How is helium used in airships
Problems with obtaining helium
The zeppelin in flightCorrect handling of the lifting gas was an essential and challenging element to move an airship safely over thousands of kilometers. In addition to guaranteeing absolute fire safety, the crew had to consider many factors such as the local air pressure, the load or the filling level of the gas cells. Due to the fuel consumption of the engines in the air, an airship constantly loses weight, but the buoyancy of the lifting gas initially always remains the same. As the weight decreased, it would continue to rise and be in danger. In order to maintain the prescribed flight altitude, the (expensive) lifting gas must be gradually released to compensate. This process is called trimming. The disadvantage of this method was that the carrying capacity of the discharged gas was lost. An example serves to clarify: LZ 126 releases up to 1/3 of the hydrogen it carries on an Atlantic journey. The gas cells had so-called maneuvering valves for releasing the gas, which could be controlled from the driver's gondola. The control element for this was the gas panel.
Gas board from LZ 129.
In the course of time, different technical methods have been developed to avoid venting the gas, especially in view of the very high production costs of helium. In addition to attempts to heat or cool the lifting gas before filling it, a ballast water recovery system was installed in the LZ 130. Ballast water could be obtained from the hot exhaust gases. These were not released directly into the environment, but cooled down, with condensation forming. This water was collected and could be pumped back and forth between different ballast tanks, depending on the flight situation.
Other important factors in the gas balance During the flight, various influences could change the carrying properties of the gas. The gas could warm up and expand as a result of intense heat, for example from the sun's rays. In contrast, rainwater could increase the total weight of an airship by several tons. The gas cells of an airship were not completely filled before take-off. With increasing altitude and decreasing air pressure, the gas expanded, so it was necessary to leave a certain percentage of the gas cell volume free. Once the airship had reached a certain altitude - the impact height - the gas cells were filled to the brim. If this critical height was exceeded, the gas could tear the gas cells. Pressure relief valves in the gas cells should avoid this.
Rebound height: Height of the highest permissible internal pressure of the gas cells.
It is important for the refueling process because the gas cells are not completely filled or the lifting gas is preheated. The lifting gas has space to expand in the gas cells. The lower the impact height, the more lifting gas can be filled in (static buoyancy), which in turn means that more payload can be carried.
Additional benefits of heliumIn addition to these technical advantages, the helium would have had other positive properties:
Problems with obtaining helium
Why was there no widespread use of helium in German airship travel?Even the zeppelin farmers did not ask themselves this question seriously until after the Hindenburg accident, although the dangers of hydrogen as a lifting gas had long been known. Not only was the passengers in danger, the entire airship was at stake. At first, however, hydrogen was used, because the crews were very experienced and very careful in handling the hydrogen; compared to hydrogen, helium has less carrying properties. Usable helium deposits existed only in the USA.
The US developed rapid, inexpensive manufacturing processes and transportation options. In 1923 the first helium airship, the USS Shenandoah, took off in the USA. Hundreds of other helium-filled airships followed. By 1935, three rigid airships had been built in the United States and one in Germany. By 1945 there were as many as 168 impact airships.
Problems of the helium tradeThe US insisted on its monopoly and did not like to supply helium to other countries. The overestimation of the military uses of the Zeppelin led to a very restrictive helium policy by the US government with regard to the storage, use and delivery of US helium. Political obstacles, bureaucratic hurdles and logistical problems were favored, which had a major impact on the helium trade. The USA operated its own military rigid airship program until 1935, at least until then this internal requirement led to export restrictions. After the completion of the LZ 130 in September 1938, there were of course also massive political reasons that ultimately led to the export ban.
1. Helium Act of 03.03.1925
The 2nd Helium Act of 1927 did not ease the helium trade and the USA always only kept one fill quantity in stock. This is why the LZ 127 is still being designed exclusively for hydrogen filling. The Hindenburg, on the other hand, was already designed for both carrier gases, hydrogen and helium. The logistical organization of the helium trade turned out to be extremely complicated. There were not enough gas containers to be found in Germany, so they had to be borrowed from all over the world. Since the borrowed containers aroused the suspicion of the German engineers, each gas cylinder had to be individually checked and approved by the German compressed gas committee.
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