Diag. at lift strut compression brace

[wirsig]

What are your thoughts regarding the diag. tube at the Compression brace located at the lift struts. The J-3 didn't have the compression tubes there and it had a different compression tube design. It uses round tube with a foot instead of the square aluminum. I've made mine similar to the J-3's but at the Pa-18 locations.
Drawing 15403:

 

[mike mcs repair]

What are your thoughts regarding the diag. tube

make darn sure you put it in the correct orientation... or your aileron cable will want to cut it in half....

 

[bob turner]

Metal spar J-3s had it too. Don't forget - Piper wouldn't just arbitrarily add weight. Triangles are stronger than rectangles.

 

[wirsig]

Good point Bob!

I've thought about it quite a bit and can't see how the diag. brace ever experiences a load. It would keep the spars from wracking if everything else was missing but to make it simple, remove the ribs from the equation, the ends of spars are fixed on the fuselage and they are then fixed to the lift struts so wracking can't happen. Do you think it was a safety measure so if the rear strut fails you can limp it to the ground. Maybe a good example is the guy in the predator control thread that shot through the strut.
I'm just curious if anyone else has wasted as much time thinking about it as I have.....

 

[Dave Calkins]

Good point Bob!

I've thought about it quite a bit
I'm just curious if anyone else has wasted as much time thinking about it as I have.....

I am not sure if its wasted time.

But...........I have spent a lot of time thinking how to get one of these turned around after someone has installed it backwards and covered the wing!!

 

[Gordon Misch]

That z-strut is definitely in compression as a consequence of the tension in the lift struts. And the triangulation would help resist twisting moment. I'm with Bob - put it in, correctly.

 

[wirsig]

Sounds good, thanks guys!