Arado SD II

Larger and substantially heavier than the preceding SD I, and utilising a more conventional unequal-span biplane wing cellule with N-type interplane struts and flying wires, the SD II was designed by Ing Walter Rethel and a sole prototype was completed in 1929 as a competitor for the HD 37, a second airframe becoming the SD III. Of mixed construction, with fabric-covered wooden wings and a welded steel-tube fuselage, the SD II was powered by a geared Siemens und Halske-built Jupiter VI nine-cylinder radial, which, with a maximum rating of 530hp, drove a large-diameter, slow-running three-bladed propeller requiring a high angle of attack on the ground. Armament remained two 7.9mm synchronised 08/15 machine guns. The SD II demonstrated rather difficult flying characteristics, but, together with the SD III, provided a basis for the series-production Ar 64.