March 1925: The Rohrbach all-metal flying boat

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An international peace treaty couldn't stop the development of a flying boat equipped with a mast and sails writes Jason Ford

The Rohrbach sea plane. Image from The Engineer's archive

Back in March 1925 The Engineer looked at the development of an all-metal flying boat that came into being by side-stepping the Treaty of Versailles.

The Rohrbach Metal Aaroplan Company of Copenhagen had developed three flying boats before entering into partnership with Scotland’s William Beardmore and Co. to develop double and multiple engine aircraft for land and marine services.


William Beardmore and Co. was an engineering and shipbuilding company with a shipyard at Dalmuir on the River Clyde that was to host the development of a flying boat made up of Duralumin, a light aluminium alloy containing varying quantities of copper and manganese that is comparable in strength to soft steel after heat treatment and aging.

According to our article, the constructional principles adopted in the Rohrbach-Beardmore system were like those in use for bridge and shipbuilding, and the structure was built up of riveted girders and plates which made it possible to employ larger wingspans and higher powers than previously used for flying boats.

“We believe also that it is the first time a flying boat of this type has been fitted with collapsible masts and sails,” The Engineer observed. “The boat can be rigged with sails in a short space of time, which greatly increases control in the water under bad weather conditions with a corresponding economy in fuel.”

Our correspondent went onto add that the flying boat was a monoplane with cantilevered wings arranged at an enhanced dihedral angle.

“A rectangular shaped fuselage to which the wings are secured forms the hull of the ship and metal stabilising floats, which give further support to the machine on the sea, are fitted,” The Engineer said. “Above the wings and raised clear of them by metal struts are the engines, an arrangement which, we learn, enables manoeuvring to be easily carried out with only one engine running.”

The flying boat was described as 54ft long, 15ft high with a ‘span over the wingtips’ of 96ft 9in and a range of 2,000 miles.

The wing is so strong that the crew can safely walk about on its surface from end to end

“The weight of the machine when fully loaded is 8140lb, which gives with a useful load of 4400lb a total a total weight fully loaded of 12,540lb,” our correspondent noted. “At ground level the machine is designed for a speed of 124mph, while it is capable of, we are informed, of flying to a height of 13,000ft and is designed to fly without losing height when loaded to three-quarters full load and with only one engine running.

“The engines which so far have been fitted to these boats are of the Eagle IX type, each having 12 cylinders with a bore of 4.5in and 6.5in stroke. When running at a rated speed of 1800 revolutions per minute, the motors are designed to develop a total of about 720 brake horsepower.”

Our correspondent further noted ‘the wing is so strong that the crew can safely walk about on its surface from end to end a feature which is of considerable value in tying up or other sea work. To the centre girders there are attached leading edge and trailing edge section boxes, which are light in construction and are hinged so that the interior surfaces can be examined and re-varnished, if necessary, at desired intervals.’

The seaplane in the article lacks a designation, but it may be fair to deduce it was the Rohrbach Ro IV, as that was the only seaplane built by the Rohrbach Metal Aaroplan Company that was licensed to William Beardmore and Co. who completed the build of one of these flying boats for the RAF.

Rohrbach Metal Aaroplan itself had its roots in Berlin but the Treaty of Versailles prohibited German companies from building large aircraft, which led company founder Dr.-Ing Adolf Rohrbach to set up shop in Denmark where parts made in his homeland could be assembled into finished products.

William Beardmore and Co went onto acquire a license to use Rohrbach’s stressed-skin construction methodology in the development of the Beardmore Inflexible, a three-engine all-metal prototype bomber aircraft. Rohrbach Metal Aaroplan would go onto develop four more flying boats.