My Airships; The Story of My Life

by Alberto Santos-Dumont

"THE BRAZIL"
SMALLEST OF SPHERICAL BALLOONS

How often have things been proved to me impossible! Now I am used to it I expect it. But in those days it troubled me. Still I persevered.

They showed me that for a balloon to have "stability" it must have a certain weight. Again, a balloon of 100 cubic metres, they said, would be affected by the movements of the aeronaut in his basket much more than a large balloon of regulation size.

Fig. 1.Fig. 2.

With a large balloon the centre of gravity in the weight of the aeronaut is as in Fig. 1, a. When the aeronaut moves, say, to the right in his basket, Fig. 1, b, the centre of gravity of the whole system is not shifted appreciably.

In a very small balloon the centre of gravity, Fig. 2, a, is undisturbed only so long as the aeronaut sits straight in the centre of his basket. When he moves to the right the centre of gravity, Fig. 2, b, is shifted beyond the vertical line of the balloon's circumference, causing the balloon to swing in the same direction.

Therefore, they said, your necessary movements in the basket will cause your little balloon to roll and swing continually.

"We shall make the suspension tackle longer in proportion," I replied. It was done, and the "Brazil" proved remarkably stable.

When I brought my light Japanese silk to M. Lachambre he looked at it and said: "It will be too weak." But when we came to try it with the dynamometer it surprised us. Tested thus, Chinese silk stands over 1000 kilogrammes (or 2200 lbs.) strain to the linear metre (3·3 feet). The thin Japanese silk stood a strain of 700 kilogrammes (1540 lbs.)—that is, it proved to be thirty times stronger than necessary according to the theory of strains. This is astonishing when you consider that it weighs only 30 grammes (a little more than one ounce) per square metre. To show how experts may be mistaken in their merely off-hand judgments I have been building my air-ship balloons of this same material; yet the inside pressure they have to stand is enormous, while all spherical balloons have a great hole in the bottom to relieve it.