Reciprocating Engine Theory and Operation Flashcards

What is the purpose of dynamic counterweights installed on an aircraft reciprocating engine crankshaft?

Answer: To dampen torsional vibration at critical resonant RPM ranges

Dynamic counterweights are pendulum-type dampers tuned to absorb and cancel specific torsional vibration harmonics that develop at critical crankshaft speeds.

What type of bearing is used for crankshaft main and connecting rod journals in most aircraft reciprocating engines?

Answer: Precision plain (sleeve) insert bearings

Precision plain insert bearings (split bearing shells) handle high dynamic loads, are easily replaced at overhaul, and rely on a pressurized hydrodynamic oil film for lubrication.

What is the primary objective of an engine break-in procedure after overhaul or cylinder replacement?

Answer: To seat new piston rings against the cylinder walls to establish proper compression and oil sealing

Break-in procedures run the engine through defined power cycles so that new piston rings wear in and conform to the microscopic contours of the cylinder walls, establishing proper gas sealing and oil control.

What is the function of the power enrichment (economizer) circuit in an aircraft float carburetor?

Answer: To enrich the mixture at high power settings to prevent detonation and provide cylinder cooling

The power enrichment circuit enriches the mixture above a set throttle position to lower combustion temperature, reducing the risk of detonation and thermal damage at high power.

What does TBO (Time Between Overhaul) specify for a certificated reciprocating aircraft engine?

Answer: The manufacturer-recommended operating interval after which the engine should be completely overhauled

TBO is established by the engine manufacturer and specifies the maximum operating hours (and sometimes calendar interval) after which complete disassembly, inspection, and overhaul is recommended to restore airworthiness.

What does a differential compression test measure on a reciprocating engine cylinder?

Answer: The leakage of compressed air past piston rings and valves to assess internal cylinder condition

A differential compression test applies regulated air pressure to the cylinder and measures leakage with a differential gauge; the location of escaping air (exhaust, intake, or crankcase) identifies the defective component.

What does an excessive RPM drop on one magneto during the pre-takeoff magneto check most likely indicate?

Answer: A defect in that magneto's circuit such as a fouled spark plug, faulty ignition lead, or internal magneto fault

An excessive single-magneto RPM drop beyond the manufacturer's limit indicates a problem in that ignition circuit, most commonly a fouled or failed spark plug or a defective ignition lead.