DGCA Technical General: Piston Engines Questions
207 exam-style Piston Engines questions for the DGCA Technical Generalpaper (CPL & ATPL). The first 12 are free below with answers and explanations — sign up free to practise all of them with progress tracking.
- Q1
What is the purpose of the magneto impulse coupling
- ATo give a retarded spark during starting
- B Reduce the rate of rotation of the magneto
- C Advance the ignition and give a hotter spark during starting
- D Automatically increases spark rate at high engine speeds
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Correct answer: A. To give a retarded spark during starting
The impulse coupling momentarily holds back and then flicks the magneto rotor round at low cranking speed, producing a strong spark that is also delayed (retarded) past top-dead-centre. This retarded, energetic spark eases starting and prevents kickback.
- Q2
What is the only force stroke in a piston engine?
- AInduction.
- BCompression.
- CPower.
- DExhaust.
Show answer
Correct answer: C. Power.
This Explanation is Coming Soon
- Q3
A magneto is switched off by
- AOpen circuiting the primary circuit
- B Grounding the secondary circuit
- C Open circuiting the secondary circuit
- D Grounding the primary circuit
Show answer
Correct answer: D. Grounding the primary circuit
A magneto is self-contained and generates its own high tension, so it cannot be turned off by removing power. Switching to OFF grounds (earths) the primary winding through the ignition switch, which prevents the primary current from collapsing and so no spark is produced.
- Q4
The four stroke working cycle is?
- AInduction, compression, power, exhaust.
- Bcompression, induction, power, exhaust.
- CPower, Induction, compression, exhaust.
- DExhaust, Induction, compression, power.
Show answer
Correct answer: A. Induction, compression, power, exhaust.
This Explanation is Coming Soon
- Q5
An impulse coupling in a magneto is provided to
- A Generate high voltage and advance the spark for starting
- B Increase the energy to the spark plug as the RPM increases.
- CGenerate high voltage and retard the spark for starting
- D Allows a low energy value when ‘continuous ignition’ is selected
Show answer
Correct answer: C. Generate high voltage and retard the spark for starting
The impulse coupling spins the magneto quickly at low cranking speed to generate a strong high-tension spark, and simultaneously delays that spark to a retarded position for starting. The retarded timing prevents kickback until the engine fires.
- Q6
In a 4 stroke engine when does ignition occur in each cylinder
- A After TDC for starting and then before TDC every 2nd rotation of the crankshaft
- BBefore TDC for starting and then after TDC every 2nd rotation of the crankshaft
- C After TDC for starting and then before TDC every rotation of the crankshaft
- DBefore TDC for starting and then after TDC every rotation of the crankshaft
Show answer
Correct answer: A. After TDC for starting and then before TDC every 2nd rotation of the crankshaft
For starting, the spark is retarded to fire after top dead centre to prevent kickback, and once running the ignition is advanced to fire before top dead centre. In a four-stroke each cylinder fires only once every two crankshaft revolutions, on its compression stroke.
- Q7
Compression ratio is?
- ATotal volume/ swept volume.
- BSwept volume/ total volume.
- CSwept volume/ clearance volume.
- DTotal volume/ clearance volume.
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Correct answer: D. Total volume/ clearance volume.
This Explanation is Coming Soon
- Q8
430.The purpose of a valve spring is to:
- AClose the valve.
- BPrevent valve bounce.
- C Allow the valve timing to vary with changing R.P.M.
Show answer
Correct answer: A. Close the valve.
The valve spring's purpose is to close the valve and hold it firmly on its seat once the cam lobe has passed; valve timing is fixed by the camshaft, and bounce is countered by fitting double springs rather than being the spring's basic function.
- Q9
What is the total volume in the cylinder of a four stroke engine
- AA value equal to the cubic capacity
- BSwept volume minus clearance volume
- C Volume between TDC and BDC
- DSwept volume plus clearance volume
Show answer
Correct answer: D. Swept volume plus clearance volume
The total cylinder volume of a four-stroke engine is the swept volume, between top and bottom dead centre, plus the clearance volume remaining above the piston at top dead centre. The clearance volume is what makes the total greater than the swept volume alone.
- Q10
After the engine has started the impulse coupling is held out of engagement by?
- AA strong springs.
- BSeveral weak springs.
- CCentrifugal force.
- DA slipping clutch.
Show answer
Correct answer: C. Centrifugal force.
This Explanation is Coming Soon
- Q11
A possible cause of the engine backfiring could be:
- AAn exhaust valve sticking open.
- B A broken push rod.
- C A sticking inlet valve.
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Correct answer: A. An exhaust valve sticking open.
An exhaust valve sticking open allows the burning charge and fresh mixture to pass into the hot exhaust system, where the unburned fuel ignites explosively, producing the characteristic backfire.
- Q12
A cylinder head temperature gauge measures
- A The temperature of the hottest cylinder
- B The temperature of all the cylinders and gives an average reading
- C The temperature of the coolest cylinder
- D The temperature of the two cylinders furthest away from each other divided by two
Show answer
Correct answer: A. The temperature of the hottest cylinder
A cylinder head temperature gauge is connected to a thermocouple on the hottest-running cylinder, so it displays that single worst-case cylinder's temperature as a guide to engine cooling. It does not average all cylinders.
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