Aerodynamics Simplified: Explaining V-Tails

by FliteTest | January 24, 2019 | (2) Posted in Tips

Confused by the V-Tail? This article is for you. 

This edition of the Flite Test Aerodynamics Simplified series is all about that weird arrangement of tail feathers you see on some unusual looking airplanes. 


Why are V-Tails used?

The simple answer is that they can be more efficient than a conventional tail. This is because there is generally less surface area needed for a V-Tail (you have two surfaces cutting through the air, not three). 


You might see V-Tails used on high-performance models, such as slope soaring or discuss launch gliders. Gliders with V-Tails can slice through the air just that little bit better when they have less draggy surface area.


How do they work?  

As we all know, a standard tail uses the rudder for yaw and the elevator for pitch - so how do V-Tail arrangements achieve these two functions?

Conventional Tail Rear View

V-Tail Rear View

For the elevator, when the stick is pulled back, both ‘ruddervators’ deflect upwards much like on a normal elevator (just think of this one as having an upward bend in the middle of it). For pushing forward on the stick, as you might imagine, the ruddervators both deflect downwards to make the airplane pitch down. 

(Rear view) Pitch up:

With the rudder, a right rudder input in the V-tail will lower the right ruddervator and raise the left one. This causes an up and left force from the right tail surface and a down and left force from the left surface. The effect of this is that the tail will be pushed left. 

(Rear view) Yaw left:

Combining both the elevator and the rudder will, as with a conventional empennage, cause the plane to rotate around the yaw and pitch axes.

(Rear View) Yaw right and down slightly:


We hope you found this article helpful. Make sure to give it a thumbs up if you learned something! 


Article by James Whomsley

Editor of FliteTest.com

Contact: james@flitetest.com

YouTube Channel: www.youtube.com/projectairaviation 

COMMENTS

Ran D. St. Clair on January 24, 2019
I would say that the use of V tails has almost nothing to do with performance. If they were better, they would be used everywhere, and mostly they are not. Some people just think they look cool. There can be practical considerations, like them being less likely to drag in the grass. There can also be some slight negatives in terms of efficiently generating pure pitch or yaw moments without also generating unwanted roll moments. Mostly, there is little or no difference in how they perform, certainly not at the level we would notice on our little models.
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Arcfyre on January 25, 2019
The most noticeable difference is that V tail aircraft are much more sensitive to being loaded tail-heavy. A V tail generates pitch authority as a vector with a horizontal and vertical component. The horizontal force generated is "wasted" in essence as it does not contribute to the desired pitch outcome.

A full scale example would be the model 35 Beechcraft Bonanzas. Models from the late 50's to the 80's were built with V tails. On longer flights, as fuel in the tanks was burned, the CG naturally moved aft. If a pilot isn't careful and doesn't plan ahead, it easily possible that he arrives at his destination flying a tail heavy aircraft with insufficient pitch authority to compensate adequately.

As the aircraft was enlarged to the model 36, the V tail was dropped for a conventional tail as the V tail was no longer able to provide the necessary control authority.

Still, nothing beats the look of a V tail.
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bracesport on January 28, 2019
I too love the look of a V tail, and soon enough i’ll be trying my first V tail home build! Yikes!
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model3113 on February 5, 2019
Yeah, V-tails look cool, and in some modeling instances are easier to run control lines for. However both halves typically have to be larger in surface area to make up for only having two stabilizing surfaces, so the drag reduction is rendered null.
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Aerodynamics Simplified: Explaining V-Tails