Lightweight garage #14 The last big German Zeppelin

Published on

20.01.2022

The vehicle

At the beginning of the 20th century, aviation was still in its infancy and the thousands of airplanes flying around the world today were still unimaginable. The first airplanes were often built mainly from wood, struts, tensioning wires and canvas and were rather small. At the same time, airships were developed, which can be divided into three categories.

Impingement airships in which the hull is held in shape by overpressure and to which the nacelle and tail unit are directly attached.

Rigid airships which, similar to a ship, have a keel and a fixed frame which is covered by fabric panels and receives its buoyancy from lifting gas cells.

Semi-rigid airships that have a supporting structure on the underside in addition to a bulging hull. This is where the engines, nacelle and tail unit are attached.

LZ 130 Graf Zeppelin II was the last German rigid airship and was designed for Atlantic crossings and trips to the tropics. Its frame was made of duralumin and its hull was made of canvas, which was coated with various coatings to protect it from the weather. The aluminum powder added to the paint for thermal protection gave the airships their characteristic silver color. LZ 130 Graf Zeppelin II had 16 lifting gas cells, which were originally to be filled with helium, but the USA refused to supply this gas and so hydrogen was used, despite its danger. To prevent an accident like the LZ 129 Hindenburg in Lakehurst, the connections between the shell and the supporting structure were coated with a conductive layer of graphite.

The lifting gas cells and the rigid hull enabled the luxurious interior of the airship. On board there were lounges, washrooms, a dining room, double cabins for 40 guests and other rooms for accommodating the crew, luggage and the operation of the airship. It was powered by four 16-cylinder Daimler Benz diesel engines and towing propellers. The continuous output of the engines was 799 hp and the maximum output 999 hp.

Although designed for journeys to distant countries, the LZ 130 Graf Zeppelin II mainly within Germany and completed 30 journeys.

The era of the large German airships ended before the end of the Second World War and LZ 130 Graf Zeppelin II was scrapped together with other airships in 1940 due to political pressure. Today, airships are mainly used for tourist purposes.

Airship LZ 130 Graf Zeppelin II - Basic data

Source: LZ 130

Commissioning	1938
Length	245 m
Diameter	41,2 m
Volume	200.000 m³
Empty weight	114 t
Payload	105 t
Payload	70 t hydrogen/50 t helium
V_max	135 km/h
Reach	12,000 km

Unknown author, Flying zeppelin, Public Domain

The technology

At the beginning of the 20th century, Alfred Wilm experimented with producing various particularly strong aluminum alloys. He applied standard steel production processes to various aluminum alloys. He discovered that the alloys exhibited greater strength and hardness after quenching and a resting period of several days. This is mainly due to the fact that some time after quenching, an initially suppressed precipitation of a second phase, a homogeneous chemical compound of two metals, in this case between copper and aluminum, takes place in the alloy. This can take place either by cold ageing (room temperature) or artificial ageing (higher temperatures).

In addition to aluminum, Wilm's alloy also contained small amounts of copper, magnesium, manganese, silicon and iron. Due to its strength, the new alloy was called duralumin. Today's high-strength aluminum alloys are often still trivially referred to as this or similar and are often used in various industries.

The lightweight construction and weight management aspect

As can be seen from the table, duralumin has more than half the density of simple steels. This means that more than half the weight of the frame can be saved. Above all, however, duralumin has a very similar tensile strength to simple steels.

Material comparison

Source

Material	Density [kg/dm³]	E-modulus [N/mm²]	Tensile strength [N/mm²]
Dural AlCU4Mg1	2,75-2,87	73.000	420-500
Pure aluminum Al99.5	2,7	70.000	75-100
Unleg. Steel S355	7,9	200.000	510
Chrome-nickel steel	7,9	200.000	500-750
Spring steel 54SiCr6	7,46	210.000	1450-1750

This made it possible to use the large scaffolding that formed the supporting structure of the rigid airships. A military airship, LZ 26was the first German zeppelin whose basic structure was made of duralumin.

Steel stove, Skeleton of a zeppelin made of duralumin, CC BY-SA 3.0

Illustration of the LZ 130 Graf Zeppelin II

This zeppelin was also the first to have a ballast water extraction system to compensate for weight loss due to fuel consumption during the journey. The water was obtained by condensation from the exhaust gases of the diesel engines. The water vapor produced during combustion was collected and cooled. The water thus obtained was fed into the ballast water tanks. In some cases, this ballast water was also filled by precipitation on the hull or by collecting water from bodies of water. However, the use of the ballast recovery system was much more reliable and independent of the weather.

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