How to animate on the axis of rotation?

Thank you! Ah, yes, and when I applied transforms to the propeller on all transforms, the origin goes back to 0,0,0 so I have to snap it back to the propeller object. What I really was struggling with it to orient the propeller to a “square” angle in the worldspace and couldn’t seem to do it (it was always off by a little bit). I tried snapping to a face of a cube but it wouldn’t do it exactly. Yet another skill I need to learn. I was hoping to get a working version of Mesh Align Plus to make it easier/more precise in the latest version of 2.8.