NCAA AME Powerplant Exam Practice Test & Question Bank flashcards

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

Otto cycle efficiency

Ideal thermal efficiency of a reciprocating engine cycle equals 1 minus 1 divided by compression ratio raised to the power (specific heat ratio minus 1). Higher compression ratio raises efficiency.

Brake mean effective pressure

A measure of an engine's ability to do work per unit displacement, calculated as 150.8 times torque in pound-feet divided by displacement in cubic inches; higher BMEP means more work per cycle.

Detonation versus preignition

Detonation is explosive burning of the end gas after normal ignition; preignition is ignition before the spark. Both raise cylinder temperature and can damage pistons and valves.

Compression ratio formula

Compression ratio equals swept volume plus clearance volume, divided by clearance volume. It is the ratio of cylinder volume at bottom dead center to volume at top dead center.

Radial engine firing order

Radial engines use an odd number of cylinders so every other cylinder fires in sequence on alternate crankshaft revolutions, giving even firing intervals and smooth torque.

Valve clearance purpose

Clearance between the rocker arm and valve stem allows for thermal expansion. Too little clearance holds the valve off its seat, causing compression loss and burned valves.

Magneto E-gap

The E-gap is the position of the rotating magnet just past neutral where flux change is greatest, producing maximum voltage. Magnetos must be internally timed to this point before installation.

Impulse coupling function

A spring-loaded coupling that retards spark timing at low cranking speed to ease starting. It automatically returns to normal timing once the engine reaches roughly 200 to 300 RPM.

Carburetor icing conditions

Most likely with outside air between about 20 and 70 degrees Fahrenheit and high humidity. It can occur at above-freezing temperatures when the throttle is partially closed and the venturi cools.

Dry-sump lubrication

Oil is stored in a separate tank, not the crankcase. A pressure pump feeds the engine and scavenge pumps return oil to the tank, allowing inverted flight and better cooling.

Stoichiometric mixture

The chemically correct air-to-fuel ratio by weight for complete combustion of gasoline, about 15 to 1. Richer mixtures near 12 to 13 to 1 give best power.

Peak EGT leaning

Exhaust gas temperature rises as mixture is leaned until peak, then falls with further leaning. Peak EGT is the reference for setting best power or best economy mixtures.

Float carburetor venturi

Airflow through the venturi lowers pressure, drawing fuel through the main metering jet. The float chamber keeps fuel level constant so the pressure difference meters fuel flow.

Accelerator pump purpose

A carburetor circuit that delivers a momentary extra charge of fuel during rapid throttle opening, preventing a lean hesitation or stumble as airflow increases suddenly.

Geometric versus effective pitch

Geometric pitch is the theoretical forward distance per revolution; effective pitch is the actual distance, equal to geometric pitch minus slip. Slip increases with load and climb.

Constant-speed governor action

Flyweights balance against a speeder spring. If RPM rises, flyweights move out and reduce blade angle; if RPM falls, the spring increases blade angle to restore selected RPM.

Propeller feathering

Rotating blades to edge-on to the relative wind so they produce no thrust, reducing drag after engine failure. An accumulator stores oil pressure to unfeather the blades for restart.

Axial compressor operation

Air flows along the engine axis through alternating rotor and stator stages, with each stage adding a small pressure rise. Many stages produce high overall compression with a slim profile.

Compressor stall symptoms

Airflow separates from compressor blades, causing a bang or rumble, fluctuating RPM, high exhaust gas temperature, and possible flameout. Reduce power and allow airflow to recover.

Turbine inlet temperature limit

The highest temperature the turbine section can tolerate, measured directly or inferred from exhaust gas temperature. Exceeding it damages turbine blades and nozzles and shortens engine life.

Turbofan bypass ratio

The ratio of air flowing around the core to air flowing through it. High bypass ratios improve propulsive efficiency and reduce specific fuel consumption at typical transport speeds.

Hot start versus hung start

A hot start has excessive exhaust gas temperature from too much fuel or early fuel introduction; a hung start fails to accelerate to idle. Both require aborting and motoring the engine.

Turbine chip detector

A magnetic plug in the oil system that collects ferrous metal particles. Significant accumulation signals bearing or gear wear and requires inspection before further flight.

Turbine igniter operation

A capacitor-discharge exciter fires high-energy igniter plugs. One igniter is normally used for starting; both may be selected for continuous ignition in icing or heavy precipitation.

Differential compression test

Regulated air is applied to the cylinder at top dead center and the gauge shows pressure as a percentage of input. Leakage location identifies rings, intake valve, or exhaust valve problems.

Magneto drop check

During run-up, switching to one magneto should cause a small RPM drop, typically 50 to 150 RPM. Excessive drop or no drop indicates ignition timing or magneto problems.

Spectrometric oil analysis

A program that measures wear metal concentrations in oil samples to detect abnormal bearing, ring, or gear wear trends before failure, supporting condition-based maintenance decisions.

Borescope inspection

A fiber-optic or video inspection of compressor and turbine blades and combustion chambers through ports, revealing cracks, erosion, and foreign object damage without engine disassembly.

Engine fire detection types

Thermocouple and resistance-type detectors sense temperature rise in the engine compartment and trigger warning lights. Continuous-loop systems also indicate the location of the fire.

Firewall function

A stainless steel or fire-resistant bulkhead separating the engine compartment from the cabin, with sealed penetrations, limiting fire spread and protecting occupants and controls.

Annual versus 100-hour inspection

The annual inspection is required every 12 calendar months for most aircraft; the 100-hour inspection applies to aircraft used for hire or flight instruction. Both follow the same scope.

FAA Form 337

The form used to record major repairs and major alterations, describing the work and approved data. It is submitted to the FAA and kept with the aircraft records.