The Siemens-Schuckert Werke S.S.W. D IV was the final Siemens fighter to see active service during the First World War and was a development of the earlier S.S.W. D II and S.S.W. D III but with modified wings.
The S.S.W. D II had been designed specifically for use with the Siemens-Halske Sh III geared rotary engine. This was an unusual engine in which the crankshaft rotated in the opposite direction to the cylinders. Both rotated at 900rpm, giving the overall engine a speed of 1,800rpm, but without some of the spin problems that came with a normal rotary engine. The first two D II prototypes were ready early in 1916, but the engines didn't appear until June. When they did the results were impressive, and three new prototypes were ordered.
Amongst them were the D IIc kurz, with a wingspan of 27ft 10.75in and a wing area of 209sq ft and the D IIc lang, which had a wingspan of 29ft 6 3/8in but an upper wing with a reduced chord and a total wing area of 195sq ft.
In December 1917 the D IIc kurz was ordered into production as the S.S.W. D III. At the same time Siemens were ordered to begin development of the S.S.W. D IV, which would be based on the D IIc lang.
The D IIc lang (7551/17) was redesignated as the D IIIc lang in October 1917. Late in the year it was given a new cowl and ailerons on the lower wing, flying in that configuration on 20 December 1917. In that configuration it took part in the first D type fighter competition early in 1918, but crashed in January 1918. After this crash the aircraft was rebuilt, this time as a D IV, with the new serial number 7554/17. This aircraft suffered yet another crash as a D IV, and was rebuilt yet again, this time with a shorter wing span as the D IVa.
The wings of the D IV were designed by Heinrich Kann, a new young member of the design team. He suggested that the upper and lower wings should be identical in plan, with a chord of no more than one meter. The new wing was shorter than that on the D IIc lang, with a span of 27ft 4 3/4in. The wing area was 40sq ft smaller than on the D III, and at 163.25 sq ft was more than 30sq ft smaller than on the D IIc lang.
Three prototypes were built early in 1918. The new aircraft was faster than the D III (although only by 6 mph). Its main advantage was its time of climb to 16,400ft or above, where it overtook the D III - it could reach 19,680ft nearly five minutes quicker than the D III.
The D IV was constructed in the same way as the D III. The fuselage had four main longerons, linked by circular transverse bulkheads. These bulkheads were linked by diagonal formers, which were covered with three-ply plywood to give the fuselage its circular cross section. The result was a very rigid structure. Although the S.H.III produced less torque than a normal rotary engine, there was still some, and the vertical tail was asymmetric in an attempt to counter this.
The engine cowling was originally a full circle, but the bottom half was cut away to improve cooling. The propeller had a large spinner, which was later given four louvers between the roots of the four blades of the propeller, again in an attempt to improve cooling.
The wings used two box spars, with 1.5mm plywood ribs. The wings were linked by V struts built of spruce. The wing was off-set to the left, with the port wing 4in longer than the starboard wing, again to counter the torque from the engine,.
A production order was placed in March 1918, and eventually 280 machines were ordered. The first aircraft went to operation units in August, starting with Jasta 14 and the Marine Luft Feld Jasta. Jasta 22 and the home defence unit Kest 2 also received the D IV. Only about fifty D IVs reached operational units before the end of the war.
The D IV was popular with its 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 a good turning circle. It was especially useful above 4,000m, where it out-flew the Fokker D VII and he suggested using the Fokker aircraft at lower levels. He did acknowledge that it had a short life span, presumably because of the overheating engine, 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, and only after some introductory flights (it shows how much strain the German air force was under by 1918 that this wasn't seen as standard practice!).
Rather oddly production of the S.S.W. D IV didn't stop at the Armistice, and instead continued well into 1919. These post war aircraft were soon scrapped, although one did survive into the 1920s, and was used by Albatros.
Engine: Siemens Halske Sh III or Sh IIIa
Power: 160hp or 200hp
Span: 27ft 4 3/4in
Length: 18ft 8.5in
Height: 8ft 11in
Empty weight: 1,190lb
Loaded weight: 1,620lb
Maximum take-off weight:
Max speed: 118.75mph
Climb Rate: 3,280ft in 1.9min
3.75min to 2,000m/ 6,560ft
6.4min to 3,000m/ 9,840ft
9.1min to 4,000m/ 13,120ft
12.1min to 5,000m/ 16,400ft
15.5min to 6,000m/ 19,680ft
Service ceiling: 26,240ft
Endurance: 2 hours
Armament: Two synchronised Spandau machine guns