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Military

AL0993 Practice Exercise Answer Key & Review
Lesson 1: Theory and Principles of Gas Turbine Engines

True - False
  1.   In cold weather, gas turbine engines take a long time to warm up to operating temperatures.

  False
  2.   The Brayton cycle has the same four basic operations as the Otto cycle, but it performs them simultaneously.

  True
  3.   When air flows through a smaller section of a duct, it increases in velocity and decreases in pressure and temperature.

  True
  4.   The turbojet aircraft is a high-speed, high-altitude one.

  True
  5.   The Army uses both turbojet and gas turbine engines.

  False

Cluster True - False
(Each of the following groups of questions is related to the statement that precedes them.

FIRST GROUP
Gas turbine engines have advantages and disadvantages. Evaluate the following statements according to the information in your text.
  6.   The power-to-weight ratio is 5.60 shp per pound for a typical reciprocating engine but only .67 shp per pound for a gas turbine engine.

  False
  7.   The turbine engine has fewer moving parts than the reciprocating engine.

  True
  8.   Foreign object damage is a major problem for a gas turbine engine.

  True
  9.   A reciprocating engine uses less oil than a gas turbine.

  False
10.   They cost a great deal more than reciprocating engines.

  True
11.   They accelerate much faster than reciprocating engines.

  False
SECOND GROUP
Which of the following statements about the operation of turbine engines are True and which are False?
12.   Army turbine engines are of the free-power design.

  True
13.   The ignition system in the combustor operates as long as the turbine engine does.

  False
14.   About 25 percent of the compressed air is used in combustion.

  True
15.   Shaft horsepower is produced by the power turbine, not by the gas producer.

  True
16.   Army helicopters have a special problem with thrust and use divergent ducts to overcome it.

  True
THIRD GROUP
The following five questions refer to the theory of gas turbine engines. Which of them are True and which False?
17.   A simple turbojet engine has one rotating unit -- the compressor/turbine assembly.

  True
18.   In a gas turbine engine, the gas stream energy which remains after the energy for the engine cycle has been extracted drives another turbine.

  True
19.   In a turbojet engine, 60 percent of the energy is used to develop thrust, and 40 percent is used to maintain the engine cycle.

  False
20.   A turbojet engine maintains top efficiency at takeoff and at low cruising speed.

  False
21.   The functions of intake, compression, ignition, combustion, and exhaust all take place at the same time in a gas turbine engine.

  True
FOURTH GROUP
About turboprop and turboshaft engines, which of questions 22 through 26 are True and which are False?
22.   In Army aircraft, rotational shaft power is produced by the same turbine rotor that drives the compressor.

  False
23.   They do not eject high-velocity gases to obtain thrust.

  True
24.   A free-power turbine allows the power output shaft to turn at a constant speed.

  True
25.   A free-power turbine is linked to the compressor turbine mechanically.

  False
26.   The power producing capability is variable to take care of different loads on the power shaft.

  True
FIFTH GROUP
Evaluate the following five questions on illustrating the principle of jet propulsion by a toy balloon.
27.   If it is inflated and the stem is sealed, the pressure is equal on all internal surfaces.

  True
28.   If the stem is released, the balloon moves in a direction towards the open end.

  False
29.   The jet of air coming from the opened end of an inflated balloon pushes against the outside air.

  False
30.   A convergent nozzle is created when the stem of the balloon is released.

  True
31.   High internal pressure acting on the skin area opposite the stem is what moves the balloon.

  True
Matching

In questions 32 through 37, match the statements in column I with the laws or principles of physics in column II by selecting the proper letter under each question. Each item in column II may be used once, more than once, or not at all.
32.   For every action there is an equal and opposite reaction.
  B.  Newton's Third Law of Motion.
33.   If it can expand, a gas under constant pressure increases in volume as it increases in temperature.
  E.  Charles Law.
34.   If the velocity of a gas or liquid increases, its pressure decreases.
  C.  Principles of pressure and velocity.
35.   A body in a state of rest remains at rest.
  A.  Newton's First Law of Motion.
36.   If the temperature of a confined gas is constant, the pressure increases as the volume decreases.
  D.  Boyle's Law.
37.   Going through a smaller duct, airflow must increase in velocity.
  C.  Principles of pressure and velocity.

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