Science Buddies: "Ask an Expert"

Hello,

I am doing the experiment on how chord length effects propeller efficiency. As part of the experiment i am placing a resistor across the two motor terminals and then attaching the alligator clips to the two two terminals to take my measurements. My question is why is the resistor run in parallel and not in series?

Thank you for your time.

drizzt04240 - There is a vast amount of literature on propeller (or wing) chord design and related efficiency. It sounds like you are trying to measure current flow through the motor, and you are correct, the way to do that is to measure the voltage drop across the sampling resistor which must be placed in series with the motor and power source. There are a lot of variables at work here, and while it is easy to measure power consumed by the electric motor driving the propeller, or different propellers, how do you measure thrust developed by the various propellers being evaluated?

Rick Marz