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pull pull system on GP Sportster

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Old 11-30-2005, 11:13 PM
  #1  
decombs21
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Default pull pull system on GP Sportster

I'm looking for advice from anyone who has tried a pull pull rudder system on the 90/120 Super Sportster (or any other similarly sized bird). Also did you use the plans' suggestion for controlling the tailwheel?

It would be nice if someone had photos as this will be my first attempt at using pull pull IF I decide to do it. I really can't think of any advantage such a system would give but nonetheless would like to try it anyhow. Maybe someone could spell out WHY the pull pull system is superior to some other arrangement as well? I'd sure like to hear it.

What I've got in the works is a set of plans from MAN for the 90/120 Super Sportster that are blown up 18% to give me an 84 inch wingspan. I've heard it said that big planes fly better! So we will soon see.

While I'm at it, I want to use a 23cc or 26 cc Zenoah gas engine. This time I do have a good reason for using a gas motor - economy and I won't have to clean the castor oil off the beast.

Maybe there's someone who has used a set of blown up plans for the Sportster before? I can't imagine I'm the only one who likes this bird and wants a custom sized model.

Dave
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Old 12-01-2005, 07:09 PM
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daveopam
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Default RE: pull pull system on GP Sportster

Dave that plane should be a blast. I still have SS 90/120. I fly it once in a while. I have also owned the 60 the 40 and the bipe. The 60 was my favorite but the 120 is a close second. I use a pull/pull on my aerobatic stuff but never on a SS. The advantage from what I know is the even pull on both sides of the rudder. It's easier for a servo to pull the surface than push it. I used Sylivan solid steel golden rods in mine. I like the ease of use and strength of these rods. You could mount the servos in the tail to balance that big gasser.?.?.?


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Old 12-03-2005, 01:35 AM
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the_madgenius
 
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Default RE: pull pull system on GP Sportster

decombs21, pullpull verses rods. Lets do a little experiment here, get a brick and a plastic drinking straw. glue the straw to the brick. Now try to push the brick away from you using only the straw, you see it will only bend. NOw pull the brick, and you can do it. So it is with the pull pull system. Your servo is pulling either way. With rods you pull one way , and push the otherway. Control surfaces in flight need a lot of force to make them deflect in flight, so it is easier on the servo to pull the surface into the slipstream than it is to push them, also you are saving on weight , as the cables weigh much less than the push rods. Also because the cables are always kept tight , the chances of in flight flutter is reduced dramatically also. I use pull pull in all my models from the humble spad to my 3D
pattern ships, and i use them on rudder and elevator.
the_madgenius , instructor downunder.
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