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Why some small piston airplanes, like Cessna 152/172, Tecnam P2008 and many more, have the vertical stabilizer with a sweepback? I don't think that those airplanes may encounter compressibility effects, so what is the reason?

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  • $\begingroup$ Because it looks cool? (Warning: TVTropes) $\endgroup$ – StephenS Mar 26 at 17:36
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Two benefits to fin sweep on a type like a 152 or 172:

Marketing, and aerodyanamics.

The airplane looks "cooler", "going fast when it's tied down" with the sharply swept fin; this makes it easier to sell to casual pilots and those who'll rent the plane to casual pilots.

However, there's also another advantage. The sweep moves the tail area to the rear without adding dead weight of structure far out in the tail. Thus rudder authority and yaw stability are gained with little increase in overall weight, compared to the previous generations of the same models in the Cessna line, for instance (look at a 180 from 1960 for comparison to a modern 182).

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The further back the fin and rudder are, the more effective they are. But the longer the fuselage is, the heavier it gets. Sweeping the fin back is a way to move its centre of pressure aft and increase its effectiveness, without lengthening the fuselage.

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  • $\begingroup$ But doesn't a swept fin has lower lift per area if comaperd to a straight fin? Is the net result better (longer arm to the fin CP vs greater lift on a fin)? $\endgroup$ – Konrad Mar 26 at 17:42
  • $\begingroup$ @Konrad Yes. But aircraft design is all about compromise to achieve the optimal solution. A moderate sweepback adds more leverage than it takes away. But sweep back too far and it takes away more than it gives back. So one aims for the sweet spot. $\endgroup$ – Guy Inchbald Mar 26 at 17:48

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