OK, I've read about 4 books now on the Hindenburg and the history of the dirigibles, including one that suggests the great crash at Lakehurst in 1937 was caused by sabotage (I can't remember the title at the moment). The overwhelming evidence suggests it was faulty flying, very tight turns made by the captain (Eckener was not aboard as a result of his anti-Nazi activities) that stressed the frame, causing a rip in the fabric and a hydrogen leak which was then ignited by St. Elmo's fire as a result of the thunderstorm which had just passed. Many storms were moving through the area, and the captain was anxious to get the ship tied down and the passengers disembarked. Eye-witness testimony of the static electricity charge and leak was not available to the board of inquiry and did not surface until several years later. There was a theory proposed several years ago that the flammable skin of the dirigible caught fire and that it was not a hydrogen fire at all. The "mythbusters" show tested his theory. Their conclusion was it was indeed a hydrogen fire. Regardless of the cause, it was the end of Eckener's dream and of what had been an extremely safe (the Graf Zeppelin had traveled more than 1,000,000 kilometers with nary an injury,) fast, and comfortable method of crossing the Atlantic.

This book is the memoir/recollections of Harold Dick, a very early certified dirigible pilot who probably made more trips in dirigibles than anyone else. He was sent to Friedrichshafen as a representative of the Goodyear company to learn as much as he could about construction and operation of the huge airships. It's fascinating.

Included are some very rare photographs including one of the Hindenburg's damaged fin. Goebbels, anxious to reap some propaganda value from the airship as soon as possible, forced the captain to lift off in difficult conditions, a strong tailwind. That, coupled with a less than fully experienced helmsman, forced the huge tailfin into the ground causing damage that had to be repaired. Eckener (see [b:Dr. Eckener's Dream Machine The Great Zeppelin and the Dawn of Air Travel|558912|Dr. Eckener's Dream Machine The Great Zeppelin and the Dawn of Air Travel|Douglas Botting|http://photo.goodreads.com/books/1175794193s/558912.jpg|1639779],) by this time anathema to the Nazis for his persistent antagonism to the little mustachioed corporal's politics, had lost control of the company. Dick, who was present when the accident occurred had a camera hidden in his coat which escaped confiscation by the Nazi authorities anxious to hide evidence of the accident.

There are also extremely interesting diagrams and drawings of the frames of the airships as well as minute detail of fuel and gas requirements. The Graf Zeppelin, for example, had twelve upper and lower gas cells, the lower ones designated as fuel cells which contained 750,000 cubic feet of "Blau" gas (not blue gas --blau means blue in German-- but named after Hermann Blau, the inventor) which was a mixture of hydrogen and propane. Blau gas had a specific gravity of 1.6 which meant that "its consumption by the engines did not lighten the ship, and hydrogen did not have to be valved off wastefully during the flight to keep the ship in static equilibrium as would have been the case if gasoline had been burned." Dick has actual weights and contents of several flights as examples of how fuels were used and weights compensated for.

Dick, who made several round-trips on the Graf Zeppelin during its regular trips to South America describes the trips in detail. The political situation in Europe being what it was, the Graf was permitted to fly over France nly through a very narrow corridor. Because the gas would be blown off through valves as the ship gained altitude, it was advantageous to fly as low as possible, usually around 650 feet, spectacular viewing for the passengers, but a security risk for the French. All photographic equipment was secured to assure the French no one was taking pictures of any military value. (In one of those interesting what-if scenarios, the Hindenburg was not permitted any flight over France, the military situation having worsened by 1937, and was forced to take a northern route over Belgium and then the English Channel, added several hours to the trip. Had they arrived earlier, they might have missed the thunderstorms.)

The 5317 mile trip to Rio de Janeiro took about 80 hours (normal cruising speed was about 72 mph), the return trip some 10 hours longer due to headwinds. On the way back they would proceed up the Rhone Valley, another problem because of frequent thunderstorms and gas venting could become a conduit for lightning to enter the ship and the hydrogen cells, not something to be encouraged, so they would go high to fill the cells to full capacity then drop by 150 feet to add a margin of gas compression so there would be less danger of automatic venting. Officers in the control car would call out the apparent location of lightning flashes and they would zigzag through the valley to avoid them. It must have been spectacular, especially since they would often fly underneath the storms where wind gusts were more likely to be horizontal rather than vertical and much easier to compensate for. Being actually struck by lightning was not considered a problem because the steel structure acted like a Faraday cage. Sloping windows provided passengers with a dramatic view of the countryside and storm.

The lifting power of any lighter than air gas is determined from the difference between it's weight for 1000 cubic feet (H=5.61 lbs) subtracted from the same volume of air (80.72 lbs) so the lift is 75.11 lbs per 1000 cubic feet. This static lifting power cannot be exceeded and is usually less if the gas is contaminated. so to lift 210,000 lbs required 3,250,000 cubic feet of hydrogen. Given that the Graf Zeppelin weighed 150,000 lbs empty it had a useful capacity of 60,000 lbs. Not a whole lot. The Hindenburg, to be economical, had to be larger for more lifting capacity and also because it was designed for use with Helium which has less lifting power. As it turned out, the invasion of Austria, made the purchase of helium from the U.S. politically impossible so the ship was forced to use hydrogen.

The fiery end of the Hindenburg, World War II, and rapid advances in aerodynamic technology ended airship passenger travel. There has been significant recent interest in using rigid airships to transport huge construction projects such as parts of bridges since they have tremendous lifting power and the ability to move large objects over long distances very economically and directly.

See this issue of Popular Science: http://books.google.com/books?id=F4f6LnrW9NgC&pg=PA78&lpg=PA78&dq=ri... ( )