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I've read this interesting Stack Exchange question about why airships have fins:

Why do blimps have fins?

Which has me wondering why the fins are almost always located in the tail section.

After some digging, I can see practical benefits, compared to putting the fins in the middle: ground clearance and avoiding the gondola.

But is there an aerodynamic reason too? After all, planes, helicopters, arrows all seem to similarly have stabilisers at the tail.

Would the airship be less stable or harder to control if the fins and control surfaces were in the middle? Or even at the front? If so, why would that be?

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    $\begingroup$ Because if they were sat in a shed elsewhere, they wouldn't work at all. $\endgroup$
    – Richard
    Oct 10, 2023 at 13:21
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    $\begingroup$ @Richard I wish someone had told me that before takeoff $\endgroup$
    – drrob
    Oct 10, 2023 at 14:22
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    $\begingroup$ Many is the time I've looked at a question on this site and thought to myself "I hope they're not typing this as they come in to land" $\endgroup$
    – Richard
    Oct 10, 2023 at 14:37

1 Answer 1

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Yes.

With fins in the middle the airship would be impossible to control. In order to work, fins need a lever arm with respect to the center of gravity. The longer, the better.

Almost all air vehicles are controlled by creating forces at a distance to the center of gravity, which in turn result in moments which allow to control attitude and direction. Airships are no exception.

While fins at the front would also create moments, they would increase the instability of the hull. Placing them at the rearmost position reduces this instability, which makes control easier. Still, airships are unstable and need constant attention by the crew. Making the fins large enough to give the airship natural stability would need much larger and heavier fins. The size of airships makes their eigenmodes slow enough so that manual control is possible.

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    $\begingroup$ Simply put: airships have fins mounted on the tail, the same reason arrows have fletching on the tail and the same reason pub darts have fins on the tail. For static and dynamic stability, the center of pressure from control fins must be aft of the center of mass. $\endgroup$ Oct 9, 2023 at 17:42
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    $\begingroup$ @drrob - lots of things would start to make sense if you played KSP. $\endgroup$
    – Mazura
    Oct 10, 2023 at 2:03
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    $\begingroup$ @MikeB ... only when computer controlled, with sufficient redundancy. This requires more weight and energy than a manual control. BTW; a canard also has natural stability due to the large wing in the back. Fins at the front do not yet make a canard. $\endgroup$ Oct 10, 2023 at 10:33
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    $\begingroup$ @MikeB Come on, Mike, do you really have to sink that low? Or did you not read until "a canard also has natural stability due to the large wing in the back"? $\endgroup$ Oct 10, 2023 at 13:32
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    $\begingroup$ @MikeB, they didn't have a stable aircraft, either. Keeping a Wright Flyer in the air was a constant battle against the aircraft's natural tendency to flip tail-first. $\endgroup$
    – Mark
    Oct 11, 2023 at 0:52

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