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Reciprocating Engines: Powerplant practice questions

Five original questions on reciprocating engines, each with the answer, an explanation and an FAA-H-8083-32B page reference.

1. Crankshafts are generally forged from what?
  1. A strong alloy such as chromium-nickel-molybdenum steel
  2. Cast aluminum
  3. Magnesium alloy
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A. A strong alloy such as chromium-nickel-molybdenum steel Crankshafts must be very strong.

Reference: FAA-H-8083-32B, Ch. 1, p. 1-8

2. How many crankshaft revolutions are needed to complete one four-stroke cycle?
  1. Two
  2. One
  3. Four
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A. Two Intake, compression, power and exhaust take 720° of crank travel, which is two revolutions.

Reference: FAA-H-8083-32B, Ch. 1, p. 1-25

3. In a four-stroke engine, at what speed does the camshaft turn compared with the crankshaft?
  1. One-half crankshaft speed
  2. Twice crankshaft speed
  3. The same speed as the crankshaft
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A. One-half crankshaft speed Each valve opens once per cycle (two crank turns), so the cam is geared to turn at half crank speed.

Reference: FAA-H-8083-32B, Ch. 1, p. 1-20

4. When does ignition normally occur in an aircraft reciprocating engine?
  1. Exactly at top dead center on the compression stroke
  2. After top dead center on the power stroke
  3. Before top dead center on the compression stroke
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C. Before top dead center on the compression stroke Magneto timing is set with No. 1 piston a prescribed number of degrees BTDC on compression.

Reference: FAA-H-8083-32B, Ch. 4, p. 4-26

5. How is compression ratio calculated?
  1. Total cylinder volume with piston at BDC divided by volume at TDC
  2. Volume at TDC divided by volume at BDC
  3. Displacement divided by the number of cylinders
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A. Total cylinder volume with piston at BDC divided by volume at TDC Compression ratio compares the volume above the piston at BDC (displacement + chamber) with the chamber volume at TDC.

Reference: FAA-H-8083-32B, Ch. 1, p. 1-34

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What does the Powerplant test cover on reciprocating engines?

The Aviation Mechanic Powerplant ACS lists reciprocating engines as one of its areas. The FAA reference for this material is FAA-H-8083-32B.