The Pfalz D.XII was the last Pfalz fighter to enter production, and was similar in appearance to the more successful Fokker D.VII, but as with earlier Pfalz aircraft appeared later than its Fokker rival and was less effective.
The D.XII evolved from the earlier Pfalz D.IIIa. The D.IIIa used a sesquiplane wing layout (with a much smaller lower wing), inspired by the Nieuport fighters that had ended the dominance of the Fokker biplanes. However by 1917 that layout had reached its limits and stronger wings were needed for the faster aircraft then being developed. Idflieg, the German department responsible for aircraft design, sent a report on the successful French SPAD S.VII, which used a form of twin bay biplane wings, with upper and lower wings of the same size.
Pfalz decided to test out the SPAD wings on a D.IIIa. The wing used on this prototype differed from the SPAD design in one way – on the SPAD aircraft there were two sets of struts on each wing, but the wings were braced as if they were single bay wings, with the bracing wires going all the way from the fuselage to the outer strut, crossing as they passed the first strut. On the Pfalz design each bay was braced independently, making it a true twin bay wing.
The modified D.IIIa was successful enough to convince Pfalz to use a development of the same wing on a new fighter, the D.XII. Like the modified D.IIIa this was a true twin bay biplane, with bracing wires for each bay, but it used N struts instead of the simple struts of the D.IIIa and SPAD. It was powered by the 160hp Mercedes D.IIIa, which was cooled by a nose radiator.
The new fighter was ordered into production in March 1918, but it was delayed by problems with the radiator. This used vertical tubes instead of the honeycomb configuration of most nose radiators. These had performed fine in cooler weather, but proved problematic in the warmer spring weather and had to be redesigned. As a result the first production aircraft didn’t reach the front until June 1918.
Earlier in the war the Pfalz monoplanes had entered service a few months after the more famous Fokker monoplanes, by which time the Fokker aircraft had already gained a good reputation and the Pfalz aircraft were considered to be inferior. The same now happened to the D.XII. The similar looking Fokker D.VII, powered by the same engine behind a nose radiator had entered service in March 1918, and was gaining a very impressive reputation. As a result the Pfalz D.XII was an unwelcome arrival at most fighter units. Only five were reported at the front on 30 June 1918, although this had risen to 168 on 31 August (compared to 828 Fokker D.VIIs on the same date).
In flight the Pfalz aircraft actually had the same rate of climb and speed as the Fokker D.VII and was slightly quicker in the dive. However it was less manoeuvrable which made it less popular with its pilots. The key difference was the wing section of the two aircraft. The Pfalz used the standard wing layout seen on most First World War fighters – a narrow wing with a sharp leading edge. In contrast the Fokker D.VII had a thicker wing with a blunt rounded leading edge. This meant that the Fokker gave plenty of warning in the form of buffeting before stalling, while the Pfalz stalled suddenly with little warning. As a result pilots of the Fokker aircraft were more willing to push their aircraft to its limits, knowing that they would get plenty of warning before stalling, while pilots of the Pfalz (and other aircraft with similar thin wings) had to be more careful. The Fokker also had a single bay wing with no external bracing wires, reducing drag and making it easier to maintain.
Pfalz were given 84 of the more powerful BMW D.IIIa engine between July and October 1918 for use in the D.XII. However no photographs showing the BMW engine in an operational D.XII. Tests were also carried out with a 195hp Benz Bz.IIIbou V-9 engine and 195hp Mana.IIIv engine. The Mana engine showed promise but the war ended before it entered mass production.
The D.XII was a good replacement for the many older aircraft still in use when it appeared in the summer of 1918, including the older Pfalz D.III and D.IIIa. However it was inferior to the Fokker D.VII. Even so around 800 D.XIIs were built. Reports from both German pilots flying it in action and Allied pilots flying it after the war agreed that it was disappointing compared to the Fokker aircraft.
Engine: Mercedes D.IIIa
Span: 9m upper. 7.9m lower
Empty weight: 712kg
Loaded weight: 892kg
Max speed: 180km/ hr
Climb Rate: 3.5min to 1,000m; 25.1min to 4,000m
Armament: Two machine guns