The Bede BD-4 is a light general aviation aircraft marketed in the United States for homebuilding since 1968. It was the first home-built aircraft to be offered in kit form. It remains one of the world's most popular homebuilts with thousands of plans issued and hundreds of versions completed to date.
Based on previous work with innovative light aircraft, the BD-1 (eventually developed into the American Aviation AA-1 Yankee) and BD-2, Jim Bede designed the BD-4, the first real "kitplane" in the world. The design was based on a high-wing cantilever monoplane of conventional design, able to be fitted either with tailwheel or tricycle undercarriage, as the builder chooses. The builder was also able to choose between building a two-seat or four-seat version. Bede wrote a 165-page BD-4 builder's book, "Build Your Own Airplane", that is still available in 2012, that gives the amateur builder a good perspective on construction techniques.
The intention was to have people with little or no fabrication experience start with a set of comprehensive plans and work up to a "bolt together" operation, with complex components provided from the "factory." In order to simplify construction, there were few curved surfaces and most of the fuselage was made up of flat aluminum sheeting. The only major components with compound curves were the engine cowling and landing gear spats which were made of fiberglass. The fuselage is constructed of aluminum angle braces bolted together to form a truss frame. An innovative wing structure employed a "panel-rib" constructed in sections consisting of a rib whose upper edge was "extended" horizontally to become one section of the wing surface. The wing was progressively built up by sliding these sections together over the tubular spar and fastening them together where they met. Although the original wing design was easy to build, current BD-4B features a redesigned, more conventional, metal wing with a tubular spar bonded to honeycomb ribs.