Howard Hughes' Hercules - The "Spruce Goose" - It flew only once on Nov. The Hercules is the largest flying boat ever built and has the largest wingspan of any aircraft in history. They really weren't sure it would lift off - but it did.
NASA Photo - front view banked in flight. The flew in a flight test program exploring high angle of attack flight and maneuverability. Its design explored the use of thrust vectoring to replace aircraft tail surfaces.