I am having a realy hard time with pull,pull rudder cables on my sig cub. First full build for me.It took me a couple hours to even fish the cables through the fuse! Wish i would have installed them before covering. I have them atatched at the servo. but when i look through the cabin they apear crossed. If i pull on the right it is atached to the right side though. Same on the left side. Witch must mean they are wraped around each other not just crossed? Crossed i have seen in other threads as okay. Wraped around can't be good though. will probably bind. Also starting to wonder about stringers and formers rubbing? Just had a thought "maybe ill remove servo arm and try flipping it around to untangle. Im getting anxious to finish the plane. Elevator & throtle servo,cowling,reciever, balance,throws,think thats all thats left. Any advice would be great ,thanks.

I would untwist them by rotating the servo arm. Might help if you have a mirror to aid or set it on its nose and maybe it will untwist itself.

usually I run one cable at a time. I run a cable then tape it to the fuse. Run the second cable and attach it loosely to the servo arm then carefully attach the second cable. It is important that the cable attachment holes are equal distance from the pivot points of the servo and rudder hinge. That is you want the cables to be parrallel. If not you will get slack or worse a tightening cable. They don't have to be real taught.

Carl

Too late now but I always install that yellow flex push rod in my fuse while it's still in the bones then just run the wire through that. I make up my own lines with 30 Lb stainless fishing leader and it slides right on through the tubes. Just something to remember on your next build.

Brent,
You just brought up a whole load of bad memories from last winter when I built the same cub. I don't know how many times I beat myself up for not doing it before covering. I didn't have a problem with twisting, but it sure was a b*&^h getting the cables through.

I think that everybody who's built the 1/5 Cub should write to Sig and tell them to revise their instruction book so that they tell you to string the cables BEFORE you cover the plane. Then the next poor b@#$%&d won't have to turn him(her)self inside out trying to get the cables in place.

papermache

Had this problem a few times on ARTF's my solution is to feed in yellow nylon push rod material from the tail forward, I secure the push rods only at the tail with epoxy, the front end is left free to float so that the angular displacement of the servo arm causes no problems then its a simple matter to install the cables through the push rods, safe in the knowledge that theyll run nice and free without damaging servo wire etc.

[quote]ORIGINAL: carlbecker

It is important that the cable attachment holes are equal distance from the pivot points of the servo and rudder hinge. That is you want the cables to be paallel. If not you will get slack or worse a tightening cable. They don't have to be real taught.

One additional point here, Make sure the control horn holes are setup so that if you drew an imaginary line between the clevis holes on each side of the rudder, it would pass through the pivot line of the rudder.

I'm just doing the final checkout and setup before heading to the field and discovered that if I go maximum throw on the rudder, the outside wire goes slack at full travel. I had just changed the horn on the servo to get a closer match to the rudder horn span. The problem was worse before. I didn't think that the 1/8" behind the rudder axis would make a difference with the pull-pull. It does. I don't think it is a big enough issue to cause me to move the horns though.

Don

Campgems, thats confusing. I am easily confused though. If the Lines aren't parallel. yet there's tension on both sides. I'm not seeing how one can go slack and on too tight. I believe it but don't understand it right now. When i went to spin my servo arm. i looked down my fuse with a flashlight and discovered both my lines had run around outside of formers[]. Soo i pulled them back out again and tried starting over without success. Iv'e tried fishing line put 8' through the back but couldn't get close too the cabin,tried making a hook to grab it from front moderate success, but already had gone around former.Also tried small galvanized wire,the supplied wire for fuel line + 18 awg solid wire. Might try that one again.thinking may have to get spare set of eyes with mirror and light "carlbecker". Or cut the covering soo i can see[].

Whew , im releived! Fellow flyer and experianced builder came over and lent me a hand. He brought a copper wire, we pulled the cables straight through in a about an hour. Im also going to take his advice and get a steel rod for the elevator and throtle. Next time if i encounter this ill run tubes all the way through the fuse.

Why do people use pull-pull cables anyway?

Seems to me that pushrods are simpler, stiff enough if you use carbon or whatever, aren't so finnicky to install, etc. etc.

Do people use pull-pull to get tighter, no-slop control? Or because it takes up less room in the cramped aft fuselage?

All you pattern heros, let's here from you.

-Balsacutter

Mainly on the Cub, the pull-pull is for scale looks, but it's used usually to allow the servo to pull in both directions and avoid control rod flex when the servo has to "push" against the resistance of airflow against the control surface. I agree with using the metal control rod for the elevator; on a Cub there shouldn't be any problem with flex, but at least the metal rod won't expand or contract and throw the trim off. I have to adjust my Sig Cub elevator trim almost every time I fly it.

I use pull pull for mainly two reasons. control is always pull and I can save 12 grams or better from a tail heavy plane. For reference the horn connection holes should be at the center of the hinge. IMHO that is a given unless you are trying for mechanical differencial - not a place I go. Pull pull is geometery and every thing needs to be centered and the same or you will get slack or worst extra tension. How much and which one depends on where the setup is off from perfect. I never achieve perfect and usually have just a bit of slack at full deflection. I try very hard to align my horns with hinges.

Carl

Wow, thanks for the great responses.

I've never seen a good drawing/description of how pull-pull is done. How do you adjust/maintain line tension, some kind of small turnbuckle on the servo end of the lines?

-Balsacutter

Here's how I did the ones on my 1/5 Cub/L-4. There are several brands (DuBro, Sullivan, Ernst, and others) of pull-pull setups available in different sizes, or you can use coated stainless leader line from your local bait and tackle shop. The ball joint connectors and threaded rod is available separately also. The rod has a small hole for the cable to go through.

Note I crossed my wires; it allows max throw and arm movement while maintaining equal tension. You can also use different size arms between the servo and rudder for increased or decreased mechanical advantage and still maintain equal tension.

I use kevlar string with straight line. I once had a radio problem when using steel wire although it seems lots of folks do not. At the rudder I use the Sullivan clevis then wrap the kevlar around tie and CA. At the servo I use a Sullivan clevis and 2-56 rod. I cut the rod at 2-3 inches and make a U or O bend. Then I loop and tie an adjustable knot so I can work out the slack. I CA the knot when tight. I can make small adjustments using the 2-56 rod at the servo then lock with the nut.

Carl