The Pfalz D.VII was one of a pair of Pfalz biplane fighters powered by the same Seimens-Halske engine, and entered service in small numbers during 1918.
In 1917 Pfalz produced their first purpose built triplane, the Pfalz Dr.I. This had an elegantly streamlined fuselage, and a very impressive rate of climb, but it used a new engine, the 160hp Seimens-Halske Sh.III counter-rotary engine. Normal rotary engines had a fixed crankshaft which the crankcase and cylinders rotated around. The propeller was normally attached to the crankcase and thus rotated at the same speed as the engine. However to get most power out of the engine it had to rotate at a higher speed than the most efficient speed for the propellers. On the Sh.III the cylinders and crankcase rotated at 1,800rpm in one direction, and were connected by bevel gears to the crankshaft, which rotated at 900rpm in the opposite direction, thus reducing the speed of the cylinders and crankcase to 900rpm. As a result the overall speed of the propeller was reduced to 900rpm, where the propeller was more effective. As a result aircraft powered by the Sh.III such as the Pfalz Dr.I had a high rate of climb. However the slower speed of rotation meant that the flow of cooling air was also reduced, so the Sh.III was prone to overheating.
The Dr.I was ready for evaluation by the start of 1918, but its triplane configuration increased drag and interference between the wings, and it was slower and less manoeuvrable than the Fokker triplane and also slower than Allied fighters.
The problems with the Dr.I had been obvious during 1917, and Pfalz responded with two related biplane designs, the D.VII and D.VIII. Both used the Sh.III engine and a fuselage that was very similar to that of the Dr.I. By this point Pfalz had a successful biplane in production, the sesquiplane D.III, but they chose to develop more standard biplane wings for the two new fighters. On both aircraft the upper wing had a span of 7.52m and the lower wing a span of 6.98m, while both had a chord of 1.30m. The D.VII was a single bay biplane, while the D.VIII used a stronger but heavier twin bay wing.
The D.VII carried unbalanced ailerons on the upper wing. On the initial prototype the rudder was balanced, the elevators unbalanced. It used a massive four bladed propeller which could use the full power of the Sh.III engine. However during its type tests at Adlershof in February 1918 it was tested with a two bladed propeller.
The initial prototype was unarmed. However photographs exist showing later prototypes carrying two machine guns and with balanced ailerons.
The D.VII carried out its flight trials in December 1917. In January 1918 it reached 6,000m in 13.7 minutes, demonstrating the same impressive rate of climb as the Dr.I.
Pfalz entered at least three designs in the First Fighter Competition, held at Adlershof in February. The D.VII and D.VIII were joined by the earlier Pfalz D.VI, which had similar sesquiplane wings to the D.III and was powered by an Oberursel rotary engine. Two winners emerged from the trials – the Fokker D.VII and the Pfalz D.VII. The D.VI was eliminated because it was slower than the two newer designs, while the D.VIII was unable to take part because of problems with its engine.
However Idfleig, the German department in charge of aircraft design, decided to carry out further tests comparing the two Pfalz designs, with the winner decided by static load tests. The D.VIII performed best in this and so was ordered into production.
Work on the Pfalz D.VII continued during 1918, in the hope that the lower weight and drag of the single bay wing would give it better performance. It must have entered production, as fifteen were found in storage at the end of the war, but it probably never entered front line service.
Engine: Siemens-Halske Sh.III
Span: 7.52m (upper), 6.98m (lower)
Empty weight: 520kg
Loaded weight: 715kg
Max speed: 190km/ hr
Climb Rate: 1.8min to 1,000m, 13.8min to 5,000m
Armament: Two machine guns