Pull Pull cable question
 

I'm installing a servo driven 180 degree bellcrank in the cabin of my 80 inch Mini Max for pull pull on the rudder. Cables will travel about 20 inches before they exit the rear of the fuselage balsa turtle deck. Leaving the bellcrank they'll travel upwards and exit. How do you locate the two exit holes in the rear of the fuselage?
There must be a trick to doing this without butchering the fuselage trying to get the cables to run free to the rudder horn without touching anything? No line of sight or it would be easier.

RE: Pull Pull cable question
 

I'm not sure I quite understand the question but it sounds like you might be having two problems: 1) figuring out how to string the cables through the enclosed fuse (normally cables are installed before covering) and 2) dealing with the fact that the cables can't run in a straight line.

As far as the first problem, I think I'd suggest putting a small fishing weight on a piece of thread and lowing that through the exit holes down to the servo location. Then attach the cable to the thread and pull it back out. Unfortunately, this is only half the problem.

To avoid allowing he cable to rub against bits fo the fuse internior full sized aircraft used pulleys. On my EIII I just used small eyelets. Unfortunately, I don't see any way of installing these without taking off the covering.

RE: Pull Pull cable question
 

Sounds like your looking for the "Visible Fuselage"...:) What you really need to do is to locate where the exit holes are supposed to be, per the full scale plane, and then work back wards. Once you locate the hole position you do what it takes to have your Pull/pull exit there. It's ok to have your cable running inside some nyrod tubing or similar product inside your fuse. Does this help?

RE: Pull Pull cable question
 

Well, what you say makes sense. Make the holes first then plumb-bob the cable location to locate the bellcrank /servo.....interesting and very good.
Yes, cables must run straight from bellcrank to control horn, no bends for me.
It will be interesting to see how many other good idea's show up here.
Thanks
Bob

RE: Pull Pull cable question
 

Your welcome and maybe I'll see you at Warbirds over Delaware!

RE: Pull Pull cable question
 

Hi!
I cant understand what the trubble is... isn't it just to fasten the lines to the control linkage on the side rudder and then drill a hole in the fuselage and then just draw the lines up to the servo???
Like this...

Regards!
Jan K
Sweden

RE: Pull Pull cable question
 

I have a scratch built 80" mimi-max in which I simply ran the cables back to the rudder for Pull pull control with an outlet just ahead of the fin on either side and run the cable direct from the servo to the rudder. It came out that it was not quite a straight shot but seemed to make little difference. I just used a short lenght of yellow inner rod as a ferule to run the cable through It worked very well.

RE: Pull Pull cable question
 

abufletcher,
I did the same with both my 80" Balsa USA Eindecker and my 1/4 scale scratch built E-III and have had no problems in the 3 years both have been flying. Best case scenario is of course to have the cables run in a straight line so they do not make contact anywhere on the fuse but this is not always possible. On the 80" Balsa USA kit I have the cables running through small plastic tubes like the ones used for control rods and on the 1/4 scale version they run through small eyelets. Both applications do the job well. Good luck to ifrarrow with whatever method you come up with.

Steve.

RE: Pull Pull cable question
 

Almost finished.
Of course the plane is still in the bones, not covered. It's just that I sheeted the rear turtle deck to give the fuselage some strength and hold things in alignment. As it's worked out (at 4:00 AM) I do my best work between 3 and 4 AM by the way. I temporally mounted the bell crank, bolted the tail feathers back on (this Mini Max has a removable rudder and stab assembly) Did some eyeball measuring with a long thin straight edge and was able to locate the two holes for a No touch, No Rub cable run from bell crank to rudder horn.
My goal from the beginning was to have the cable system travel straight thru without touching anything.
Somewhere I read that pull pull should never touch anything, apparently that isn't true, interesting. Next time I'll use the plastic sleeve method and save myself a lot of trouble.
Thanks for all the interesting idea's.

RE: Pull Pull cable question
 

If you ever get a chance to eyeball a 1:1 Piper Cub, have a look at how the ailerons work. The setup is closed-loop pull-pull, and the cables run through guides and around pulleys to change directions several times as they wander from the bottom of the sticks up the strut, into the wing, back to the aileron, then from the aileron to the front of the wing and across through the top of the cabin to the other wing.

The cables also cross each other inside the wing. I dunno who designed that setup, but I betcha it took a case of Stoly.