Hey all,
For my internship I have to carry out a batch of experiments on an electric motor - propeller combination for a drone in order to determine the most efficient motor - propeller choice. At my disposal I have a 6 DoF load-cell to which I mount the motor and which can then give me readings on thrust and torque. I will be using only the readings for thrust in the vertical axis and the torque about the vertical axis. I also have at my disposal a stroboscope to measure propeller RPM. I do not have a wind tunnel and thus all my experiments will have to be static-thrust (hence, advance velocity of propeller =0).
I have read a few papers on the subject (see
here and
here) and all of them use the advance/free-stream velocity as their independent variable because they all have a wind tunnel and so can plot graphs of (something) vs. advance ratio (=distance the propeller moves forward through the fluid during one revolution/diameter of the propeller). What's worse, they define the propeller efficiency proportional to advance ratio; since in a static test the advance ratio =0, then the formula for efficiency would give me propeller efficiency=0 which is obviously not true!
My question : how do I calculate propeller efficiency for a static test? Is there a way of changing free-stream velocity in order to "emulate" a wind-tunnel (some kind of idea like moving air around the wing rather than the wing through the air?)?
If you have done such experiments or know of experiments that have been done by others, please suggest to me what to measure and to compare keeping in mind that I am searching to find the optimal
electric motor - propeller combo. So far, my idea is (excluding efficiency calculation which I hope you will be able to help me out with) to record:
- Motor model (pick 5 types)
- Propeller model (pick 5 types)
- Prop thrust --> thrust coefficient
- Prop torque --> torque coefficient
- Motor current draw
- Motor terminal voltage
- RPM of propeller
The experiment will go like this: for each motor type, test 5 prop types where for each prop type I apply different signal types to the motor (=> different duty cycles) in order to determine the best signal type for that motor-propeller combo. In total with 5 motor and prop types and, say, 5 different duty cycles it will make for a [5 X 5 X 5] thrust reading matrix of in total 125 elements. Therefore I will have to do 125 experiments.
I appreciate your help for the efficiency calculation and also for suggesting, if you can, what other data I should collect!
Best to you!
