LZ 129 Hindenburg
Published on May 6, 2007 at 3:44 pm.
2 Comments.
Filed under aeronautics.
Here’s another non-astronomy entry.
70 years ago today, the era of the great airships came to an end. Yes, Zeppelins (giant rigid airships) continued to fly for a few years, and airships still fly today in the form of blimps (smaller non-rigid airships). But the large rigid airships would never again be popular, and the airplane would become the air travel method of choice. Whenever anyone speaks of the great Zeppelins, or whenever any talks about hydrogen used in transportation (either as lifting gas for an airship or as fuel for a motor) people think of the events of May 6, 1937. On that day, LZ 129, the Hindenburg, caught fire and crashed at the Lakehurst Naval Air Station in New Jersey in the United States of America.
The Hindenburg was constructed by Luftshiffbau Zeppelin in 1936. She was a truely impressive airship. Hindenburg was huge: 41 meters (135 feet) in diameter and 245 meters (804 feet) long. That is more than three times longer than a Boeing 747, and over six times wider than the 747’s cabin width. LZ 129 was named for Paul von Hindenburg, the recently deceased German president. The Hindenburg could accomodate 72 passengers, though on this, its last trip, it only had 36 on board, along with 61 crew members. Luxury accomodations for passengers were provided in inboard cabins. Hindenburg was originally designed to have a mixture of helium and hydrogen as lifting gasses; however, most of the worlds helium came from the United States, and at this time the US had an embargo on helium sales to Nazi Germany. As a consequence, the Hindenburg’s gas cells were filled with hydrogen. Both hydrogen and helium are lighter than air, and both were used in airships. Hydrogen is lighter and has a better lifting capability than helium. The problem with hydrogen, though, is that it is very flamable, unlike helium with can not burn.
On this, its last flight, Hindenburg departed Frankfurt, Germany, late on May 3, 1937. Stong headwinds over the Atlantic slowed the great airship, and bad weather in New Jersey further delayed arrival. The Hindenburg was orginally scheduled to arrive early in the morning on May 6, 1937. However, a strong cold front was moving through New Jersey at the time, so the captain of the airship, Max Pruss, decided in the interest of safety to delay arrival to avoid the bad weather, instead cruising along the coast line showing off sights from the air to the passengers from Boston to New York. Finally, late in the day, he decided to make his approach to the Lakehurst Naval Air Station. The approach was shortly after a thunderstorm in the area, and lightning was still visible in the distance, but the Hindenburg was already 12 hours late for its arrival. The airship moved over the landing site, and dropped ropes to the waiting ground crew. The ropes then pulled steel cables up to the airship. Those cables were connected to large winches that were to haul the airship down to the mooring mast. Suddenly a flame appeard at the rear of the airship. Then, great tongues of fire erupted and the flaming airship settled to the ground. The Hindenburg crash was not the first airship disaster, nor the worst. However, it was the most widely covered airship crash, and one of the most widely covered crash by any aircraft. The air station had a large number of media, including several camera crews. Journalist Herbert Morrison was also recording the event for radio news coverage, where his heartfelt exspression of “Oh the humanity!” is one of the most famous quotations in aviation history. Amazingly, though, for all the dramatic nature of the fire and crash, nearly 2/3 of the passengers and crew survived! Only 35 people on board (and 1 on the ground) died in the accident. A far greater tragedy was the crash of the ZR 4 Akron, a US Navy airship that was filled with non-flammable helium instead of hydrogen. 73 of the 76 people aboard the Akron died when it crashed in April of 1933.
To this date, no one knows really what happened to cause the crash of the Hindenburg. Theories abound, though. One theory that has never been put to rest is the idea that the crash was caused by sabotage. The Zeppelin company had received bomb threats, and a specific threat had been made against the Hindenburg prior to the flight. These threats were taken seriously enough that Luftwaffe security officers were on board the Hindenburg on its final flight. Proponents of the sabotage theory point out that the airship was 12 hours late arriving. Had it arrived on time, a time bomb would have detonated while the craft was moored, and perhaps no lives would have been lost. However, no evidence was ever found of a bomb, and there was a security presense on board.
A more likely scenario is that the fire was accidental, triggered by a spark. The flight was delayed due to thunderstorms, and there was still lightning in the vicinity. It would not be unusual to expect that the airship may have picked up a static charge. This static charge could have been discharged by the steel mooring cables pulled up to the airship. Also, landing preparations within the airship may have discharged the static charge.
Hydrogen gets a lot of blame in the accident. Indeed hydrogen is flamable. However, hydrogen burns very quickly with a very pale light blue flame. When you look at the pictures of the burning Hindenburg you clearly see a barely visible light blue flame giant tongues of orange flame. Huh? What’s that about? Well, the problem is two fold. The gas bags had to hold in hydrogen gas. Hydrogen molecules are very small, and the bags were made of cloth. The bags were sealed with a mixture of paraffin and something similar to gasoline. Both are flamable. Also, the outer skin of Zeppelins was coated with a dope consisting of cellulose acetate butyrate, iron oxide, and alluminum powder. This mixture is exceedingly flamable when applied, but far less so when applied. It likely would not burn unless otherwise ignited. Most likely the flames visible come from the gas bags and the airship’s skin. But, interestingly the skin, which was somewhat conductive, was separted from the duralumin frame by non-conducting cables. This had the interesting possibility of making the Hindenburg into a giant capacitor, which could have become electrically charged by the nearby thunderstorm. Landing procedures may have shorted these components, creating a spark. But, the spark had to ignite something. Probably, just a spark would not have ignited either the gas bags or the skin of the airship. So, what could have been ignited. Well, that might just have been the hydrogen. In preparation for landing, hydrogen was vented. This vented hydrogen would have mixed with air to form an explosive mixture. Then, a spark, or even lightning, could have ignited the hydrogen. Crew members had previously noticed a tail heaviness for the craft, so there may have been a leak in one of the aft gas bags, or perhaps a venting valve stuck open, or partially open. The hydrogen could ignite, thus igniting either the skin or the gas bags (or likely both), which would then be further fueled by hydrogen escaping from the burning bags itself burning, adding to the fire. The flames that you see in the photos are probably mostly from the gas bags and the skin burning, accelerated by the hydrogen. But, in all likelihood, if this were the scenario, building the craft of non-flammable materials would have made it safe to fly, even when filled with hydrogen.
But, the fact remains that when people talk about hydrogen, they think of the images of the Hindenburg fire, and that dooms hydrogen use in lighter-than-air craft, and it also is a major hurdle to convincing people to use hydrogen as a fuel supply.
-Astroprof
Images courtesy Wikimedia
Mike on October 30, 2007 at 2:29 am: 1
Such a pity that this one disaster led to the end of such an elegant technology. I am currently designing a small dirigible which will be lifted with hydrogen gas, and I have no qualms about using it instead of helium. To me, helium is a sluggish, inefficient lifter when compared to hydrogen and there is only one choice if you want to fly in a lighter than air craft.
Adrienne on April 27, 2008 at 1:22 pm: 2
1) the Hindenburg could accomodate upto 2,656 people
2) Hydrogen gas does NOT burn blue! it burns a near invisible red-orange color (see Mythbuster’s episode The Hindenburg Mystery, they demonstrate what happens when you burn hydrogen, it produces a semi-invisible red-orange flame)