Whew... from your description your cables may just be too tight?... it really is hard to tell.

So, here's the basics af pull pull:

If your cables are a straight shot to the rudder:
1) The servo arm width must equal the rudder control horn width
2) The rudder control horn pivot point should be over the rudder hinge line if possible... behind it if not possible.
3) If the rudder control horn pivot point is over the hinge line, then the servo arm should be straight. If not, it should have an offset to the rear equal to the distance of the control horn's offset behind the hinge line.

If your cables are crossed:
You will need extra offset... if they are crossed write back and I will tell you how to figure out the right amount.

As an option, look at www. swbmfg.com. Give him a call, he will help. He will tell you what dimensions to measure and set you up with something that works. In a plane that size, you mught want a tiller bar (ball bearing thingy), but there are lots of guys running 35% planes with a servo connected directly to the rudder, and I'm pretty sure a 35% Extra's rudder is bigger than a 120" B-17's.

You can also call Jerry at www. nelsonhobby.com. He's pretty good as well.

Good luck.