Question on torque

.:John:.

I am trying to figure out how powerful the motors I am using need to be.

Ok, so if something has 3 lb-ft (NOT FOOT-POUNDS) of torque, what does that mean if a propeller if two feet long? Does that mean that each foot would receive 1.5 pounds of force?

Phil Pilgrim (PhiPi)

I assume you mean the total length is two feet (i.e. a one-foot radius). So the force exerted at the tip by one blade, in the direction of rotation, would be three pounds. If you split the load between both blades, the force at the tips would be 1.5 pounds each. Had the propeller been twice as long, the force(s) would be reduced by half. In more general terms, the force F at the end of a lever arm of length L when a torque T is applied at the fulcrum (axis) is:

····F = T / L

-Phil