Junkers T 29 29 pioneered the patented Junkers "Doppelflügel" "double wing" control system - whose concept was used through to the Third Reich's Junkers Ju 87 "Stuka" dive bomber - using full span ailerons, later used for both ailerons and flaps, hinged just below the wing trailing edge and fully exposing the entire control surface cross-section to the slipstream, forming a slot between the two surfaces. In normal flight these were used as standard ailerons, but they could be lowered like flaps for landing whilst retaining the differential movement needed for lateral control. The fuselage was flat sided with rounded decking, the Junkers
Junkers marked on the J-9's landing gear wheel covers. The corrugated duralumin wing and fuselage "skin" introduced in the J-series became a trademark of Junkers aircraft built in the 1920s and '30s. Development continued during the course of World War I, including a growing (but troublesome) partnership with Fokker, as the "Junkers-Fokker Aktiengesellschaft". Several Junkers designs were licensed to Fokker during this period. The visual similarity of Junkers and Fokker aircraft during the next decade, especially after Reinhold Platz adapted some of the Junkers design concepts, but mostly crafted in wood for the Fokker designs' wing structures instead of the all-metal