Circle on the tail

[CaptainMorgan]

What is the circle on the base of the tail of the airplane? I almost always see it in pictures, but I can not find out what it is there for.

 

[Commander91gm]

I'm assuming you mean the small black plug - although it's painted on some airplane. It is access to a bolt on an arm that is part of the elevator assembly.
If you're talking about the circle on the front at the bottom - that would be the air intake for the overhead vents. There's a vent above each seat similar to the kind of vents you have in commercial airplanes. Later planes actually have a NACCA scoop on the right side rather than the what we call donut hole in the front

 

[CaptainMorgan]

I'm assuming you mean the small black plug - although it's painted on some airplane. It is access to a bolt on an arm that is part of the elevator assembly.
If you're talking about the circle on the front at the bottom - that would be the air intake for the overhead vents. There's a vent above each seat similar to the kind of vents you have in commercial airplanes. Later planes actually have a NACCA scoop on the right side rather than the what we call donut hole in the front

Thanks this is exactly what I was looking for!

 

[Jaybird]

If you’re looking to spend some money Captain, and who isn’t that owns a Commander, there’s an aftermarket replacement for this “donut” dorsal fin to a replacement fin which has the intake on the side, aka the NACCA scoop as Joel says. It’s very easy to change out. Like everything, it is rumored you pick up a few knots airspeed due to the aerodynamics improvement. Yeah right.

It’s funny, the other day some kid lineman asked me what that hole was for and I told him I thought it was the intake for the APU on the plane.

 

[gmores]

Well I wouldn't say it's 'very easy' to change out to the NACA scoop. I had about 6 hours of trimming and work to get it to fit correctly.