I have had many a T-tail ship, and always want to have the pull force of the servo dedicated to the "up" movement of the elevator. Lets face it, when you are in a jam, it is usually "up" you are relying on!

So with that in mind, what is so great about this system?

Well, firstly it can be adapted for virtually any T-tail. Secondly, the way it works, it not only creates the pull system, but adds quite a bit of ridgidity to the fin.

It also makes it very easy to remove the rudder/elevator mechanism should one of those gravity related mishaps occur (oops).

Have a look at figure 1. That's It! ...well almost.

figure 1 (click to enlarge)

A couple of things to keep in mind:

figure 2 (click to enlarge)

I use a laminated (2x1/16) ply to make the bellcrank. Then drill as many holes to reduce the weight as possible, without reducing the structural integrity of the bellcrank (same with the fin post).

The proportions are important! (you may need to make some samples from scrap balsa to test first). In figure 2, the distance "x1" will determine the amount of throw the belcrank has (x2). You may want to keep an eye on the width of the bellcrank in regards to this as well.

The length of the bellcrank is dictated by the hight of the fin, but REMEMBER, if the distance of "x3" does not equal "x4" in relation to the pivot point, you will either be increasing or reducing the throw producted by the servo, depending on which arm is the longer (this could come in handy in some instances).

I use a Graupner ball coupling at each end, but there are many others out there. I suppose you could use a clevise with a hole in the bellcrank, but have never gone there!

Making the pivot point is very easy and just needs two sizes of brass tubing that fit snugly between each other. The outer is affixed to the bellcrank (I used epoxy) while the inner is afixed to the baring walls. The outer also acts as the spacer to keep the bellcrank centered.
See figure 3 for a closeup.

figure 3 (click to enlarge)

Finally - fiiting the unit! I use silicone to mount the whole thing! Mainly because I have installed it in glass fuses, but also that if I get something wrong, I can slice the silicone with a scalple and reset it! Some also say that using silicone as the adhesive for the fin post acts as a shock abosorber - to some extent.

Use these images on as a guide - they are not to scale.