J.Herris Pfalz Aircraft of WWI (A Centennial Perspective on Great War Airplanes 5)
The 'Missing' Fighters: Pfalz D.IX, D.X, D.XI
According to a report of the AIACC (Aeronautical Inter-Allied Control Commission), one Pfalz D.IX with a Mercedes engine of 160 hp was built. On June 28th 1918 the pilots at Adlershof were informed that a Pfalz Parasol with Sh.III engine could he inspected. In an AIACC report a Pfalz D.X with Sh.III engine is mentioned. Of the Pfalz fighters in the range D.IX-D.XV, only one was equipped with a rotary engine, the Pfalz Parasol. A video showing the nose of the Parasol has the cowling and four-blade propeller of the aircraft below. Based on these facts the Parasol can be identified as the D.X. The D.XI may have been a single-bay prototype whose twin-bay contemporary evolved into the Pfalz D.XII, similar to the relationship of the D.VII to the D.VIII. However, no evidence for this aircraft has been found in any records and it is more likely the D.XI was never built.
For many years the existence of the Pfalz D.X could not be proven. The D.X was described as powered by the 160 hp Siemens-Halske Sh.III counter-rotary engine, and was thought to be the parasol monoplane fighter whose nose is just visible in an official film shot in 1918. Little was known of this type, which not go into production. However, a photograph of the entire aircraft was finally found in Gustav Bauer's photo album. The D.X was clearly a parasol monoplane derivative of the earlier D.VII an D.VIII biplanes. Unlike the simpler Fokker E.V/D.VIII, its wing required substantial bracing, which created more drag. The competing SSW D.VI parasol monoplane used the same Siemens-Halske Sh.III engine and also had much simpler wing bracing. No technical information has survived.