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DAVID SCHWARZ  (DECEMBER 20, 1852,KESZTHELY, HUNGARY – JANUARY 13, 1897, VIENNA)  OCCUPATION     INVENTOR KNOWN FOR:    CREATED THE FIRST FLYABLE RIGID AIRSHIP

David Schwarz


(December 20, 1852,Keszthely, Hungary – January 13, 1897, Vienna)

Occupation     Inventor
Known for:    created the first flyable rigid airship

David Schwarz (December 20, 1852,Note a Keszthely, HungaryNote b – January 13, 1897, Vienna[1]) was a Croatian[2] aviation pioneer of Hungarian-Jewish descent.[foot 1][3][4][5]

Schwarz created the first flyable rigid airship. It was also the first airship with an external hull made entirely of metal. He died before he could see it finally fly. Sources claimed that Ferdinand Graf von Zeppelin purchased the patent from his widow,[3] but Hugo Eckener disputed this.[6]

Contents:

Life

David Schwarz was the son of Jewish parents. He was a wood merchant and spent most of his life in Zagreb, then part of the Kingdom of Croatia-Slavonia, Austro-Hungarian Empire, now Croatia.

Although Schwarz had no special technical training, he busied himself with technology and developed improvements for woodcutting machinery.[3]

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Airship thoughts

Schwarz first interested himself with airships in the 1880s. This occurred as he stayed in a Croatian log cabin at the start of winter to supervise the treefelling in a newly purchased forest. As the work took longer than planned he had his wife send him literature to while away the evenings. Because the works of Charles Dickens and Victor Hugo did not appeal to him, an assumption arising from one of his wife's letters, she sent him a work from Aristotle and a Mechanics textbook. Although Schwarz became excited, it is not altogether clear this inspired him to build his own airship. The wood business suffered due to his obsession and, like other airflight pioneers, his project attracted mockery. Nevertheless his wife Melanie supported him. Schwarz busied himself using aluminium for construction, then a very new material.[3]

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In Russia and the first airship

David Schwarz worked out the construction of his all-metal airship. He then offered his documents to the Austria-Hungary war minister. Great interest was shown, but no one was ready to provide financial support.[3]

The Russian military attaché, a technically educated man, advised Schwarz to demonstrate his airship in St. Petersburg.[3] There, an airship following Schwarz's idea was built in 1893.[3][7][8] Schwarz and later also his widow assumed that test flights would also be made there, but this did not happen. He began construction late 1892, with industrialist Carl Berg supplying the aluminium and necessary funding.[9] Sources report problems arose during gas-filling. George Whale wrote that on "inflation, the framework collapsed".[7] Dooley cites Robinson's detailed dimensions, weights and engine performance, and reports several deficiencies in the design: Schwarz apparently intended the metal skin to hold the gas directly without gas bags; Russian engineer Kowanko pointed out the lack of a ballonet would cause stresses on the skin during ascent and descent; the skin was not airtight; temporary "filling bags" were also not airtight, Schwarz and the manufacturer both blaming each other; and finally the skin imploded after filling directly and waiting.[10]

The specifications of this first airship were:[11]

* gas volume: 3,280 cubic metres (116,000 cu ft)
* empty weight: 2525 kg
* gross lift: 958 kg
* power: four cylinder engine weighing 298 kg, 10 horsepower (7.5 kW) at 480 rpm
* ballast and fuel: 170 kg
* equipment and three people: 385 kg
* net lift: 85 kg

The circumstances of Schwarz's return is unclear, reports were of a hasty departure from Russia.[3]

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Back in Germany and construction at Tempelhof

AIRSHIP - DAVID SCHWARZ  (DECEMBER 20, 1852,KESZTHELY, HUNGARY – JANUARY 13, 1897, VIENNA)  OCCUPATION     INVENTOR KNOWN FOR:    CREATED THE FIRST FLYABLE RIGID AIRSHIP

AIRSHIP - DAVID SCHWARZ  (DECEMBER 20, 1852,KESZTHELY, HUNGARY – JANUARY 13, 1897, VIENNA)  OCCUPATION     INVENTOR KNOWN FOR:    CREATED THE FIRST FLYABLE RIGID AIRSHIP

AIRSHIP - DAVID SCHWARZ  (DECEMBER 20, 1852,KESZTHELY, HUNGARY – JANUARY 13, 1897, VIENNA)  OCCUPATION     INVENTOR KNOWN FOR:    CREATED THE FIRST FLYABLE RIGID AIRSHIP

In Germany in 1894, Carl Berg procured a contract to build an airship for Royal Prussian Government, citing Schwarz as idea-provider.[12][13] Carl Berg had already experience in working and developing the then new aluminium, and was to later deliver parts for Zeppelin's first airship. With financial and technical help from Berg and his firm, the airship was designed and built.

The construction began in 1895 at the Tempelhof field in Berlin.[14] For a time the Prussian Airship Battalion put its grounds and personnel at Schwarz's disposal.[15] The pieces were produced in Carl Berg's Eveking Westphalia factory and under the direction of Schwarz, assembled in Berlin.[16] A gondola, also of aluminium, was fixed to the framework. Attached to the gondola was a 12 horsepower (8.9 kW) Daimler engine that drove aluminium propellers. One of the propellers was used to steer the craft.[7]

In 1896 June Carl Berg was in Moscow and sent a card to his stepfather, apparently indicating that he had searched for information on Schwarz and became cynical of delays and was nearly convinced he had been swindled.[17]

Due to delays, the airship was first filled with gas on 1896-10-09 and tested, but the results were not satisfactory because the hydrogen gas delivered by the Vereinigten Chemischen Fabriken from Leopoldshall (part of Staßfurt) was not of the required quality and did not provide sufficient lift. (Some sources mention a test was done on October 8, 1896.[18][19]) It was reckoned that gas with a density of 1.15 kg per cubic metre was needed. Gas with that quality could not be produced until 1897-01-13, the day of Schwarz's death.[3]

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Death and maiden flight

Schwarz did not live to see the maiden flight of his airship. Between 1892 until 1896 he was often traveling, which had affected his health. In 1897-01-13 he collapsed in the street in Vienna by the restaurant "Zur Linde" and died minutes later in a hallway from heart failure. Historical sources[20] speak of a "Blutsturz"[3] (a term meaning either hemoptysis or hematemesis). Shortly before, he had received news that his airship was ready to be filled with gas.[3]

The city of Vienna honoured David Schwarz with an Ehrengrab (a memorial grave) and with a Grabmal (a kind of tomb) at the Zentralfriedhof.[3][21]

Carl required confirmation of Schwarz's death, suspecting he had fled to sell his secrets.[22] Nevertheless, Berg resumed the work with Melanie, Schwarz's widow and together with the Airship Battalion they completed the airship with the addition of a gas relief valve.[22]

This second airship had these specifications:[23]

* gas volume: 4610 cubic metres
* length 38.32 metres
* elliptical cross-sectional area: 132 square metre, 15.4 metre wide, 18.2 metre high,
* engine: 12 horsepower (8.9 kW) Daimler weighing 508 kg
* vertical airscrews: three 2.6 metre diameter, two on hull, one above gondola[24]
* horizontal airscrew: one mounted under the gondola
* skin: 0.2 mm aluminium plates riveted to framework

Sean Dooley analysed the engineering structure from the drawings and considered it deficient such that the skin took most of the shear stresses, as could be seen in the photo in flight.[25]

The second airship tested with partial success at Tempelhof near Berlin, Germany, on 3 November 1897. Battalion mechanic Ernst Jägels[26][27] climbed into the gondola and lifted off at 15:00.[26] The ship broke free of the ground crew, and because it rose too fast Jägels disengaged the horizontal propeller.[26] At about 130 metre altitude the driving belt slipped off the left propeller, causing partial loss of steering, the ship "turned broadside to the wind, and the forward tether broke free."[26] As the ship drifted up to 510 metres the belt slipped off the right propeller, thus losing all steering.[26] Jägels then opened the newly fitted gas release valve and landed safely, but the ship turned over and collapsed.[26]

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Legacy

Starting around the time of the trial flight crash, and for decades after, various reports were written, some often conflicting and misleading.

Later, Berg, and also his son would write negatively of his experiences with Schwarz.

Sources vary, some[who?] say Count Ferdinand von Zeppelin purchased the patent from his widow in 1898, others claim he used the design, however Dr Hugo Eckener addressed these claims as legend stating:

"Count Zeppelin negotiated with Herr Berg's firm for the purchase of the aluminium for his own ship. The firm, however, was under contract to supply aluminium for airships exclusively to the Schwarz undertaking. It had to obtain release from this contract by an arrangement with Schwarz' heirs before it could deliver aluminium to Count Zeppelin. That is the origin of the legend.
—Dr. Hugo Eckener[6]

Cvi Rotem (1903–1980) wrote the only known biography titled David Schwarz: Tragödie des Erfinders, Zur Geschichte des Luftschiffes, and Robinson reviewed the 187 page manuscript in the March 1984 issue of Buoyant Flight.[28] Cvi Rotem wrote that both Berg and Schwarz wished to keep their work secret.

Between 2000-12-03 and 2001-04-29 the Museen der Stadt Lüdenscheid held an exhibition which covered Berg, Schwarz and Zeppelin history from 1892 to 1932, which displayed papers, photographs and remnants.[29][30][31]

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The Construction and Testing of the Airship

AIRSHIP - DAVID SCHWARZ  (DECEMBER 20, 1852,KESZTHELY, HUNGARY – JANUARY 13, 1897, VIENNA)  OCCUPATION     INVENTOR KNOWN FOR:    CREATED THE FIRST FLYABLE RIGID AIRSHIP

David Schwarz (1852 - 1897) was a wood merchant from Zagreb, Croatia. Although he did not have an official technical education, he still knew a lot about mechanics and construction of airships as that was his hobby. He was fortunate enough to realize his dream - the construction of the world's first directable all-metal airship.
He made a contract about the construction of the airship with Carl Berg, a German factory owner. All the parts for Schwarz's airship were made by Berg's engineers and technicians in his factory, and in order to complete the airship over thousand plans were made. During the construction Schwarz was greatly assisted by major Hans Gross, who was an excellent balloon pilot. Just like Schwarz, Gross was also very enthusiastic regarding the airship project.
At that moment very little was known about the airship. The German emperor Wilhelm II himself visited several times the hangar on Tempelhof field near Berlin, where the parts produced in Berg's factory were put together. Carl Berg invested large sums of money in this project, bearing in mind that he will earn much more by building and selling airships. Schwarz also realized that the eventual success of his airship would solve all his problems.
As he was aware of the basic laws of aerodynamics, Schwarz gave his airship a pointed forward part. Journalists said that his airship resembled a pencil, while military observers thought that the airship was shaped like an artillery shell. Many people worldwide - balloon builders, engineers, enthusiasts, scientists - were not merely interested, but amazed by the construction of Schwarz's airship. Schwarz was indeed writing a new chapter in the history of flying, and he had already proven some scientists to be wrong when it came to the construction of his airship (a famous German physicist Hermann von Helnholz (1821 - 1894) insisted that airships should not be built out of metal as they would be too heavy to fly.

It is interesting that very little was written about Schwarz and his airship in Croatian newspapers of that period. Agramer Tagblatt has not even mentioned him, while a small article appeared in Zagreb daily newspaper Obzor on September 11th 1896. This is the complete text of the article: "The day before yesterday we received a telegram sent by an amateur journalist. He informed us that David Schwarz from Zagreb has invented an airship which he hopes he could direct on his own free will. The inventor is now finishing his airship on Tempelhof field near Berlin. The huge airship is built out of aluminium alloy, the composition of which is being kept secret by the inventor. The first test with that airship will be carried out on 27th of this month, when the German general staff returns from the inspection trip to Vienna."
This was the first news in Croatia about the project of David Schwarz.
The German government was very interested in the invention of David Schwarz. It is interesting to point out that the same German government only two years before refused the idea of its own general Ferdinand von Zeppelin, about the construction of a directable airship. One has to bear in mind, though, that Zeppelin's ideas were just theoretical, while Schwarz made detailed plans of the airship. As Zeppelin had no knowledge to create similar plans of his own airship, he was not only interested in Schwarz's airship, but he also wanted to cooperate with him. Schwarz refused any kind of cooperation.

AIRSHIP - LATTICED PROPS FROM SCHWARZ'S AIRSHIP - DAVID SCHWARZ  (DECEMBER 20, 1852,KESZTHELY, HUNGARY – JANUARY 13, 1897, VIENNA)  OCCUPATION     INVENTOR KNOWN FOR:    CREATED THE FIRST FLYABLE RIGID AIRSHIP

Latticed props from Schwarz's airship

The airship was completed in summer 1896, and was ready for testing. However, Schwarz was hesitating mostly due to health problems - he had a weak heart. Also, he was expecting the emperor Wilhelm II to attend the official public flight that was supposed to take place on September 27th. The emperor could not come and the flight was cancelled. Schwarz would not wait any longer. He wanted to test his creation.
Finally, on October 8th 1896 the process of filling the airship with hydrogen began. The quality of hydrogen was not satisfactory. This meant that the expected lift force of 1.15 kN per square metre could not be achieved. The airship was taken out of the hangar in which it was put together. Dozens of soldiers were holding steel cables which were tied on every side of the airship in order to prevent the airship from lifting before the airship's engine started working. The engine was thoroughly tested and it proved not to be only reliable, but also strong enough to move the airship.
The test is described in an article in Obzor: "Yesterday, on Thursday, October 8th 1896, Schwarz's airship managed to lift only a few metres above the ground, while the soldiers were holding it with ropes. It is said that the gas used in the airship was bad, and thus the airship could not perform as expected. It was decided that the airship would be filled once again with good gas and tested."
It was an unforgettable day for Schwarz. All humiliations, sufferings and harassment that he experienced previously were defeated. True, the airship lifted only a few metres, but the engines were working perfectly and the propellers were turning as they were supposed to. This meant that the airship could be directed on one's free will. It was no longer a balloon carried by wind without the control of a few people carried in a basket. It was a directable airship.

After that test Schwarz was very excited. He had many ideas about how to use airships; he created a vision of air traffic. Airships would, he thought, become faster and stronger, transporting passengers, mail, many different sorts of cargo across vast distances in short time. Hours, not days, would be needed to reach distant continents.

AIRSHIP - THE FOUR - CYLINDER, 16 HP DAIMLER ENGINE OF SCHWARZ'S AIRSHIP - DAVID SCHWARZ  (DECEMBER 20, 1852,KESZTHELY, HUNGARY – JANUARY 13, 1897, VIENNA)  OCCUPATION     INVENTOR KNOWN FOR:    CREATED THE FIRST FLYABLE RIGID AIRSHIP

The four - cylinder, 16 hp Daimler engine of Schwarz's airship

It was arranged that the inventor himself would prove the value of his project on January 15th 1897. Schwarz left Zagreb on January 12th and headed for Berlin. When he was leaving he said to his wife and children: "They do not believe me, but they will after I die." He spent the first night in Vienna. On January 13th he sent a telegram to his wife saying: "I am well, and tomorrow I will arrive in Berlin. The flight is the day after tomorrow." He also sent a telegram to Berlin: "I am arriving tomorrow. Please start filling the airship with hydrogen." He was very happy and very excited. He could hardly wait to continue his trip to Berlin. Around noon he and some of his friends went for lunch to one of the most famous restaurants in Vienna, Zur Linde. After a few spoons of soup he started feeling nausea and dizziness. "I do not know what is wrong with me... I feel sick as I have never felt before.", he said to his friend. The friend advised him to go outside and breathe some fresh air. As soon as Schwarz entered the hall of the restaurant, he leaned against the wall with his hands and, after a minute, collapsed and died. He was 45 years old.
The Austrian Society of engineers and technicians buried David Schwarz in a honorary tomb with a nice headstone on the central Wien cemetery. The Universities of Berlin and Wien awarded him posthumously with the title of honorary engineer. Despite all this his name will soon disappear from the history of mankind.
The German general staff and the Society for aerial navigation continued to show interest in Schwarz's airship. When Schwarz was making a contract with the German government about the construction of the airship, it was also agreed that Schwarz would have an exclusive right to build airships for the next 30 years. There were many people who were pleased by Schwarz sudden death. Among these were certainly Germans who could not believe how much care and honour was given to this Croatian wood merchant, and who, therefore, tried to erase Schwarz's name from the history of technological development. This was one of the reasons why the German government not only wanted to get rid of the contract which now existed between the government and Schwarz's heirs, but also started to favour count Ferdinand von Zeppelin, whose ideas were until Schwarz's death constantly refused by the same government. Zeppelin was, of course, very pleased with the new situation. He possessed enough technical information about Schwarz's airship, which he obtained illegally from the factory of Carl Berg. Nobody can deny Zeppelin's enthusiasm and wish to build a similar airship. But, if we take in consideration Zeppelin's education and the fact that he knew very little about technical sciences, then it is obvious that he could have been only an organizer and an advocate of the usage of airships. Schwarz was, on the other hand, although he did not have an official technical education, so educated in this sense, that his ideas were worked out in detail by technicians and engineers during the construction of the airship.
The German army was aware that airship is a new kind of weapon. It could be used for reconnaissance, troop transport, bombing. Apart from that, German colonies in Africa were full of raw materials which would enable the construction of many such airships.

AIRSHIP - SCHWARZ'S AIRSHIP FLYING 400 METRES ABOVE TEMPELHOF FIELD DURING ITS TRIAL FLIGHT - DAVID SCHWARZ  (DECEMBER 20, 1852,KESZTHELY, HUNGARY – JANUARY 13, 1897, VIENNA)  OCCUPATION     INVENTOR KNOWN FOR:    CREATED THE FIRST FLYABLE RIGID AIRSHIP

Schwarz's airship flying 400 metres above Tempelhof field during its trial flight

Schwarz died before he could see his airship flying properly. Nevertheless, his wife Melanie, an energetic and wise woman, went to Berlin just after the funeral to continue the work of her husband. She was trying to organise a trial flight. The flight was supposed to show and prove the value of the airship. However, she encountered numerous problems. The German military circles were annoyed by the fact that the airship was not of German origin, and they were trying to sabotage Melanie Schwarz's efforts whenever possible. Still, the trial flight was carried out. The German emperor wanted to be present during the trial flight of the airship, but he had to attend a meeting with the Austrian emperor Franz Joseph I. The trial flight took place above Tempelhof field. The airship performed as expected. However, when the airship was flying at the height of 460 metres one of the propellers stopped working, because its driving belt fell down. The airship crashed and was severely damaged. Still, the German Ministry of army gave flattering acknowledgements in its official opinion about Schwarz's airship. The same opinion was repeated on September 30th 1908 in the magazine Neue Freie Presse. Despite all this, not one German officer was allowed to steer the airship during its trial flight. Why? It was an order. Clearly, someone in the German army did not want the trial flight to take place. After the trial flight Zeppelin gave Melanie Schwarz 15, 000 Marks in order to obtain some information about the airship and to continue using the information that he already possessed.
The testing of the airship which took place on October 8th 1896. was carried out without the presence of the public. This proved to be Schwarz's big mistake. If the public had been present, then nobody would have been able to cover up and belittle Schwarz's invention or even, later, deny its precedence and originality. [32]

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Technical Characteristics of Schwarz's Airship

For the lift of his airship Schwarz anticipated the usage of hydrogen. Hydrogen is a dangerous inflammable gas. Schwarz's airship, therefore, consisted of 12 separate compartments, each filled with hydrogen. The pointed forward part of the airship was 11 metres long, the central, cylindrical part was 24.32 metres long and the rear part, that was shaped like a hemisphere, was 3 metres long. The airship's total length was 38.32 metres, and it was 12 metres wide. The airship's outer casing consisted of long aluminium foils 0.18 - 0.20 mm thick, which were riveted to the skeleton of the airship and were impervious to air.
The skeleton of the airship consisted of 34 aluminium latticed props of different shapes and sizes. There were 13 oval openings in the lower part of the airship that were used for filling each of 13 separate compartments with hydrogen.
The airship's gondola was made out of thin aluminium plates, and was hanged on four props that were connected to two strong props of the airship's skeleton.
The Daimler engine had 16 hp and it propelled all four airship's propellers. There was one propeller on each side of the of the airship. These propellers were 2 metres wide were propelled via driving belts. The main propeller was 2.6 metres wide and was located 3 metres behind the airship's gondola. This propeller was also propelled via by a driving belt. The fourth propeller was hanged directly below the gondola and was propelled by a long shaft. This propeller was supposed to support lifting and descending of the airship. The main propeller was axially movable, which thus enabled the airship to fly in any direction wanted.
The engine's exhaust pipe was installed in such a way that exhaust fumes could not ignite the hydrogen. The aluminium skeleton of the airship, as well as the casing of aluminim foils is the most important invention in the development of airships. It is also one of the main reasons why Schwarz's creation is called an airship, and not a balloon. Up to that moment there were several attempts to create successful directable balloons. However, the installation and usage of an engine on a gondola of a balloon proved very dangerous. Namely, the silk out of which a balloon is made of is very flammable, and this, therefore, increases the possibility of hydrogen catching fire. The tragic death of dr. Karl Wölfert is an good example for this.
The weight of Schwarz's airship was 3, 560 kg, the estimated speed was 25 km/h, and the airship could reach at least the height of 250 metres. The force of lift of the airship was 3, 800 kg. This means that the airship could lift and carry one person and 130 kg of ballast.  [33]

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Footnotes

1. ^
* Note a: Sources for date of birth vary: Library of Congress cites Rotem, Ẓ. giving 1850-12-07, and cites Brockhaus giving 1850-12-20[1]
* Note b: Library of Congress cites Brockhaus place of birth as Zalaegerszeg, Ungarn (Hungary).[1] Note in the mid-19th century Zalaegerszeg was in a confusing state

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Citations

1. ^ a b c LOC
2. ^ http://books.google.com/books?id=vkpLh-XBcG0C&pg=PA34&dq=%22David+Schwarz%22++aviation+croatian&hl=en&ei=RJ9jTLyhGoTn4AbyteDgCg&sa=X&oi=book_result&ct=result&resnum=1&ved=0CCwQ6AEwAA#v=onepage&q=%22David%20Schwarz%22&f=false
3. ^ a b c d e f g h i j k l German wikipedia editors
4. ^ Facts you didn't know
5. ^ Jewish Science and Technology Books: Personalities
6. ^ a b Count Zeppelin: The Man and His Work, translated by Leigh Fanell, pages 155-157, 210-211. London -- Massie Publishing Company, Ltd. -- 1938 (ASIN: B00085KPWK) (online extract)
7. ^ a b c George Whale, 1995, Chapter II / Early airships and their development to the present day / Germany
8. ^ he had started work at least by 1892-05-02 when Russian War Ministry agreed to allow him to build it there, after being rejected by the Austro-Hungarian War Ministry. Dooley, A.183 citing Robinson, p2
9. ^ Dooley, A.184 citing Robinson, p1 and Berg, Berg and Schwarz signed a contract 1893-08-23
10. ^ Dooley, A.185-A.186 citing Robinson, pp2-3
11. ^ Dooley, A.185 citing Robinson, pp2-3
12. ^ Dooley, A.186, Berg signed a contract with the Royal Prussian Government in 1894-12-16 with himself as builder and Schwarz as source of the ideas. Berg and Schwarz signed a contract on 1894-12-21
13. ^ Dooley, A.186-A.187 Fig. 18. Battalion engineer Tenzer and Berg's engineers made drawings shown in Figure 18 titled Luftschiff David Schwarz das erste Luftschiff des starren Systems, erbaut von Commerzienrat Carl Berg.
14. ^ Dooley, A.187
15. ^ Dooley, A.186, in the Prussian Airship Battalion's hangar
16. ^ Whale, Dooley, A.184. Accounts vary, George Whale wrote that the Berlin firm of Weisspfennig and Watzesch built it while Sean Dooley cites Douglas Robinson as stating these were Carl Berg's engineers.
17. ^ Eckhard Trox et al., 2000. Objektliste.pdf exhibit list from now-stale Traum von Fliegen museum site
18. ^ Sucur, Ante (2004). "The Airship of David Schwarz / The Construction and Testing of the Airship". http://croatian-treasure.com/airconst.html. Retrieved 19 October 2009.
19. ^ rr0.org quoting 'Obzor'
20. ^ Rosenkranz, Hans (1931). Ferdinand Graf von Zeppelin: die Geschichte eines Abenteuerlichen Lebens. Ullstein. p. 58.
21. ^ Plot: group 63, row 36, number 13. Grabstellensuche der Stadt Wien, Simmeringer Hauptstraße 234 2. Tor 1110 Wien
22. ^ a b Dooley A.191
23. ^ Dooley A.191 citing Robinson page 4
24. ^ Whale writes the central screw was for steering
25. ^ Dooley A.192
26. ^ a b c d e f Dooley A.193
27. ^ Schnitzler writes Jägels was a completely inexperienced airshipman, a former Prussian Unteroffizier
28. ^ Dooley A.183
29. ^ Eckhard Trox 2000, Museen der Stadt Lüdenscheid German press release, and book: ISBN 978-3929614435
30. ^ Schnitzler 2000
31. ^ extended from 2001-03-04
32. ^ http://croatian-treasure.com/airconst.html
33. ^ http://croatian-treasure.com/airconst.html

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References

* Dooley, Sean C., The Development of Material-Adapted Structural Form - Part II: Appendices. THÈSE NO 2986 (2004), École Polytechnique Fédérale de Lausanne
* Hugill, Peter J. 1995. World Trade Since 1431: Geography, Technology, and Capitalism, JHU Press, ISBN 0801851262, page 258: "two unsuccessful airships in 1897, that of David Schwartz of Austria being important because of its aluminum structure and covering (Beaubois, 1976, 29-31)"
*
* Schnitzler, Norbert. 2000. WWW-Tipp der Woche 24/2000 (German summary of museum exhibition)
* Whale, George. 1995. British Airships, Past / Present / Future, ISBN 1426400748, BiblioBazaar (October 26, 2007) (also 1996 Gutenberg version)
* Editors of German Wikipedia David Schwarz – Wikipedia (current version)

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