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PPL Buddy
Ground School

Section 14 of 14

Quick reference card

  • Four-stroke: suck, squeeze, bang, blow (induction, compression, power, exhaust). Two crank revolutions, one power stroke. Camshaft turns at half crankshaft speed.
  • Horizontally opposed, air-cooled. Higher compression ratio = more power, needs higher fuel grade.
  • Dual ignition: two magnetos, two plugs per cylinder, for reliability and better burn. Magnetos are engine-driven and self-contained: the propeller is always live.
  • Mag check: small RPM drop on L and on R within limits (e.g. max ≈ 175 RPM drop, ≈ 50 RPM L-to-R difference). No drop = a live (un-earthed) magneto, a fault.
  • Detonation = explosion of the end gas after the spark (low grade, hot, lean, high power). Pre-ignition = ignited early by a hot spot.

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