A History of Aeronautics

by Evelyn Charles Vivian; W. Lockwood Marsh

Meusnier, a French general, first conceived the idea of compensating for loss of gas by carrying an air bag inside the balloon, in order to maintain the full expansion of the envelope. The brothers Robert constructed the first balloon in which this was tried, and placed the air bag near the neck of the balloon, which was intended to be driven by oars, and steered by a rudder. A violent swirl of wind which was encountered on the first ascent tore away the oars and rudder and broke the ropes which held the air bag in position; the bag fell into the opening of the neck and stopped it up, preventing the escape of gas under expansion. The Duc de Chartres, who was aboard, realised the extreme danger of the envelope bursting as the balloon ascended, and at 16,000 feet he thrust a staff through the envelope—another account says that he slit it with his sword—and thus prevented disaster. The descent after this rip in the fabric was swift, but the passengers got off without injury in the landing.

Meusnier, experimenting in various ways, experimented with regard to the resistance offered by various shapes to the air, and found that an elliptical shape was best; he proposed to make the car boat-shaped, in order further to decrease the resistance, and he advocated an entirely rigid connection between the car and the body of the balloon, as indispensable to a dirigible.[12] He suggested using three propellers, which were to be driven by hand by means of pulleys, and calculated that a crew of eighty would be required to furnish sufficient motive power. Horizontal fins were to be used to assure stability, and Meusnier thoroughly investigated the pressures exerted by gases, in order to ascertain the stresses to which the envelope would be subjected. More important still, he went into detail with regard to the use of air bags, in order to retain the shape of the balloon under varying pressures of gas due to expansion and consequent losses; he proposed two separate envelopes, the inner one containing gas, and the space between it and the outer one being filled with air. Further, by compressing the air inside the air bag, the rate of ascent or descent could be regulated. Lebaudy, acting on this principle, found it possible to pump air at the rate of 35 cubic feet per second, thus making good loss of ballast which had to be thrown overboard.

Meusnier’s balloon, of course, was never constructed, but his ideas have been of value to aerostation up to the present time. His career ended in the revolutionary army in 1793, when he was killed in the fighting before Mayence, and the King of Prussia ordered all firing to cease until Meusnier had been buried. No other genius came forward to carry on his work, and it was realised that human muscle could not drive a balloon with certainty through the air; experiment in this direction was abandoned for nearly sixty years, until in 1852 Giffard brought the first practicable power-driven dirigible to being.

Giffard, inventor of the steam injector, had already made balloon ascents when he turned to aeronautical propulsion, and constructed a steam engine of 5 horse-power with a weight of only 100 lbs.—a great achievement for his day. Having got his engine, he set about making the balloon which it was to drive; this he built with the aid of two other enthusiasts, diverging from Meusnier’s ideas by making the ends pointed, and keeping the body narrowed from Meusnier’s ellipse to a shape more resembling a rather fat cigar. The length was 144 feet, and the greatest diameter only 40 feet, while the capacity was 88,000 cubic feet. A net which covered the envelope of the balloon supported a spar, 66 feet in length, at the end of which a triangular sail was placed vertically to act as rudder. The car, slung 20 feet below the spar, carried the engine and propeller. Engine and boiler together weighed 350 lbs., and drove the 11 foot propeller at 110 revolutions per minute.

As precaution against explosion, Giffard arranged wire gauze in front of the stoke-hole of his boiler, and provided an exhaust pipe which discharged the waste gases from the engine in a downward direction. With this first dirigible he attained to a speed of between 6 and 8 feet per second, thus proving that the propulsion of a balloon was a possibility, now that steam had come to supplement human effort.

Three years later he built a second dirigible, reducing the diameter and increasing the length of the gas envelope, with a view to reducing air resistance. The length of this was 230 feet, the diameter only 33 feet, and the capacity was 113,000 cubic feet, while the upper part of the envelope, to which the covering net was attached, was specially covered to ensure a stiffening effect. The car of this dirigible was dropped rather lower than that of the first machine, in order to provide more thoroughly against the danger of explosions. Giffard, with a companion named Yon as passenger, took a trial trip on this vessel, and made a journey against the wind, though slowly. In commencing to descend, the nose of the envelope tilted upwards, and the weight of the car and its contents caused the net to slip, so that just before the dirigible reached the ground, the envelope burst. Both Giffard and his companion escaped with very slight injuries.

Plans were immediately made for the construction of a third dirigible, which was to be 1,970 feet in length, 98 feet in extreme diameter, and to have a capacity of 7,800,000 cubic feet of gas. The engine of this giant was to have weighed 30 tons, and with it Giffard expected to attain a speed of 40 miles per hour. Cost prevented the scheme being carried out, and Giffard went on designing small steam engines until his invention of the steam injector gave him the funds to turn to dirigibles again. He built a captive balloon for the great exhibition in London in 1868, at a cost of nearly £30,000, and designed a dirigible balloon which was to have held a million and three-quarters cubic feet of gas, carry two boilers, and cost about £40,000. The plans were thoroughly worked out, down to the last detail, but the dirigible was never constructed. Giffard went blind, and died in 1882—he stands as the great pioneer of dirigible construction, more on the strength of the two vessels which he actually built than on that of the ambitious later conceptions of his brain.

In 1872 Dupuy de Lome, commissioned by the French government, built a dirigible which he proposed to drive by man-power—it was anticipated that the vessel would be of use in the siege of Paris, but it was not actually tested till after the conclusion of the war. The length of this vessel was 118 feet, its greatest diameter 49 feet, the ends being pointed, and the motive power was by a propeller which was revolved by the efforts of eight men. The vessel attained to about the same speed as Giffard’s steam-driven airship; it was capable of carrying fourteen men, who, apart from these engaged in driving the propeller, had to manipulate the pumps which controlled the air bags inside the gas envelope.

In the same year Paul Haenlein, working in Vienna, produced an airship which was a direct forerunner of the Lebaudy type, 164 feet in length, 30 feet greatest diameter, and with a cubic capacity of 85,000 feet. Semi-rigidity was attained by placing the car as close to the envelope as possible, suspending it by crossed ropes, and the motive power was a gas engine of the Lenoir type, having four horizontal cylinders, and giving about 5 horse-power with a consumption of about 250 cubic feet of gas per hour. This gas was sucked from the envelope of the balloon, which was kept fully inflated by pumping in compensating air to the air bags inside the main envelope. A propeller, 15 feet in diameter, was driven by the Lenoir engine at 40 revolutions per minute. This was the first instance of the use of an internal combustion engine in connection with aeronautical experiments.

The envelope of this dirigible was rendered airtight by means of internal rubber coating, with a thinner film on the outside. Coal gas, used for inflation, formed a suitable fuel for the engine, but limited the height to which the dirigible could ascend. Such trials as were made were carried out with the dirigible held captive, and a speed of 15 feet per second was attained. Full experiment was prevented through funds running low, but Haenlein’s work constituted a distinct advance on all that had been done previously.