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An-225's vertical stabilizer (nose view) which are not vertical An-225's vertical stabilizer (tail view)

I am trying to understand the aerodynamic consideration that the two vertical stabilizers of this gigantic Antonov An-225 are not simply made vertical and are slightly pointing in. Then my questions are:

  • What is the reason?
  • What is the degree they lean?
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I'm fairly sure (but have no sources to confirm) that the reasons are purely structural. The vertical stabilisers are simply set at a right angle to the horizontal one. This is just the easiest thing to do, and it also provides better clearance with deflected lower rudders. The aerodynamic consequences of this (for such small angles) are pretty minor.

Now there are good aerodynamic reasons to have dihedral on the horizontal stabiliser (which causes the whole tilt), but this is a different question, and it applies to many airplanes.

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  • $\begingroup$ Some pretty good answers on horizontal stabilizer dihedral/anhedral here: aviation.stackexchange.com/q/26277/520 $\endgroup$ – Fred Larson Nov 11 '19 at 18:00
  • $\begingroup$ That also possible. But however, hard to believe such a multi millions dollar cost airplane is just simply made without a very strong valid reason. $\endgroup$ – AirCraft Lover Nov 12 '19 at 18:40
  • $\begingroup$ This is the strongest reason possible: it's cheap, easy and 'good enough'. Besides, remember that in Soviet economy, the question of efficiency was treated differently, and that An-225 was never meant to be produced in significant numbers: it's a quick adaptation of An-124. $\endgroup$ – Zeus Nov 12 '19 at 23:27
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I'd guess that they wanted to avoid an acute angle between the lower part of the vertical stabiliser and the horizontal - not for structural reasons but to limit interference drag.

They could have made the top piece vertical and just kicked out the bottom part, but then the rudder would have to have been made in two parts (or the hinge wouldn't have worked!)

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    $\begingroup$ Each rudder is in two parts anyway. $\endgroup$ – Zeus Nov 11 '19 at 23:10

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