wrote in message
...

The simplest way to make a helicopter go faster is to simply increase
the rotor rpm. That way, the differential of lift as the helicopter
goes faster and faster is less significant than a slower turning
rotor. That is, at 400 mph tip speed and at 100 mph forward velocity,
you have a 200 mph differential or 50% of the tip speed. At 1000 mph
tip speed, you still have a 200 mph differential speed but its only
20% of the tip speed.

So in this example, a helicopter with a 1000 mph tip speed could go
forward at 250 mph before hitting 50% differential.

I'm not sure what the actual tip speed is, but I know that a lot of
modern fully articulated systems run at tip speeds just under the
speed of sound in order to significantly reduce the chances of ground
resonance.

Dennis.

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.