The fully articulated hub design is susceptable to ground resonance
when landing. By increasing the rotor speed to just under the speed
of sound, that is, so nothing goes faster than the speed of sound even
at max forward velocity, the risk of ground resonance when landing is
significantly reduced. There are other advantages to speeding up a
fully articulated hub, but not flying apart when you land is a big
one.

Dennis.


"mm" wrote:

Real helicopters use a tip speed on the order of 700-800 ft/sec (475-545
mph), well below the speed of sound. This has nothing to do with ground
resonance. It is driven by blade loads, vibration & stability, and noise at
high speeds.



Dennis Hawkins
n4mwd AT amsat DOT org (humans know what to do)

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