Here is a pic I drew. It will take a while to describe it so I may come back to it tomorow.

remember

Moment = radius * Applied Force

Or

"Torque (Oz-In) = Arm length (In.) * Force on the surface"

In our linkage systems we have two different moments we need to consider.
1. The moment applied on the servo
2. The moment applied on the control surface

The torque of a servo is given in (Oz.-in.) nomatter how far away from the center you read. It in the end relates to (Oz. - In).

The length of your control arm on the surface and the size of the control surface determine how much load is place on the push rod either in compression or tension.

The ratio of the lengths between the servo arm and the control horn determine how the load gets multiplied to the servo. (Can be seen in sample 3,4)

You may notice that the longer both the control horn and servo arm are the less load is applied in the push rod. This is not necessarily the moment (torque) applied to the servo.
Sample 1,2)


As you can see the worst set up you could have would be case 4. It could be prone to flutter. The slop in the linkages are multiplied to the control surface. The servo would likely have to be run in the 50-60% ATV range

The best system would be #3. This in moest planes would require the servo to be operated in the 100-125% ATV


I will stop here for tonight. If I am way off let me know. Im not saying this is the gospel, you don't have to beleive me. But the theory is right out of my Dynamics book.


Session entry #2

As you can see. If you have a really big control surface, and a short control horn you create large stress on your push rod.

In the Giant scale planes, I beleive they use really long control horns and servo arms. Thus reducing the load on the push rod. (Less bending, Less Chance of failure do to fatigue)

I feel the longer you can make your control horns and servo arms while mantaining a proper control deflection/servo movement ratio, the better off you are.
Now we have to be realistic about this too! We don't want or need 2.5 inch control horns on our jets!

This will make for good chatting!
Later
Dustin