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Prop Theory

Gemini Sparkle

Key Takeaways:

  • A reader describes a peculiar RPM surge observed on P-51 Mustangs during takeoff, hypothesizing it's caused by the propeller stalling and unstalling, and seeks expert clarification.
  • Another reader elaborates on propeller aerodynamic effects, explaining the spiraling slipstream (corkscrew effect) and gyroscopic precession's role in taildragger yaw.
  • A third reader advocates for the continued relevance of Automatic Direction Finder (ADF) for VFR navigation in Canada, citing its reliability and long-range utility as an alternative to VORs and GPS in areas with limited coverage.
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Good article on props (“Propeller Theory 101,” November). Many years ago, I had an old airplane that when you applied power rapidly on takeoff, you would get a surge in rpm that I think was caused by the prop first being stalled, and then “unstalled.”

The airplane was a North American P-51 with a 1490-hp Merlin engine driving a four-blade Hamilton-Standard prop, which was geared down to where it was only turning 1400 rpm or so. (I could afford it back then; I paid $12,000 for it and it came with a new spare engine in a crate!)

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