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Control rod question

Old 10-30-2008, 08:17 AM
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bigal126
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Default Control rod question

I am building my first RC plane. It's a midstar. It's going great. Right now I am getting ready to install the servos and the control rods for the rudder and elevator. I read on another thread that a suggestion would be: "Don't use the nylon pushrods. Replace them with one piece metal pushrods so you don't have to deal with changes in temperature affecting your trim settings."

Forgive my ignorance, but does that mean route a metal rod only from the servo to the control horn? No plastic tubing? I am familiar with that because I used to build control line planes back in the 70's, but never RC. I think that could be done with this plane beacause it's a straight shot from the servo to where the control rod exits the fuselage. One small bend in the wire is all that will be required.

Is that a good idea? If it is, then what diameter control rod would you use? I see 4-40 and 2-56 sizes are available.

If it is not, and the plastic tubing must be used, are the sig supplied ones adequate, or should they be upgraded. What would be a good upgrade?

Any advise is appreciated. This is all totally new to me.
Old 10-30-2008, 08:49 AM
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cold_reboot
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Default RE: Control rod question

No, they mean don't use the nylon push rod, you will still use the nylon guide tube that runs through the fuse. It's usually a grey tube, largest diameter, that the nylon pushrod would go through, just use a metal pushrod instead of the Nylon rod that comes with the kit, everything else is the same. I'd use 2-56 rods (what I used on my 4*), 4-40 is overkill in my opinion on a Midstar and will only add more tail weight. It is a pretty straight shot, your right, but the longer the rod is the more flex you'll get, especially while flying with wind resistance against your control surfaces pushing back. The guide tube will keep them from flexing like that. My LHS sells individual pushrods in a standard length (yours may as well) or Great Planes sells a little package containing the Rods, Guide Tubes, Nylon clevis's and other little tid bits in "36 inch length (which is what I used for the 4*).

Sullivan also makes the equivalent thing called Gold-n-Rods...you can go to Tower Hobbies and search "Push Rods" (make sure you note the length and don't order something to short, you can cut a rod shorter easier than you can stretch it longer). The sets usually come in lengths of "36 and "48....I think. Just cut the rods the length you need.
Old 10-30-2008, 08:57 AM
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RICKSTUBBZ
 
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Default RE: Control rod question

In all honesty, your first plane. Use the supplied plastic push rods. You will likely never notice the trim difference when temps change. If you use metal rods, bushings of some sort (usually plastic and not metallic) or the outside plastic tubes from those supplied should be used to prevent the rod from bowing under presure. In this case 2-56 is sufficient for 40 size or smaller planes.

Once you get to the stage of more precise flight (plane 2 or 3) then start worrying about more precise set-ups.

Good Luck
Old 10-30-2008, 08:58 AM
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robert92679
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Default RE: Control rod question

I have the Kadet LT-40 (another SIG model) that uses the nylon push rods. In eight years I can't say I ever noticed a trim problem. They have been very reliable (and durable!). I would build it with the supplied parts.
Old 10-30-2008, 09:17 AM
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LesUyeda
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Default RE: Control rod question

When NyRods first came out they DID change length drastically with temperature. The manufacturer apparently reformulated and solved the majority of the problem. If your airplane is so sensitive that it will notice the difference, it should probably not be considered a trainer.

Les
Old 10-30-2008, 09:45 AM
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Alex7403
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Default RE: Control rod question

if you installed the outer tubes already you can use sullivan composites rods 2-56 instead of the nyrods.
one of 48" would be enough: http://www3.towerhobbies.com/cgi-bin...?&I=LXFV43&P=7
the composite does not affected by heat

Alex
Old 10-30-2008, 11:16 AM
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TexasAirBoss
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Default RE: Control rod question

I don't think the Nyrod changes length very much, I think the airplane does. The coefficient of linear expansion is much higher for the balsa than it is for the plastic. So trim changes are because the airplane itself has expanded in the heat or contracted in the cold. If the Nyrod manufacture did improve their product, then they must have made it expand and contract more.

The easiest type of rod to install is the stock plastic rod. BUT, this is easily changed out later if you don't like it. So, you aren't locked in.

Many modellers will try to avoid using the Nyrod brand pushrod, if they can. Sometimes, nothing else will work. They do tend to introduce a tiny bit of "slop" to the control linkage that is noticable in precision aerobatics and higher performing models. For trainers, its not that big of a deal.

Those composite rods look very interesting !! I would like to try those. They might just be the best answer.
Old 10-30-2008, 11:55 AM
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bigal126
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Default RE: Control rod question

Actually, I am building the plane for someone else as their second plane. He's beat up his trainer enough.
Since he won't be doing precision areobotics, I'll stay with the stock rods. Just thought I'd ask before I get into it.

Thanks for all your help!

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