1. Analyze the causes of failure in the case of the Hindenburg disaster (materials/human/design/poor maintenance/extreme conditions). Which causes were most important? Defend your answer with specific arguments. (at least 400 words)
On the engineering side, the Hindenberg used hydrogen gas for buoyancy but hydrogen is very flammable. A spark possibly from static buildup ignited the hydrogen filled airship which then spread rapidly along the flamable skin. So according to Carl Jablonski, "a small flame became a big flame". So the situation was more complex than this. Jablonski said that during a 12-hour holding pattern, a bracing wire snapped and punctured a hydrogen gas cell resulting in hydrogen leaking and building up withing the airship in places it shouldn't have been. Then dropped wet mooring ropes to tie down the Hindenberg resulted in static electricity discharge that ultimately ignited first this leaked hydrogen then the rest of the hydrogen [4]. So now we can explore this is more detail.
From a material view, the Hindenberg was built with a wooden wigid structure with fabric skin. Both of this materials are flamable but the question is how quickly will a fire spread along them. That is, can a small fire spread fast enough like in the Hindenberg to fail like it did? This is one area of controversy because some have argued that even if the hydrogen did catch of fire, it would not have spread so rapidly along these structures.
Another view is that of human factors. According to Carl Jablonski, the US government would not sell helium which was produced only in Texas to German airship companies forcing them to rely on the volatile hydrogen. This was clearly then not an engineering limitation. In fact, German airships had an excellent safety record and the Hindenberg had made many prior successful trips. Thus, it can be said that these ships were well designs with the exception of a potential fatal flaw in the use of hydrogen. Further, Carl Jablonski states that the crew were very safety concious.
Extreme conditions also were detrimental and pushed the normally safe crew to do things they enver should have done. Poor weather including storms and high winds forced the Hindenberg into a holding pattern along the coast waiting for improved weather. When a window of opportunity opened for a 1 hour of improved weather, the normally safety oriented crew rushed. The ship made several sharp terms that resulted in the aforementioned cable snapping and damaging the hydrogen cells.
So in sum, these combination of factors were resulted in the crash of a well designed airship due to the fatal flaw of hydrogen igniting as a result of actions that never should have been performed.
2. How are current airships different from historical airships, in terms of materials and design? Describe how understanding the causes of failure of the Hindenburg (and similar ones, such as the failure of the airships Macon or Shenandoah) are helping engineers to create better designs. (at least 400 words)
The Macon was the result of a sequence of events following structural repairs due to a forced climb the year prior. The crash occured before all repairs were complete. Structural failure due to wind shear, a very sudden change in wind direction with altitude. As a result, structural components punctured gas cells resulting in helium leaks. Coupled with the rapid intentional release of ballast, the Macon rised to a higher altitude before settling and descending to the sea gently. There were few deaths due to warm weather, safety precautions such as life jackets and rafts.
The Macon crashed due to a violent updraft that resulted in structural limitations being exceeded.
On the safety precautionary side, safety has increased dramatically. It is common for commercial airliners that cross any major body of water to have rafts and life jackets per regulations. A modern ocean crossing airship would need to take similar precautions.
Modern airships, as well as some of historical airships following Hindenberg, use helium due to its non-flammability. Modern airships such as the Aeroscraft below have a rigid structure unlike the Goodyear blimp which maintains its shape by being inflated [1].
The Aeroscraft
Like the Hindenberg, the Aeroscraft uses a rigid structure but rather than wood, uses carbon fiber and aluminum which are non-flammable and better resist heat. Undoubtedly, modern airships would likely have some methods to control fire.
Other likely safety features are non-flammable coatings, methods to prevent static buildup, and early warning systems. For example, modern commercial aircraft have many sensors and instrumentation that can warn the pilot of abnormalities such as fire or fuel leaks and allow the pilot to make immediate corrections or emergency landings before the situation worsens. Such sensors and systems were not an option in the days of the Hindenberg but are fortunately now commonplace.
The use of modern computing techniques such as Finite Element Analysis allow for greater digital "testing" of structural designs for many situations, thus ensuring that the aircraft has significant computational testing before any real world tests. These computer methods and simulations will allow engineers to verify that the airship can withstand a wide variety of structural loadings including those that damaged the Shenandoah.
Overall, engineering progress is made due in part to experience sometimes from disasters. Learning from the past will allow engineers today to gain valuable insight. As technology improves, engineers will be able to develop more advanced airships. However, even here, there are the risks associated with new technology.
3. Pick one of the types of materials analysis techniques discussed in the videos, and explain how it could be used to help engineers determine the cause of failure in another case (either hypothetical or a real case you look up). What sort of information can it provide? (at least 250 words)
X-ray fluorescence or XRF is a modern non-destructive analysis technique. Using x-rays and the deflected ray, a characteristic spectrum is obtained which indicates material composition. X-ray fluorescence is invaluable in assisting engineers in determining whether a structure’s material is to specification.
One use is in analyzing material coating. For example, aircraft engines operate at very high temperatures so their blades are coated in special alloys to give them high temperature resistance and wear resistance [2]. XRF will assist engineers in checking the whether or not a manufactured blade’s coating is to spec.
Various other components such as bolts and nuts for use in extreme conditions are coated for environmental resistance. XRF will assist engineers to checking the quality of such coatings.
Other uses are in analyzing weld quality [3]. A weld is a method of joining to materials that melt the two parts together with a filler material. In welding, the filler material in the form of a rod or wire will have some varying compositions from the parent materials to account for various chemical effects. Thus, weld material selection is critical to achieve the desired mechanical properties and corrosion resistance. XRF will assist engineers in analyzing welds to determine if they are of the correct type.
NTSB investigations of vehicular crashes may also make use of XRF to investigate the material composition of various critical components. By determining whether or not a particular metal is the correct type for example, engineers can then determine if structural failure is the cause of the accident.
References
[1] https://gizmodo.com/5972973/the-titanic-aeroscraft-is-finished--and-its-awesome
[3] https://www.olympus-ims.com/en/insight/tips-for-measuring-welds-with-xrf/
Reflection
As far as aircraft go, I am familar with fixed wing aircraft only so it was very fascinating to learn about about airships. In my research, I found that airships are seeing a small rise (pun not intended) particularly for heavy lift and operations from areas without runways.
I was particularly fascinated by how in retrospect, some accidents seem very obvious. For example, why did the Hindenberg engineers use hydrogen intead of Helium. Why did they make a wooden structure instead of a metal one? In a sense, people today may take for granted the engineering that results in technological advances. For previous designers, things that we know now may not have been obvious. Likewise, there are things we still don't know today but in the future may become known and when that happens, people may look back and think we should have noticed.
Perhaps with the rapid increase and growth of space flight technology, we may see this happen.