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Prop Theory

Gemini Sparkle

Key Takeaways:

  • A P-51 pilot describes a puzzling RPM surge during takeoff, theorizing it was caused by the propeller momentarily stalling and unstalling, and seeks expert explanation.
  • Another contributor elaborates on propeller dynamics, clarifying the distinct effects of spiraling slipstream and gyroscopic precession, distinguishing the latter from torque.
  • An aviation enthusiast advocates for the continued relevance of ADF (Automatic Direction Finder) in Canada for VFR navigation, citing its reliability with powerful broadcast stations in areas with limited VOR 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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