We just had an incident (Friend) that involved a GSC 2 blade with some VW derived engine in a direct drive situation. The blades were trimmed short to stay within 80% mach 1 tip speed at around 3600, full throttle RPM. Unfortunately the blades separated form the hub after about 4 hours flying.
Fortunately both blades left the engine simultaneously. The motor mount fractured at one point but three points did not fail. The engine stayed with the airplane revving way high with no load until ignition was killed.
The pilot (300+hour student) was able to return to the field and dead stick land without damage to the Kitfox 1. As I understand it when the engine separates from the airplane the resulting imbalance will make the airplane hopelessly uncontrollable. This incident has pretty much killed my interest in direct drive VW engines along with GSC Propellors. Pobably there is an equation out there that could have told these experimenters that this was going to be risky business. Perhaps the inertia value was exceeded?
Nick's comments caught my attention because "shedding blades" is such a harmless sounding expression.