, rather than through a venturi. It resists icing better than a carburetor and gives more even fuel distribution.

The cockpit control that sets the fuel-to-air ratio delivered to the engine. Leaning improves efficiency at altitude and reduces fouling, while full rich is used for high power settings to protect the engine from detonation.

The proportion by mass of fuel to air entering the combustion chamber. Approximately 15:1 is chemically ideal for gasoline, but engines are typically run richer at high power to control temperatures.

The volume swept by one piston through a full stroke, calculated from bore and stroke. Total engine displacement is that value multiplied by the number of cylinders and is used to compare engine size.

The small gap between the rocker arm and the valve stem that allows for thermal expansion. Too little clearance can hold a valve open and burn it; too much causes noise and altered valve timing.

A lubrication system in which oil is stored in a separate tank and scavenged from the engine by a pump, rather than stored in the crankcase. It permits inverted flight and provides a steady oil supply in aerobatic aircraft.

A valve that allows oil to bypass a clogged filter so lubrication continues, at the cost of unfiltered oil reaching bearings. Indication of bypass is often a rising oil temperature or a filter differential pressure warning.

The two primary indications of lubrication system health. Low pressure may indicate pump wear, leakage, or low level, while high temperature can indicate cooling problems, low oil quantity, or excessive engine load.

Sheet metal covers and internal air-directing panels that channel cooling air around cylinders and accessories. Missing or damaged baffle seals cause hot spots and high cylinder head temperatures.

A measurement of cylinder head heat, used to monitor cooling adequacy. Excessive values may result from lean mixtures, high power, poor baffling, or high outside air temperature and can lead to detonation or valve damage.

The angle between the propeller blade chord line and the plane of rotation. Higher pitch takes a larger bite of air for a given rpm, trading acceleration for cruise speed.

A propeller whose blade angle is automatically adjusted by a governor to hold a selected engine rpm as load changes. It lets the engine run at an efficient speed while the pilot sets power with manifold pressure.

A flyweight-controlled hydraulic unit that senses engine rpm and adjusts oil pressure to change blade angle. It maintains the rpm selected by the cockpit control against changes in airspeed and power.

The angle of a propeller blade at a specific station, measured between the blade's chord and the plane of rotation. Blade angles vary along the blade to keep thrust distribution efficient.

The difference between the theoretical distance a propeller would advance in one revolution and the actual distance traveled. Slip increases with load and is normal; excessive slip indicates inefficiency.

The absolute pressure of air in the engine intake manifold, displayed on a gauge in inches of mercury. It is a primary indicator of power output in engines with constant-speed propellers.

The compressor and turbine are each built of stages, where a rotor stage of blades is followed by a stator stage of vanes. Multiple stages progressively raise or extract energy from the gas stream.

A disruption of smooth airflow through the compressor causing a loud bang, power loss, and high exhaust temperature. Causes include abrupt throttle changes, distorted inlet air, and foreign object damage.

Internal passages and film cooling holes that bleed compressor air through turbine blades and vanes to keep metal temperatures within limits. Loss of cooling air can lead to blade creep or burn-through.

The temperature of gas leaving the turbine, used to monitor turbine engine power and protect hot section components. Excessive values may indicate overfueling, cooling problems, or turbine damage.

Damage to compressor or turbine blades caused by ingested debris such as stones, birds, or ice. It can cause vibration, performance loss, and compressor stalls and must be inspected and blended out.

Servicing of a rechargeable battery that requires electrolyte level checks and distilled water addition. It must be handled with care because electrolyte is corrosive and the battery can deliver very high current.

Substances such as Halon, dry chemical, or carbon dioxide used to suppress fire by cooling, smothering, or interrupting the chemical reaction. Agent selection depends on the fire class and the area protected.

Sensors and indicators that detect overheat or fire in engine compartments and alert the crew. Systems require periodic testing and careful maintenance to avoid false warnings or missed detection.

Inspection of engine mounts, cowling, hoses, wiring, controls, and fireproofing to verify the engine is properly installed and safe. It verifies security, clearances, and freedom of control movement.

A mandatory regulatory notice requiring inspection, repair, or modification of a product to correct an unsafe condition. Compliance must be recorded and is required for the aircraft to remain airworthy.

A written record of work performed, including description, date, and signature of the authorized person. Accurate entries document airworthiness and must be retained for the period required by regulation.

The formal action by which an authorized mechanic or inspector certifies that maintenance has been properly completed and the aircraft is airworthy. It requires proper records and a signature.

Safe practices for storing, using, and disposing of fuels, solvents, and other chemicals, including use of personal protective equipment and proper labeling. Spills and vapors must be controlled to prevent fire and exposure.