If I remember the story properly, in summary:

The two as opposed to three blades was recommended by Ivo due to their belief of a poor harmonic situation happening from the 3:1 gearbox in conjunction with the two cylinder engine. The ultralight would need three blades to efficiently use the hp of the engine, where the medium can handle it with only two.

Therefore Ivo says use a two blade medium, with a 582 and a 3:1 gearbox.


(Not to mention it costs more... )