Ok Credence thank you for your vary detail response, I understand now. Is there some formula(s) that I can use to design my airfoil (for collective pitch), based on RPM, weight or any other factors I should be concerned with. I have to be honest I have not done much searching the net with the new info you’ve given me, but both you and Tippy seem vary knowledgeable so I was hopping I could get one last little nudge.

Thank you, you’ve been vary helpful