Everybody dreams of flying. Leonardo da Vinci sketched dozens of prototypes for flying machines based on the anatomy of birds. The Wright brothers finally worked out the details four centuries later. Yet even in this age of space shuttles, supersonic jets and ultralight airplanes, the quest to build the perfect personal flying machine still lures the world's inventors.
Nobody is pursuing the dream of solo flight with more fervor than two Americans, Paul Moller and Michael Moshier. They have very different ideas of what a personal flyer should look like, but each is equally convinced that his vision--decades in the works--is...