[King]

What's your flavor on Pull Pull or a linkage set up for Rudders and why???

Been using Pull Pull on most everything even glow since I learned how and liked it....Liked it as it works out to be the same throw both ways, with linkage seemed to always ended up with EPA's set way different to get same deflection both ways.....and easy to gang but have seen linkage in the rear with one on both sides and also ganged on one side.......

What's you flavor and why

[dkjens]

I'd say it all depends on where you have to mount the servos for proper CG. It's way harder to get the pull-pull geometry perfect (so cables stay taught at all positions) than it is to get the push-pull right.

[crabby]

im with dkjens
way easyer and quicker to go push pull and alot less frustrating

[Mithrandir]

Ummm... who ever said is isn't "Right" to have a little slack at full travel???

[GmanBIll]

My sentiments exactly Myth, "who said it is not right", I want to know where I can go over some physics with them.

[Bodywerks]

The working cable is the only cable that needs to stay taught in positions other than neutral. Even when switching rudder directions, the original working cable is still the working cable all the way up to the neutral position, due to the air load on the rudder, so it still stays tight and, once you are at and passing neutral, both cables are tight and the other cable becomes the working cable and it stays tight, and so on.
As for which one I prefer, I prefer push-pull unless CG becomes a factor.

[TManiaci]

I'm with Jens. If you take the time to get symmetrical geometery, you won't see slack in the lines at any time. With 3D flying, I am sure you get reverse pressure on the surface. Also, that slack line represents backlash, or slop... so when you push the other way, that slack has to be taken up before surface movement. Wrong in every respect in my mind.

I find it perplexing that some of you better pilots are arguing that sloppy controls are not an issue!?!?

I get that as long as you are keeping a consistent load on the surface, one cable should carry the load. But, what about the counterbalance surface that somewhat minimizes a lot of the load. If that surface area forward of the hingeline is effective in flight, then the load on the cable(s) should be far less than it is when your testing controls no-load on the ground.

[Mithrandir]

Originally Posted by TManiaci

I'm with Jens. If you take the time to get symmetrical geometery, you won't see slack in the lines at any time. With 3D flying, I am sure you get reverse pressure on the surface. Also, that slack line represents backlash, or slop... so when you push the other way, that slack has to be taken up before surface movement. Wrong in every respect in my mind.

I find it perplexing that some of you better pilots are arguing that sloppy controls are not an issue!?!?

I get that as long as you are keeping a consistent load on the surface, one cable should carry the load. But, what about the counterbalance surface that somewhat minimizes a lot of the load. If that surface area forward of the hingeline is effective in flight, then the load on the cable(s) should be far less than it is when your testing controls no-load on the ground.

Tony... it isn't a problem.... I have never seen a rudder flop up against the slack line in the past 700 3D flights I have done.....

If the cables are tight in the middle and fairly tight for the 10 degrees or so either side of center... it isn't a problem.

The counter balance helps reduce servo load... it does not eliminate it.... If the counter balance is too big.. then the rudder is unstable... that is the rumor about the 3.0 compy extra.. the counter balance was too big and it tended to hunt in yaw.... in this one specific example.. tight cables thru the entire range of travel are less bad.

[dkjens]

Man, reading a little to much into my statement, aren't we. I said it's way harder to get the geometry perfect, I didn't say it has to be perfect. Although, if you have to much slack and set your rudder throws to as much as elevator trailing edge cut-outs allow, don't go rudder stick happy on the ground, because that slack will let the rudder travel into the elevator and you can easily punch a hole in the rudder that way. I like to have it as perfect as possible, for all reasons mentioned here, but it doesn't always happen.

[Bodywerks]

I'm with Jens. If you take the time to get symmetrical geometery, you won't see slack in the lines at any time. With 3D flying, I am sure you get reverse pressure on the surface. Also, that slack line represents backlash, or slop... so when you push the other way, that slack has to be taken up before surface movement. Wrong in every respect in my mind.

There is no servo on the planet fast enough to move the rudder in the other direction faster than the air trying to push it back to center. There are no conditions of flight where the air loads on the rudder would be reversed. The only times it might be remotely possible is a down-wind taxi(who cares) or a tailslide where the engine is completely cut to idle.
I'm not saying you should induce gobs of slack on the non-working cable, but a little bit of slack, or at least looseness, is actually preferred so that you don't induce unnecessary loads on the shaft bearing of the servos or the hinges of the rudder.