The Pfalz Dr.I was a triplane fighter with a very impressive rate of climb, but it used an unreliable engine and by the time the first evaluation versions were ready in 1918 was slower than contemporary fighters, so never entered production.
After the appearance of the Sopwith Triplane Germany responded with a series of triplane designs of its own, most famously the Fokker Triplane used by the Red Baron. Pfalz also attempted to produce a triplane fighter, starting in 1917 with a conversion of an existing Pfalz D.III. This aircraft proved to be slower than the standard D.III, and the idea was abandoned.
Pfalz had more success with their first purpose-built biplane, the Pfalz Dr.I. This was an attractive aircraft, powered by an experimental 160hp Seimens-Halske Sh.III counter-rotary engine. Its fuselage had a circular cross section, faired smoothly into the engine cowling. The bottom wing was faired into the bottom of the fuselage, the middle wing was just below the top of the fuselage and the upper wind was held up on streamlined interplane struts, with a single strut between the lower and middle wings, V shaped outer struts between the top and middle wings and ‘n’ shaped struts between the upper fuselage and centre section of the upper wing. It had a larger than usual propeller, to take advantage of the slower rotation speed provided by the Sh.III engine.
The upper wing was the largest, with the biggest chord (1.1m) and carried the controls. The middle wing had the smallest chord at only 50cm. The wings were staggered, with the leading edges almost in line (although the middle wing was slightly in front of the line), but because of the different chords the trailing edges were uneven.
In contrast the Fokker Dr.I had a rather more elegant wing layout, with all three wings having the same 1m chord. As a result they were neatly staggered from top to bottom. They were also shorter than on the Pfalz aircraft, with the tip wing having a span of 7.19m (compared to 8.55m on the Pfalz), dropping to 5.725m on the lower wing (compared to 7.92m). and the gap between the wings was bigger. Total wing area was similar, with both having around 17 sq. m of wings, but the Fokker layout was more effective, with the larger gap between the wings reducing the interference in airflow between the wings.
The Pfalz Dr.I performed very well in trials in August 1917, reaching 5,000m in 11.5 minutes, making it the fastest climbing German aircraft of the First World War. In comparison the Albatros D.V, the main fighter at the time, needed 35 minutes to reach the same height. As a result an evaluation batch of 10 aircraft was ordered.
However the new Sh.III engine was an experimental design, and was proving unreliable. In a normal rotary engine the crankshaft was stationary while the crankcase and cylinders rotated around it. The propeller was normally attached directly to the crankcase, so rotated at the same speed as the engine. This normally meant that the propeller was rotating faster than its most efficient speed. On the Sh.III the cylinders and crankcase rotated in 1,800 rpm in one direction, while the crankshaft, which was connected to it via bevel gears rotated in the opposite direction at 900rpm. This reduced the overall speed of rotation of the crankcase and cylinders, and thus the propeller, to 900rpm, where it was much more efficient (thus the very high rate of climb). However the slower speed of the cylinders reduced the cooling air flow, so the Sh.III was prone to over heading.
As a result the ten evaluation examples of the Dr.I didn’t reach the front until April 1918. By this point it was slower than contemporary Allied fighters, and was also less manoeuvrable than the Fokker Dr.I triplane. As a result it never entered production.
In an attempt to produce a triplane with more reliable engines Pfalz also produced the Pfalz Dr.II, powered by a 110hp Oberursel Ur.II and the Pfalz Dr.IIa, which used the 110hp Seimens-Halske Sh.I (a lower powered but more reliable version of the Sh.III). These were smaller aircraft than the Dr.I, but the lower powered engines reduced their performance and neither entered production.
The basic design of the Dr.I was also evolved into two biplanes, the Pfalz D.VII and Pfalz D.VIII, both of which did enter production although in small numbers.
Engine: Siemens & Halske Sh.III
Upper wing span: 8.55mm
Upper wing chord: 1.10m
Middle wing span: 8.10m
Middle wing chord: 0.5m
Lower wing span: 7.82m
Lower wing chord: 0.70m
Gap upper: 0.78m
Gap lower: 0.75m
Empty weight: 510kg
Loaded weight: 705kg
Climb Rate: 1.5min to 1,000m; 11.5min to 5,000m
Armament: Two fixed forward firing machine guns.