A turboprop delivers most of its output as
Answer: A
The turbine extracts nearly all the available energy to the shaft, leaving perhaps five to ten per cent as residual jet thrust. That division is the essential difference from a turbojet, where the whole of the energy leaves as jet momentum.
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A turboshaft engine differs from a turboprop in that its shaft power drives
Answer: B
The gas generator is essentially identical and only the load differs, which is why the same core often appears in both roles. Having no propeller means there is no residual jet thrust worth counting in the output rating.
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A free power turbine arrangement has
Answer: C
The gas generator can run up to speed while the output shaft remains stationary, which makes starting far easier and lets the load be applied gradually. It also allows the two shafts to run at whatever speeds each part of the machine prefers.
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A fixed shaft or direct drive turboprop has
Answer: D
Everything turns together, so the starter must accelerate the propeller as well as the compressor. The arrangement responds quickly to power changes but demands more from the starter and from the control system at low speed.
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A reduction gearbox is essential on a turboprop because
Answer: A
A gas generator may turn at twenty or thirty thousand revolutions a minute where a propeller wants one or two thousand. Reduction ratios above ten to one are common, and the gearbox is a substantial part of the engine's weight and cost.
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Equivalent shaft horsepower credits a turboprop with
Answer: B
The residual jet contributes real thrust, so it is converted to an equivalent power using an assumed propeller efficiency. Quoting shaft power alone would understate the engine, and the two figures are always distinguished carefully in ratings.
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A constant speed propeller maintains
Answer: C
The governor senses speed and adjusts blade pitch to load or unload the engine as required. Holding the speed constant is what makes torque a direct measure of power, which is why turboprops are set on torque rather than on rpm.
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On a turboprop with a governed propeller, power is set using
Answer: D
Correct answer: Torque
The propeller governor holds the shaft at a constant selected speed, so in
\[ P = T\omega \]the angular speed is fixed and the power delivered is directly proportional to the torque. Torque is therefore the parameter the pilot sets and limits against. Rotational speed says nothing about power once it is governed, exhaust gas temperature is a limit rather than a setting, and fuel flow is not displayed as a primary power indication.
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Feathering a propeller means
Answer: A
A windmilling propeller on a failed engine produces enormous drag and a strong yawing moment. Feathering reduces that drag to a small fraction, which is why the action is one of the first items on any engine failure drill.
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Reverse pitch on a turboprop is used to
Answer: B
Correct answer: Produce retarding thrust after landing
Turning the blades past fine pitch into a negative angle makes the propeller accelerate air forward, so the thrust acts rearward and helps decelerate the aircraft after touchdown. It is highly effective at high speed, when the propeller is handling a great deal of air, and it saves brake and tyre wear on short or contaminated runways. Feathering is the opposite extreme of blade angle, used in flight after a failure, and reverse is not used in flight at all.
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