Originally Posted by
IFMU
A shroud is not needed for noise control. They have a clutch. I can tell you the X2 main rotor is orders of magnitude quieter than any single rotor helicopter that I've heard. I don't believe this is due to stiffness, just awesome aerodynamics. Regarding vibration, the X2 vibes were lower than a UH60 when it was cruising at 250 kts. We got it there using conventional balancing methods cleaned up with AVC.
Ultralight gyros? How is that relevant?
Thanks for your input. A shroud would be useful for when the prop is engaged. It is difficult to believe Sikorsky would sell any noisy helicopters if all they had to do was change the aerodynamics of the blades.