one possibility (at least on my homemade dualhelix) is to have "blowout, ie spring loaded flaps) where the curved blade meets the shaft on some portion(s) of the unit.
if it gets to spinnin' too fast the flaps will spill part of the wind
also
in the case of my helix, there seems to be some tendancy to reach a velocity, in high winds, where the oft mentioned drag factor begins to somewhat limit further increase speed
AND
then build the tower/bearings STRONG eneough to handle 'er!
thanx
spinner
