I was able to get back to the lathe and machine up a good hub following the drawing above. Half way though machining the taper, I realised why I was having such difficulty with the taper changing each time I did a very slight cut. The transverse slide on the tool carriage was wobbling! It has a good .5 mm slop from side to side which made the angle I was setting (and constantly changing), variable and somewhat arbitrary. I became aware of this just in time to save this hub (attempt #3) and to machine the taper with a clamp on the cross carriage to hold it in the same place each cut. In hindsight, this is why attempt #2 was a failure.
I am assuming there might be some kind of backlash adjustment on the slide for this sloppy carriage. If not, we will have to investigate some repair or other.

I have been working on a mock up of the pickup hall sensor mount. Alternatives are to make it out of welding grade aluminium and get a proffessional to weld it for me, or to make it in steel and weld it myself. I need extra weight up front anyway.

This is purely an academic question: Could the propellor hub be made out of steel? This model will need more weight anyway, so if it would be suitable, and I was doing it again, I would do it in steel.

I'll post a picture later; the site is not cooperating at the moment.