When I was in Vietnam, we routinely had to asked the Chinooks to slow down!
rif raf,
I was using different hinge materials at that time. I was never sure if it was the design or poor material choices. I later disovered what the problem was...it was my choice of airfoils. I was using an 8H12 airfoil blades that has an up reflex to it. When the blade start to advance, the up relex made the blade pitch up uncontrollable. Over time, I had changed the head design several times but still had the pitch up problem. The only common factor was the 8H12 airfoil. Then I changed the blade airfoil to a profile with a slight down relex...it now works better. The model still pitches up but not to where it's uncontrollable.
Now I'm working on the control mixing. At this scale, any change is difficult. To begin the work on the controls I'm using the MC-4 tandem helicopter's lay-out as a refence. It's the simplest control system that I can find.