# My Airships/Chapter 14

THE BUILDING OF MY "NO. 6"
ON the very evening of my fall to the roof of the Trocadero hotels I gave out the specifications of a "Santos-Dumont, No. 6," and after twenty-two days of continuous labour it was finished and inflated.
The new balloon had the shape of an elongated ellipsoid (Fig. 10), 33 metres (110 feet) by its
great axis and 6 metres (20 feet) by its small axis, terminated fore and aft by cones.
"No. 6." FIRST TRIP
In all my constructions, except the big-bellied balloon of the "No. 3," I had depended much on the interior compensating air balloon (Fig. 5, page 119) fed by air pump or rotary ventilator. Sewed like a closed patch pocket to the inside bottom of the great balloon, this compensating air balloon would remain flat and empty so long as the great balloon remained distended with its gas. Then, as hydrogen might be condensed from time to time by changes of altitude and temperature, the air pump or ventilator worked by the motor would begin to fill the compensating air balloon, make it take up more room inside the great balloon, and so keep the latter distended.
Inside the balloon of my "No. 6" I now sewed such a compensating balloon, capable of holding ​60 cubic metres (2118 cubic feet). The ventilator that was to feed it formed practically a part of the motor itself. Revolving continually while the motor worked, it would serve air continually to the compensating balloon whether or not the latter would be able to hold it. What air it could not hold would escape through a comparatively weak valve ("Air Valve," Fig. 10) communicating with the outer atmosphere through the bottom of the air balloon, which was also the bottom of the great outer balloon.
To relieve the great balloon of its dilated hydrogen when necessary I supplied it with two of the best valves I could make ("Gas Valves," Fig. 10). These also communicated with the outer atmosphere. Imagine, now, that after a certain condensation of my hydrogen the interior compensating balloon should have filled up in part with air from the ventilator and so maintained the form of the great balloon rigid. Shortly after, by a change of temperature or altitude, the hydrogen would begin to dilate again. Something would have to give way, or the balloon would burst in a "cold explosion." What ought to give way first? Evidently the weaker air valve ("Air Valve," Fig. 10). Letting out part or all of the air in the ​interior balloon, it would relieve the tension of the swelling hydrogen; and only afterwards, should this not be sufficient, would the stronger gas valves (Fig. 10) let out precious hydrogen.
All three valves were automatic, opening outward on a given pressure from within. One of the hypotheses to account for the terrible accident to the unhappy Severo's dirigible "Pax" is concerned with this all-important problem of valves. The "Pax," as originally constructed, had two. M. Severo, who was not a practical aeronaut, stopped up one of them with wax before starting on his first and last voyage. In view of the decreasing pressure of the atmosphere as one goes higher the ascent of a dirigible should always be slow and never great, for gas will expand on the rise of a few yards. It is quite different from the case of the spherical balloon, which has no interior pressure to withstand. A dirigible whose ​envelope is distended by great pressure depends on its valves not to burst. With one of its valves stopped with wax the "Pax" was allowed to shoot up from the earth, and immediately its occupants seem to have lost their heads. Instead of checking their rapid rise one of them threw out ballast—a handful of which will send up a great spherical balloon perceptibly. The mechanician of Severo is said to have been last seen throwing out a whole bag in his excitement. Up shot the "Pax" higher and higher, and the expansion, the explosion, and the awful fall came as a chain of consequences.
AN ACCIDENT TO "No. 6"
My daily practice with the new air-ship ended, 6th September 1901, in a slight accident. The balloon was reinflated by 15th September, but four days later it crashed against a tree in making a too sudden turn. Such accidents I have always taken philosophically, looking on them as a kind of insurance against more terrible ones. Were I to give a single word of caution to all dirigible balloonists, it would be: "Keep close to earth."
The place of the air-ship is not in high altitudes, and it is better to catch in the tops of trees, as I used to do in the Bois de Boulogne, than to risk the perils of the upper air without the slightest practical advantage.