Chris,

One of the reasons for which most of the available threaded metal pushrods are 12" is that if they are too long and are not supported along the fuselage, tend to bend when are pushing against the control surface (not when are pulling).

Note that some are plastic, wire or cable that slide inside a plastic sleeve, which should be properly supported along the fuselage.

There is also the pushrod built up with carbon fiber tubes or balsa wood stick and both metal ends.

Then, there is the pull-pull system, which are two cables or strings that connect each side of the servo's horn to two horns in the control surface.

Check these links out:

http://home.flash.net/~dynamic3/sig/007.htm

http://home.flash.net/~dynamic3/sig/008.htm

http://www.sullivanproducts.com/Prod...sMainFrame.htm

http://masportaviator.com/2008/10/26...ainer-part-ii/