O.Thetford, P.Gray German Aircraft of the First World War (Putnam)
Rumpler 7D 1
This aircraft was the first of a series of experimental single-seat fighters which led eventually to the D I in 1918. The wooden, multi-stringered, streamlined fuselage was ply-skinned, then wrapped with doped fabric. The wings were orthodox, the upper wing being of parallel chord, the lower with a curved (dragonfly profile) trailing-edge. The engine was neatly cowled and combined with an extrusion of the fuselage to support the upper wing, which was not "gulled" as has been reported in the past. A flush radiator was mounted in the upper wing to port of the centre-line. Wide chord interplane struts of I-section braced the wing cellule. Engine, 160 h.p. Mercedes D III.
Rumpler 7D 2
Another prototype in the Rumpler D 1 evolution, the 7D 2 had the fuselage ply-skinned only fore and aft, the centre portion being simply fabric covered. It was also made deeper, and the lower wings built into it with smaller fairings. The upper wing, now with centrally mounted radiator, was supported on a more orthodox centre-section, found necessary to improve view from the cockpit. For this reason too the wide I-struts were replaced by more conventional twin struts. Engine, 160 h.p. Mercedes.
Rumpler 7D 4
Next development in this prototype series was the replacement of the twin interplane struts with single struts of "C" section in an endeavour to reduce drag. The radiators were now of the frontal "ear" type, placed low on the fuselage sides adjacent to the leading edge of the lower wings. They undoubtedly negatived any drag saving that had been effected by the revised wing-bracing system. Engine, 160 h.p. Mercedes. As far as can be ascertained, the 7D 5 did not differ visibly from the 7D 4.
Rumpler 7D 7
The Rumpler 7D 7, which followed a quadruplane project (7D 6), appeared to differ very little from the 7D 4, the only apparent variation being the encasement of the bracing cables in streamline casings. Engine fitted was now the more powerful 180 h.p. Mercedes D IIIa. Armament, twin Spandau machine-guns.
Rumpler D I (8D 1)
As may be seen, the eventual Rumpler D I did not differ markedly from its immediate prototypes. The introduction of balanced, overhung, ailerons may be noted; also the modification of the vertical tail surfaces to an exact triangular profile. The machine was said to have good flight characteristics except for sharp turns, when it too easily went into a spin. Two of these machines, 1552/18 and 1553/18, participated in the mid-summer D types Competition. Another, re-engined with the 185 h.p. B.M.W., took part in the third Competition in the autumn of 1918. Engine, 180 h.p. Mercedes IIIa. Span, 8.42 m. (27 ft. 7 1/2 in.). Length, 5.75 m. (18 ft. 10 3/8 in.). Height, 2.56 m. (8 ft. 4 3/4 in.). Area, 16 sq.m. (173 sq.ft.). Weights: Empty, 615 kg. (1,353 lb.). Loaded, 805 kg. (1,771 lb.). Speed, 180 km.hr. (112.5 m.p.h.) at 5,000 m. (16,400 ft.). Climb, 5,000 m. (16,400 ft.) in 26.5 min. and in 17.2 min. when fitted with high-compression engine. Duration, ca. 2 hr. Armament, twin Spandau machine-guns.
W.Green, G.Swanborough The Complete Book of Fighters
RUMPLER 7D 1 Germany
Evolved in parallel with the two-seat 7C 1 and embodying similar aerodynamic and structural features, the 7D 1 single-seat fighter was the recipient of an Idflieg (Inspectorate of Flying Troops) contract for three prototypes, flight testing commencing in the spring of 1917. The Idflieg requirement called for a speed of 103 mph (165 km/h) at 16,405 ft (5 000 m), that altitude being attained in 31.5 minutes, and an endurance of 1.5 hrs. An armament of two synchronised 7,9-mm LMG 08/15 machine guns was specified and provision for oxygen breathing apparatus requested. A second identical prototype was designated 7D 2. Flight testing revealed that the pilot’s field of vision was seriously impaired by the broad-chord interplane struts and there were aerodynamic problems associated with the upper wing/fuselage junction. Furthermore, there were servicing difficulties related to the engine installation. In consequence, the 7D1 and 2 were abandoned in favour of a more conventional fighter, the 7D 3.
Max speed, 109 mph (175 km/h).
Service ceiling, 22,965 ft (7 000 m).
Span, 26 ft 10 3/4 in (8,20 m).
Length, 19 ft 4 1/4 in (5,90 m).
Height, 8 ft 6 1/3 in (2,60 m).
RUMPLER 7D 3 Germany
The shortcomings displayed by the 7D 1 and 2 led the Rumpler team to evolve a more conventional derivative fighter retaining the same structural precepts. This, the 7D 3, retained the Mercedes D III engine, but a more orthodox installation was adopted, the flush radiator being centrally mounted in the wing centre section which was raised above the forward fuselage decking by means of a cabane structure. The broad-chord I-type interplane struts were discarded in favour of more conventional twin struts. The 7D 3 was tested during the summer of 1917, but it may be presumed that results were not entirely satisfactory, as, by the late autumn, work had begun on an entirely new aircraft, the 7D 4, intended to participate in the first D-type contest that was to take place at Adlershof early in the following year. No further details of the 7D 3 are available.
RUMPLER 7D 4 Germany
To compete in the first D-type contest (20 January - 12 February 1918), intended to select single-seat fighters for service introduction in mid-1918, Rumpler built two prototypes of the 7D 4. One prototype was completed with a conventional twin-strut cellule and the other with a cellule employing "reverse-C” interplane struts braced by fabric-wrapped triple cables. The fuselage structure remained unchanged, but in an attempt to eradicate some torsional problems experienced earlier with this type of construction, a thin plywood veneer skinning was applied to the nose and tail sections to increase rigidity. Again, the Mercedes D III engine was retained and specified armament was two 7,9-mm LMG 08/15 synchronised guns. Flight testing of the 7D 4 had commenced by October 1917, and during the D-type contest the example fitted with "reverse-C” interplane struts attained an altitude of 16,405 ft (5 000 m) within 23.8 min. This prototype was considered to afford excellent visibility from the cockpit, but was, by consensus, somewhat temperamental in handling and difficult to land. Nevertheless, it appeared to possess sufficient promise to warrant an order for a pre-series of 50 examples of a developed version (7D 7) for further investigation and possible operational evaluation. Another prototype was completed as the 7D 5, this differing essentially in having an automobile-style frontal radiator. No specification for the 7D 4 is available.
RUMPLER 7D 7 Germany
Too late to participate officially in the first D-type contest, the 7D 7 was an improved derivative of the 7D 4 with the "reverse-C” type interplane struts. A new Gottingen aerofoil was employed for the wing, which had control surfaces of marginally reduced area, the cockpit was smaller and was moved forward 13 4/5 in (35 cm), and the buried wing radiator gave place to ear-type radiators mounted immediately above the lower wing roots. Flight testing proved the 7D 7 faster than the 7D 4, and an unofficial climb to 16,405 ft (5 000 m) within 18 min was reported. The 7D 7 was powered by the 160 hp Mercedes D III engine and possessed an armament of two synchronised 7,9-mm LMG 08/15 machine guns, static load testing and flight evaluation occupying the period 22 February to 1 May 1918. Some disconcerting twisting of the tail was encountered during certain manoeuvres, calling for structural reinforcement, the Idflieg reporting in May 1918 that the 7D 7 was "unacceptable for the Front and would be rebuilt.”
RUMPLER 8D 1 (D I) Germany
To overcome the lack of rear fuselage rigidity experienced during testing of the 7D 7, the fabric-wrapped, multi-stringered fuselage structure first featured by the 7C 1 and 7D 1 was finally and reluctantly abandoned in favour of a stronger, more conventional semi-monocoque of diagonally-wrapped strips of glued plywood. The wing cellule was reinforced, balanced ailerons were fitted, and the fin and rudder were redesigned and enlarged. Designated 8D 1, this revised fighter provided the standard for the 50 pre-series aircraft previously ordered from Rumpler as D Is. Three pre-series D Is powered by the 160 hp Mercedes D IIIa engine and one powered by the 180 hp D IIIau high-compression engine participated in the second D-type contest (27 May - 28 June 1918), the last-mentioned attaining an altitude of 16,405 ft (5 000 m) in 18.7 min compared with 27 min required by the D IIIa-engined D I. Excellent climb and altitude capabilities notwithstanding, the evaluation pilots’ consensus of the D I was unfavourable, particularly criticised being aileron response - which was considered slow and erratic - the gliding and landing characteristics, and the level of vibration. One D I powered by a 185 hp BMW ma engine participated in the third D-type contest (10-22 October 1918), being the only contender to attain an altitude of 26,900 ft (8 200 m), but the fighter was deemed of ‘‘limited usefulness” in close-in combat. Military acceptance testing of the Rumpler fighter had still to be completed at the time the conflict terminated when 22 had been built. Another 27 were completed after the Armistice. The following data relate to the standard D IIIa-powered D I.
Max speed, 112 mph (180 km/h) at 16,405 ft (5000 m).
Time to 16,405 ft (5000 m), 23.75 min.
Endurance, 1.5 hrs.
Empty weight, 1,356 lb (615 kg).
Loaded weight, 1,775 lb (805 kg).
Span, 27 ft 7 1/2 in (8,42 m).
Length, 18 ft 10 2/5 in (5,75 m).
Height, 8 ft 4 3/4 in (2,56 m).
Wing area, 179.33 sq ft (16,66 m2).