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Sharks and whales have them in the middle of their body, so why not planes?

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    $\begingroup$ because planes =/= sharks and whales $\endgroup$ – yuritsuki Nov 30 '14 at 14:30
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    $\begingroup$ Didn't the Wright flyer have vertical stabilizers in the front? $\endgroup$ – user4408 Nov 30 '14 at 18:29
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    $\begingroup$ The Wright Flyer had it's horizontal stabilizers at the front (like modern canards), but the vertical stabilizer/rudder was at the rear. upload.wikimedia.org/wikipedia/commons/f/f9/… $\endgroup$ – Jon Story Nov 30 '14 at 20:52
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    $\begingroup$ It's the difference between aerodynamics and aquadynamics. Flying and swimming are not as comparable as assumed. $\endgroup$ – Mast Dec 1 '14 at 12:56
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    $\begingroup$ Not all of them have the vertical at the rear - in fact, the Pterodactyls used active stabilization with their long snouts and the fin at the rear of their heads. Also, the Hotol project proposed a forward fin with active control. $\endgroup$ – Peter Kämpf Jan 27 '15 at 20:10
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With sea creatures the dorsal fin acts as a keel providing the actual sideways force during the turn. They remain level while turning.

Planes on the other hand bank to turn where the sideways force is provided by the lift of the wings.

To provide yaw stability the vertical stabilizer should be as far from the center of mass as possible. They are not in front because that would be unstable as the minor deviation from straight ahead would increase the force into the deviation rather than provide a force to counteract it.

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    $\begingroup$ Exactly. Having the vertical stabilizer in the rear makes the aircraft behave much like a wind vane. If one side of the aircraft or the other is facing the airstream, the air will push against the vertical stabilizer, forcing the nose to point back into the wind. As racket freak said, this provides stability in the yaw axis. For aircraft that are designed to be stable (as opposed to, say, fighters and aerobatic aircraft,) aerodynamic stability is designed into the airframe in all 3 of the rotational axes. $\endgroup$ – reirab Nov 30 '14 at 21:17
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    $\begingroup$ This is one of those answers where I wish there was a video. Nice answer nonetheless. $\endgroup$ – Quazi Irfan Dec 1 '14 at 2:29
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    $\begingroup$ @reirab - most modern fighter aircraft are designed to be unstable, as it helps with agility. Stability is provided by computers, who can correct the instability much faster than a human pilot $\endgroup$ – Jon Story Dec 1 '14 at 11:28
  • $\begingroup$ @JonStory Yes, that's why I said "as opposed to, say, fighters and aerobatic aircraft." Both of those classes of airframes are typically designed to be unstable for increased maneuverability and rely on the pilot and/or computers to provide stability. $\endgroup$ – reirab Dec 1 '14 at 16:43
  • $\begingroup$ Apologies, I must have misread your post $\endgroup$ – Jon Story Dec 1 '14 at 18:46
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The vertical stabilizer is for "stability". By having it aft of the center of gravity, it will generate a side force that will correct out any undesired yaw.

Try throwing a paper airplane or a dart backwards, and watch how it flips around due to this stabilizing force to have the stabilizer in the rear.

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To add to other answers, vertical stabilizers also have control surfaces on them, and in order to maximize the effect of those control surfaces, you have to have them as far out from the center of horizontal rotation as possible.

Why not in front:

Stabilizers create drag. Drag is pulling backwards. When they are in the back, that's a natural resting point for them and thus they actually try to keep plane stable in one direction. Move them to the front and you would get a force that constantly tries to turn you butt-first :)

Example you can try at home:

Imagine a swinging door. The closer you move the door handle to the hinges, the more force is required to open the door. same applies to the airplane. If you place the rudder in the middle it will mostly push plane to the side instead of turning it.

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