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Many fighter jets have double vertical stabilizers, e.g. F-14, F-15, F/A-18, F-22:

enter image description here

On the contrary, most GA planes and airliners do not. While there are certainly exceptions in both categories, I think it is fair to say that this design is, comparatively, far more common in fighter jets.

What is the advantage of double vertical stabilizers? Why is it common in fighter jets?

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Redundancy in case of combat damage. – SMS von der Tann Feb 15 at 13:09
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As these planes push the edges of what controllable flight is, they need control surfaces that most planes don't. Many of these planes couldn't even fly without the complicated computer systems they run on, and the vertical "stabilizers" do way more than just control the yaw like they do on commercial/GA aircraft. – Ron Beyer Feb 15 at 13:25
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Since you've posted an F/A-18, here you can get an idea what else this vertical stabilizers do: aviation.stackexchange.com/questions/19214/… – jklingler Feb 15 at 13:31
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Advantages of twin vertical fins was thoroughly covered here: aviation.stackexchange.com/questions/24020/… – A. I. Breveleri Feb 16 at 4:13
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I'd also like to point out that this depends a lot on "design culture", i.e. all the examples you posted are from the U.S.A. In contrast, European fighter-jet design generally has a single vertical stabilizer, but in contrast has long emphasized delta-wings and canards, which are largely absent in U.S. design. – Steve Heim Feb 16 at 6:18
up vote 20 down vote accepted

Though the reasons for having twin vertical stabilizers vary from aircraft to aircraft and is mainly a design decision, there are some advantages in having twin vertical stabilizers.

  • Having twin rudders increases the redundancy, which is important for combat aircraft in case of battle damage.

  • Having twin vertical stabilizers helps in reduction in height, though this is mainly an issue with naval aircraft. As an example, both the S-3 Viking and A-5 Vigilante had to fold their vertical tails for fitting inside hangars.

A-5

By USN - www.navsource.org 1, Public Domain, https://commons.wikimedia.org/w/index.php?curid=3109863

  • In case of twin engined aircraft with engines spaced wide apart, having twin rudders helps in getting sufficient rudder authority in case of an engine failure.

  • Having twin vertical stabilizers reduces their size, resulting in reduced stress at stabilizer root and reduction in weight.

  • One advantage of having twin vertical stabilizers is that the location of vertical tails helps in having control authority at high alpha (where the fuselage/wing can blank a single vertical stabilizer).

  • In modern stealth aircraft, having a twin tail enables them to be canted, helping in reducing RCS. Except for tailless aircraft (like B-2), almost all other stealth aircraft have canted twin tails.

  • Some aircraft, like A-10 had twin tails that were designed to mask engine exhaust from ground to ensure better survivability.

In the end of the day, having a single or twin vertical tail is a design decision and is taken based on the requirements. For example, preliminary designs of the A-5 Vigilante had twin tails, while the final design had a single tail, while it was the other way in case of F-14 Tomcat.

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Also, from what I understood, the rudders serve also as "ailerons" and/or "speed brakes" when put in the opposite direction w.r.t. each other. Is that right? – yo' Feb 16 at 8:33
    
@yo' you mean if they both face inside or outside? The primary effect observed is that it gives them additional "elevator" authority -- that is, they help the airplane pitch up more. The amount additional drag or "speedbrake" effect is negligible vs. the pitching moment it causes. To see what I mean, look at the elevator: it also causes drag when deflected, but it primarily causes a large pitching moment. In addition to the many good reasons already listed, twin v-tails can help reduce overall mass by allowing the elevator to be smaller while the airplane can achieve the same pitching moment. – Manuel J. Diaz Feb 16 at 22:57

There are a few reasons many fighter/bomber designs have 2 vertical stabilizers:

  • one large tail produced more shear force at the root, 2 smaller tails mean less force at the vertical stabilizer root. This allows for a lighter structure
  • redundancy if one tail is damaged. The US navy philosophy is 2 is better than one, this makes sense given that its aircraft spend much of the time over oceans where there's few alternative landing sites
  • twin tails are shorter than one big tail, and vertical height is a consideration on carrier aircraft
  • twin engines spaced apart make for a wide fuselage back which can create a blanking effect with a single tail in the middle, 2 tails mean that there's always one vertical stabilizer that is effective
  • Twin tails create less of a radar cross section, and allow the tails to be angled to deflect radar signals away from airborne radar sources
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Also smaller size means less radar reflecting surfaces. – Sami Feb 15 at 14:27
    
True @Sami, I'm not sure it's a major reason for most designs but certainly for some. – GdD Feb 15 at 14:42
    
I guess I would characterize it as a nice bonus. – Sami Feb 15 at 17:53
    
"The US navy philosophy is 2 is better than one" -- Too bad they didn't get what they wanted out of the JSF program... :/ – SnakeDoc Feb 15 at 20:20
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@MSalters I think that for an aircraft that needs a vertical stabilizer, an assymetric one is better than none, isn't it? :) I think it's similar to losing one of your 2 engines (in case you've got 2 of them)... – yo' Feb 16 at 8:35

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