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

Verified

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 airplanes in the mid-1930s, with their adoption often spurred by incidents or design needs, leading to two main types: a low, straight blade and a large curved extension.
Initially, dorsal fins were often mistakenly thought to enhance directional stability, but their true and most important function is to prevent "rudder lock."
Rudder lock is a dangerous condition where the rudder stalls at large sideslip angles and becomes stuck, which the dorsal fin mitigates by acting as a vortex generator to maintain high-energy airflow over the rudder.
While crucial for larger, faster aircraft with mechanical controls, modern powered controls and improved designs have made dorsal fins less necessary, though some may still be present for aesthetic reasons.

See a mistake? Contact us.

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.