Henri Mignet was never quite able to master an airplane with three-axis controls, and built at least seven flawed attempts at simplified controlled flight. His seminal try, the HM-8 Pou de Ciel (literally, Louse of the Sky, or more familiarly, Flying Flea) became first a matter of celebration for amateur aviators and then a cause of scandal, being banned in Britain following a series of fatal crashes. The “formula”, as proponents called Mignet’s tandem wing configuration, was sorted out after wind tunnel tests in England and America uncovered the flaw that caused the craft to pitch down in an unrecoverable dive. (For a well-illustrated history of Mignet’s design, see Henri Mignet and his Flying Fleas by Ken Ellis and Geoff Jones. Although out of print, used copies are available at Alibris and Abe Books, at higher prices than your editor paid for his new copy 25 years ago.) Later models of the formula have proven to be safe, stable fliers, …