| Zeppelin-Staaken E-4/20 | |
|---|---|
| Role | Airliner |
| National origin | Germany |
| Manufacturer | Zeppelin-Staaken |
| Designer | Adolf Rohrbach |
| First flight | 1919 |
The Zeppelin-Staaken E-4/20 was a revolutionary four-engined all-metal passenger monoplane designed in 1917 by Adolf Rohrbach and completed in 1919 at the Zeppelin-Staaken works outside Berlin, Germany. The E-4/20 is likely to have been the first 4-engined all-metal heavier-than-air aircraft ever built. The Zeppelin company is today better known for their Zeppelin airships or lighter-than-air dirigible aircraft. However, during and after the First World War the Zeppelin company also manufactured a number of innovative groundbreaking aircraft, including heavy bombers.
The E-4, designed in 1917, was completed in 1919 and test flown between 1920 and 1922 when it was broken up on the orders of the Allied Control Commission. Some surviving photos in the Smithsonian collection show smiling passengers embarking and disembarking from the aircraft so it is also possible that it saw some limited service as an airliner.
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The Zeppelin-Staaken E-4 represents a revolutionary step in aircraft design philosophy and construction. At a time when most aircraft were small single-engined biplanes made of wood and canvas, here was a large—102-foot wingspan—(by comparison a modern Boeing 737 jet has a 93-foot (28 m) wingspan) all-metal four-engined stress-skinned, semi-monocoque, cantilevered-wing monoplane with enclosed cockpit, accommodation for up to 18 passengers plus crew, including 2 pilots, radio operator, engineer and steward as well as full r/t communications, w.c., galley and separate baggage / mail storage. In short, a modern airliner. With a maximum speed of 143 mph, cruising speed of 131 mph, a range of about 750 miles (1,210 km), and a fully loaded weight of 18,739 lbs, it was a giant for its time. Outperforming almost all Allied aircraft of the day, it is little wonder the Allied Control Commission ordered its destruction in 1922 out of fear that Germany might convert it for use as a strategic bomber. Its like was not seen again until the mid to late 1930s when aircraft with a similar design were produced in Britain, France and the USA. It is interesting to note that Rohrbach designed this civilian passenger aircraft in 1917 at the height of the First World War. Analogies of large passenger aircraft designed in time of war can be made with the groundbreaking Lockheed Constellation and Vickers Viscount, both civilian passenger aircraft that were designed during the Second World War.
Designed by Adolf Rohrbach, the E-4 included numerous innovations, including its all-metal monocoque construction, onboard facilities such as lavatory, kitchen and radio communications as well as its notable and sturdy monoplane load-bearing box-girder wing constructed of dural metal which formed both the wing's main girder and the structure of the wing itself. Skinned with thin sheets of dural metal to give the aerofoil shape necessary for a wing, the girder section wing had the leading and trailing edges attached to it. This superb and innovative wing was robust and self-supporting.
The Zeppelin-Staaken E-4/20 was a product of the innovative Zeppelin Airship company. Count Ferdinand von Zeppelin, founder of the Luftschiffbau Zeppelin GmbH (Zeppelin Airship Construction Co.) was himself a major aeronautical innovator, creator of the groundbreaking giant aluminium alloy framed Zeppelin lighter than air dirigible airships and later developer of the German R-Planes. As early as 1874 Zeppelin had written a paper on the construction principals of a guidable balloon and focused on the design and construction of Zeppelins from the 1880s on. He was beaten to the draw in the construction of the first dirigible by several pioneers including David Schwarz, an Austrian Jew, who built powered aluminium airships in 1892 and 1896, first in Russia and later for the Prussian Army at Tempelhof, Berlin. Schwarz's design was for an aluminium-skinned dirigible with a skin of metal of just 0.2mm providing much of the structural integrity of the vehicle. With this innovation Schwarz pre-figured monocoque stressed skin construction. However, his technique was too far ahead of the metals and metallurgy of his day and was not wholly successful. Schwarz died the day gas of sufficient purity could be delivered to fill his airship. His airship subsequently flew, proving the concept but it collapsed due to a capsize on landing. Schwarz's pioneering use of metal skin for an aircraft and his steps toward a monocoque form of construction as early as 1892 is largely overlooked by aeronautical historians but it likely had an impact on German aero-engineers who some years later successfully pioneered techniques of aircraft construction that used similar principles to Schwarz's.
Count Zeppelin used an entirely different and practical construction method for dirigibles of an internal structural framework of aluminium girders containing gas bags or balloonets to hold the volatile hydrogen lifting gas and an outer skin of lightweight fabric. This method of airship construction laid down the pattern used for all subsequent rigid airships. Between 1909 and the outbreak of war in 1914, Zeppelins carried 37,250 people on over 1,600 flights. By comparison in the same time frame a mere handful of people flew in heavier than air aircraft. Zeppelin was one of the first aeronautical pioneers to apply stringent scientific principals to the design of aircraft, focusing on issues like power-to-weight ratios of prime movers (engines), using the then new metal aluminium for structural components and so forth. Zeppelin heard of the success in Russia of Igor Sikorsky's pioneering 4-engined Le Grand and Ilya Muromets aircraft. From the outbreak of war in 1914 the 4-engined Ilya Muromets class of aircraft were used as heavy bombers. The German government saw the potential for large strategic bombers and issued a design standard which was used by several manufacturers to produce Riesen-Flugzeuge (Giant Aircraft) or R-Planes. The most successful design and manufacturing company of R-Planes was Zeppelin which was also the only company to manufacture R-Planes in series production, the notable R-VI.
Notwithstanding their success and impact on subsequent aviation history, R-Planes receive minimal coverage in most histories of aircraft, perhaps because they were designed and built by the losing side in the 1st World War. It is to be hoped that in future they will get their rightful recognition, along with Sikorsky's pioneering 4-engined aircraft, for their contribution to the development of multi-engined large aircraft.
It is little surprise that Zeppelin gathered around him some of the best and brightest aeronautical designers and engineers, notable among these were Claude Dornier, Hugo Junkers and Adolf Rohrbach. Dornier and Junkers subsequently went onto become household names in their own rights with their highly successful aircraft companies. Rohrbach is less well known but played an equally significant role in the development of aircraft design, construction and performance.
Designer Adolf Rohrbach (1889-1939), like Donier and Junkers, went on to found his own aircraft company, Rohrbach Metalflugzeug GmbH (Rohrbach Metal Aircraft Co.) where he designed and built a number of innovative and groundbreaking civil all-metal airliners, notably the Ro-VIII trimotor as well as some groundbreaking flying boats.
Rohrbach, like his countryman Junkers, pioneered modern all-metal stressed-skinned semi-monocoque monoplane aircraft during the First World War. They set the pattern for aircraft design and construction still used today. Junkers' hallmark was the use of corrugated metal for extra strength and rigidity, this proved a dead end and is no longer in use today, though it was much emulated around the world in the 1920s and '30s, for example the Ford Trimotor, Farman, and Tupolev TB-3 (Ant-6).
Rohrbach by contrast was able to safely achieve robust high (for the day) stresses and loadings using smooth skinned fuselages and wings and thus set the way for modern smooth skinned aluminum aircraft. The achievement represented by the E-4/20 is that it is the first modern passenger plane in shape, layout, facilities and construction, as photographs and line drawings of the E-4/20 demonstrate.
The Zeppelin-Staaken E-4/20 represents the point at which aircraft transformed from string and canvas to streamlined enclosed metal monoplanes. In the words of the Smithsonian Institution's "Airspace Mag" (see link below) the E-4's designer, Adolf Rohrbach, is the man who could have been Germany's Boeing or Douglas but for an unfortunate twist of fate that the ACC deemed the E-4/20 too advanced to be allowed to go into serial production and ordered its destruction, even declining offers to sell it to an allied country. Nonetheless its impact on the development of civil aviation around the world can be seen in the designs that emerged 10 and 20 years later from the likes of Lockheed, Boeing, Douglas and De Havilland.
Wingspan: 31m / 101 ft 8 inches
Length: 16.6m / 54 ft 6 inches
Wing area: 106m2 / 1,140.97 ft2
Weight: 8,500 kg / 18,739 lbs (take off weight)
Engines: 4 x Maybach IVA 190KW
Max Speed: 230 km/h 143 mph
Cruise Speed: 211 km/h 131 mph
Max Range: 1,200 km / 746miles
Load: 12 - 18 passengers
Crew: 3 - 5