SSW D.III-D.IV (Windsock Datafile 29) (Repost)

The Siemens-Schuckert Werke (SSW), the giant German electrical combine, became involved with aeronautics in 1907, but it was not until mid-1916 that the firm began large-scale aircraft production, embarking on a journey that would lead to what many consider to be the finest fighters of 1918: the SSW Dill and D.IV biplanes. It should not escape the attention of the reader however, that their commendable performance rested primarily upon the superb 160hp Siemens-Halske Sh.lll rotary engine that in an 'over-compressed' version could produce up to 22()hp at higher altitude than any comparable German or Allied engine.
The beginning
In June 1916. German aircraft manufacturers were requested by the Inspektion der Ftiegertruppen (Idflieg — Inspectorate of Aviation Troops) to submit proposals (or a sequiplane fighter patterned on the Nieuport 11 fighter.1'' Already involved in building giant bombers but eager to expand its aircraft activity, SSW opted to reduce development and start-up time by building a direct copy of the Nieuport 11. known as the SSW D.I. Upon approval of the D.I prototype in October. SSW obtained a contract for 150 (later increased to 250) aircraft on November 18 1916. Production was cancelled in June 1917 after only 65 aircraft had been delivered because the type had been superseded by superior Allied and German fighters. The one bright spot was the exceptional climb rate of 5000 metres ( 16,404 ft) in 20.5 minutes achieved by the modified D.lb 1231/17 fighter on July 24 1917. Such stellar performance was made possible by the over-compressed ( 140hp rating) version of the nine-cylinder. HOhp Sh.l rotary engine that, like all Siemens-Halske rotary engines, was a counter-rotary; the propeller and cylinders rotated (at 900 rpm) in opposite direction to the crankshaft. The advantages were increased airscrew and cooling efficiency, better fuel economy, reduced drag, lower weight and near elimination of gyroscopic effect.