Dorsal Fins: Why Do Airplanes Have Them

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

Peter Garrison

Wednesday, December 18, 2024 at 08:51 AM ET

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Edited By: tccjeremy

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

Key Takeaways:

Dorsal fins began appearing on aircraft in the mid-1930s, evolving in various forms (e.g., straight blade, curved extension) and were initially believed by some to improve directional stability.
The primary aerodynamic function of a dorsal fin is to prevent "rudder lock," a condition where the rudder stalls at large sideslip angles, by acting as a vortex generator to maintain high-energy airflow over the fin and rudder.
While crucial for larger, faster aircraft with mechanical controls, many modern aircraft no longer require dorsal fins due to powered flight controls or inherent design, though some may remain for aesthetic reasons.

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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.