An airplane with a pair of similar-sized wings stacked in vertical alignment is called a biplane. Its two main wing planes sit one above the other and are usually connected by struts and bracing wires.
Biplanes were especially important during aviation's pioneering years because their stacked-wing structure could provide substantial lift and strength with relatively short wingspans. The Wright Flyer, the first powered, controlled airplane to achieve sustained flight in 1903, used a biplane arrangement. Many early military and training aircraft also followed the design.
The configuration has a drawback: airflow around the two wings interferes, creating more drag than a comparable monoplane. Better materials, stronger internal structures, and faster aircraft gradually made monoplanes dominant by the late 1930s. A biplane should not be confused with a tandem-wing aircraft, whose main wings are arranged one behind the other, or a triplane, which has three vertically stacked wing planes.