sexta-feira, 15 de junho de 2012

The science behind involucres and valves of Santos=Dumont Dirigibles

Santos=Dumont used the ascensional force of hydrogen in almost all of his dirigibles. Unlike modern balloons that make use of hot air, the hydrogen envelopes were sealed and the internal pressure should be controlled through valves.

The technology of gas balloons is quite old; this Illustration from the late 19th century shows Jacques Charles performing an experience with the first hydrogen gas balloon in August, 27th 1783, at the Champ de Mars, Paris.

The system to obtain hydrogen was invented by French balloonist and manufacturer Gabriel Yon (1835-1894). It consisted of placing a bit of iron filings in dilute sulfuric acid inside two large tanks. Hydrogen bubbles were formed and pumped through tubes inside the water to be cleaned of impurities. Finally it was stored in a steel tank under pressure.

The association hydrogen envelope and petrol explosion engines was very dangerous, dozens of hydrogen dirigibles exploded or burned in the years, the most famous of them was the Hindenburg disaster that took place on May 6, 1937, as the German passenger airship LZ 129 Hindenburg caught fire and was destroyed during its attempt to dock at the Lakehurst Naval Air Station killing 35 people.

This High-speed videography at thousand frames per second makes it possible to observe in detail the sequence of events after the balloon has been lit with a match.
Santos=Dumont made use of the technology available at that time to create dirigibles very safe with regard to anti-flammability and the most perfect envelope was used in his Dirigible Number 6.

As observed in several accidents that happened before the conquest of the Deutsch prize, Dumont knew that the envelope could not be too long because it ran the risk of bending the middle, as happened with his Dirigible Number 1 and 2. He also knew that he should take a very special care with expansion and contraction of hydrogen at different altitudes as happened with Augusto Severo.

Augusto Severo was a Brazilian congressman who devoted his life to dirigibles, he died tragically on May 12, 1902, when he performed maneuvers with his dirigible named Pax in Paris. Fifteen minutes after his takeoff from the Park Vaugirand the rigid envelope broke down due to expansion of hydrogen through the rarefied atmosphere, releasing hydrogen directly over the internal combustion engine and caused a huge explosion, flame debris fell on the Avenue du Maine, causing uproar in the city.

In the chart above shown in Figure 1 a sudden escape of hydrogen and in figure 2 the fan is used to inflate the cuff to prevent the internal envelope fold in half.
In the chart above we see in Figure 1 the Dirigible Santos=Dumont Number 6 ascended up far, the atmosphere was thin and the pressure inside the envelope went high. In figure 2 the safety valve automatically opens to prevent collapse of the envelope.
In the chart above we see in Figure 1 Santos Dumont voluntarily decides to empty the envelope. In figure 2 he turns the fan on to inflate the cuff preventing the envelope fold in half.
Santos=Dumont knew how to compensate for variations in pressure by safety valves that worked automatically, letting out the gas when the pressure increased significantly and closed automatically when the pressure returned to normal. Manual valves and an inner inflatable cuff was inflated with a fan and emptied directly from his nacelle.

He also took great care with his envelope, demanded that it was always well sewed and varnished to prevent leaks, above we see Santos Dumont at Lachambre & Machuron headquarters overseeing the manufacture of his envelope. He also made sure to keep the balloon far away enough from the engine exhaust pipe, it could burn the delicate envelope made of Japanese silk.