The Dornier Rs.I was a large three-engined biplane flying boat, designed by Claudius Dornier and built during 1914-15 on the German side of Lake Constance. It never progressed beyond taxi-ing trials as it was destroyed in a storm.
Claudius Dornier made a distinct impression with Count Ferdinand von Zeppelin while working on the still-born giant civil airship in 1913, who promptly set him up as chief designer of the Zeppelin-Werke at Lindau, responsible for building large patrol flying boats. Dornier's first design to be built was the Rs.I. This was a large aircraft (Riesenflugzeug in the German classification) constructed largely of high-strength steel for highly stressed parts, and Duralumin (aluminium alloy) for low stress parts. The large biplane wings sat atop the fuselage and were braced with four complete sets per side of Warren strut style interplane structures comprising 'V' struts, which obviated the need for drag inducing wire bracing. The wing structure was formed with built-up steel spars, four in the top wing and three in the lower wing, and duralumin ribs riveted to the spars and braced internally. The fuselage was also made up from formed steel members built up into a framework which was then covered with fabric or dural sheeting. The powerplant arrangements were unorthodox, with the two outboard engines housed inside the bulky fuselage each driving a pusher propeller via shafts and bevel gearboxes, and a central pusher engine in a nacelle between the wings.
The Rs.I was completed by October 1915 and rolled out at Seemos for trials. On 23 October, during a taxi test, the port propeller and/or gearbox parted company with the aircraft causing damage to the gearbox mountings and the upper wing. The opportunity was taken to move the outboard engines into nacelles identical to the centre engine and mount them between the wings, on an independent structure with cat-walks for engineers to attend to engines in flight. This gave much better clearance for the propellers from spray, which was very likely to have been the cause of the port gearbox/propeller incident. Taxi trials recommenced but with little success till on 21 December 1915 a Foehn wind blew up during trials. Unable to beach the giant flying boat, attempts were made to ride out the storm on the lake, but the moorings gave and the Rs.I was dashed to pieces on the lakeside rocks. This giant aircraft is noteworthy for the construction materials used, let alone the sheer size of it, being the largest aeroplane in the world at the time of its launch.