I think there is more to it than torque. Some servos have weak gear trains but good torque while others do not hold up well to the vibration of small glow motors.
I would not be afraid of a 15 to 20 oz torque servo in a 1/2a plane given a strong gear train and resistance to vibration .
I agree with the previous poster that HS 65 servos are great for 1/2a or even a bit larger. I personally prefer HS81 servos over HS65 servos because they are a bit cheaper and a bit stronger but at the expense of size and weight. They are slightly heavier and larger.
The problem is that many micro servos are designed for use in electric aircraft and are often not robust enough for the harsher environment of 1/2a glow planes. Unfortunately the only way to know for sure is to give a servo a try and see how it holds up OR by asking others what has worked for them.
Neither I nor my 1/2a friends have had good luck with HS55 servos in glow planes, they soon succumb to the vibration and cause random problems followed by total failure.
Last edited by 049flyer; 08-12-2014 at 03:31 PM.