Servos - How Much Torque Required?

[Erfolg]

The question was "how much torque is required".

 

If question which servos are acceptable, then certain 9g are less good than others. Their are metal geared servos of similar size to the 9g envelope.

 

I do reflect that one of my inflight servo failures, was with a costly, high branded servo (on elevator). I lost a tooth or more, luckily got it down. In life there are few 100% guarantees.

[Peter Jenkins]

16 minutes ago, Erfolg said:

The question was "how much torque is required".

 

If question which servos are acceptable, then certain 9g are less good than others. Their are metal geared servos of similar size to the 9g envelope.

 

I do reflect that one of my inflight servo failures, was with a costly, high branded servo (on elevator). I lost a tooth or more, luckily got it down. In life there are few 100% guarantees.

Had the servo in question been involved in a crash Erf?  I've always replaced the gear train of any crashed servos, where they are still available, before using it again.  It's rarely the electronics that are damaged unless you really arrive at very high speed!  If I can't get spare gear trains I'll scrap the servo.

[Erfolg]

Peter, it was a long time ago and I do not remember that clearly. Being a glider, I probably had a lot of heavy arrivals, trying to hit the spot (often just being a bit of cloth.). 

 

 

[Gunnar Borseth]

I have a very simple rule of thumb regarding servo torque. Servo torque should be equal to the weight of the finished plane. Double on rudder if its an aerobatic model. Jets, pylon racers and other may need more, but as a rule of thumb this works well for me. 

[Nigel R]

Devil's advocate, how do you know that works well?

 

It certainly doesn't apply for 3d models.

 

Fast models tend to have smaller surfaces and will require less torque.

 

 

[Gunnar Borseth]

I have never had an in-flight servo failure in 37 years of flying. That makes me think I’m not completly wrong. My models also «feels» right to me when I fly them. Very subjective and non-scientific of course. 
 

Being a rule of thumb it will not always be correct. As you point out, 3D models need more torque. At least for the more aggressive manouvers.