Sounds like you don't have enough servo to handle the remaining 50%. If you can note the rudder angle on the ground and then in the air, you should see if the servo is strong enough to hold it.
Originally posted by Joe B.
Applied about 50% rudder to fly knife edge, applied remaining 50% and no noticable increase in angle. Is this my plane, wrong prop choice, etc? Rudder servo is a Tower TS-67 (?) with around 90oz/in at 6.0v. Plane is a Sig 1/4 scale Cap. Is there some 'trick' to getting it to go correctly? The only reason I'm not immediately suspecting the rudder is that I had a smaller cap that I let my instructor preflight a while ago and he did a knife edge loop right off the bat and I was never able to do so. Perhaps I'm not getting the sticks right, the entry, etc? Any help appreciated.