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This is an IL-62. On the tail of the aircraft, there is a large cone, protruding out of the vertical and horizontal stabilizer which is called acorn. I am trying to figure out what is the aerodynamic explanation for its presence over there.

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    $\begingroup$ Welcome to Aviation.SE! I think this is a well done first question. I can't find any exploded-diagram type views for that, but I'm guessing that it is a housing/cover over the actuators that move the all-moving tail surface up/down. $\endgroup$ – Ron Beyer Nov 8 '18 at 22:52
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    $\begingroup$ Thanks! I guess you are right, probably a housing for actuators or antenna. $\endgroup$ – Topcatmki Nov 9 '18 at 6:54
  • $\begingroup$ That is an anti-shock body or Küchemann carrot, an aerodynamic improvement - there is little to fair over ahead of the intersection between the horizontal and vertical tail surfaces. $\endgroup$ – Peter Kämpf Jan 10 '19 at 23:20
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It's doing one or both of two things:

  1. Fairing in some kind of projection as Ron said, may be an antenna or a mass balance.
  2. Fixing an airflow disturbance at the T intersection. Bullet fairings are a common band aid for that sort of thing.

Russian designs seem to be big on bullet fairings.

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It is a Küchemann body (or Küchemann carrot), a body which lowers the slope of the cross sectional area over the streamwise direction, reducing shocks and wave drag.

Please read this answer if you are unsure why aircraft experience more drag as they approach the speed of sound. By stretching the aircraft body over a larger length, the gradients in the cross sectional area distribution can be made more shallow such that the air has more opportunity to make way for the aircraft. These bodies are a typical feature of 1950's airliners and subsonic bombers, and even tip or overwing tanks can serve as a drag reduction device when properly shaped. Today, the flap track fairings of airliners serve the same purpose.

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