RE: Servos for 1/4 scale Cub?
Whip momentum of a control surface can cause considerably higher loads than the control surface experiences in normal flight and can destroy a standard servo with no warning.
For example, if you let the tail drop hard to the ground on landing, the size and weight of the elevator can strip the standard servo gears from whip momentum. I've even seen aileron servos strip out (1/3 scale Cub) when those huge barn door ailerons slammed down on a less than gentle landing.
I always figure that "giant scale rules apply" when installing servos into an aircraft with more than 80" wingspan. It's about that point where control surfaces start getting larger, and it's also at that point where an extra pound of servos doesn't make any appreciable difference to the aircraft because larger airplanes can handle extra weight easily due to their larger flying surfaces.
Besides, there are lots of 80oz+ size servos made that are now available in "standard" size servo cases and weights. There is no excuse at all to NOT use stronger servos in the larger aircraft. I personally consider 80oz. a minimum for any giant control surface, with an 80oz+ on EACH aileron, 80oz + on EACH elevator half, and 120oz+ on the rudder by itself.
Highflight