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photograph of left side of C27J

Here is a picture I took. You can see some pieces on the vertical stabilizer, but only on one side. I imagine this is for an aerodynamic purpose, but I am not sure. What do you think about its purpose?

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Those are vortex generators. In this case they are to mitigate bad handling if it loses the “worst case” (critical) engine:

Seventeen vortex generators were added to the left-hand side of the vertical stabiliser just forward of the rudder. These energise the airflow over the rudder, increasing its effectiveness when deflected to counteract yawing moments generated by an engine failure.

Source: Flightglobal

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    $\begingroup$ Wonder why was it done on one side only. Is it more critical to loose one of the engines than the other? $\endgroup$
    – Alex
    Commented May 27 at 15:55
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    $\begingroup$ Probably related to both props spinning in the same direction. $\endgroup$ Commented May 27 at 16:10
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    $\begingroup$ @Alex The propellers rotate clockwise as seen from behind $\rightarrow$ the critical engine is the one on the left $\rightarrow$ when the left engine is inoperative the airplane yaws nose left $\rightarrow$ the left surface of the vertical stabiliser becomes the low-pressure side of the airfoil $\rightarrow$ it make sense that that side is the most sensible and needs vortex generators $\endgroup$
    – sophit
    Commented May 27 at 19:45
  • $\begingroup$ The twin engine prop graphic and explanation near the bottom of the page at <airplaneacademy.com/…> contains more useful information about this topic. $\endgroup$
    – AeroAndy
    Commented May 28 at 19:01
  • $\begingroup$ thank you for the information, it's very interesting, i will dig deeper in it with the website you've shared. $\endgroup$
    – L'aviateur
    Commented May 29 at 5:44

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