I bought my 1st blade 3 years ago on ebay. 48 inch wooden "Progressive Pitch" with an air foil. The guy said that it could break the sound barrier so I guess that would mean that the "Tip Speed" would go between 6 to 700 MPH. He eventually taught me how to carve blades and since my pole got damaged 3 weeks ago, (see "post my photos"), I straightened the pole and decided to make a smaller and lighter mill and carved a new 46 inch blade so last night at 1:30 in the morning while we were having 40 to 50 MPH winds, the thing woke the whole house up. Instead of a mild whirling sound, it sounded much more like a Harley Davidson. Lasted about a minuit and a half. What a "Rush"! Tom, is that what you meant about "Supersonic"? Anyone else ever expirence anything like that?