DGCA Technical General: Engine Performance & Power Questions
84 exam-style Engine Performance & Power questions for the DGCA Technical General paper (CPL · ATPL · PPL). The first 12 are free below with answers and explanations — sign up free to practise all of them with progress tracking.
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Q1
The Manifold Pressure Gauge fitted to a supercharged engine measures:
- A The absolute pressure in the induction manifold.
- B The differential pressure across the supercharger compressor.
- C The ratio between the atmospheric pressure and the cam rise at the supercharger inlet.
- D The pressure upstream of the throttle valve.
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Correct answer: A. The absolute pressure in the induction manifold.
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Q2
An Automatic Boost Control Unit:
- A Prevents detonation and dissociation in the cylinder.
- B Maintains an automatic preset boost pressure.
- C Maintains the correct mixture strength for the boost pressure set.
- D Sets the posiion of the waste gate to ensure the preset boost is maintained.
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Correct answer: B. Maintains an automatic preset boost pressure.
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Q3
The use of a turbo-charger on an engine will:
- A Improve the exhaust scavenging efficiency.
- B Raise the volumetric efficiency of the engine.
- C Cause an automatic rise in the engine R.P.M. as altitude is gained.
- D Cause an automatic rise in engine power as altitude is gained.
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Correct answer: B. Raise the volumetric efficiency of the engine.
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Q4
413.When is the "Reference RPM" of an engine established?
- A When the engine is first installed in an aircraft
- B Before the first flight of the day.
- C By the engine's manufacturer during Type Testing".
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Correct answer: A. When the engine is first installed in an aircraft
The reference RPM is established when the engine is first installed in the aircraft, during the initial ground running and trimming; it then serves as the datum against which later performance checks are compared.
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Q5
The motive force used to drive the turbo-charger is:
- A Torque from the crankshaft via a spring drive unit.
- B Torque from the accessory gearbox.
- C Energy from the exhaust that would otherwise have been wasted.
- D Energy from the reduction gearbox.
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Correct answer: C. Energy from the exhaust that would otherwise have been wasted.
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Q6
A turbo-supercharger impeller is driven by
- A A connection through a gearbox connected to the crankshaft
- B Diversion of exhaust gases by the waste gate using energy that would otherwise have been wasted
- C Excess torque from the reduction gearbox
- D A ram air turbine
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Correct answer: B. Diversion of exhaust gases by the waste gate using energy that would otherwise have been wasted
A turbo-supercharger is exhaust-driven: its turbine is spun by exhaust gases that would otherwise be wasted, with the waste gate regulating how much gas is diverted to the turbine, which in turn drives the compressor impeller. There is no mechanical drive from the crankshaft.
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Q7
The power increase that occurs with initial increase in altitude when an engine has an internal supercharger fitted, is due to:
- A The reduced weight of mixture being passed to the engine.
- B The decreasing density of the atmosphere.
- C The reducing exhausts back pressure.
- D The increasing charge temperature.
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Correct answer: C. The reducing exhausts back pressure.
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Q8
What would happen if the waste gate of a turbocharged engine seized in the descent?
- A Compressor will overspeed
- B Blow the turbine blades off
- C MAP may exceed its maximum permitted value in the induction manifold
- D RPM may exceed its maximum permitted value
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Correct answer: C. MAP may exceed its maximum permitted value in the induction manifold
If the waste gate seizes closed in the descent, all the exhaust gas continues to drive the turbocharger even as power is reduced, so the manifold absolute pressure can rise above its maximum permitted value, over-boosting the engine.
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Q9
Rated Altitude is:
- A The height at which the boost pressure ceases to be effective with a specific R.P.M. set.
- B A comparison between the boost pressure at sea level and that at a given altitude.
- C The maximum altitude at which Rated Boost can be maintained with a specific R.P.M. set.
- D The altitude at which the waste gate becomes fully shut.
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Correct answer: C. The maximum altitude at which Rated Boost can be maintained with a specific R.P.M. set.
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Q10
505.A typical piston engine has a maximum thermal efficiency of:
- A 70%
- B 80%
- C 30%
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Correct answer: C. 30%
A typical piston engine converts only about 30% of the fuel's heat energy into useful shaft power; the rest is lost mainly through the exhaust and the cooling system.
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Q11
The speed of the turbine of a turbo-charger is controlled by:
- A The diversion of exhaust gases.
- B Controlling the exit of the exhaust gas passing out of the eye of the impeller.
- C The use of a variable controller.
- D An automatic gearbox positioned between the turbine and the impeller.
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Correct answer: A. The diversion of exhaust gases.
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Q12
The turbo-charger waste gate is spring loaded towards:
- A The open position.
- B The closed position.
- C A neutrally balanced partly open position.
- D The maximum boost position.
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Correct answer: A. The open position.
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