1917 Curtiss-Goupil Duck. The aircraft was originally designed by Frenchman Alexandre Goupil in 1883 but only took off the drawing board when American aviation pioneer Glenn Curtiss built a working replica.
Eshelman Flying Flounder - photo and video
Nyberg Flugan steam-powered aircraft - photos
1919 Ricci R4 concept transatlantic seaplane - photos
Caproni Ca.60 Transaereo flying boat - photo
1907 Multiplane - photo