I'm carrying out a project on Variable Pitch Propellers for UAVs and especially self-adjusting or Passive Variable Pitch Propellers that change pitch due to aerodynamic forces and Pitching Moments.
At the moment I'm working on a single element (sectional airfoil) using blade element theory for three different stages of the aircraft: Take-off (with a given high RPM,e.g 2000), Cruise (medium RPM,e.g 1000) and landing (low RPM e.g 500) and corresponding free stream velocities 0 , 80, 20 m/s respectively.
However while I'm trying to calculate first Lift and Drag and then Pitching Moments, I realized that there are unknown factors needed for the calculations such as lift and drag coefficients as well as Angle of Attack on that sectional blade element.
The purpose is to use at first a symmetric aerofoil with no camber and I was wondering whether I have to use a commercial aerofoil such as NACA and if so, how to get the Cl and Cd from this aerofoil.
My questions are:
How to calculate the angle of attack or pitch angle while I know their subtraction?
Do I need to give some values for a new parameter that will help to find these calculations or RPM, Vinf, and r of the propeller is enough?
What about the chord length; do I need to give a random value there?
I am sorry if some of the questions are silly but I'm coming from a different background and I'm fresh in the aerodynamic field.