How do you determine what size servo to use on a certain size airplane? What size on the different control surfaces? Putting togeather a 110 rascal dections said at least 60 in/ounces of torque. The different control surfaces recieve a different amount pressure in a different manuver. Is a 60 large enough for this large an airplane?

Depends on how you plan to fly it.

Are you going to shoehorn a Saito 2.20 on the nose and fly it hard? I'd use 80-100oz servos.

If you're going to use a 120 size engine and putter around, the 60oz servos will probably be fine.

Actually the plane is fine with standard 40oz servos. But Sig RECOMMENDS 60oz servos on the flight control surfaces.

http://www3.towerhobbies.com/cgi-bin...&I=LXCXU0&P=ML

First off we are only talking control surfaces so a standard servo is plenty for the throttle.
I try to match or exceed manufacturers recommendations no matter how I plan on flying it. Reason? I never know what the future will bring so it will be ready for anything I, or the next owner, will throw at it.
If 60 oz. servo is recommended then I look around for something reasonable. Example:
http://www3.towerhobbies.com/cgi-bin...&I=LXDTB3&P=ML
72oz. at 4.8v or 90oz. at 6v for $25 each.
Fair price and it exceeds recommendations.

Thank you RCpilot and Misseleman: The info sure helps and much cheaper than 100's ,I thought I needed .

I kinda have a little thing according to size, most small .40 sized I use HS-425bb or eqivlant except pull-pull rudders, I user HS-645 or equivlant. Up to .60 sized I use HS-635 or 45's all around or equivlant digital. And anything bigger up to 35% I use HS-5645 except on rudder, I use HS-5995TG or equivlant digital and on 35% to 41% I usally use HS-5995 all around or equivlant digital. All used with 6v if possible.

R/CBOONE72: Good Info. Going to salt it away for future use. The 72 , is that your age or something else.

Also remember that you also have to go by the size of the control surface itself and how you have your linkages set up.

I have a small Extra 300s that has rather thin aileron surfaces. Even a standard servo has no problem moving the surfaces as the surface is so thin in width that there is very little lever moment on the horns.

On the other hand fly something with practically a flying tail configuration or a huge aileron, then you'll need a lot of torque or multiple servos.

In addition you must take into account the linkages mechanical configuration.

If you have it set up for maximum mechanical advantage with low surface movement, a standard servo may suffice, even on a larger plane. Reverse this and set up for maximum throw, and even a high torque servo may have a hard time.