"SANTOS-DUMONT No. 4"
Above all this there stretched the balloon, 39 metres (129 feet) long, with a middle diameter of 5·10 metres (17 feet) and a gas capacity of 420 cubic metres (nearly 15,000 cubic feet). In form it was a compromise between the slender cylinders of my first constructions and the clumsy compactness of the "No. 3." (See Fig. 7.) For this reason I thought it prudent to give it an interior compensating air balloon fed by a rotary ventilator like that of the "No. 2," and as the balloon was smaller than its predecessor I was obliged to return again to hydrogen to get sufficient lifting power. For that matter, there was no longer any reason why I should not employ hydrogen. I now had my own hydrogen gas generator, and my "No. 4," safely housed in the aerodrome, might be kept inflated during weeks.
Fig. 7
In the "Santos-Dumont, No. 4," I also tried the experiment of placing the propeller at the stem instead of the stern of the air-ship. So, attached to the pole keel in front, the screw pulled, instead of pushing it through the air. The new 7 horse-power motor with two cylinders turned it with a velocity of 100 revolutions per minute, and produced, from a fixed point, a traction effort of some 30 kilogrammes (66 lbs.).
The pole keel with its cross pieces, bicycle frame, and mechanism weighed heavy. Therefore, although the balloon was filled with hydrogen, I could not take up more than 50 kilogrammes (110 lbs.) of ballast.
I made almost daily experiments with this new air-ship during August and September 1900 at the Aéro Club's grounds at St Cloud, but my most memorable trial with it took place on 19th September in presence of the members of the International Congress of Aeronautics. Although an accident to my rudder at the last moment prevented me from making a free ascent before these men of science I, nevertheless, held my own against a very strong wind that was blowing at the time, and gave what they were good enough to proclaim a satisfying demonstration of the effectiveness of an aerial propeller driven by a petroleum motor.
MOTOR OF "No. 4"
A distinguished member of the Congress, Professor Langley, desired to be present a few days later at one of my usual trials, and from him I received the heartiest kind of encouragement.