Aviation Words — Ventral Fin

December 2019 - As we all know, "fin" is another word for "vertical stabilizer." Normally fins are mounted on the top rear of the fuselage and form part of the empennage. Occasionally an aircraft will have a supplementary fin on the belly of the aircraft, below the normal vertical stabilizer for extra directional stability. This is known as a ventral fin or strake. The ventral part is from the Latin "venter," meaning belly, and is used in human and fauna descriptions to relate to the front or belly aspect. "Strake" comes, not surprisingly, from the nautical world and refers to a length of planking on the belly of a ship.

Beechcraft Duke with ventral fins.

The ventral fin is apparently added when the fuselage shields so much of the vertical stabilizer at higher angles of attack that a fin is appended to the belly. This is often used to prevent yaw, especially in twin-engine aircraft where only one engine is operating. To gain more stability, two ventral fins are often installed, as seen in the photo of the Beechcraft.

My friend James Eby sent me the following description of his addition of a ventral fin to his BushCaddy.

"The ventral fin came about from looking at other floatplanes. Many floatplanes had ventral fins and/or horizontal stabilizer winglet projections. I was curious as to why this was. The reason found was that with the addition of floats to a plane, there may be insufficient vertical stabilizer area to recover from a stall/spin situation. As my plane is nose heavy with the big LOM engine, I thought better safe than sorry and a little weight aft won't hurt. I sent the design to an engineer (one who does not want involvement with the spars), and he said they were fine. There was no engineering as to size or design other than my 'better safe than sorry' guess from looking at other planes. Just to make sure, I added a lower fin along with the upper after discussions with my test pilot and the engineer."

Ventral fin added to a BushCaddy.

In backing through the alphabet, looking for words that would fascinate you, I could have chosen "X-ray" as the next word, but that would have been too easy. Besides, you would not have found it that fascinating at all.