This excerpt describes the balloon at the beginning of the twentieth century and how it was flown.
Balloon competitions became a fashionable sport early in the present century. They were principally held by Aero clubs of various countries. The Aero Club of the United Kingdom was founded on September 24, 1901, by Mr. F. Hedges Butler during a balloon voyage, on which he was accompanied by his daughter, by the Hon. C. S. Rolls, and by Stanley Spencer. The oldest aeronautical society in the world is the Aeronautical Society of Great Britain, founded in 1866 by Glaisher and others, with the Duke of Argyll as president. This Society, of course, is concerned with every branch of aeronautics from the scientific point of view. A ladies' Aero club was established in Paris in 1907, and ballooning became very popular with the fair Parisians. The first Englishwoman to ascend in a balloon was Mrs. Sage, in the year 1785.
The history of ballooning is marked by several calamities. There is no need to recapitulate them. Almost without exception these calamities were due to foolhardiness and inexperience. The principal peril is that of being driven out to sea, and to this cause the majority of the disasters have been due. The bursting of balloons in the air has seldom led to fatal results for the balloon in that event forms a kind of parachute and falls gently to earth. That with proper precautions ballooning is perfectly safe is shown by the fact that during any year in Great Britain many hundreds of ascents are made, and very rarely are they marred by even a trivial accident.
In the first enthusiasm caused by man's achievement of mechanical flight, it became the fashion to deride the balloon as out of date, or, at the best, a plaything. "We will leave the balloon to the society folk who like to experience and make a sensation. We will leave the balloon to fashionable Saturday afternoon crowds at Hurlingham," said one ardent new disciple of aviation. The attitude was excusable, although it ignored certain very important facts.
Ballooning had, indeed, at its worst, been the mere showman's business, or a somewhat purposeless - albeit delightful and healthful - sport. But it should not have been overlooked that, even during the excitement caused by mechanical flight, France and Germany continued steadily to build military balloons, spherical as well as dirigible, whilst some notable projects for geographical exploration with the aid of balloons were put forward.
The balloon, since man first ventured to soar aloft, has been and will remain one of the principal methods of exploring the atmosphere, and undeniably the most pleasant. Ballooning is a delightful, health-giving pastime, in which the comparatively feeble and nervous can engage with impunity. It will continue to be the handmaiden of the sciences of meteorology and aviation, and, with the advance of mechanical flight and the increasing need to know and understand the laws of the aerial ocean, ballooning will increase in importance and value.
Balloons are vessels made of a special cotton fabric or of silk, varnished; or, more generally of late years, of rubber-treated fabric. They are inflated either with coal gas or with hydrogen, and they rise because these gases are much lighter than air. The first balloons were filled simply with hot air.
Hydrogen is the lightest of all gases, being about one-eighteenth the weight of air, although the hydrogen used in ballooning is never quite pure, and usually weighs about one-fifteenth as much as air. It is an elementary substance, and is without smell or taste.
In combination with air, hydrogen is highly inflammable and explosive, and it burns with a non-luminous flame of very high temperature. This quality is utilized in the hydrogen blow-pipe.
The danger of fire is the chief menace to airships, and elaborate precautions have to be taken to prevent the sparks from the motor coming into contact with escaping gas. This gives to lighter-than-air craft their particular weakness and vulnerability, and there is no means at present known of completely avoiding the danger. In the later Zeppelin airships, however, the space between the gas-containers and the outer case was filled by the inert gases discharged from the cylinders of the petrol engines. This promised a certain amount of protection, but failed to fulfil the promise, as was shown in the destruction of more than one of these craft by bombs.
Coal gas has, approximately, one-half the specific gravity of air. Its weight varies according to its degree of purity. The weight of the air, under different conditions of atmospheric pressure, varies also. But for ordinary ballooning we can assume that coal gas is half the weight of air.
A toy balloon containing ordinary lighting gas, which is not, as a rule, pure coal gas, but a mixture of coal and water gas of a very inferior quality for balloon purposes, will ascend into the air to a considerable height. Even this small amount of gas is sufficiently buoyant to lift the weight of the envelope which encloses it. And it will ascend until it reaches an altitude where the weight of the surrounding air is not more, volume for volume, than that of the gas plus the weight of the envelope. As a matter of fact, the toy balloon will almost certainly burst ere it reaches that height.
The respective weights of air and balloon gases are, in round figures, given here:
Air. At sea-level (or Bar. 3O" 60° Fahr.) 1000 cubic feet. 75 lbs.
Coal gas. At sea-level (or Bar. 3O" 60° Fahr.) 1000 cubic feet. 371 lbs.
Hydrogen. At sea-level (or Bar. 3O" 60° Fahr.) 1000 cubic feet. 5 lbs.
Hot air weighs less than cold air, and can, therefore, be employed as a lifting agent. Its advantages for ballooning would be overwhelming if by its means a big lift could easily be obtained, but in view of the fact that, in order to obtain an equal lift to that of coal gas, a temperature of 400° Fahr. would have to be maintained, hot air is for most ballooning purposes impracticable: the hot-air balloon must be of enormous relative bulk, and the difficulties of maintaining the temperature are great. The days of the Montgolfier balloon, however, are by no means past, and considerable promise is held out by a French contrivance for heating the air in the balloon by a compact and safe form of petrol stove, the heat from which can be easily regulated. By this or by some similar method it is hoped that reasonably long journeys will be possible, altitude being regulated by the amount of the flame.
The "buoyancy" of a gas is the difference between its weight and the weight of an equal volume of air. Knowing the approximate weight of each, it is easy to calculate the lifting-power, for practical purposes, of a given quantity of gas. A balloon of 10,000 cubic feet of hydrogen filled at sea-level in a temperature of 60° Fahr. has a lift of about 700 lbs., the difference between the weight of its gas and that of the air it displaces: of such a balloon the envelope, network, basket, and equipment would weigh nearly three hundredweight, leaving about 400 lbs. for aeronaut and ballast. The lifting power of a balloon of the same size filled with coal gas would be no more than about 375 lbs.
A moment's reflection will show that even if a lighter gas than hydrogen were available the advantage would be small. Supposing such a gas weighed 1 lb. per 1000 cubic feet as against the 5 lbs. of hydrogen, a gain of only 4lbs. per 1000 cubic feet would be obtained, or 40 lbs. in a 10,000 cubic feet balloon - a very small advantage even supposing the lighter gas were no more costly to produce, or that there were no countervailing disadvantage, such as greater liability to leak through the envelope.
The gross weight of balloon, passengers, and ballast are, just before the ascent, adjusted until it about balances the weight of the air displaced. It is then in equilibrium, and on lightening its load the balloon will rise from the ground and ascend to that level at which its weight again exactly balances that of an equal volume of the air surrounding it. The balloon leaves the ground lighter than air, and it ascends until it is of the same weight as the air. The weight of the air, volume for volume, steadily decreases with altitude. The bigger the "lift" given to a balloon by discarding ballast the higher it will ascend before it reaches equilibrium.
The neck of the balloon is opened before starting, so that the expanding gas will not burst the fabric. During the ascent gas pours out through the open neck of the balloon, which, however, remains fully inflated while it is climbing. The weight of the gas, although of the same volume as at the start, diminishes; but so also does the weight of the surrounding air. The decrease is in the same ratio, and the lift, therefore, steadily diminishes. For example, a 10,000 cubic feet balloon has a lift of 700 lbs. when it contains 50 lbs. of gas and displaces 750 lbs. of air. On ascending to a height of 2,000 feet, if the temperature is the same, the gas it contains and the air it displaces will weigh less by about one-fifteenth part in each case.
The lift of the balloon will then be:
|Air||750 lbs.||less one-fifteenth (50 lbs.).||700 lbs.|
|Gas||50 lbs.||less one-fifteenth (31⁄3 lbs.).||462⁄3 lbs.|
The figures given are only approximate, but they serve to show the principle. With every further increase of altitude there is a decrease of lift, and this decrease can be calculated by the simple process of estimating, first, the degree of expansion as indicated by the reading of the barometer, and then by reckoning the weight of a given volume of air and of gas and taking the difference, allowing also for temperature. Thus, the barometer at a height of 4,000 feet reads about 26 inches. Taking a 10,000 cubic feet hydrogen balloon, then, and basing the calculation on the fact that at 30" Bar. and 60° Fahr. 10,000 cubic feet of air weigh 750 lbs. and 10,000 cubic feet of hydrogen weigh 50lbs. - (10,000 x 30")/26" = 11,500, which is the volume to which the original 10,000 cubic feet, both of the air and of the hydrogen, will have expanded at 4,000 feet. The balloon has lost the odd 1,500 cubic feet of gas through the open neck, and the 10,000 cubic feet of gas that remain now weigh 10,000/11,500 of 50 lbs. The air it displaces weighs 10,000/11,500 of 750 lbs. The result is about 44 lbs. and 650 lbs. respectively, and the lift of the balloon has gone down to about 606 lbs.
Temperature affects the density of all gases, and therefore of the air, to the extent of 1/500th part for every degree Fahr. Air at 40° Fahr. therefore weighs 20/500ths more than at 60° Fahr. A balloon filled in low temperature has a bigger lift than if filled in warm weather: it contains heavier gas; but the air it displaces is also heavier. On the other hand, if the low temperature occurs after the balloon has left the ground the effect is to contract the gas in the balloon, which becomes, therefore, of smaller volume, displacing less air and giving reduced lift. This causes the balloon to stop rising or, from equilibrium, to descend, until ballast is thrown out to restore the balance.
PARTS OF A BALLOON
A. The valve.
B. The valve-springs.
C. The ripping-panel.
E. Valve-line. F. Neck.
G. Neck-line. H. Hoop.
J. Basket. K. Grappler.
At the top of the balloon is a valve, opened by a cord which comes down through the neck into the car. This cord, when pulled, opens the valve inwards, and the gas streams out through the top of the balloon. When the pull is released the valve shuts with a snap, for it is strongly springed.
If the balloon at any time is in equilibrium in shadow, and then passes into warm sunshine, the gas expands and the balloon climbs to a higher altitude. Sooner or later the gas overfills the balloon, and some of it pours out through the open neck. If desired the climbing can be checked by opening the valve.
If the sun decline, or cloud is entered and the balloon receives a deposit of moisture from the mist, or if it rains, or if low temperature condenses the gas, the balloon descends, and it is necessary to throw out ballast if a continuation of the journey is desired. In many cases the discharge of a couple of handfuls of sand is sufficient to stop the descent.
Throughout the voyage a small quantity of gas is percolating through the fabric of the balloon. The voyage could continue indefinitely if it were not for waste of gas and expenditure of ballast. Sooner or later, however, comes the time when but little ballast is left, and a descent must be made. Then the aeronaut looks out for a good landing-place, and he may open the valve in order to descend at a given spot rather than be driven past it. On coming within a few yards of the ground he may pull open the "ripping panel," which is a large aperture in the side of the balloon near the top. It is lightly sewn up for the purpose of each voyage, but is easily torn open. By this means the balloon is deflated quickly, and a trouble that used to beset balloonists - that of being dragged along the ground in the wind by the slowly deflating balloon - is avoided. Sometimes the grapnel, or anchor, is used in landing.
Regard must be paid to atmospheric conditions if a long journey is desired, and since the utility of ballooning rests on the possibility of making long voyages, this requires a full knowledge of the technique of ballooning. When it is desired to make a long voyage, it is best to start at night, in order to avoid the sun's heat. At night a balloon usually keeps a steady equilibrium, and little ballast need be thrown away. The temperature is constant, and the gas does not expand and escape to any appreciable extent.
To fill a balloon with coal gas takes from three to five hours. To fill it with hydrogen supplied from tubes, in which it is stored in a state of great compression, less than one hour suffices. Hydrogen is nearly always used in military ballooning, the tubes being easily transported in wagons. It is often convenient to take a portable hydrogen-making plant into the field. For military purposes gold-beater's skin balloons are often used for captive ascents, because they retain the gas so well that they remain inflated, sometimes, for weeks. The cost of inflation with coal gas varies from £4 to £15, according to the size of the balloon. Roughly speaking, a balloon of 50,000 cubic feet capacity will take £5 10s. worth of coal gas. Hydrogen for such a balloon might cost about £25; but it is impossible to specify exactly the cost of hydrogen, which, as a by-product of certain manufacturing processes, should in some localities cost less than coal gas.
In the chapter on Navigation of the Air it will be explained that there is no motion in a balloon relative to the air. A balloon travels with the air. Its direction and speed can only be determined by the aeronaut by observing the ground below. When out of sight of earth, in clouds, or above them, it is impossible to ascertain the direction or the speed.
In addition to the ordinary winds from various points of the compass, there are upward and downward currents of air. An upward current chiefly affects the balloon through the loss of gas caused by its expansion in ascending to a greater altitude. With a downward current the gas condenses, and it is generally necessary to throw out ballast, in order to restore equilibrium. Usually in such cases the effect amounts to very little. It is different, however, when we consider the remarkable conditions sometimes set up by thunderstorms. Then a balloon becomes difficult to manage. It is alternately drawn upwards and swept downwards with embarrassing suddenness.
It is necessary to recognize that the balloon is completely at the mercy of the wind. True, there are occasions when the balloonist can, by ascending or descending into a different stratum of air, meet a different current and modify his direction, and even, on occasion, retrace his path, or make for some desired destination. But it is not often that much can be accomplished in this way, and the balloonist can never depend upon finding a favourable current.
As to the material of which balloons are made, cotton has one drawback, in that it is not the lightest material that can be used. That, of course, is gold-beater's skin, the cost of which puts it out of the question for nearly everything but military needs, where considerations of expense have to be sacrificed to the one aim of utility. Gold-beater's skin has for years been used by Great Britain in military balloons, but is now being supplanted by other materials. Silk is a very good fabric in point of lightness and gas-retaining capacity, but it soon deteriorates. A cotton balloon should stand three years' usage and still remain in good condition.
The cordage varies from the size of ordinary twine in the upper part of the net to that of a clothes-line, about a third of an inch in diameter, as it reaches the hoop, and runs there from to support the car. It should be of the best hemp. The necessity for strength is obvious when one remembers that the cordage has to support, in the larger balloons, a weight of more than a ton. The hoop is an important feature. Built of white ash in four separate rings, spliced together and strengthened by a steel core, it is almost impossible for it to break. The hoop is often made of wood, strengthened by steel cord wound round it.
The strength and durability of a balloon's basket and tackle have often been demonstrated in a startling way.
In a gentle breeze they have come into contact with buildings and pulled walls over. The author took part in a descent in Russia in a gale, when the basket was hurled against a bank in a wind of sixty miles an hour, and although the shock was so violent as almost to stun the aeronauts, the basket simply bent to the strain, and it even endured a terrific drag over ground for half a mile without sustaining damage.
The trail-rope of a balloon serves a variety of purposes, its chief use being to preserve equilibrium at a low altitude. When it is trailing along the ground, any descent on the part of the balloon will result in a greater length of the trail-rope falling on the ground, thus relieving the balloon from so much of its burden. On the other hand, any slight ascending movement results in the lifting of some of the rope off the ground. The extra weight of this is thus borne by the balloon, whose ascent is checked to that extent. Prolonged voyages are often possible by the aid of the trail-rope. At night, and also when at sea, it enables the balloonist to ascertain his direction according to the compass. The direction in which the trail-rope drags out in contact with land or with water is, of course, the direction from which the wind is blowing.
Some small amount of dirigibility is obtainable with the use of the trail-rope, but so slight as to be of very little value. Its retarding effect on the balloon is very little, but just enough to enable the wind to be felt, when the balloonist, by setting up a sail, may steer a point away from the wind's course.
Sea-floaters, answering at sea the same purpose that the trail-rope serves on land, have been tried. One type is a cylinder with tapering ends. The two extremities are air-tight compartments, while the main body is hollow, but at one end is pierced with holes through which water readily pours. The tilt at which the floater travels can be regulated from above, so that the aeronaut can, at will, empty some of the water out of the floater or allow more water to pour in.
With the exception of small unimportant details of construction, and the introduction of the ripping panel, the balloon has, however, not made any progress for a century. It is incapable of being improved radically, except by the discovery of some means by which the gas could be retained indefinitely, or kept at an even temperature, enabling a balloon to remain in the air for a very long period.