Knife Edge Pitching
 

Mike first of all I welcome you to RCU. I am a great admirer of you and always enjoyed your articles at horizon hobby website about pattern & 3D.

Mike I am using JR PCM 9X with a pattern aircraft.This aircraft has very slight pitching in Knife edge towards the canopy and also slight roll pitching which I correct when doing long Knife Edge passes.If I use Mixing functions to correct should I program this mixing to all time ON and what are the effects on other manoeuvres which do not require knife edge or activate it only during knife edge only?

I also have a second pattern plane which is Hanno Pretner`s Magic.It has the most solid knife edge I have ever seen. It does perfect hands off knife edge when going from right to left but when I do knife edge from left to right it pitches towards belly moderately.Based on your experiance what could be the cause of this non-symetrical behavior?I ve corrected this by using mixing but I just want to know what is causing so.

thanks

RE: Knife Edge Pitching
 

For mixes to correct for pitch or roll couple, I leave them on all of the time. My theory is that a model couples all of the time so some mix is needed. Reality is that they dont couple to the same degree all the time, its effected by attitude, speed, CG, etc, however its normally close enough not to create a problem. If a model needs a mix that is so extreme that it causes significant problems in other attituds the model probably has bigger problems.

I havent seen a Magic for a while. Never had one, but I always loved the Curare which was Prettner's model prior. Normally when a pattern model shows asymmetric pitch couple I look for a warp in the stab, or an elevator set lower than the other.
When you say going from left to right I dont know which side its on, so lets assume its a right roll into KE so top rudder is left. If its pitching toward the belly, look at the right hand elevator and see if its low (or that stab half warped so the TE is low toward the tip). You might try adjusting the right elevator neutral up a little and see what you get. Its alway a trade off though, so it will start to effect loop tracking as well. If its the other side that has the pitch, do thesame to the left elevator. Experiment and see what happens.

Mike