I fly RC helis. The blades are super stiff (carbon fibre/fibreglass)
They are generally designed with a pitch range of +12 to - 12 degrees.
This is for doing stunts (called 3D, flying upside down etc) but also an angle of -3 degrees will provide you with a nice zero airspeed autorotation, generally speaking. Probably need a lot less if you've got some forward airspeed or are flying into a steady breeze...
This video should explain the concept I'm talking about, it's well worth the 4 mins of your time
https://m.youtube.com/watch?v=y7XKWYdMT78