For those who can't read this, the highlights IMO are that they got solid 24" flywheels up to 3,850rpm which corresponds to 15,600 pounds/inch centrifugal force, rim speed 395 ft/second. Flywheels consisting of two semicircles bolted together got to half the rpm's and 3,750 pounds/in of force on rim. Basically joints are a no-no. A spoked (bicycle style) flywheel hit 4,050 rpm.
EDIT: the above erroneously read 395 ft/minute. Fixed it to read ft/second.