Aircraft Engines and Systems

Fuel Flow Measurement

• Fuel flowmeters measure fuel flow volume, fuel pressure, and fuel flow mass in continuous-fuel injection systems.
• Fuel pressure drop is measured across the metering valve, not the manifold valve or fuel nozzles.

Turbine Engine Instruments

• Monitor turbine inlet temperature to minimize the possibility of a “hot” start.
• Motor-driven impeller and turbine fuel flow transmitters transmit data mechanically, not using aircraft electrical system power or fuel pressure.
• Tachometers are calibrated in percent of engine RPM, not actual engine RPM or percent of engine pressure ratio.

Reciprocating Engines

• In a conventional reciprocating engine, the fuel/air mixture is ignited shortly before the piston reaches the top of the compression stroke.
• Cast iron piston rings may be used in chrome-plated cylinders, and chrome-plated rings may be used in plain steel cylinders.

Propellers

• The pilot valve in the governor of a constant-speed propeller is actuated by governor flyweights, not engine oil pressure or governor pump oil pressure.
• Permanently sealing and partially filling some propeller hubs with dyed oil helps to dampen pressure surges and prevent too rapid changes in propeller blade angle.
• During engine operation at speeds lower than those for which the constant-speed propeller control can govern in the INCREASE RPM position, the propeller will remain in the full LOW PITCH position.

Turbojet Engine

• The velocity of subsonic air as it flows through a convergent nozzle increases.
• A hot start is indicated if the exhaust gas temperature exceeds specified limits during turbine engine start-up.
• Hot section inspections for many modern turbine engines are required on a time or cycle basis, not only at engine overhaul or when an over temperature or over speed has occurred.

Centrifugal Compressor

• The two functional elements in a centrifugal compressor are the impeller and diffuser, not turbine and compressor or bucket and expander.

Turbine Engine Maintenance

• Hot spots in the combustion section of a turbojet engine may indicate faulty igniter plugs, dirty compressor blades, or malfunctioning fuel nozzles.
• A dual axial-flow compressor improves the efficiency of a turbojet engine by increasing the velocity of the air entering the combustion chamber.

Engine Performance

• Engine operating flexibility refers to the ability of the engine to run smoothly and give the desired performance at all speeds, not to deliver maximum horsepower at a specific altitude or meet exacting requirements of efficiency and low weight per horsepower ratio.

Reciprocating Engine Maintenance

• If piston ring gaps happen to be aligned during a differential pressure compression check on a cylinder, the test results may indicate a worn or defective ring(s).
• Grinding the valves of a reciprocating engine to a feather edge can result in excessive valve clearance, pre-ignition, and burned valves.

Engine Operation

• Conditions that increase an engine’s tendency to detonate include high manifold pressure, high intake air temperature, and late ignition timing.

Test your knowledge of aircraft engines, including fuel systems, injection systems, and turbine engine operation. Covers key components, measurements, and safety considerations.