O.Thetford, P.Gray German Aircraft of the First World War (Putnam)
Siemens-Schuckert D. Dr I
This extremely unusual triplane fighter was built during 1917 and powered by two high-compression Sh I engines giving 120 h.p. The engines were mounted fore and aft of the central nacelle in "push-pull" fashion, and the tail assembly was carried on tubular outrigger booms. Aerodynamic problems were not fully appreciated or understood, and this interesting prototype crashed on its maiden flight in November 1917; it was not rebuilt. Engines, 2 x 120 h.p. Siemens-Halske Sh I. Span, 10.9 m. (39 ft. 9 1/4 in.). Length, 5.8 m. (19 ft. 0 3/8 in.). Area, 30 sq.m. (324 sq.ft.). Weights: Empty, 680 kg. (1,496 lb.). Loaded, 910 kg. (2,002 lb.). Armament, twin Spandau machine-guns.
J.Herris Siemens-Schuckert Aircraft of WWI (A Centennial Perspective on Great War Airplanes 12)
SSW Dr.I & Dr.II
As might be expected during the German Triplane Craze of 1917, SSW also built a triplane fighter. The fuselage of SSW D.I 3752/16 was used together with its 110 hp Siemens-Halske Sh.I counter-rotary engine and it received the new number 3053/17. Initially it had 8.6 m span and 5.3 m length, with an empty weight of only 425 kg and maximum weight of 632 kg. After a crash during flight testing it was rebuilt with larger wings (details unknown) and weighed more; empty weight was now 500 kg and maximum weight was 695 kg. It reached 4,700 m in 20.6 minutes. Unfortunately, no photographs of this aircraft have been found despite the fact that it was completed in July 1917 and flew for some time.
A second triplane design, the Dr.II, with more powerful 160 hp Siemens-Halske Sh.III and using a D.IIb fuselage, was scrapped during construction. Serials were assigned for two aircraft, 3054-3055/17; these were later applied to the SSW D.VI prototypes.
SSW DDr.I & DDr.II
In June 1917, at the height of Idflieg’s 'Triplane Craze', SSW presented the DDr.I design to Idflieg, which quickly approved it. The "Flying Egg" was powered by two tandem 125 hp Siemens-Halske Sh.Ia engines and fitted with two synchronized machine guns, then the standard German fighter armament.
Insufficiently stable, the DDr.I crashed on its first flight in November 1917. This eventually resulted in cancellation of the DDr.I and a proposed, more powerful derivative, the DDr.II powered by two 160 hp Siemens-Halske Sh.III engines.
Centerline thrust can provide improved performance compared to conventional twin-engine designs while eliminating asymmetric
thrust problems in case of engine failure. The later Dornier Do-335 is a good example of the potential of a properly designed centerline thrust aircraft; it was significantly faster than similar aircraft of more conventional layout. However, the 'latticetail' design of the DDr.I had too much drag, which was surely aggravated by its triplane wing cellule. Even if the DDr.I had acceptable flying qualities it would likely have been too slow, although it might have demonstrated a good rate of climb. Use of two engines in a fighter would also have aggravated Germany's chronic engine shortage.
Siemens-Schuckert DDr.I Specifications
Engines: 2x125 hp Siemens-Halske Sh.Ia
Wing: Span, Upper 7.20 m
Wing Area 18.1 m2
General: Length 5.3 m
Empty Weight 510 kg
Loaded Weight 695 kg
Climb: Dr.IIa: 4,700m 20.6 min
W.Green, G.Swanborough The Complete Book of Fighters
SIEMENS-SCHUCKERT (SSW) Dr I Germany
In parallel with development of the D II, the SSW evolved a single-seat triplane fighter, the Dr I. First flown in July 1917, the Dr I was powered by a 110 hp Siemens-Halske Sh I nine-cylinder rotary engine and employed a D I fuselage. In the course of flight testing, the Dr I crashed and was seriously damaged. During reconstruction the wing area was increased by 31.22 sq ft (2,90 m2), and in this rebuilt form the fighter climbed to an altitude of 15,420 ft (4 700 m) in 20.6 min. A development of the design, the Dr II with a 160 hp Sh III engine, was discontinued at an advanced stage in construction. The following data relate to the Dr I prior to reconstruction.
Empty weight, 1,124 lb (510 kg).
Loaded weight, 1,532 lb (695 kg).
Span, 28 ft 2 5/8 in (8,60 m).
Length, 17 ft 4 2/3 in (5,30m).
Wing area, 194.83 sqft (18,10 m2).
SIEMENS-SCHUCKERT (SSW) DDr I Germany
Dubbed unofficially the ‘‘Flying Egg”, the DDr I represented one of the earliest examples of the twin-engined centreline thrust concept, 120 hp Sh Ia rotary engines being mounted fore and aft of the pilot in an abbreviated nacelle, with the tractor engine driving a two-bladed propeller and the pusher engine driving a four-blader. An equi-span staggered triplane with the rudders and elevator carried by tubular steel outriggers, the DDr I carried an armament of two synchronised 7,9-mm LMG 08/15 machine guns. The design found favour with the Idflieg, to which it was presented in June 1917, the prototype flying for the first time in November, but crashing on its maiden flight. Engine control problems and inadequate stability revealed during the brief flight of the DDr I led to cancellation of a more powerful version of the basic design, the DDr II with Sh III engines.
Empty weight, 1,499 lb (680 kg).
Loaded weight, 2,006 lb (910 kg).
Span, 35 ft 9 1/8 in (10,90 m).
Length, 19 ft 0 1/4 in (5,80 m).
Wing area, 322.93 sq ft (30,00 m2).