Rohrbach Metall-Flugzeugbau?

[stepwilk]

Here's an obscure one, but you all-knowing people haven't let me down yet:

In the late 1920s, Kurt Tank went to work for a German flying-boat manufacturer, Rohrbach Metall-Flugzeugbau. Their airplanes were all-metal (obviously), but would they at that time have been aluminum--yeah, I'm a 'murrican--or steel?

[MReyn24050]

The Rohrbach Ro VIII Roland is described in John Stroud's book "European Transport Aircraft since 1910" as follows:- "The Roland was of similar construction to the earlier type, with wide-chord metal box spar and duralumin covering to the untapered wing.... The flat-sided all metal fuselage had a straight top line and curved underside. The tailplane was attached low down on the fin and the whole tail unit fixed to the fuselage by four steel fittings."

[stepwilk]

Well, that's the problem: all the reference material I have says the hulls were "metal," as does that reference, which thus is no help.

But since it specifies that the wings were aluminum-covered but doesn't say the same of the fuselage, I'm wondering if that means the hull was sheet steel. Also, the fact that the tailplane was attached to the hull by "steel fittings" makes me think the same, since steel-to-aluminum contact would be a bad idea, especially in salt water.

[MReyn24050]

The Rohrbach Ro VIII Roland I – the standard aircraft of Iberia

In January 1926 DLH ordered at the Rohrbach-Metall-Flugzeugbau GmbH, Berlin two Rohrbach Ro VIII Roland I (Roland standing for Rohrbach Land) aircraft. It was for Adolf Rohrbach the first commercial transport aircraft to be taken in service. The prototype flew before September 1926 and was on September 5 presented to the press at Berlin-Tempelhof. The first two aircraft were subsequently delivered to DLH and this order was followed by a new order for an additional five aircraft for delivery in 1927. The Rohrbach Ro VIII Roland I was a high-wing cantilever monoplane powered by three 230 hp BMW IV six-cylinder water-cooled inline engines. It had an open cockpit, though later versions were fitted with covered cockpits. The rectangular fuselage was covered with duralumin and housed ten passengers. Two of the engines were mounted in the wing and one in the nose.


I would say that duralumin was also used to construct their seaplanes as sheet steel would be far too heavy. One could check by comparing the various empty weights of similar types.
Mel

[stepwilk]

message removed.

[chiglet]

Sheet steel is another matter, however--i.e. what's used to make automobiles.
And they rust....:E
Seriously, I feel that the skinning must have been Dural, with "crytical" internal bits, steel.

[stepwilk]

Of much more concern to a seaplane is the fact that aluminum corrodes badly in salt water. Whenever I flew a floatplane into salt water, it needed to be hauled out and hosed off thoroughly with fresh water. Rust would be a minor problem compared to salt water causing dangerous intergranular corrosion.

[MReyn24050]

duralumin

An alloy of aluminum that contains copper, manganese, magnesium, iron, and silicon and is resistant to corrosion by acids and sea water.

For sheet products, corrosion resistance can be greatly enhanced by metallurgical bonding of a high-purity aluminium surface layer. These sheets are referred to as alclad, and are commonly used by the aircraft industry.

[stepwilk]

Ha! The Edo floats that I usually flew--sometimes PeeKays--were made of Alclad and thoroughly zinc chromated, but we still needed to hose 'em off with fresh water.

I have seen plenty of intergranular corrosion on a variety of Cessnas and Pipers, all of which use Alclad and are zinc chromated. It's like thinking undercoating will keep your car from rusting.

[Brian Abraham]

From http://www.flightglobal.com/pdfarchive/view/1927/1927 - 0319.html
As in the case of earlier Rohrbach flying-boats, the " Rocco " is of all-metal construction, the term " all-metal " in this case being synonymous with duralumin construction, which is the material used exclusively with the exception of a few wing fittings and bracing struts, which are of steel. A feature of Rohrbach construction is that the covering or skin, as it is usually called in modern aircraft parlance, is designed as a stress bearing part of the general structure. This applies of course, to flying-boat hulls in general, but in the case of the Rohrbach machines, it also applies to the wings, which are covered with sheet duralumin forming part of the wing box. This wing box may be considered as one very large spar, extending from tip to tip of the wing and, in a fore and aft direction, very roughly half-way in the wing chord to a short distance aft of the leading edge. This wing box is built up in the form of a front and rear member corresponding approximately to the front and rear spars in more orthodox types of construction, joined at intervals by fore and aft bulkheads or formers, the skin being riveted to both spars and formers. In addition, the thickness of the skin varies from point to point in the wing according to local stresses, the change being effected partly by using sheet duralumin of different gauges and partly by lamination.

The more or less closed box construction of the Rohrbach wing has necessitated a somewhat unusual arrangement of the leading and trailing edges. These are hinged to front and rear spar at short intervals, and are attached in such a manner that by undoing a number of small bolts the leading and trailing edges can be swung up or down in such a manner as to enable an inspection of the interior of the wing box to be made, or even minor repairs to be effected. Also, should any sea water have got inside the wings, in taxying in a very rough sea, for instance, the water can be drained out, and leading and trailing vdges opened so as to enable air to get at the interior of the wing and dry up any water that may have collected in out-of-the-way corners. The boat hull is of the fiat-sided variety, "this form evidently having been chosen in order to avoid as far as possible the somewhat expensive panel beating which is necessary where sheet material has to be bent over a double curvature.

An exception is formed by the planing bottom of the hull, which, in the latest type "of Rohrbach, is of pronounced " V " formation, the "flat-bottomed hulls of the earlier Rohrbachs having, we believe, given a certain amount of trouble owing to leakage as a result of hard landings. There are two steps in the hull, as in most modern flying-boats, the steps being of the closed variety.

In the detail construction of the hull, as well as in that of the wings, only flat sheet and open sections are employed in order to afford cheap construction and ease of inspection. Thus, it is claimed that no hidden rivets are found anywhere in the structure, all riveting being open to inspection from both sides. Furthermore, both during actual construction and in use later on the open sections employed render the operation of protecting the material against corrosion easier and more certain. A number of bulkheads divide the boat hull into watertight compartments, and all the doors in the cabin are so made as to be watertight when closed, thus reducing the risk of sinking in case of damage in one compartment, It is even claimed that the buoyancy of the hull is such that with all doors and windows closed the machine would remain afloat with two adjacent compartments damaged.

A similar principle applies to the out-board wing floats, and as a safeguard against the machine turning over in case of damage to a wing float the outer few feet of the wing itself have been formed into watertight boxes, so that if a wing float is punctured, and the machine begins to heel over, the wing tip will meet the water, and by the buoyancy of the wing tip boxes, acting on a long lever arm, will effectively prevent the machine from turning right over, although it would naturally be over at a rather uncomfortable angle.

[stepwilk]

Thank you, Brian--you're The Man.