Reciprocating Engine Systems Flashcards
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What is a primary advantage of a dry-sump lubrication system compared to a wet-sump system for a reciprocating engine used in aerobatic aircraft?
Answer: It provides a more consistent oil supply to components regardless of aircraft attitude.
A dry-sump system uses an external oil tank and a scavenge pump to return oil from the engine. This design ensures the pressure pump has a constant supply of oil, preventing oil starvation during aerobatic maneuvers like inverted flight where a wet-sump pickup could become uncovered.
A technician is performing an internal timing check on a magneto. The E-gap is defined as the point where the:
Answer: breaker points begin to open, a few degrees of rotation past the magnetic neutral position.
The E-gap, or efficiency gap, is the precise point in the magneto's rotation, just past the neutral position, where the breaker contact points are set to open. This position ensures the most rapid rate of change in magnetic flux, which induces the maximum voltage in the primary coil for the strongest spark.
During an engine overhaul, a mechanic installs new piston rings but aligns the gaps of all rings on one side of the piston. What is the most likely consequence if the engine is operated this way?
Answer: Significant loss of compression and engine power due to blow-by.
Piston ring gaps must be staggered around the piston (e.g., 180 degrees apart) to create a longer path for combustion gases to travel. Aligning the gaps provides a direct path for these gases to escape past the piston into the crankcase, a condition known as blow-by, which results in a severe loss of compression and power.
Which of the following best describes the primary function of the baffles and flexible seals within the cowling of an air-cooled aircraft engine?
Answer: To direct the flow of cooling air tightly against the cylinder cooling fins.
Baffles and seals are critical components of a pressure cooling system. They form a high-pressure area above and in front of the cylinders and a low-pressure area below and behind them. This pressure differential forces cooling air to move through the cylinder cooling fins, ensuring heat is effectively carried away from the engine.
A pilot flying an aircraft with a float-type carburetor experiences a gradual loss of RPM and engine roughness. The outside air temperature is 60°F (15°C) with high humidity. What is the most probable cause of this issue?
Answer: Carburetor icing restricting airflow to the engine.
The combination of fuel vaporization and the venturi effect in a carburetor can cause a significant temperature drop. With high humidity, this can cause moisture in the air to freeze inside the carburetor, even at ambient temperatures as high as 70°F (21°C). This ice restricts airflow, causing a richer mixture, power loss, and engine roughness.
In a normally aspirated reciprocating engine, what is the primary factor that causes a decrease in volumetric efficiency as the aircraft climbs to a higher altitude?
Answer: A decrease in the density of the ambient air.
Volumetric efficiency measures how effectively an engine fills its cylinders with the fuel/air mixture. As altitude increases, the air becomes less dense. A normally aspirated engine, which relies on atmospheric pressure to fill the cylinders, will draw in a smaller mass of air on each intake stroke, reducing its volumetric efficiency and power output.