Ok I am building a 1/5 98" Curtis Robin and am going to be using a pull pull system on the rudder to make it look scale. My question is should I use a 2-56 system or a 4-40 system? The aircraft will be powered by an OS 91FS and will not be subjected to any large g-loads or abrupt controll inputs. I will be using Hitec HS525BB sevos for the rudder and elevator. So what would you recomend 2-56 or 4-40? Thanks in advance.

Since all loads are in tension on a pull-pull system, you can get by with smaller diameter hardware. Just make sure that any threads are good ones (I distrust rolled threads).

Ok now one more question. Would you recomend that the cables be crossed or just run straight back?

It doesn't matter, either way. I do suggest that you run some nylon guide lines inside the fuselage though, as you may have to restring the line at some time. The nylon guides also help in the exit openings (easier to have a nice clean outlet) and prevents the line from cutting into the covering at the exit.

I HAVE AN 80IN GILES 202 WITH THE PULL PULL RUDDER SYSTEM. I USED 4/40 SYSTEM. THE WAY I LOOK AT IT, IF ITS BIGGER IT MUST BE BETTER.

Phillco, If bigger is always better, why don't you get some 1/2" steel cable for your pull-pull?

Obviously, with airplanes, weight is always a BIG factor. Using oversized structural components is poor design. A properly built airframe should be on the verge of failure at it's most severe load condition. Big airplanes are built this way.

Tom

greenboot IT THAT WHAT YOU USE!

The difference in weight between 4-40 and 2-56 just isn't enough to risk a plane over. I had a 60 size stick with pull-pull on the elevator and rudder. After about a year and having restrung with fresh cable once, the threads on the 2-56 pulled out during flilght.
The plane made a smooth balistic arc into the pavement. Seemed the barrel of the clevis had actually opened up enough to let the cable coupler pull out. Now I look for higher quality clevises and cable couplers (eye-bolts, actually)n the 4-40 size.