AME Reciprocating Engine Theory and Operation 1 — Questions and Answers
Question 1: What is the correct firing order of the Lycoming O-320 four-cylinder horizontally-opposed aircraft engine?
- 1-3-2-4 (Correct answer)
- 1-4-2-3
- 1-2-4-3
- 1-3-4-2
Correct answer: 1-3-2-4
The Lycoming O-320 uses a 1-3-2-4 firing order to evenly distribute power strokes across the crankshaft and minimize vibration.
Question 2: What does TDC stand for as used in reciprocating engine terminology?
- Total Dead Center
- Top Dead Center (Correct answer)
- Terminal Drive Cycle
- Top Drive Compression
Correct answer: Top Dead Center
TDC (Top Dead Center) is the piston position at its highest point in the cylinder bore, marking the boundary between the compression and power strokes.
Question 3: At what point in the 4-stroke operating cycle does ignition typically occur?
- At the beginning of the intake stroke
- Near the end of the compression stroke slightly before TDC (Correct answer)
- At the start of the exhaust stroke
- At the midpoint of the power stroke
Correct answer: Near the end of the compression stroke slightly before TDC
Ignition is timed to occur slightly before TDC on the compression stroke so that maximum combustion pressure develops just after TDC for optimal power output.
Question 4: What is the primary safety advantage of a dual independent magneto ignition system in a reciprocating aircraft engine?
- It doubles the engine's rated power output
- It provides redundancy so the engine continues running if one magneto fails (Correct answer)
- It automatically adjusts ignition timing with altitude changes
- It eliminates the need for battery power during flight
Correct answer: It provides redundancy so the engine continues running if one magneto fails
Dual magnetos are self-contained and independent of each other, so a failure of one magneto in flight does not stop the engine since the other continues to provide ignition.
Question 5: What type of lubrication system is standard on most horizontally-opposed aircraft reciprocating engines?
- Dry sump with a remote external oil tank
- Wet sump with oil stored in the engine crankcase (Correct answer)
- Total loss oiling using pre-mixed fuel and oil
- External hydraulic oil shared with the flight controls
Correct answer: Wet sump with oil stored in the engine crankcase
Most horizontally-opposed aircraft engines use a wet sump system where oil is stored in the engine crankcase sump and circulated by an engine-driven gear pump.
Question 6: What is the primary function of applying carburetor heat in a piston-engine aircraft?
- To increase engine power during high-altitude cruise
- To prevent or eliminate ice formation inside the carburetor (Correct answer)
- To lean the fuel-air mixture during descent
- To pre-heat the induction air before cold engine start
Correct answer: To prevent or eliminate ice formation inside the carburetor
Carburetor heat routes warm air from around the exhaust manifold into the induction system to raise air temperature above freezing and prevent or melt carburetor ice.
Question 7: What is the most common cause of detonation in a reciprocating aircraft engine?
- Using aviation fuel with an octane rating lower than required (Correct answer)
- Operating with an excessively rich fuel-air mixture at cruise
- Running the engine at low RPM and low power settings
- Having too much ignition advance on both magnetos
Correct answer: Using aviation fuel with an octane rating lower than required
Using fuel with insufficient octane rating allows the compressed fuel-air charge to auto-ignite explosively (detonate) rather than burning in a controlled progressive manner.
AME Reciprocating Engine Theory and Operation 1
What is the correct firing order of the Lycoming O-320 four-cylinder horizontally-opposed aircraft engine?