Do a search on Yahoo and you will find a bunch of servo torque calculators. I just look at the plane and decide what I want to do with it. I then look for servos that I think will make it respond like I want it to. I don't have much experience on the larger planes. I'm sure that they have their own methods. My next plane is a Funtana. I know that I want a servo that centers well due to the large control surface, which probably means I'll go digital. I'm going to get the 40 size so a huge amount of torque is not needed, but I wouldn't mind a faster servo. I will also ask around and see what others are using for servos in this plane.

I think that the speed of the servo depends more on the taste of the pilot.

I also keep my plane sizes down, which helps control the cost of the servos. One day I might get smart and downsize my fleet for a few large planes.

http://www.coloradogliders.com/servo...calculator.htm