Is there a rule of thumb regarding the placement of a control horn, other than putting the pivot point over the hinge line? I'm currently building a 1/4 scale sport type low wing plane.
What exactly I'm referring to is; should I use one with an extremely long arm so as to have the mount as far away from the hinge line as possible, is closer better. Or is it that you just
use one that places the mount in a beefier part of the control surface and call it good?

Thanks,

Paul

Basically, the closer to the hinge line, the better.

I think I understand your question- by refering to a horn that mounts further from the hinge line, do you mean like the DuBro heavy duty horns (as opposed to a conventional nylon horn that screws into a nylon backing plate)? If that's what your asking, it depends on a couple things. For example, I assembled a Skyshark Edge ARF that had ailerons that did not lend themselves to correct positioning of the horn pivot holes directly over the hinge line. To do so, I would have had to let the nylon horn protrude into the hinge movement space, interfering with the range of motion. As a result, I had to move the horns a little further away from the hinge line to get full range of motion.

If you use the horns that mount further out on the control surface (like the DuBro HD 6-32 or 8-32), there is no danger of the horn interfering with the range of motion like in my previous example. If there is a small "footprint" for the horn mount, install a hard point so the horn has some solid material to torque on. You don't want to mount a small footprint horn in soft balsa and have it flex and eventually damage the surface and get sloppy loose.

GP and DuBro both make some heavy duty nylon control horns of the conventional "sandwich" style too. They are pretty bulky, but work well.

Hope that helps

Here's a link to the Dubro horns I was refering to: [link=http://www3.towerhobbies.com/cgi-bin/wti0001p?&I=LXEMF9&P=7]HERE[/link]

That is exactly the horns I was refering to.I could get by using the 5/8 long horns. But by using the 1" or even the 1.25" horn it would allow me to either mount them in a more structurally (sp) sound spot. I guess what I was wondering the most was, does it give the servo more leverage to mount the horn further away from the hinge line? Instead of theservo having to short moment arm ( relative to the hinge line) , it could have a longer moment arm. These are relatively large control surfaces, so I thought any leverage help would be a good thing. I hope this made sense.

Thanks for all your help,

Paul

Paul, yes- the longer your control horn, the more leverage you get. This sounds good, but only to a point. You need it short enough to allow the amount of throw required for your desired sensitivity on control. (If it's a 3-D plane, you can also get huge throws by using an extra long servo arm.) I usually try to set the pushrods to the farthest adjustment holes as possible, then adjust to get the desired throws. Hope that makes sense.