Determineing pounds thrust for propellers

[Curious George]

If I have a 72 inch propeller I want to use to vertically lift something, how do I determine how many rpms I need to achieve each pound of thrust. Im not sure of the pitch yet. Oh also, How effective will going from say a 2 blade prop to a 3 or 4 blade prop be in achieving more thrust?

[The_Big_K]

Originally Posted by Curious George

If I have a 72 inch propeller I want to use to vertically lift something, how do I determine how many rpms I need to achieve each pound of thrust. Im not sure of the pitch yet. Oh also, How effective will going from say a 2 blade prop to a 3 or 4 blade prop be in achieving more thrust?

An unanswered question here! Aeronautical engineers - you there?