Engine Components and ConstructionAircraft & Engines — DGCA CPL practice questions
Question 1 of 5
The thermal efficiency of a typical piston engine is approximately:
All 5 questions — Engine Components and Construction
Aircraft & Engines · DGCA CPL. The correct option is marked on each.
Q1. The thermal efficiency of a typical piston engine is approximately:
- A.10-15%
- B.25-28%✓
- C.50-55%
- D.70-75%
Why: Only about a quarter of the fuel's heat energy becomes useful work; the rest is lost to exhaust and cooling.
Q2. The camshaft of a four-stroke engine rotates at:
- A.Crankshaft speed
- B.Twice crankshaft speed
- C.Half crankshaft speed✓
- D.Propeller speed
Why: Each valve must operate once per cycle (two crank revolutions), so the camshaft turns at half crankshaft speed.
Q3. Excessive valve (tappet) clearance causes the valve to:
- A.Open early and close late
- B.Open late and close early✓
- C.Remain open
- D.Bounce at low RPM
Why: Too much clearance delays opening and advances closing, shortening the valve period; too little may stop the valve closing fully.
Q4. Compression ratio is the ratio of:
- A.Total cylinder volume at BDC to volume at TDC✓
- B.Bore to stroke
- C.BHP to IHP
- D.Charge weight to cylinder volume
Why: CR = total volume (piston at BDC) ÷ clearance volume (piston at TDC).
Q5. Cylinders are not fired consecutively in order to:
- A.Save fuel
- B.Reduce vibration and crankshaft load✓
- C.Simplify the ignition system
- D.Increase volumetric efficiency
Why: A spread firing order (e.g. 1-3-4-2) distributes power impulses, reducing vibration and crankshaft stress.