Sweep on Vertical Stabiliser

[Boffin]

Can someone please tell me what the reason is for sweeping the leading edge of the tail fin? I notice that on some older aircraft, some tail fins have vertical tail fin leading edges. What intrigues me is with some light aeroplanes (eg a Cessna 152), even though the leading edge of the wings are unswept, the leading edge of the tail fin is swept.

 

[i278]

Boffin...

On light, low speed aircraft (<250 kts) the only reason to sweep a tail back is appearance. Backward sweep reduces the effectiveness of tail surfaces, so they need to be bigger, all else equal. On the Cessna line, the change from the original 'straight' tail to the classic swept tail apparently cost them 3 kts in cruise, but tripled sales. (Note: I don't have any data to back up that last bit, though--just towing the party line)

But whatever the case, on typical light GA aircraft, backward sweep (and usually taper) of wings or tail surfaces are just for looks. Which, to be fair, is perfectly valid reason.

Regards

 

[JeanAlesi]

I agree with I278 about the aesthetics of sweeping the tail. However, I strongly disagree that tapering wings are &quot;just for looks&quot;. Wing tapering have a huge impact on the core aerodynamics, especially on the 3D effects and mean aerodynamic chord. I wont go as far as saying tapering is &quot;good&quot; or &quot;bad&quot;, as each design has its drawbacks....etc.

Generally you can get away with making a tail look attractive for a small weight and drag penalty on GA airplanes. Not with wings though, I have never seen a wing designed to &quot;look cool&quot;. Important point, when we talk sweep, I think quarter chord sweep, not leading edge.

The aerodynamic reason engineers sweep tails (in high speed a/c) to ensure that the tail has a higher critical mach number than the wing. Also sweeping the tail with a larger angle than the wing ensures that the wing will stall before the tail (provided that other factors do not tip the scale the other way around).