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Dorsal Fins: Why Do Airplanes Have Them—or Not?

They're not just some added lateral area—they're a vortex generator.

The dorsal fin is a curiosity. Some airplanes have them, some don’t. [Getty Images]
Gemini Sparkle

Key Takeaways:

  • Aircraft dorsal fins, first appearing in the mid-1930s following early incidents and initially thought to improve directional stability, developed into two main types: a low, straight blade or a large, curved extension.
  • The actual primary function of a dorsal fin is to prevent "rudder lock," a condition where the rudder stalls at large sideslip angles, by generating a vortex that maintains high-energy airflow over the fin and rudder.
  • While crucial for larger, faster aircraft with mechanical controls to overcome rudder lock, dorsal fins are less common on modern planes due to advanced powered controls or inherent design, with some current installations possibly serving aesthetic purposes.
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Reluctance to throw useless things away has at least one benefit: After a sufficient passage of time, they become historical artifacts.

I still have 14 single-spaced typewritten pages chronicling the first five months of flying my first homebuilt, Melmoth, in 1973-74. The document, now slightly frayed but bidding fair to defy the silverfish for another century or two, ends with the admission that “it is getting tedious and pointless to record all these trivia.” Rereading it today, I came to the same conclusion well before the final page.

Peter Garrison

Peter Garrison taught himself to use a slide rule and tin snips, built an airplane in his backyard, and flew it to Japan. He began contributing to FLYING in 1968, and he continues to share his columns, ""Technicalities"" and ""Aftermath,"" with FLYING readers.

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