When the French Nieuport 17 fighter, reached the front lines in March 1916, it proved superior over existing German fighters. Soon captured examples were whisked away to German aircraft manufactures with the request to produce an improved craft.
|D.II undergoing stress testing|
Development work on the D series aircraft continued with the introduction of the new Siemens-Halske Sh.III engine, which developed 160 hp. The new engine was fitted to a series of original prototype designs from Siemens, the D.II, D.IIa and D.IIb. These featured a much rounder and wider front fuselage to hold the larger engine, leading to a rather stubby-looking aircraft which pilots later referred to as the flying beer barrel. Flight tests started in June 1917, and while the aircraft did not have a very high top speed, they showed outstanding rates of climb. The only serious concern was the extremely long landing gear needed to keep the huge 2-bladed prop clear of the ground.Three more prototypes were ordered, two D.IIc with longer span wings and one D.IIe, with the original sized wings. After completion in October 1917, the design proved promising and in December an order for twenty D.IIc was placed with a smaller 4-bladed propeller, that allowed for shorter landing gear legs. A second order of 30 aircraft in February 1918.
|First production D.III|
However, after only seven to 10 hours of service, however, the Sh.III engines started showing serious problems with overheating and piston seizure.
In late May 1918, the D.III was withdrawn from service for upgrading and Jasta II replaced its D.IIIs with the older Fokker Dr.I.
In the words of the Jasta.II commander, Hptm Rudolf Berthold, "The Siemens fighter must be made available again for front-line use as quickly as possible for, after elimination of the present faults, it is likely to become one of our most useful fighter aircraft.",
The engine problem was later traced to the Voltol mineral oil that was used to replace the now-scarce castor oil.
Furthermore, the close-fitting engine cowling provided inadequate cooling to the engine.
All remaining D.III aircraft were returned to the Siemens-Schuckert factory, where they were retrofitted with new Sh.IIIa engines and cutaway cowlings that provided improved airflow. A further 30 new production D.IIIs incorporated these modifications. Total production amounted to about 80 aircraft.
A D.III wing redesign by Heinrich Kann, a new young member of the design team, resulted in three prototypes being built early in 1918.
The new aircraft, which would be designated D.IV, was faster than the D III (although only by 6 mph). Its main advantage was its time of climb to 16,400 feet or above, where it overtook the D III and it could reach 19,680 feet nearly five minutes quicker than the D III.
A production order was placed in March 1918, and eventually 280 machines were ordered (only 123 were completed). The first aircraft went to operation units in August, starting with Jasta 14 and Jasta 22. Only about fifty D IVs reached operational units before the end of the war.
The D IV was popular with the pilots. Staffelfuhrer Lt Lenz, the first pilot at Jasta 22 to receive the new aircraft wrote a glowing report on it in October 1918. He described it as the best single seater at the front, with superior climbing ability and maneuverability was good. It was especially useful above 4,000 meters, where it out-flew the Fokker D VII and he suggested using the Fokker aircraft at lower levels. He did acknowledge that engine overheating was still a problem and recommended that it should be used as an interceptor rather than on patrols. He also thought it was best used by more advanced pilots.
Production of the D.IV continued after the cease-fire, with many being sold to Switzerland where they operated into the late 1920s.
References for this blog may come from Wikipedia, WW1 Aviation.com, Warplanes of the First World War, The Complete Book of Fighters, The British Fighter since 1912, theaerodrome.com and others.