Boxing Tail Section

[jon s. blocker]

I am building a new fuselage and want to box the tail section. I have seen a simple X, I have seen a box from lower longerons to the diagonal above that longeron, I have seen a box from the lower longeron up to the middle longeron. Any opinions on which is the best method? Is a simple X good enough, or is it best to make one of the previously listed boxes? It will be a PA11 type fuselage. I am putting a Lyc 0290D on it. It is beefed up in front as per Wag Aero plans. The firewall is kicked forward to put the thrust line to zero degrees, Balanced PA20 tailfeathers, no electrics. Very simple, as light as possible. Any suggestions on the boxing of the tail would be appreciated. Thank you, Jon

 

[Seaworthy]

Jon

There was just a thread a few days back r/t torsioning of PA-12's and 18's and related issues. Different tail braces were mentioned and their success.

 

[Seaworthy]

http://www.supercub.org/forum/showthread.php?45187-Tail-Shakes&highlight=Tail+brace

Barney helping?

 

[flybynite]

Hi Jon,

I started with a rectangular box on the tail of my 12, then changed to an X when I replaced the tail section with one from univair. The box interfered with the side and bottom stringers and the top cross piece had to be carefully placed to not interfere with the elevator controls. The X , on the other hand, is made of shorter segments of tube and is tacked where they intercept. The geometry is stronger and marginally lighter. No interference either.



Cheers
Wayne

 

[Darrel Starr]

I don't really know which is best but I went this route:


Elevator cable clearance is not a problem:

For comparison, here is the Univair style "X" brace.



This one is an Airframes Inc. wide body. Like mine but without the top tube, just three:

I once talked to Roger Borer. He told me that he had discovered that the tail post could be significantly strengthened by pushing a 4130 tube down in it to form a stiffening sleeve. With the vertical fin off, just measure how long the sleeve could be and still get the fin back on. Don't weld it in, just use a tube that will fit with very little clearance. I did that too.

 

[docstory]

This one is an Airframes Inc. wide body. Like mine but without the top tube, just three:
View attachment 12059

The top tube is there. It's just placed a little further aft to eliminate any elevator cable slap.

 

[Darrel Starr]

Yes, I see it now.