A slotted plain flap fixed below the trailing edge of the wing, and rotating about its forward edge.[17] When not in use, it has more drag than other types, but is more effective at creating additional lift than a plain or split flap, while retaining their mechanical simplicity. Invented by Otto Mader at Junkers in the late 1920s, they were most often seen on the Junkers Ju 52 and the Junkers Ju 87 Stuka, though the same basic design can also be found on many modern ultralights, like the Denney Kitfox. This type of flap is sometimes referred to as an external-airfoil flap.[18]