Originally Posted by
hoistop
Mr. Bolkow deliberatelly beefed up the titanium hub, as no one exactly knew, how this will work. The result was, that there is a big fudge factor in rotor design, that can withstand a lot of loads, plus the design, where excessive flapping, etc. is not such a problem.
I think that BK-117 has the same rotor hub, even it is much heavier.
Yepp, but with the BK117D2 (H145) the head reached its limit. The bearings need replacements more often and the hub on top needed the screw holes drilled bigger...
Still, something designed for MTOW 2.5to still working on 3.7to is quite remarkable!
For the 3.8 to you now need the D3 with five blades ;-)