What are you using for "D"?

F = 4DT/L where T is tension, D is deflection, and L is cable length.

So for 1" deflection at 1000# cable tension, you would need 32# force to get 1" deflection. 15# would be 469# tension.

If you're using a different value for deflection, of course the numbers are different. 15# with a 1/2" deflection means 938# tension.

Quote Originally Posted by rwanttaja View Post
My Fly Baby's bracing system is *roughly* the same as the C-3s, in that there isn't "cross bracing" like a biplane. With a biplane, two opposing turnbuckles oppose each other, and you can alternately adjust them to get the pair of bracing wires very tight. In contrast, on the Fly Baby, like the C-3, tightening turnbuckles pull the wings tighter to the fuselage; there's no direct opposition from the wires on the other side.
That's not quite correct. Despite not being crossed, the vertical component of tension from the upper and lower wires still oppose each other. Monoplane or biplane, the horizontal component of tension pulls the wings tighter to the fuselage.