mustangman177

By having too much rudder surface, can this in any way create a problem with the knife-edge performance of a airplane ?

I just completed my uproar 60, and from the advice of a fellow modeler, they suggested lengthening the rudder by an additional 2" to improve the knife edge performance of the plane. Upon flying the airplane I did not see any improvements.the airplane would not hold a knife edge. One thing I did notice is that the standard Futaba 138 servo does not quite give enough power to move the rudder under pressure. Should I substitute the servo with a more powerful one to handle the additional stresses put on it by the additional rudder size therebygiving the knifedge performance ?

Thanks in advance. Cary

Joss Stick

My Feedback: (1)

Rudders are like fun and money. You can't have too much of any of them. The more surface you have, the more authority you have. It's quite possible that the model wouldn't hold knife edge because the servo wasn't sufficient to hold it or even give it full throw. Replace the servo with a servo that has more torque and speed.

I'm not sure what the torque is on a 138 but I'm guessing around 40oz + or -. The speed may be around .25 or so. Try something in the 60oz range with a speed of .15 or so.

You might wonder what the speed as to do with it. I did too until I put a faster servo on a rudder. There is a time delay, although very small between the time you pull it into knife edge and actually apply rudder to hold it. If you have a slow servo, then the plane has started to drop before the rudder gets to full deflection. A faster servo will get it there ... well faster.

This might sound like a bunch of bull to some of the experts here, but if you think about it, it makes sense.