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I've seen several aircraft with 2 vertical stabilizers and 2 rudders. This could be an H-tail like the B-25 Mitchell or the A-10 Warthog, or something more sleek like the Su-27.

However, I got to thinking, are there any airplanes that have 2 sets of horizontal stabilizers and thus 2 pairs of elevators? This would be a sideways H-tail. I guess it would be sort of like a bi-plane, but in the tail only.

Do these exist somewhere? Why or why not?

Experimental planes are okay.

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    $\begingroup$ Two small vertical stabilizers are sometimes used in place of 1 single big one, which is usually the highest point of an aircraft. This way you can lower the height of the plane and get a bigger plane that fits into small, old hangars. Using double horizontal stabilizer doesn't give that advantage, as the width of a plane is determined by it wings anyway, so you can make the tail pretty much as wide as you like, no need for doubling. $\endgroup$
    – Agent_L
    Oct 31, 2016 at 11:29

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Most of the initial aircraft made by Wright brothers had the twin horizontal stabilizer setting. However, the elevators in these cases were set in the front, rather than back, as is the norm now.

Wright Flyer II

By Wright brothers - OhioLINK Digital Media Center, Public Domain, Link

Quite a few of the early aircraft had a 'box' like configuration, notably the Santos-Dumont 14-bis, which made the first public powered flight. Again, though the pitch control was through the box like structure, it was more of a canard than a horizontal stabilizer.

14-bis

Santos-Dumont 14-bis; image from Wikipedia

One of the earliest aircraft with a 'proper' twin horizontal (as well as vertical) stabilizer was the aptly named Bristol Boxkite

Bristol Boxkite

Bristol Boxkite; By Hpeterswald - Own work, CC BY-SA 3.0, Link

Another good example is its predecessor, the Farman III, which had two horizontal stabilizers and a single vertical tail right in the middle, forming a perfect sideways 'H'.

Farman III

Farman III; By C.C. Pierce & Co. - http://digitallibrary.usc.edu/cdm/ref/collection/p15799coll65/id/12574, Public Domain, Link

You can see that most of these are early aircraft, which had structural limitations. As the aircraft design matured, the 'conventional' layout became the norm as a single stabilizer assembly can be used to achieve the necessary pitch control.

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  • $\begingroup$ When the stabilizer is in the front, is it still a stabilizer? Or a destabilizer? $\endgroup$
    – user3528438
    Nov 28, 2017 at 22:29
  • $\begingroup$ Also, the 14bis was not, strictly-speaking, an airplane (no full three-axis control). $\endgroup$
    – Vikki
    Sep 27, 2019 at 23:25
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The double decker horizontal tail was a popular choice for large biplanes, even into the 1930s. Below is a picture of the Zeppelin Staaken R VI giant airplane and below it a Handley-Page H.P.42 passenger aircraft from 1931.

Zeppelin Staaken R VI over Leipzig

Zeppelin Staaken R VI over Leipzig (picture source)

Handley-Page HP42 passenger aircraft

Handley-Page HP42 passenger aircraft (picture source)

As with the wing, a braced biplane tail makes for a stiff, lightweight structure. An unbraced biplane tail was also chosen by Hermann Dorner for his light attack aircraft, not for weight reasons, but to reduce tail span in order to allow the tail gunner a larger firing arc. The picture below shows a Hannover Cl II. I guess this design comes closest to the requested "sideways H tail".

Hannover Cl II

Hannover Cl II with raised tail, probably for compass calibration (picture source)

I have yet to find a monoplane with a biplane tail. Biplane tails vanished together with biplane wings.

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    $\begingroup$ Great finds, thank you. $\endgroup$
    – DrZ214
    Oct 31, 2016 at 10:27
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    $\begingroup$ Did the Hannover CL have elevators in all horizontal stabilizers? Or just the bottom ones? $\endgroup$
    – DrZ214
    Oct 31, 2016 at 12:35
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    $\begingroup$ @DrZ214: Both planes had elevators. See here for an overview drawing. $\endgroup$
    – Peter Kämpf
    Oct 31, 2016 at 14:58
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There is quite a famous example of this!

Wright Flyer, Wikimedia https://en.wikipedia.org/wiki/File:Wright_Flyer_photo_D_Ramey_Logan.jpg

but other than the Wright Flyer, I don't know of any.

My layman conjecture as to why this is not more common is that the tail only needs to be large enough to counteract the moment that CG exerts relative to the center of pressure of the wing. Large tail surfaces can balance large torque loads, but that is aerodynamically inefficient compared with maintaining a reasonable CG range.

Another aspect of that particular concern is that you can alternatively just make the tail boom longer to create a larger torque arm for the tail surface.

My answer to "why not" is that it's just not necessary. There are too many other ways to address control and stability issues to justify increasing the complexity with a double-horizontal stab.

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  • $\begingroup$ Ha! Never noticed this about the Wright Flyer. Maybe I should specify modern control surfaces, and a vertical stabilizer. $\endgroup$
    – DrZ214
    Oct 31, 2016 at 5:56
  • $\begingroup$ Some truly magnificent photos of men in their flying machines! $\endgroup$
    – Gusdor
    Oct 31, 2016 at 13:15
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The only recent example I can think of (and it's still only in the design & prototyping stage so may not even count) is the Beriev BE-2500 super-heavy amphibious craft.

enter image description here

This has a couple of very unique features; first and foremost, it's designed to operate either as an aircraft or as a ground-effect craft, flying very close to the ground on a cushion of air. This is why it has such an enormous wing area, and why the elevators have to be at the top of the rudders so as to not disturb the airflow around the wings. Secondly, it's also amphibious - with two large pontoons providing buoyancy and balance in the water. These are set as far apart as possible for balance, and are structurally connected to the rudders, giving a unique layout.

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    $\begingroup$ Straight out of Kerbal Space Program... $\endgroup$
    – Vikki
    May 24, 2018 at 23:14

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