I've just got going a 23cc Petrol Kalt Helicopter and I am using flat bottom blades (non-Symmetrical).
When ever the collective is in the negitive pitch range it seems that with increasing head speed, the pitch becomes even greater negitive as if it is feeding back.
So much so that if I idle up in slightly negitive pitch, the collective pitch servo does not have enough grunt to bring it positive??
If I start with slightly positive pitch, then it is fine and i have complete control over the collective??

Any ideas welcome!!!!