O.Thetford, P.Gray German Aircraft of the First World War (Putnam)
Zeppelin-Lindau (Dornier) Rs IV
Last of the war-time Dornier flying-boats, the Rs IV was launched in October 1918, construction having started the previous January. In cross-section the hull was much narrower than formerly, and lateral stability on the water was achieved by lifting-cum-flotation surfaces, which were later to become a famous Dornier flying-boat characteristic, in use right up to the Second World War and later termed sponsons. The high-slung fuselage was now metal skinned, and a much simplified tail assembly of cruciform pattern was designed.
With the narrower hull, the power eggs perforce were closer together and were slightly staggered to allow maximum-diameter airscrews to be used. This feature improved asymmetric flight characteristics. After the Armistice No. 8801, which was Rs IV's Naval No., was dismantled during 1919.
The lessons learned by Dornier from this four-year research programme were culminated in the many successful commercial flying-boats built between the two World Wars.
Engines, four 245 h.p. Maybach Mb IVa. Span, 37 m. (121 ft. 4 7/8 in.). Length, 22.3 m. (73 ft. 2 in.). Height, 8.55 m. (28 ft. 0 5/8 in.). Area, 226 sq.m. (2,441 sq.ft.). Weights: Empty, 7,000 kg. (15,400 lb.). Loaded 10,700 kg. (23,540 lb.). Speed, 145 km.hr. (90.625 m.p.h.).
G.Haddow, P.Grosz The German Giants (Putnam)
Dornier asked the German Navy for a confirmation of future orders (on 21 June 1917) and the Navy replied that it intended to order more aircraft from Dornier, although the contract was not placed until the Rs.III was completed. The letter which the Dornier concern then wrote to the Navy in late July 1917 documents the background of the fourth and final R-flying-boat built by Dornier during the war. The letter ran in part:
We gratefully acknowledge receipt of your letter of 19 July 1917, from which we happily learn that the Navy is going to award us a contract to build another R-plane. Since we will probably not be mistaken if we assume it is to be a flying-boat, we shall begin to gather the necessary material ...
In the meantime, we have again thoroughly investigated ways in which the new 1000 h.p. machine (Rs.IV) could be improved over the Rs.III. In particular, we have once more examined whether a biplane or triplane configuration would be an improvement. But we have come to the conclusion that, with respect to weight and aerodynamic characteristics, we cannot expect either of the above configurations to provide any advances over the monoplane. We are presently also investigating if the elimination of the high fuselage in favour of a conventional flying-boat hull will offer any advantages. The weight of the machine would not change appreciably. We fear, however, that a hull-type fuselage would have considerably greater twisting due to larger steering-control movements than in the Rs.III ...
It remains for us to discuss our standpoint in the matter of engine gearing. It is our opinion that a transition to gearing is premature, and we should like to await the experience of other firms in this regard ...
The primary task, as we see it, is to thoroughly work out the details. This attention to detail can only be possible if the configuration of the machine is not greatly changed.
Although preliminary design work was well under way during the middle of 1917, the contract for the Dornier Rs.IV was not awarded until January 1918. At that time two flying-boats, numbered 8801 and 8802, were ordered by the Navy and construction work began at once.
At a meeting between Dornier engineers, Schulte-Frohlinde and Presser on 30 January 1918 a number of design decisions were formulated. Since Staaken experience had shown that the commander preferred the forward machine-gun position during critical moments, it was decided to provide the Rs.IV with a comfortable observation post. Initially it was envisaged to have a raised cabin similar to the Staaken R.52 with a machine-gun ring situated above a glassed-in nose. Two pilots were placed further back in a bulged-out section to obtain good visibility to all sides and provide adequate room in the rather slim fuselage. However, this proposal was discarded in favour of the more conventional raised cabin.
The drawings and photographs show that the Rs.IV retained the basic Rs.III configuration, but with overall design refinements. The appearance of the Rs.IV was more modern, embodying the characteristic rounded and smooth forms typical of all-metal construction. Even wider use was made of stressed-skin construction, a technique Dornier had been investigating on several smaller land biplanes.
The Dornier sponsons are to be seen for the first time on the Rs.IV, a feature which was a hallmark of Dornier seaplane design for many years. Dornier developed the sponson configuration to reduce the size of the hull and to cut down drag and weight. The sponson, because of width and surface area, increased lateral stability and take-off (planing) performance without undue weight or drag penalty. The beam of the hull was reduced to 3•65 metres from the 4•7 metre beam of the Rs.III hull. The sponsons (which had a span of 8 metres) formed an integral part of the hull structure. As a result, the weight of the Rs.IV was about 600 kg. less than the Rs.III.
The hull was of all-duraluminium riveted stressed-skin construction; it consisted of fourteen bulkheads covered with a thin metal skin reinforced on the outside by inverted U-shaped longerons running the length of the hull and internally strengthened by a series of diagonal frames. A small amount of steel was used for highly-stressed parts. A machine-cannon and machine-gun were located in raised bow and stern hull turrets respectively. A position for two mechanics was located in the centre of the hull between the engines. Surrounding the mechanics' position were ten 300 litre fuel tanks built into the hull which contained a fuel supply sufficient for ten hours flying time.
Owing to the narrower hull, the tandem ungeared engines were set closer together than in the Rs.II and Rs.III. This necessitated staggering the nacelles to provide propeller clearance. The nacelles were broadened to include space for a mechanic's position and oil tanks between the engines. The front engines were fitted with offset nose radiators, while the rear radiators were mounted on brackets above the nacelles.
The wing mounting was strengthened by several additional struts, running directly from the wing to the hull. An enclosed ladder shaft connected the starboard nacelle with the upper fuselage; an unusual feature, since connecting ladders in R-planes were generally left open. The shaft was eliminated in the civil version. The all-metal wing retained the same span, area and structural features as the Rs.III wing, but the wingtips were rounded and the cable bracing modified by the addition of king posts at half-span position.
The 60 foot fuselage was a true stressed-skin monocoque structure devoid of all internal cross bracing. Duraluminium skin was riveted directly to the frame with inverted U-shaped reinforcement stringers riveted along the fuselage exterior. The only steel to be found in the fuselage consisted of small corner braces and attachment points where the cables joined the fuselage. The nose of the fuselage contained a machine-gun mount which doubled as the commander's observation post, followed by the pilot's cockpit and a sound-proofed wireless operator's cabin. A dorsal machine-gun position was located just in front of the trailing edge of the wing.
The fuselage terminated in a graceful tail assembly consisting of faired fins and balanced rudders fitted above and below the fuselage. The single tailplane was cable braced and a one-piece elevator ran along the entire length of the tailplane. The tail assembly was built entirely of duraluminium shapes in the usual Dornier fashion.
The Rs.IV made its first flight on 12 October 1918 on Lake Constance piloted by Oberflugmeister Weiss and Schulte-Frohlinde. During a test flight landing the fuselage was badly buckled. Before the Rs.IV could be repaired Armistice intervened; consequently, Dornier chose to rebuild the flyingboat into a twenty-passenger civil transport. The pilot's cockpit was shifted to the hull. The fuselage was intended but never fully outfitted as a passenger cabin; machine-gun positions were removed and other small modifications carried out.
In its civil form the Rs.IV underwent extensive tests, and by June 1919 a very thorough and complete evaluation report had been prepared. With one forward engine stopped, it could maintain altitude; but with a rear engine stopped the Rs.IV lost height. The Rs.IV had good flying qualities, was easy to fly, but like the Rs.III somewhat slow to respond to the ailerons. The sea-handling characteristics were good, although the flat forward hull lengthened the take-off run because it pushed large masses of water before lifting on its step.
The tests on the effectiveness and sea-handling properties of the sponsons were not fully completed, since only calm weather flights had been conducted. However, under these conditions no defects were noted. Trials in heavy seas would require the reconstruction of the forward hull. The decreased performance of the Rs.IV as compared to the Rs.III was blamed on the greater drag of the hull, engine nacelles and sponsons. Unfortunately, the Rs.IV had to be scrapped on 17 April 1920 to abide with Allied treaty stipulations.
A French team of experts from the Inter-Allied Control Commission exhaustively studied the Rs.IV after the war, and they were fascinated by the advanced construction techniques applied throughout. Dornier had been uncompromising, for the Rs.IV was built completely from formed strip and built-up shapes, prompting the French to remark that "in the total structure, not a single piece of tubing is employed".
The sponsons received their first exhaustive tests in the post-war Dornier Gs.I, a twin-engined flying-boat originally intended for the German Navy. Throughout the years the sponson and tandem engine layout remained the trade-mark of Dornier aircraft, until quite recent times.
Colour Scheme and Markings
The Dornier Rs.IV military version carried narrow Latin crosses outlined in white spanning the full wingtip chord. Latin crosses were carried on both upper and lower vertical tail surfaces. The upper wing surfaces were covered with naval lozenge patterned fabric. The civil Dornier Rs.IV did not carry any markings. The exterior hull parts were painted with a bituminous mixture.
Type: Dornier Rs.IV
Manufacturer: Zeppelin-Werke, Lindau G.m.b.H., Seemoos, Lake Constance
Engines: Four 245 h.p. Maybach Mb.IVa engines
Span, 37 m. (121 ft. 4 1/2 in.)
Chord, 6•5 m. (21 ft. 4 in.)
Length, 22•7 m. (74 ft. 6 in.)
Height, 8•37 m. (27 ft. 6 in.)
Propeller diameter, 3•1 m. (10 ft. 2 in.)
Propeller centres, 3•15 m. (10 ft. 4 in.)
Hull length, 14•2 m. (46 ft. 6 in.)
Hull beam, 3•7 m. (12 ft. 1 1/2 in.)
Sponson width, 8 m. (26 ft. 3 in.)
Wings, 226 sq. m. (2432 sq. ft.)
Tailplane, 21 sq. m. (226 sq. ft.)
Elevator, 8•8 sq. m. (95 sq. ft.)
Fins, 2•8 sq. m. (30 sq. ft.)
Rudder, 4•5 sq. m. (48 sq. ft.)
Ailerons, 18 sq. m. (193,7 sq. ft.)
Empty, 7237 kg. (15,955 lb.)
Fuel, 1455 kg. (3208 lb.)
Crew (5), 410 kg. (904 lb.)
Passengers (20), 1500 kg. (3307 lb.)
Loaded, 10,600 kg. (23,369 lb.)
Hull, 1560 kg. (3440 lb.)
Wing Loading: 46•5 kg./sq. m. (9'5 lb./sq. ft.)
Maximum speed, 138 km.h. (85,7 m.p.h.)
Take-off speed, 95 km.h. (59 m.p.h.)
Landing speed, 90 km.h. (56 m.p.h.)
from 400-800 m. (1312-2624 ft.) in 14 mins.
from 400-1000 m. (1312-3281 ft.) in 22 mins.
from 400-1400 m. (1312-4593 ft.) in 36-4 mins.
from 400-2000 m. (1312-6562 ft.) in 53•5 mins.
Duration, 10 hrs.
Fuel: 3000 litres (660 Imp. Gals.)
Service Use: None
Flight, September 18, 1919.
THE (GERMAN) DORNIER "GIANT FLYING-BOAT"
FROM A CORRESPONDENT
IN view of its unusual arrangement, a few notes concerning the Dornier monoplane flying-boat, which was under construction when the Armistice was signed, may not be without interest. The machine was built by the Zeppelin Works at Lindau on Lake Constance, and was designed by the chief designer of that firm, Herr Dornier, who is Swiss by birth. As the accompanying diagrams show, the machine is a monoplane, and is, in a sense, of the flying-boat type, although it might be better described as a single-float seaplane. An idea of the size of the machine may be formed when it is pointed out that the wing span is 36 m. (118 ft.). The power plant consists of four Maybach motors, each of 260 h.p., driving two tractors and two pushers.
The fuselage is placed above the wings, and in it are housed gunners and other crew. The pilots are seated down in the boat, or central float, which also accommodates gunners, one in the nose and one in the stern. In the boat, between the pilots and rear gunner, are placed the petrol tanks, which have a capacity sufficient for a 10 hours' flight. The machine carries a crew of nine, which may be constituted as follows: Two pilots, two gunners in the "hump" on top of the fuselage, one wireless operator in the nose of the fuselage, two gunners in the boat, and two engineers. With full load the machine has attained a speed of 145 km./hour (about 90 m.p.h.). One of the finest flights made by the Dornier was a non-stop trip from Lake Constance to Norderney, the Naval Air Station in the North Sea.
With regard to construction, it should be pointed out that there is no wood in the machine, the wings, fuselage, boat and engine mountings being made of Duralumin. The Zeppelin firm have also during the War constructed all-Duralumin single-seaters and two-seaters of the twin-float type.