Alan,
It would be really interesting to find the formula for the propeller efficiency for the C/L stunt to make the attempts to assess efficiency less subjective.
I'm not Alan, but coincidentally I owe him a report on a prop he made. I recommend this:
https://arc.aiaa.org/doi/abs/10.2514/6.1983-190 . You could also Google Javaprop. The figure of merit you want is probably not efficiency, but a high negative rate of change of efficiency with airspeed. A local guy went to great lengths to make an airplane that would work with a very inefficient prop.
Howard,
Cool idea! 3D printing is ideally suited for such task. I wonder what is the final strength v/s weight ratio for such spinners.
I am, however, (or used to be) Howard. Beats me, but so far it's strong enough. Because my airplanes have ballast in the nose anyhow, the only adverse effect of spinner mass is the gyroscopic moment. I was constrained by wanting: the same slope at the base as the Great Planes spinner I originally used with a 2B prop, a nose radius that was FAI legal at the time, and to accommodate a backwards prop. Now that I've been using the printed
prop spinner, I prefer it to alternatives. It paints nicely, too.