Getting slack out of pull-pull cable...HELP!

[Rishelman]

I've tried all the normal stuff and can't get the slack out of my cables past about 25 deg. deflection.

My main question is: does anyone know if putting the clevis pivot either in front of or behind the hinge line help with this.

I read somewhere on FG about putting it in front of the hinge line, but don't know if that's true or not. I've just always put it at the hinge line with no trouble. Would like a couple opinions from people who have experience in this before I hack up my planes rudder for trial and error.

thanks
Rishelman

[FlyinTiger]

SWB has a tiller arm that is offset slightly when the rudder horn is on the hinge-line. It is something about how the geometry changes when at large deflections and the arm rotating on an arc.

http://www.swbmfg.com/

Click on "Rudder Trays/Kits" on the left hand drop-down menu to see what the offset tiller arms look like.

I have one of these on my plane with the cables crossed and it keeps the cables pretty uniform across the whole deflection of the rudder.

Good luck!

[JoeAirPort]

Most of the planes out there have some slack on the non-pulling cable. It's not worth worrying about. Just make sure there's no slack at center, but not too tight, and go fly.

[jamesrxx951]

i had a similar issue and found most of the slack was because i didn't have the servo arm centered correctly. after i centered my servo arm and readjusted most of the slack went away.

[Flybye Steve]

There are two factors that must be correct on a pull pull system in order to avoid slack in the cable. One; If The pivot point (where the cable joins the control horn) on the rudder is "On the hinge line" then you should have a straight arm on the servo (no offset). If the pivot point is not on the hinge line, the offset on the servo arm must be the same as the difference between the pivot point and the hinge line. Note; This can be sometimes difficult to achieve since the servo arms are usually offer with a standard 1/4 inch offset and that may not match the difference on the rudder.
Second; The center distance between the cable attachment points on the rudder must match the center distance on the servo arm. This is easy to accomplish on rudder control horns that are adjustable. If the hole locations are fixed however, It may be difficult to find a servo arm with a matching center distance.

[Rishelman]

Thanks for the input.
I am currently using a 3" offset arm from SWB. It is listed as for use "when cables cross". I also installed the Du-Bro adjustable horn so I could put the horns in or out as much as I wanted. Nothing I do really changes anything. I've put the horns the same distance apart as the servo arm, narrower, wider, no change. Even if I could get it to be worse, at least I could see a change, maybe give me a clue where to improve it.

I took the plane out to the field this weekend to ask some of the guys who have been around a while. They all thought I was making a big stink about nothing, explaining the theory of why it would be no problem to fly it that way.
I might be fretting a little, but you guys should see HOW MUCH slack occurs past a certain point in the deflection. The cables just flop around, I can probably wiggle the clevis back and forth a 1/2" either way loosely.

I do appreciate the ideas, keep 'em comin'.
thanks
Rishelman

[bodywerks]

There's more to it than just that. If the control arm is not parallel to the servo arm, not on the same plane with each other, and/or not on the same centerline, you will have slack on the non-working cable.
HOWEVER, and this has been BEATEN TO DEATH - so long as the slack on the non-working cable is not so bad that it flails around and droops to the floor of the fuse, there is NOTHING TO WORRY ABOUT. Once an air load is present on the surface that slack becomes a non-issue.

[bodywerks]

	Quote:
	I am currently using a 3" offset arm from SWB. It is listed as for use "when cables cross".

You don't always need an offset arm with cables crossed, so that might be part of the problem.

[wfield0455]

This link sums things up pretty well... http://www.swbmfg.com/rudex.html

I think if you have your pivot point on the rudder hinge line and the length of your rudder horn and your servo arm are equal, then you shouldn't be using an offset servo arm.....

Wayne

	Quote: Originally Posted by Rishelman
	Thanks for the input. I am currently using a 3" offset arm from SWB. It is listed as for use "when cables cross". I also installed the Du-Bro adjustable horn so I could put the horns in or out as much as I wanted. Nothing I do really changes anything. I've put the horns the same distance apart as the servo arm, narrower, wider, no change. Even if I could get it to be worse, at least I could see a change, maybe give me a clue where to improve it. I took the plane out to the field this weekend to ask some of the guys who have been around a while. They all thought I was making a big stink about nothing, explaining the theory of why it would be no problem to fly it that way. I might be fretting a little, but you guys should see HOW MUCH slack occurs past a certain point in the deflection. The cables just flop around, I can probably wiggle the clevis back and forth a 1/2" either way loosely. I do appreciate the ideas, keep 'em comin'. thanks Rishelman

[JoeAirPort]

I agree. You probably just got the wrong arm, especially if your cables are straight. The thing is you could fly like it is and really be fine. Or if it makes you feel better, and I bet it would, just get the 3 or 4" straight arm. That would depend on where your slots are located in the tail. You can use the control horn/servo arm width to center the cables in these slots....which IS important. Since your horn width is adjustable you could probably use the 3" or 4" straight servo arm. And of course the servo arm width should match the horn width....if the cables are straight...and the horn pivots on the hinge line...and the horns are not crooked...and the cables are the same length...etc etc etc.

Bottom line with pull pull rudders: If your cables are tight only at center (but not too tight), and go slack only away from center (but not falling on the floor), and your cables don't rub on anything, you can go fly.

[ace20]

Hi, I don't mean to hijack this thread but I am having similar problems. I have a pull/pull setup on my comp arf 3.0 meter extra. The cables are tight throughout the whole range of travel, but when the rudder is centered, i can move it a 1/4 in without the servos moving and also on a high speed pass the rudder wags. Any suggestions?

Thanks,
Anthony

[JoeAirPort]

Are you saying it moves 1/4" only at center? Not at other positions? If it's that loose everywhere you probably just need to tighten the cables a little bit. Just not too much or you get other problems....like a trashed servo or broken hinges.