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Turbine Engines: Powerplant practice questions

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

1. A gas turbine's variable-volume, constant-pressure cycle is known by what name?
  1. Otto cycle
  2. Brayton cycle
  3. Diesel cycle
Show answer

B. Brayton cycle The Brayton cycle is a variable-volume, constant-pressure cycle, often called the constant-pressure cycle.

Reference: FAA-H-8083-32B, Ch. 1, p. 1-58

2. How does an axial-flow compressor move the air it compresses?
  1. It flings the air outward by centrifugal action
  2. The air keeps moving in its original direction of flow
  3. It reverses the airflow between each stage
Show answer

B. The air keeps moving in its original direction of flow Keeping the air in its original direction avoids the energy loss caused by turns.

Reference: FAA-H-8083-32B, Ch. 1, p. 1-38

3. On a turbofan, what determines the bypass ratio?
  1. The amount of air bypassed around the engine core
  2. The number of turbine stages
  3. The exhaust gas temperature limit
Show answer

A. The amount of air bypassed around the engine core Fan air that does not pass through the core is bypass air; its amount relative to core flow sets the ratio.

Reference: FAA-H-8083-32B, Ch. 1, p. 1-36

4. Depending on fan design and bypass ratio, about how much of a turbofan's total thrust can the fan produce?
  1. 20 percent
  2. 50 percent
  3. 80 percent
Show answer

C. 80 percent The fan's thrust more than makes up for the reduced thrust of the core (gas generator).

Reference: FAA-H-8083-32B, Ch. 1, p. 1-56

5. When can turbine nozzle guide vanes usually be adjusted?
  1. During engine overhaul and assembly
  2. In flight, by the fuel control
  3. Never; they are fixed for the life of the engine
Show answer

A. During engine overhaul and assembly Adjusting them improves how efficiently the gas stream strikes the turbine blades.

Reference: FAA-H-8083-32B, Ch. 1, p. 1-47

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What does the Powerplant test cover on turbine engines?

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