Rohrbach Ro IV

from Wikipedia, the free encyclopedia
Rohrbach Ro IV
Beardmore Inverness L'Air December 15,1928.jpg
Beardmore BeRo. 2 Inverness
Type: ocean-going flying boat
Design country:

German EmpireGerman Empire German Empire

Manufacturer:

Rohrbach Metal Aeroplan Co A / S, Copenhagen

First flight:

September 1925

Number of pieces:

2

The Rohrbach Ro IV was a seaworthy flying boat that was built for the British Air Ministry in the 1920s. The German manufacturer Rohrbach Metallflugzeugbau in Copenhagen and the British William Beardmore and Company built one each with the name Beardmore BeRo.2 Inverness . However, the performance of the all-metal aircraft was disappointing in many respects, so that no further license production took place in Great Britain.

history

prehistory

At the beginning of the 1920s, England attempted to catch up on the backlog in the construction of all-metal aircraft by licensing constructions for the Rohrbachwerke. The focus was on gaining knowledge in the area of ​​manufacturing processes for duralumin assemblies . In 1923 the Air Ministry ordered a large land plane from Rohrbach, which was called the Beardmore BeRo.1 Inflexible in England . This was followed in 1924 by the order for two Ro-IV flying boats based on the Ro III.

Kurt Tank , who had been involved in the development of the Ro III since April 1924, contacted the facility responsible for the acceptance flights in England, where he learned that they were already planning to carry out the Ro IV after testing Marine Aircraft Experimental Establishment (MAEE) in Felixstowe . The reason for this was that, first and foremost, one did not trust monoplane aircraft and, secondly, an aircraft made of metal was far too heavy. The aircraft of the future should be safe and this can only be guaranteed with double-deckers .

Development and construction

After the temporary closure in 1921, the Scottish heavy machinery and shipbuilding company reopened its aircraft construction department in Dalmuir in 1924 and a short time later concluded a license agreement with Rohrbach. The Air Ministry then ordered two aircraft from Beardmore under the designation BeRo.2 Inverness . With the new name, the ministry may have wanted to disguise the fact that with the order it was helping to circumvent the conditions of the Versailles Treaty, in which Germany was still forbidden to build military aircraft.

According to the order of November 22, 1924, Beardmore was to build the machine according to the requirements of the Air Ministry Specification 20/24. According to this, two water-cooled Napier Lion V with 450 hp each instead of the 360 ​​hp Rolls-Royce Eagle used in the Ro III and Ro IIIa should serve as the drive . The military serial numbers N183 and N184 were assigned. Rohrbach manufactured the assemblies for the first Ro IV (N183) in Berlin and then had them assembled at the Copenhagen-Kastrup plant , where the machine also carried out its first test flights. After a 960-km-flight, with a fuel stop in Texel , the N183 on 18 September 1925 reached Felixstowe .

Testing at the MAEE

The testing by the MAEE in Felixstowe showed many inadequacies of the Ro IV. For example, dangerous vibrations occurred in the tail unit area, and corrosion was found on the outside and inside of the fuselage despite a protective coating. Many design details were judged to be unnecessarily heavy without being particularly durable. The metal paneling of the wings lost its rigidity and the ribs tended to push through the metal. Due to the flat bottom of the boat, splash water reached the propellers during the landings and twice the step of the boat hull collapsed during hard landings due to the shock load.

Compared to contemporary constructions such as the English Electric Kingston , the Inverness had poor performance values. In the upper speed range the controllability was described as good, at low speeds the Inverness was dangerously unstable despite the large V-position . In the overall assessment, the MAEE came to the conclusion that due to the “negligible” military payload, together with the poor performance values ​​and “inadequate” controllability, the aircraft can neither be used for military nor for civilian use.

Beginning in 1926, the Royal Aircraft Establishment (RAE) then carried out wind tunnel studies to improve the aerodynamic properties. On the basis of the 1:25 model of the aircraft used and a propeller model in 1: 9, however, no usable results could be found on the causes of the poor flight performance.

After about a year of flight testing, the N183 had achieved a total flight time of 32 hours, after which it was transferred to the RAE. On May 20, 1927, the machine was turned on its back for further stress tests and the wings were loaded with sacks filled with bullets . The aim was to determine the breaking strength of the wings with the pressure point far forward .

There are different assessments of the reasons why the first machine was built by Rohrbach himself and not Beardmore. It has been suggested that it was simply convenient for Beardmore to have Rohrbach build the aircraft. Other opinions were that Beardmore wanted to deliver the Rohrbach aircraft to the Air Ministry at the earliest possible point in time, as the work with the Inflexible was already far behind schedule.

Second machine

Beardmore assembled the second machine (N184) in Dalmuir from assemblies supplied by Rohrbach at the same time as the previously ordered Inflexible. Both planes went through a construction period of about three years, not least because of problems with the procurement of the duralumin sheets in the right thickness, and the N184 was only completed in November 1928. The first flight took place on November 30, 1928 with take-off and landing on the River Clyde . The long construction allowed some improvements to be made over the N183. This affected the cooling system of the engines, the fuel supply, raised engine nacelles and better braced support floats.

However, this meant that the weight of the N184 increased significantly compared to the N183. The flight performance and characteristics became even worse as a result, and the stresses on the crew led to rapid fatigue. In April 1929, the MAEE recommended canceling the test program, after which the machine was probably scrapped.

construction

The fuselage had a rectangular cross-section. The inner fuselage frame was planked with flat sheet metal that was not bent, which simplified production and was inexpensive. The duralumin construction differs significantly from a half-shell construction . All aerodynamically relevant control and lift surfaces had a rectangular floor plan with a constant profile thickness over the entire length. The fin of the rudder was moveable and could be trimmed with the help of a Flettner rudder .

The strong V-position of 6 ° prevented undercutting the wing tips in heavy seas. The front and rear spars, together with cross braces, ribs and planking, formed the torsionally and flexurally rigid box spar. The wing nose and end ribs also formed individual boxes that were screwed to the central box spar. These boxes were easy to change and simplified spare parts inventory by dividing them into sections of equal size. In the area of ​​the inner wing, the end rib boxes served as fuel tanks.

The engines sat on bearing blocks welded from steel profiles above the wing, where, like the two-bladed wooden propellers from Schwarz, they were largely protected from splashing water. The engines were easily accessible from a person standing on the wings. The small distance between the engines resulted in good longitudinal stability in single-engine flight. The fuel supply could be carried in four tanks with a total capacity of 2500 l (554 gal.) In the rear part of the central wing. There were also two tanks in the front wings, each holding 157 l (34.5 gal.).

The two-step hull still had the flat bottom of the Ro III and not the heavily keeled hull of the Ro IIIa. The Ro IV was therefore not based on the Ro IIIa, as is often rumored in the literature. For rescuing the flying boat from the water and for maneuvering on land, there was a so-called "rescue vehicle" per wing, on which the flying boat could roll into the water and back on land with its own power.

Technical specifications

Parameter Data
crew 4th
length 17.36 m
span 28.67 m
height 4.96 m
Wing area 70.67 m²
Wing depth 2.64 m
Empty mass 4360 kg (N183), 4800 kg (N184)
Takeoff mass 5675 kg (N183), 5975 kg (N184)
Top speed 176 km / h at sea level (N183)
Climb performance 173 m / min in 300 m (N183)
Service ceiling 2670 m (N183)
Engines 2 × Napier Lion Series V with 450 hp each

See also

literature

  • Philip Jarrett: Beardmore's Heavy Metal Monsters . In: Airplane Monthly February 1990, pp. 74-79
  • John Stroud: Rohrbach Flying Boats (Wings of Peace) . In: Airplane Monthly, January 1991, pp. 50-54
  • "All-Metal Flying Boats For Britain" . Flight International, July 17, 1924, pp. 449-451
  • Peter London: British Flying Boats . Sutton Publishing, 2003, ISBN 0-7509-2695-3 , pp. 94-96
  • "The Beardmore-Rohrbach" Inverness "Flying Boat" . Flight International of September 24, 1924, p. 617 f.
  • Fred Gütschow: The German flying boats - flying boats, amphibious flying boats and projects from 1909 to the present . Motorbuch Verlag, 1978, ISBN 3-87943-565-0 , pp. 246-252
  • Hans-Jürgen Becker: Seaplanes - flying boats, amphibians, float planes (Die deutsche Luftfahrt Volume 21) , Bernard & Graefe Verlag, 1994, ISBN 3-7637-6106-3 , p. 130 f.

Web links

Individual evidence

  1. ^ Photo of the Rohrbach-Kastenholm on Flight from July 17, 1924
  2. ↑ Recovery vehicle for landing the flying boat (here at the Ro II)
  3. ↑ Airplane Monthly February 1990, p. 78