a propeller essentially is a wing which rotates around an axis parallel to the flight velocity. wings operate best at a certain angle of attack, which is an angle at which wing 'sees' the flow. now, propellers rotate and tangential velocity increases from root to tip. airflow velocity is obviously constant. tangent of angle between relative velocity and prop section is air velocity / tangential velocity. we want angle between propeller section and relative velocity to constant, since tangent changes from root to tip , we need to change angle of propeller section itself.
I don't think the twist is mainly for the thrust, this will be largely due to the pitch of the propeller, (or is this what YOU mean by twist)?
There are numerous things to be taken into account in the design of a propeller.
Have a look at the sites below.
to push the air/water in a specific direction. If it had no twist it would be like slicing the air with a knife and nothing would happen (other than the plane failing to move/falling out of the sky)
in the most recent jet turbines those twist are the most efficient design made and studied through the years of aeronautical experts/engineers to create maximum thrust with less effort.
A propeller is a screw, you are "screwing" through the air like a real screw is pulled into wood.
To create thrust.
