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Since a V-tail is lighter and generates less drag than a conventional empennage, why has this solution been put away from production?

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    $\begingroup$ V-tail design is in production. One of most recent addition is SF50. $\endgroup$
    – Farhan ♦
    Oct 27, 2017 at 19:01
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    $\begingroup$ Related explanation of V-tail effectiveness in damping. $\endgroup$
    – mins
    Oct 27, 2017 at 19:24

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Controllability and redundancy. Airliners are certified according CFR 14 Part 25, which specifies that upon engine fail the aircraft must still be able to fly and climb: it must have more than one engine.

After an engine has failed, the rudder must be deflected in order to compensate for the asymmetric thrust of the remaining engine. With a V-tail, this means that after engine fail, there is less pitch authority: pitch and yaw surface deflections are coupled. A V-tail has two control surfaces that combine aircraft yaw control and pitch control, which goes well until one of the surfaces hits a stop.

https://img.rcgroups.com/http://www.vvsss.com/ezone/v-tail.gif?h=b07Nxx_byxTYTzxk_sDclA

Reduced pitch control due to an engine failure would be unacceptable for an airliner. For a single engine plane with the engine in the centreline, this yaw trim condition would not happen.

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    $\begingroup$ isn't it roll/yaw coupling? $\endgroup$
    – user3528438
    Oct 27, 2017 at 22:50
  • $\begingroup$ @user3528438 roll can be compensated with ailerons, in a v-tail there is not another control surface for compensating for pitch when the yaw control has to compensate for asymmetric thrust. $\endgroup$
    – Owen
    Oct 27, 2017 at 23:39
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    $\begingroup$ @user3528438 What is meant is that on a V-tail, the control surfaces placed there substitute the conventional rudder and elevator and are thus effecting yaw and pitch control combined. On an (asymmetric) engine failure, some - often significant enough to actually dimension the rudder in the first place - yaw control surface deflection is required which would then reduce available pitch deflection due to the same control surfaces being used for both. $\endgroup$
    – Cpt Reynolds
    Oct 27, 2017 at 23:43
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    $\begingroup$ But arent the surfaces enlarged to compensate for double duty? Ref be33/36 vs v35. $\endgroup$
    – acpilot
    Oct 28, 2017 at 5:11
  • $\begingroup$ @acpilot Yes they can be, however there are practical limits: enlarge them enough and the advantage of smaller tail surfaces is gone. Engine fail means lower speed, higher required elevator & rudder deflections etc. All works out OK for centreline single engines - except for the fishtailing that is reported. $\endgroup$
    – Koyovis
    Oct 28, 2017 at 5:38

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