The core of the Flightsail VII was a pod-and-boom style fuselage, the pod component of which was in the form of a thick airfoil with integral pontoons at its bottom to aid stability in water. This fuselage could be fitted with flexible, hang-glider-like wings and be flown by having it towed aloft by a speedboat. It could either be left as such and operated in this form (known as a Seasprite) or serve as "Stage I" for the Flightsail VII.
In "Stage II", the builder would add a 90-125 hp powerplant to the aircraft, mounted in a nacelle set on struts above the fuselage pod while retaining the flexible wing. In "Stage III", the flexible wing would be replaced by a conventional, strut-braced monoplane wing mounted high on the fuselage.[1]
Thomas H. Purcell, Jr., chief designer of a series of kite-gliders and other aircraft on October 27, 1961, had his maiden flight in a Rogallo wing four-boomed kite hang glider which he called FlightSail, Mk I,[2] based on the Rogallo-Ryan Aeronautical wing in its known simple format. Differently, the "Seasprite" emphasized a large amphibious fuselage. Purcell did not patent the MK I or II, but sold plans around the world. He was granted an approved patent US3614032 regarding the staged-build "Seasprite" type along with variations.