Dornier Rs . II The Dornier Rs . II was a biplane flying boat , designed by Claudius Dornier and built during 1914 - 15 on the German side of Lake Constance . Initially this aircraft was powered by three engines mounted inside the hull driving three pusher propellers via gearboxes and shafts . The later version was powered by four engines in two push - pull nacelles mounted between the wings . Design and development . After a disastrous storm which wrecked the Rs . I , Dornier continued development of large seaplanes with the Rs . II . The design and construction drawings of the Rs . II had been prepared during 1915 and the airframe was completed rapidly after the loss of the Rs . I . Although resembling the Rs . I , there was little in common with the Rs . II , which had a much broader , shorter hull , low aspect ratio upper wing and open lattice tail unit . The Rs . II , ( Navy serial no 1433 ) , as launched in 1916 , consisted of a sesquiplane flying boat with a short but very broad fuselage and a tail unit supported at the end of a long open lattice box framework of tubular booms cross braced with cables . The short lower wings were intended to support stabilizing floats but these were found unnecessary due to the inherent stability of the broad hull . The tail unit comprised a biplane elevator assembly with a small separate tailplane above a pair of all - flying rudders and the large upper wing was supported by struts which also supported the propellers . Power was supplied by three Maybach HS engines mounted inside the hull , transmitting power to the three propellers via clutches , gearboxes and shafts . The three propellers were mounted as pushers aft of the wing support structure at about mid - gap . Radiators for the internally mounted engines were mounted as a wide slab on the hull aft of the pilots cockpit . The wing structure was formed by three built - up girder spars of triangular section with aluminium wing rib s spaced fairly wide apart ; the wing fabric was sewn to special eyelets , which were attached to the framework at evenly spaced intervals . The lower wings were attached directly to the fuselage , touching the water when afloat , improving water - borne stability . The low aspect ratio upper wing was supported by a central frame work and N strut assemblies at 1 / 3rd span and 2 / 3rd span . Incidence of the upper wing was adjustable by altering the length of the forward N - strut tubes . Flying controls were fairly conventional despite their size , with unbalanced ailerons on the upper wing and a large biplane elevator unit trailing a small tailplane and small rudders under the tailplane . To improve lateral control at low speeds , and improve spin resistance , the tip incidence was washed - out , ensuring that the inner wing sections stalled first . The hull , constructed of steel bulkheads and stringers with Duralumin skinning on the sides and bottom , but fabric on parts of the upper decking , housed the crew in a cockpit near the nose , who were protected by a raised coaming . The engines and fuel lines were also housed inside the hull ; they could be serviced in flight by a mechanic . Operational history . On 17 May 1916 the Rs . II left the hangar at Seemoos for initial taxiing trials with Schroter at the controls , with Graf Zeppelin , Dornier and other important people from the Zeppelin works observing from Zeppelin ' s motor boat " Württemberg " . Initial attempts at taking - off were unsuccessful , attributed to the very calm conditions not allowing the hull to un - stick , they also highlighted the unacceptable rudder power for manoeuvring on the water . The first modification involved adding a third tall rudder between the original rudders . Flight tests resumed on 30 June 1916 , take - off attempts were made with the wing incidence set at one , then two degrees and finally at three degrees which was successful at 07 : 30 hours . Two more flights were made that day and a further three flights proved the need for changes to the tail framework and tail surfaces ; large diameter metal tubes replacing the upper booms and fixed fins fitted between the boom ends , as well as reducing the area of the central rudder and improving the planing surface shape . Ready for continued flight tests on 17 July 1916 , the RS . II still showed poor take - off characteristics and the aircraft was sluggish in roll . Rudder authority was also lacking as it was found impossible to maintain straight flight with the centre and starboard engines throttled back . During these tests the port transmission began to vibrate and eventually it failed , causing the port propeller to break . The aircraft dropped onto the water from about 10 m ( 33 ft ) , bounced into the air where the centre propeller transmission broke loose , damaging the tail boom as the aircraft settled with the tail boom in ruins . Second version . Rebuilding of the Rs . II was completed by 5 November 1916 , with Schroter piloting the aircraft on its second flight the next day . The much revised Rs . II had four more reliable Maybach Mb . IVa engines fitted in push pull nacelles mounted on struts above the hull at approx . mid gap . Initially the biplane tail cellule was retained with large fins and rudders attached to the tail boom side members ; the tail unit was later made more conventional with a large tailplane and twin fins with rudders . Take - off performance was improved by moving the step further aft but the take - off run was still excessive . The upper wing was also lowered by shortening the centre section struts and moving the mounts for the side struts to halfway down the sides of the fuselage . Other changes included aerodynamic balance surfaces for the ailerons , lower wings with reduced chord and rounded tips . Flight tests of the revised Rs . II were still dogged by engine problems with the engines either over - cooling when un - cowled , or overheating when fully cowled , not to mention spark plug and equipment failures exacerbated by a lack of spare parts . During May 1917 , while practising landings , the Rs . II landed hard , breaking the central boom support . Unaware of the damage , the pilot attempted to take - off again , but the sagging tail forced the Rs . II back on to the water , where the tail broke off and sank to the bottom of Lake Constance . By June 1917 the cumbersome tail unit had been replaced by a cleaner design with a single tailplane and finely formed fins and rudders mounted at the end of each boom . The new boom structure was much stronger and of simpler design . Evaluation by the SVK ( " Seeflugzeugs - Versuchs - Kommando " - Seaplane Testing Command ) , was carried out from 23 to 26 June 1917 testing various engine off configurations and water - borne handling . Given a qualified clean bill of health , the Rs . II was prepared for a transit flight to Norderney on the North Sea coast to carry out seaworthiness trials . Due to the recurring problems with the engines and the lack of clean high grade fuel , the Rs . II was required to carry out a practice delivery flight to ensure that the aircraft could reach its destination . During one of these practice flights , number 4 engine back - fired violently and number 1 engine ' s propeller disintegrated , showering the wings and hull with splinters . With two engines shut - down the pilot throttled back number 2 and 3 engines , gliding to a safe landing . The damage caused by the disintegrating propeller was deemed uneconomical to repair .