I figured it out.
go out and try to see how much pull you are getting roughly with what you have.
If it is less then ~ 2 lbs then you can use a kitchen ingredient weight machine. Or if it more, some other type of small spring scale. They are pretty accurate or at least repeatable so they will show the difference between wing angles. You could just mount it on the front of the pylon somehow, maybe just hold it there, and have the rope pull on what is normally the top of the scale to compress it.