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Test pilot Bill Fell was zooming southward, approaching Sikorsky’s [LMT] runway outside West Palm Beach, Florida, at about 190 knots when he decided that was as fast as the S-97 Raider should fly for spectators below. The aircraft was vibrating in a way that felt different, owing to a new piece of vibration-control software loaded onto the aircraft in an ongoing search to push the compound helicopter toward 220 knots—a speed that would likely put the Raider, or a Raider…
