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Hypothetically, if I wanted to create a multi-engine airplane with the best single-engine handling characteristics/lowest Vmc, would moving the vertical stabilizer far back be beneficial (even if it looked weird)?

My school of thought is that: At low airspeeds, the rudder is less effective. If I can't increase the amount of airflow over the rudder, will giving the rudder a massive arm allow the plane to have more directional control at lower airspeeds with the increased torque?

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    $\begingroup$ Also there will be a torque arm that goes from each engine to CG. So making the engines as close to CG can help reduce the size and arm of the tail. $\endgroup$
    – Jeff A
    Jan 23, 2020 at 3:16

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Yes providing a longer vertical tail arm is very beneficial for control in case of engine failure.

During the pre-design phase of an aeroplane the Tail Volumes are determined: area of horizontal and vertical tail, times the moment arm. This answer gives more info on some statistical data and methods.

Of course, optimal dimensioning is paramount since we're dealing with aerodynamics and we want to limit drag. The tail arm is usually limited to the useful fuselage length, leaving the tail area to be the main design parameter.

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    $\begingroup$ Alternative, go for push-pull :-) $\endgroup$
    – user14897
    Dec 23, 2019 at 23:14
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    $\begingroup$ Or english electric lightning $\endgroup$
    – jkztd
    Dec 24, 2019 at 7:41
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The engines can be in push-pull configuration, or stacked on top of each other, to keep them on the centerline. If that can't be done then simply put them as close to the centerline as possible. Put more (presumably smaller) engines on the aircraft so that the loss of a single engine has lesser effect on performance. A larger rudder further back would help also.

I recall reading about someone that built a custom light airplane to fly over the Amazon forest. As I recall it was to take close up photographs of the canopy. A concern was an engine loss over such a remote area, and in the low altitudes they'd be flying. The plane had two pusher props close to the centerline and a larger than typical rudder. This was so it could fly for extended periods on a single engine and not fatigue the pilot. I also recall that they'd kill one engine in flight so they could fly slower and get better pictures, which in my mind negated much of the advantage of two engines.

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    $\begingroup$ Shutting down an engine in flight might save gas, but it doesn't "let you fly slower." If anything, engine-out, you have to consider not only a margin above stall speed but also above Vmca. $\endgroup$
    – Ralph J ♦
    Jun 21, 2021 at 4:10
  • $\begingroup$ @Ralph J: Consider the Rutan Voyager. $\endgroup$
    – jamesqf
    Jun 21, 2021 at 5:22
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    $\begingroup$ @jamesqf, Voyager was a pull-push configuration, which this apparently wasn't, and even that couldn't fly any slower on one engine. $\endgroup$
    – Jan Hudec
    Jun 22, 2021 at 0:32

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