Pull pull or Push Pull

[Bartman]

i was thinking a CF tube across the horizontal stab with a single control horn inside the fuselage like a Pitts has, but all in one piece instead of two halves like the Pitts. a couple of spikes to bury in the elevator halves would keep it from dislodging.
similar for the wings as you've said would work too.

 

[Terryscustom]

Pull-pull and push pull both work fine
The ideal push-pull system is two servos, one pushing when the other pulls. This set up is more critical than pull-pull, as the geometry and programming has to be perfect in order to avoid one servo fighting the other at all points of the travel.
Single servo push-pull is not ideal: pulling action is fine, but each time the servo pushes, you are essentially trying to de-hinge the rudder, and resistance from the hinges at the control horn location is what makes the rudder turn. With hard flying and lots of rudder use, these hinges often don't last very long.

Exactly, well described. I really like pull-pull but often for simplicity so the push-pull. No matter what the plane, when I do use a push-pull single servo in the tail I add at least one hinge and sometimes two. depending on how it is set up from the factory.

OK @Terryscustom there's your next project !!!

I'm eyeball deep in projects, sorry!!! There have been some interesting things tried in the past I know. I remember a thread on another forum some time ago where a guy was building a composite plane with aileron servos inside the fuse, but then it kinda fizzled out. For our size I just don't think you can beat simple drop in torque and mechanical advantage set ups.

 

[stangflyer]

I've also used both. And though the pull/pull on my big 260 has proven to be very reliable and incredibly precise, I've also had to do more to maintain that setup. My preference is (if) the airframe allows for push/pull... (which the 260 doesn't), that's the way I go.

 

[boggintuff]

Thanks guys! Now just have to figure out which would suit my 3dhs 106' edge. Would like to try push pull but I believe the edge has a tendency to be tail heavy.

I went push pull in my 106" with 7954's and DLE-120 on Jtec mufflers up front. If I had to do it over I would have went pull pull as I needed quite a bit of weight forward to balance and it was a royal pain in the ass. I you are going with canisters it might be a little more favorable in the balancing aspect of it.

Also if you do decide to do push pull you absolutely have to have one servo on each side of the fuse. You will NOT be able to put 2 on the same side as you run into clearance issues with the elevator. I have posted my setup, which others have had to do also, in the build thread on FG. You will also have to use the forward most servo bay in the tail and buy turnbuckles.

 

[camss69]

If push pull is an option I try to go that way. Zero maintenance, easy setup, positive control... Just way less hassle.

 

[TnAeroNut]

i was thinking a CF tube across the horizontal stab with a single control horn inside the fuselage like a Pitts has, but all in one piece instead of two halves like the Pitts. a couple of spikes to bury in the elevator halves would keep it from dislodging.
similar for the wings as you've said would work too.

Back when I was flying pattern, one of the "big dogs" told me the elevator halves should be coupled mechanically because it's impossible to get two servos to move exactly the same. That's easy to see even with the best two-servo set up if you tape down long sticks (one from each elevator half), and watch from the side as the sticks track each other. I know I'm not good enough to to feel the roll effect when the halves don't move together just a little bit, but for the precision freak it's the way to go. Also, pattern flyers live with a very tough 5kg weight limit, so a single servo helps there, too.