К концу войны также было изготовлено два опытных бомбардировщика R VIII. Этот самолет имел увеличенные размеры (размах крыльев составлял 48 м), "классический" фюзеляж, в носовой части которого размещалась кабина, а в средней части - шесть двигателей Басс и Селве мощностью 300 л. с. Крылья имели одинаковый размах, верхнее возвышалось над фюзеляжем на кабане. На центроплане верхнего крыла была установлена пулеметная турель, обслуживающий ее стрелок поднимался по лестнице внутри профилированной трубы.
O.Thetford, P.Gray German Aircraft of the First World War (Putnam)
Siemens-Schuckert R VIII
After completion of the R I to R VII series of three-engined bombers, the S.S.W. design team applied their knowledge to producing plans for the ambitious, six-engined R VIII. Construction was begun in February 1918 on two of these colossal machines, R 23/16 and R 24/16, but only the first aircraft was ever completed, and even that never flew. During ground trials early in 1919 the transmission gear failed, a propeller flying to pieces and extensively damaging the airframe, which was never rebuilt, due to the restrictions of the Armistice. Engines, six 300 h.p. Basse and Selve BuS IV. Span, 48 m. (157 ft. 6 in.). Length, 21.7 m. (71 ft. 2 3/8 in.). Height, 7.4 m. (24 ft. 3 3/8 in.). Area, 440 sq.m. (4,752 sq.ft.). Weights: Empty, 10,500 kg. (23,100 lb.). Loaded, 15,900 kg. (34,980 lb.). Speed, 125 km.hr (78.125 m.p.h.) estimated. Ceiling, 4,000 m. (13,120 ft.), estimated. Duration, 8 hr., estimated.
G.Haddow, P.Grosz The German Giants (Putnam)
The SSW R.VIII was the largest aircraft in the world at the time of its completion, a mammoth aircraft even when judged by today's standards. Its record 158 foot wingspan was not surpassed for nearly a decade following World War 1. The R.VIII was Siemens-Schuckert's final contribution to the German R-plane effort. The design projects from which the R.VIII eventually evolved were first mentioned in November 1916, when Idflieg wrote, "In spite of constant pressure, the work on the 1000 h.p. project does not seem to have progressed very far." Indeed, SSW wanted to gather more experience with the R.7 before proceeding on the project, much to Idflieg's consternation. A second project was also mentioned. "SSW feels that discussion of a 2000 h.p. aircraft is completely out of the question at the moment. Their attitude stands out in contrast to the other R-plane manufacturers, who are diligently pursuing the problem." However, in light of their discouraging experiences and financial losses with the R.2/7 series and their growing fighter aircraft activity, it was understandable that SSW would view further R-plane construction with half-hearted interest. But two factors were responsible for the reawakening of the firm's enthusiasm in the middle of 1917. Idflieg, ever anxious to strengthen its R-plane squadrons, continued to apply pressure for a new giant bomber design. Secondly, the last aircraft of the R.2/7 series was nearing completion (the R.2), and SSW was reluctant to let its investment in experience and facilities go to waste. In the summer of 1917 a contract was signed for the construction of two R-planes at a cost of 750,000 marks each. Based on the ideas of Dr. Reichel, these aircraft were designed by Dipl.-Ing. Harald Wolff, head of the SSW design bureau, and bore the designation SSW R.VIII 23/16 and 24/16. Records do not exist to explain why these aircraft received a 1916 order number, but it is possible that they were ordered under funds made available for the large R-plane allocation of 1916.
The specifications for the R.VIII called for a climb of 4500 metres in 120 minutes carrying a useful load of 5250 kg., and a speed of 130 km.h. was required at 2500 metres. Initially the R.VIII was to have been powered by six 260 h.p. Mercedes D.IVa engines, but these were dropped in favour of the new and more powerful 300 h.p. Basse & Selve BuS.IVa engines, which were in the process of becoming operational.
A full-size wooden mock-up was built, consisting of fuselage, centre wing section, gear-box, drive assembly and the various machine-gun positions. Photos show a fully-enclosed rotating nose turret believed to be the first of its kind, but it was not mounted in the finished aircraft. After examining the proposed design, Idflieg engineers concluded that the fuselage was too short, and their recommendation to lengthen it by 2 metres was accepted. A second recommendation to place an additional machine-gun in the floor of the nose was rejected, as the R.VIII was intended for night bombing, and every ounce of weight was to be spared. A fully retractable gun position for rear defence, also under consideration at one time, was not adopted for the same reason.
The wooden mock-up was completed in the autumn of 1917, but because SSW engineers were heavily engaged in the design and construction of fighters, preparation of the working drawings was delayed. As a consequence, Idflieg assigned several full-time engineers to the R.VIII project. New calculations based on latest engineering developments and operational requirements necessitated increasing the wing area and the span to 48 metres. Because the Dynamowerk shops could not accommodate this size, a new assembly hangar was erected which was finished in October 1917. Work on the R.23 began immediately, and by January 1918 the fuselage framework was assembled. Other parts, such as landing gear, controls and gear-boxes, were well advanced.
In January 1918 an Idflieg report stated that the R.23 would be flight-ready by the end of March, but by March the completion date had been put ahead to June 1918, and actually the assembly of the R.23 was still in progress in November 1918. The delay was due to the protracted delivery of the BuS.IVa engines, which had difficulty in passing qualification tests and problems experienced with the drive and transmission system.
The six 300 h.p. Basse & Selve BuS.IVa engines were mounted internally in two rows of three engines, each separated by a broad cat-walk. The two backward-facing front engines were coupled to a common gear-box which drove two two-bladed tractor propellers through outrigger shafts. The remaining two pairs of engines, mounted face-to-face and also coupled to a common gear-box, drove two four-bladed pusher propellers. Operational reliability and long-range performance were the prime reasons for this unusual engine arrangement. The R.23 was designed to cruise using only the four rear engines after having released its bomb load and to fly in a shallow glide using only the two forward engines. Six individual combination friction and centrifugal-key clutches actuated by a hand-wheel provided means for separately engaging or disengaging the engines. The propellers were arranged in tandem and mounted on robust struts at a mid-gap position.
In a concerted effort to avoid a recurrence of the engine-cooling problems, SSW carefully investigated improved radiator designs and performed numerous flight tests in a Gotha bomber. Large circular water and oil radiators enclosed by a Venturi-type shroud were finally chosen. These were based on the Junkers nozzle radiator principle, and besides being more efficient had the advantage that the airflow could be closely controlled for optimum cooling and prevention of boiling or freezing of the radiator water. Another improvement founded on previous experience consisted of placing the major portion of the exhaust stacks in the slipstream. The development of left- and right-hand engines had made this desirable feature possible.
In spite of having been increased in length, the bulky rectangular fuselage of the finished aircraft still appeared short in relationship to its broad wingspan. The steel-tube fuselage framework was braced with diagonal tubes throughout to provide greater rigidity. The nose and entire engine-room was metal-skinned, and the remainder was covered with fabric.
An observation/bombardier's cabin was located in the extreme nose, surmounted by a machine-gun position. The open cockpit for two pilots was situated directly over the front engine pair and commanded a fine view to all sides. A fully-enclosed cabin for the commander/navigator directly behind the cockpit contained a map table, compass, navigation equipment and the like. The large engine-room stretched from below the cockpit to a few feet behind the trailing edge of the wing. It was ventilated by windows in the upper decking and by portholes in the side of the fuselage. The engine-room was followed by a wireless cabin containing receiving and sending gear, Bosch power supply, aerial spool and associated equipment. The dorsal gun position, located above the wireless cabin, was intended for two machine-guns mounted on brackets on either side. A ventral gun position for a prone gunner was located in the compartment behind the wireless cabin.
An unusual feature which the R.VIII shared with the Schutte-Lanz R.I was the streamlined enclosure which protected the ladder leading to the upper wing machine-gun post. It also contained a gravity tank in which additional engine cooling water was stored. Parachutes were stored in the nose compartment and near the rear exit door.
The huge four-bay wings constructed primarily from wood were carefully designed to achieve highest strength-to-weight ratio from the wooden spars and ribs. The fuel tanks were located in the lower wing roots outboard of the fuselage, and contained sufficient fuel for 8 hours flying time. Protection from gunfire was provided by a fire-proofing system devised by Prof. H. W. Fischer, but further details on this are unknown.
Ailerons were mounted on both upper and lower wings, and these marked the sole appearance of the newly-developed and patented Flettner servo-controls or trim tabs in R-planes. The inventor, Anton Flettner, began his career prior to the war, when he attempted to devise a remote-control device using "Herzian" waves for circus horses. It was to be a sensational finale in the Schumann Circus, but the horses refused to co-operate under the load of a radio-equipped saddle that punched and pricked! At the beginning of the war Flettner's ingenuity came to the attention of the ever-visionary Graf Zeppelin, who put Flettner to work investigating the remote control of Zeppelins and flying weapons. In 1915 Flettner constructed a wireless remote-control miniature tank equipped with a flame cutter to sever barbed wire and iron stakes. The tank was demonstrated before short-sighted military experts, who saw no need for such a device, and the project was dropped. However, Idflieg, recognizing the potential value of these experiments, engaged Flettner to investigate wireless remote control systems for pilotless aircraft then under development by Idflieg. Writing in 1926, Flettner refused to divulge details concerning this interesting work, with one exception. It was during this time that the servo-control device was invented by Flettner as an aid to automatic control of pilotless aircraft. It was not long before this innovation was specified for all German bombing aircraft, but it came too late in the war to be widely used. SSW co-operated with Flettner in this work and consequently was one of the first aircraft firms to employ the Flettner control surfaces. It was natural that the R.VIII should be equipped with this device.
Basically an improved version of the system used on the SSW R.I, the tail assembly was comprised of a single tail plane fitted with a balanced elevator. A pair of auxiliary elevators were mounted below the tailplane and gave the tail unit a false biplane appearance. A large central rudder was hinged to the fuselage and also was equipped with two small auxiliary rudder surfaces located in the gap between the elevators. A simple and robust undercarriage used spring shock absorbers, and was similar to the undercarriage of the earlier SSW R-planes.
The war ended before the R.23 was completed, but work continued under the sanction of the German Government, which wanted to explore its potential usefulness as a commercial transport. On 1 March 1919 the R.23 left the assembly hangar under its own power and performed various taxying tests. At the request of Lt. Offermann, the R.23 test pilot, the couplings between the port and starboard engines were disconnected for the projected test flights. On 6 June 1919, with the full flight crew aboard, the R.23 was undergoing engine tests with the rear engines at 800 r.p.m. (propellers at 400 r.p.m.) when the port rear four-bladed propeller flew apart, severely damaging the aircraft. The port upper wing collapsed, the propeller support struts were torn and bent, and the gear-box and lower wing were damaged, but the fuselage remained virtually intact. At first it was planned to use replacement parts from the R.24, but on 26 June J919 the Government cancelled the repair work of the R.23 and the completion of the R.24, which was about three-quarters finished.
On 24 July 1918 three additional improved bombers designated SSW R.VIIIa, numbered R.75 to R.77, were ordered, and preliminary construction work begun in November 1918 ceased at the end of the war. A significant change was to equip the R.VIIIa series with Brown-Boveri turbo-superchargers driven by a 160 h.p. Mercedes D.III engine.
The SSW R.VIII was the largest aircraft built by any nation during the war. As such, it represented the limit to which wooden wing construction could be efficiently taken. Had the development of R-planes continued, the R.VIII would have been rapidly surpassed by the Junkers, AEG, Staaken and SSW all-metal monoplanes, which were at various stages of design at the war's end.
After the SSW R.IV proved unsuitable SSW engineers hoped to be able to use the R.VIII as a carrier for the wire-guided missiles they were developing. As a matter of fact, Rea and Siemens engineers, as early as August 1917, had discussed the development of radio-controlled glide-bombs weighing between 300 and 1000 kg. The controls were to be based on the Flettner patents. SSW did build several low-silhouette monoplane gliders that could fit under the wings of the R.VIII; however, they were never air-launched and all work on the project ceased in December, 1918. Recently it has come to light, that Idflieg was considering using R-plane borne parasite aircraft to provide in-flight defence.
Colour Scheme and Markings
The R.23 was covered with printed camouflage fabric, and the metal-skinned portion was painted to match the printed polygons of the fabric. The under surfaces of the wings and fuselage were painted in a light colour. Narrow Latin crosses edged in white were carried on the wingtips and on the fuselage sides. The three rudder surfaces were painted white and the central one bore a straight black cross.
Manufacturer: Siemens-Schuckert Werke G.m.b.H., Siemensstadt, Berlin
Engines: Six 300 h.p. Basse & Selve BuS.IVa engines
Tractor, 900 r.p.m.
Pusher, 700 r.p.m.
Span, 48 m. (157 ft. 6 in.)
Chord upper, 5•2 m. (17 ft.)
Chord lower, 4•5 m. (14 ft. 9 in.)
Gap, 5•2 m. (17 ft.)
Sweepback, 2 1/4 degrees
Length, 21•6 m. (70 ft. 10 in.)
Height, 7•4 m. (24 ft. 3 in.)
Maximum fuselage width, 2•2 m. (7 ft. 3 in.)
Propeller centres, 7•6 m. (24 ft. 11 in.)
Areas: Wings, 440 sq. m. (4734 sq. ft.)
Empty, 10,500 kg. (23,152 lb.)
Loaded, 15,900 kg. (35,060 lb.)
Wing Loading: 35 kg./sq. m. (7•2 lb./sq. ft.)
Maximum speed, 125 km.h. (77•7 m.p.h.)
Ceiling, 4000 m. (13,124 ft.)
Range, 900 km. (559 miles)
Cost: 750,000 marks