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|D.IV replica displayed at Luftwaffenmuseum der Bundeswehr|
|Number built||123 (by the end of the war)|
The Siemens-Schuckert D.IV was a late-World War I fighter aircraft from Siemens-Schuckert (SSW). Considered by many[who?] to be the best fighter to see action during the war, it reached service too late and was produced in too few numbers to have any effect on the war effort.
Siemens-Schuckert's first production fighter aircraft was the Siemens-Schuckert D.I, which was based closely on the French Nieuport 17. Apart from the use of the Siemens-Halske Sh.I, a geared rotary engine in which the cylinders and the propeller rotated in opposite directions, the D.I was in fact a fairly literal copy of the Nieuport. By the time production D.Is appeared in 1917, the design was no longer competitive and after 95 had been built, production was cancelled, the type serving mainly as advanced trainers.
Development work on the Siemens-Halske Sh.I culminated in the Siemens-Halske Sh.III, which developed 160 PS (120 kW). The new engine was fitted to a series of original prototype designs from the SSW works, 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's with shorter and longer span wings, and the D.IIe with the original sized wings. After completion in October 1917 the design proved to be worth producing, and in December an order for twenty long-span D.IIc's was placed with a smaller 4-bladed propeller that allowed for shorter landing gear legs. These aircraft, now known as D.III, started delivery in January and were followed by an order for thirty more in February.
All fifty were delivered to front-line units in May, where they proved popular. However, after only 10 hours of service the engines started showing serious problems, overheating and eventually seizing. Although Siemens blamed the problem on the Voltol-based oil that was used to replace scarce castor oil used to lubricate the engine, the planes were withdrawn from service and replaced by Fokker D.VII's. When they were removed Rudolf Berthold, commander of JG.II, noted that he felt the Siemens fighter be made available again for front-line use as quickly as possible for, after elimination of the present faults, it is likely to be become one of our most useful fighter aircraft.
A version of the Sh.III passed a full 40-hour endurance test in June and the planes were cleared to return to service in July. In the meantime they had been upgraded with the addition of a new rudder, balanced ailerons and a cut-away cowling for better cooling. Some sources also claim that the original engines were replaced with the improved 200 PS (150 kW) Sh.IIIa engines. An additional thirty new aircraft with these features were also built and all eighty of the improved design soon entered service in home defense units where their high climb rates made them excellent interceptors.
Meanwhile, the short-span D.IIc prototype had been further refined, and with narrower-chord upper and lower wings, using the Göttingen 180 airfoil, each of 1.00 meter dimension from leading to trailing edge, the performance improved noticeably, both in top speed and in climb rate. An order for this model, now known as the D.IV, was placed in March 1918, and followed with several additional orders as the qualities of the design became obvious. The planes started reaching operational units in August, but of the 280 ordered only 123 were completed by the end of the war, about half of those reaching operational units. In October 1918 it was officially described as superior by far to all single-seaters in use.
Although the short landing gear and limited prop clearance led to tricky landing, the plane was otherwise easy to fly. It had a very short take-off run, and at heights above 4,000 m (13,100 ft) was faster and more manoeuvrable than the Fokker D.VII. Its most notable feature was its phenomenal rate of climb and extremely high service ceiling—it could reach 6,000 m (19,700 ft) in less than 14½ minutes. In 36 minutes it could reach 8,100 m (26,600 ft), about 1,200 m (3,900 ft) higher than the Fokker's maximum altitude.
Production of the D.IV continued after the cease-fire, with many being sold to Switzerland where they operated into the late 1920s. With the signing of the Treaty of Versailles all aircraft production in Germany was outlawed, and the aircraft portion of SSW disappeared. Siemens-Halske remained, later reorganizing into Bramo.
In May/June 1918 a sesquiplane, two bay derivative, the D.V participated in the Adlershof trials. Three were built.
Data from German Aircraft of the First World War 
- Crew: 1
- Length: 5.7m (18 ft 8½ in)
- Wingspan: 8.35 m (27 ft 7⅞ in)
- Height: 2.72 m (8 ft 11 in)
- Wing area: 15.1 m² (163 ft²)
- Airfoil: Göttingen 180, of 1.00 meter chord (both wings)
- Empty weight: 540 kg (1,190 lb)
- Loaded weight: 735 kg (1,620 lb)
- Powerplant: 1 × Siemens-Halske Sh.III 11-cylinder geared rotary engine, 118 kW (160 PS)
- Maximum speed: 190 km/h (103 knots, 119 mph)
- Service ceiling: 8,000 m (26,200 ft)
- Wing loading: 48.7 kg/m² (9.94 lb/ft²)
- Power/mass: 0.16 kW/kg (0.099 PS/lb)
- Endurance: 2 hours
- Climb to 1,000 m (3,300 ft): 1.9 min
- Climb to 6,000 m (19,700 ft): 15.5 min
- Gray & Thetford, p.563
- Gray and Thetford 1962, p.216-217.
- Gray, Peter, and Thetford, Owen. German Aircraft of the First World War. London:Putnam, 1962.
- Munson, Kenneth. Aircraft of World War I. London: Ian Allen, 1967. ISBN 0-7110-0356-4.
- Green, William; Swanborough, Gordon (1994). The Complete Book of Fighters. Godalming, UK: Salamander Books. ISBN 1-85833-777-1.
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