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pull pull system

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Old 01-19-2003, 02:44 AM
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haz
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Default pull pull system

I just installed a pull pull system on the Elevator of a global Ultimate bi-plane. What i need to know is how tight should the cables be?
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Old 01-19-2003, 04:18 AM
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Tippie
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Default pull pull system

Let's see if I can get this discussion going! I haven't installed a pull-pull on an airplane as yet. I was going to put one on an electric with a speed 400 but changed my mind. I asked the LHS that same question and was told that you can tolerate a little slack in the lines. You don't want them as tight as a fiddle string and not so loose that they droop. Check the adjustment and make sure there is no binding or stress on the servo when you operate it full throw in each direction. The reason, as I understand, is that the pull is not necessarily equal in both directions. As an example. If your rudder servo is not on the center line with the rudder there will be unequal pull in each direction, thus unequal rudder throw in each direction. (Probably so little difference you would ever notice) Same goes for the elevator, if the output arm on the elevator servo is not on the same plane with the elevator the pull, up and down, will be unequal. It's not a side to side alignment issue with the elevator but rather a up and down alignment. Thus, don't make it too tight.
Is there any hint about pull-pull adjustment in the kit instructions?
The answer given to me about the servo alignment business makes sense when you give it some thought. If you are not centered one side of the linkage is shorter than the other and the shorter side will give more deflection (throw).
Now we'll see what kind of argument that stirs up.

Good luck
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Old 01-19-2003, 07:35 AM
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haz
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Default pull pull system

So does the servo have to be on the center line of the hinge for a Elevator ? Because i did not set mine up like that. My elevator hinge is up and down and the servo side to side oppsite the elevator. In other words should my evevator servo be mounted on its side?
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Old 01-19-2003, 04:27 PM
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Default Servo does not have to line up with control horns

There is no reason that the servo and the control horns have to line up. It is OK to have the servo rotated 90 degrees to the control horns. As long as the cables are reasonable straight to the surfaces, you are OK. I have one system where the cables must make a bend between the servo and the rudder. Works fine. Where the wires go around the bend, I use a yellow inner rod to keep them in place.
As far as tightness, I have found this to be non-critical. Do not try to get them "guitar-string" tight. Just a couple pounds of force is plenty. As long as they are not slack, then they work fine.
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Old 01-19-2003, 04:30 PM
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Tippie
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Default pull pull system

No, don't change your servo mounting. I don't think the elevator alignment would or could be quite as critical as the rudder. Don't get me wrong, with neither of the servos not being aligned it will not prevent the airplane from performing good. It's just that the pure competitive flyers may see a problem with misalignment. Just leave the elevator servo as you would normally, with the arm horizontal.
I'm not trying to cause panic with the pull-pull system and the alignment of the servo's, just pointing out a fine tuning of the action. I think your original question was how tight the lines should be. You didn't say if you were using wires (stainless cables) (carbon fiber rod) or some type of line such as Kevlar (no stretch) or nylon or other material that has minimal stretch. Again, as I was informed by someone that used pull-pull quite a bit that it should be adjusted just a little loose without a droop just in case there is any change in the movement tension from one side of the throw to the other.
Just fly it the way you installed it and if it doesn't perform as well as you like then make some adjustments as to alignment and/or tension. Another reason for not needing the pull-pull tight is that it is as described, pulling one side or the other, not pushing. As long as there is a resistance force on the surface you are operating the pull to that side of the surface will be tight. And as long as your aren't pylon racing at 175 mph you shouldn't experience any flutter of the control surfaces.
Let's see if anyone can add to the issue or provide another answer.

Just trying to make it interesting. HA
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Old 01-20-2003, 09:59 PM
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Default pull pull system

As in all setups, use the holes furtherest away from the center of the control arms and servo horns that you practically can. This will minimize slop without the lines having to be too tight.

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Old 01-21-2003, 12:25 AM
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BretR
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Default pull pull system

This site helped me out with understanding how to setup a pull-pull system.

http://members.cox.net/bdfelice/
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Old 01-21-2003, 01:45 AM
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Ernie Misner
 
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Default pull pull system

>> This site helped me out with understanding how to setup a pull-pull system.

http://members.cox.net/bdfelice/

Thanks Bret.... that is one interesting site!!!

Ernie
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