Comparing apples to apples.

I think that torque and speed specifications (if all use the same standards) are helpful, but not as much as we think. And they can lead us into a number of misconceptions.

As most control systems need the servo to move from their current position to another position in order to change the position of a flight control surface (in heli's that would be the swashplate or t/r pitch slider) then it is very important for it to have power available ASAP to do so. This is what makes the biggest difference between the standard analogue servo and a digital one.

The analogue servo may spec at 100 in. oz. of torque but it has to move about 15 degrees before it has developed that torque. On the other hand even a poor digital will develop full torque after only about 3 degrees of movement. To test this, take your servo, power it up and try to move it by hand, you will find that the standard analogue servo will move a bit before building up enoough current to stop your push. Then try it on a digital servo, now you will find that even a weaker one will hold fast because it was able to ramp up to full power as soon as it detected a force trying to change its desired position.

In other words the analogue will give a "mushier" control at center. If ones helicopter control system is not very precise (has a lot of slop in the various bellcranks and control arms), then "feeling" the difference will be a lot harder then if ones helicopter has a tight precise control system.

This is also why a slower (e.g. .22) digital servo will perform a lot better on any gyro then will a much faster analoque (.06). This is because when attempting to hold the tail on heading against outside forces, the gyro will give a multitude of small commands for movement from the servo, as the analoque takes time to ramp up, it in effect will be slower then will the digital. That is because the speed spec is the speed for 60 degrees of travel. So the analoque may have a higher top speed (0.06 compare to 0.22) over a distance (60 degrees) but the other will have a much faster acceleration speed. The digital will attain its top speed within 3 degrees while the analogue will do so in 15.

Like two cars with different acceleration and top speeds. One will win in the quarter mile (digital) but the other in a one mile run.

I hope tis helps more flyers understand the spec relationships and differences in types of servos better.