I don't really get whats the purpose of dorsal fins and what they do with the flow over the vertical stabilizer. I noticed on most single tail configured aircrafts are equipped with a dorsal fin like the f 16.
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$\begingroup$ The F-16 doesn't have a dorsal fin.. but it does have a largish fairing at the root of the fin. If this is what you're talking about then its function is probably to cover the stab-fuselage joint. It does have ventral fins on the underside which serves to enhance stability. $\endgroup$– AnilvCommented Aug 16, 2018 at 4:31
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$\begingroup$ @Anilv at the front of that fairing joint there is a small fin, which I believe is what the OP is referring to. $\endgroup$– Notts90Commented Aug 16, 2018 at 11:50
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1$\begingroup$ Can you add a picture with some markings to help us understand please? $\endgroup$– dalearnCommented Aug 16, 2018 at 19:58
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1$\begingroup$ Related: What is the purpose of a dorsal fin such as on the Boeing 737? $\endgroup$– foootCommented Aug 26, 2018 at 15:23
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3 Answers
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There are two features that you may be referring to.
A) Is an antenna that is shaped to provide low drag. Not all F16 have this.
B) The true dorsal "fin":
- increases structural strength
- decreases drag by providing a fillet for the vertical stabilizer,
- improves stability about the vertical axis,
- and specifically in the case of the f16 (when installed) aerodynamically blends the drag chute pack (box at base of Rudder)
- many aircraft use this as a convenient air intake for equipment or auxiliary cooling.
answered Aug 16, 2018 at 17:27
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$\begingroup$ Adding to point 5, as an F-16 lover, on the A and B models the fin is shorter than in C and D models. Also, in D and F models there is the option to have a complete dorsal spine, going from the end of the cockpit to the vertical stabilizer, longer or shorter depending on the presence of the drag chute. $\endgroup$ Commented Aug 31, 2018 at 15:03
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If you are asking about the aerodynamic purpose of a dorsal fin, then dorsal fin actually increases the angle of side slip to get maximum side force. At high side slip angles, it produces stable vortices along the surface of the vertical tail which produces higher suction force over vertical tail, thus increasing the side force.
So in absence of the dorsal fin at high side slip angle, aircraft would have stalled i.e. just as jwzumwalt said, it provides stability along the vertical axis. According to me as F-16 is a fighter aircraft which requires high maneuverability, it would require a dorsal fin to stabilize at high side slip angles.
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The fin acts as a directional stabiliser, but not all aircraft or fighters have them. The Horten IX (Gotha Go 229) was a notable flying wing fighter design that didn't have a fin.
