Originally Posted by
noneofyourbusiness
Rigid rotor for noise control? We know that people who build ultralight gyrocopters want flexible rotor blades for "ride comfort". If the blades are too stiff, these enthusiasts complain about the flight comfort. If the vibration issue is overcome, do rigid rotors work the air less, and thereby substantially reduce noise? Or not? We know Boeing is pursuing a single main rotor design as a replacement for the Apache, with a pusher propeller. Bell is pursuing a single main rotor design for FARA, which we do not know if it will have a pusher prop. Does the Raider for a special forces variant add a shroud around the pusher prop for further noise reduction? A single main rotor should be quieter than dual counter-rotating rotors.
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?