Flying machines

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ifd 7

Preface v..

CHAPTER PAGE

Introduction

A T the present day the fascinating problem '**■ how to make a successful flying machine is attracting attention in all civilised countries. A valuable prize has actually been won in France by a navigable airship which has been propelled over a given course, starting from a definite locality and returning to the same place in a limited period of time. The custom of regarding any attempt to navigate the air as an indication of madness on the part of the experimenter has passed away, and is now replaced by a feeling of anxiety that one's own country shall not be forestalled in the art of ariation. Sir Hiram Maxim, the well-known engineer and inventor, has stated years ago that one half of the leading scientists in the United States are of the opinion that mechanical flight is possible.

The subject is attractive because of the large amount of chance or luck which exists in respect to it. There is no industry manufacturing airships as a commercial article ; no one has so far made a flying ship or apparatus which can not only ascend into the air with a load, but can be driven in any desired direction under normal conditions of wind and weather. There is so much possibility that an experimenter may by accident discover the true direction in which to proceed. Work on a large scale can only be done at very heavy expense, but probably the majority of experimenters in this field would in any case commence by trials with model machines. Eeally useful experience can be gained at comparatively trifling expense in this way, and a would-be conqueror of the air can fairly assume that without actual experiment of some sort no reliance can be placed upon his designs, however pretty they may look on paper. Designs of airships have ranged themselves into three classes. There have been those who have taken the principle of buoyancy as their basis of construction ; they are those who look for the solution of the problem by an apparatus which is " lighter than air." The examples are balloons. Others hold a contrary opinion, directing their efforts to the perfection of machines which are " heavier than air," disregarding entirely the principle of buoyancy, and contend that the machine must raise itself as well as have the power to move in a horizontal direction. The examples are kites, the term aeroplane having been introduced to define this type of construction, and machines in which some form of screw propeller or vibrating plane is relied upon to produce the lifting effort. The third division of designers appears to be those who have adopted the principle of buoyancy as affording a temporary expedient which would serve until further disco-

PLATE I. -Dr. Barton's Airship in Flight.

(The Ascent of July, 1905.) Facing page 8.

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^ CO a > vvi*i very would render practicable the use of machines " heavier than air." The earliest designers seem to have adopted the idea of machines heavier than air, but probably no reliable information exists as to what was actually accomplished. Designs of more or less fantastic shape have been proposed, but only appear upon paper ; any real attempts have all occurred during comparatively recent years. Some inventors were no doubt men of capability, and deserved to have met with some success, but they were not sufficiently cautious or methodical, and in making ambitious trial flights with their machines met with fatal disaster. A great deal of very useful and reliable work has, however, been accomplished by men of scientific ability, and placed on record ; the novice can, therefore, make himself acquainted with the results of the experiments and utilise them as a starting point for his own work, whether his faith is in a ship which is lighter or heavier than air. Such data will give him an idea of the size and proportion of parts to accomplish a given result. In considering the problem of aerial navigation it is necessary to realise that the atmosphere is a decidedly real and tangible thing. Because air is invisible the mind does not easily picture its existence, hence the novelty of imagining it to be of service in sustaining and transporting material objects. Aeronauts have, however, recorded their experience of descents in which the air appeared to be a substance like jelly. Air has a definite weight, 100 cubic inches weighing 31 grains ; the wind which we feel exerts a palpable pressure, and is merely air in a state of eddies and flow of currents. This wind pressure is capable of exerting an enormous amount of force, architects and engineers when designing large or tall structures require to take this fact into serious consideration. A wind which is blowing with a velocity of 10 to 15 miles per hour would exert a pressure of onehalf to one pound upon every square foot of surface directly exposed to it, and yet is only a very modest breeze indeed. A storm wind blowing at about 50 miles per hour presses with more than 12 lbs. upon each square foot of surface directly exposed to it, whilst a hurricane wind exerts more than four times this pressure.

It is therefore quite reasonable to assume that a medium which is capable of producing such effects can be utilised as a means of communication and transport. To be completely successful, however, an airship must not only be able to lift itself and a load, but have the power to proceed against such winds in a horizontal direction. Buoyancy alone is not sufficient, it will enable the ship to proceed with a favourable wind astern, and to ascend and descend, but not to proceed against a wind of the most moderate force. An airship competes against other forms of travel on land and water. In each the traveller is already able to proceed in any direction, irrespective of the conditions of the weather, except in rare instances of storm and stress ; even then he may be able to maintain his position until the weather moderates. If airships are to justify their existence they must be able to do this also, and to do it on a commercial basis, having regard to the particular sense in which any one may be used. The first airships to achieve any degree of success, and the only ones at the present time which are practicable as a means of aerial locomotion, are balloons. They depend entirely upon the principle of buoyancy -to rise and sustain themselves and their load in the air. The principle is briefly this — if any body floats in equilibrium in a fluid the weight of the body is equal to the weight of the fluid which it displaces. If the weight of the body is less than that of the fluid displaced by it the body will rise. For example, if a sealed tin can containing air is forced below the surface of a tank of water and then released it will at once rise to the surface, because it is much lighter than the equivalent bulk of water. If the can is loaded until its weight is exactly equal to that of the equivalent bulk of water, it will remain in equilibrium below the surface. Any slight change in the weight of the can and its contents will cause it to rise or fall until a state of balance is produced due to the varying density of the water at the different depths. The weight of water displaced by the can in every instance exactly balancing the weight of the can and its contents. The density of the atmosphere varys to a very much

12 FLYINS MACHINE!.

greater extent than the density of water for a given vertical distance.

It is therefore possible to adjust the position of equilibrium within much smaller limits of movement than in the case of a body immersed in water. Water is, however, about 800 times as dense as air for any given volume, the floating body must therefore be so much larger to support a given weight in air than in water. Any apparatus used for the purpose of propulsion must also be very much larger as it cannot grip the less dense medium so well. It does not follow, however, that it need be useless or less efficient provided that the shape and proportions are suitable to the conditions of working.

A balloon is simply a device for displacing a sufficient quantity of air to balance its weight and that of the load to be lifted. The shape does not affect this part of the problem, it is merely a question of size. The less the weight of the component parts of the balloon the smaller it will need to be to lift a given load. For this reason such materials as silk, cane, and rope or thin steel wire are much used for the construction of balloons and their equipment. The substance contained in the balloon to take the place of the air displaced must be less dense than air, because the difference between its weight and that of an equivalent quantity of air is a measure of the lifting power available. The best arrangement would be a vacuum in the balloon as that would give the greatest possible difference between the weights of the cubic space in the envelope or container and the equivalent quantity of air. Such a method has actually been thought of by early designers but owing to the fact that the atmosphere exerts a pressure of approximately 15 lbs. per square in. in all directions, the envelope must be strong enough to withstand this pressure if it contains a vacuum. An envelope having sufficient strength to withstand the accumulated pressure upon such a large surface as possessed by an average balloon would weigh more than the air displaced and the balloon would not rise. If the envelope contains a gas the pressure of the air can be balanced, or more than balanced, by the expansive property of the gas, therefore the envelope can then be made of exceedingly light material. It then remains to procure a gas which is much lighter than air ; such a gas is hydrogen, 100 cubic ins. of which will only weigh about 2*14 grains, or about one-fifteenth the weight of a similar quantity of air. This is the substance which will give the greatest lifting power as it is the lightest thing known. Owing to the expense of generating pure hydrogen, however, coal gas, which is hydrogen mixed with carbon, is generally used for inflating modern balloons. Being a commercial product it is comparatively cheap and gives a good lifting effort, but the very best effect is produced by pure hydrogen. The difference between the weights of the completely equipped balloon and that of the quantity of air displaced need only be about 10 lbs. in favour of ascension, such margin gives sufficient ascending power to take the balloon to a considerable height.

A certain amount of extra weight is attached to the balloon in form of paper or sand so that a reserve of lifting power is obtained. When the aeronaut desires the balloon to rise he throws away some of this weight thus increasing the buoyancy ; if he desires to descend he permits some of the gas to escape by opening a valve thus decreasing the buoyancy. With this power of ascending and descending he can place the balloon at different elevations and move horizontally according to the direction of the air currents met with. This gives a certain amount of control over the direction in which the balloon will travel without the use of propelling apparatus, as air does not necessarily travel in one direction only at all degrees of elevation. If the balloon is made to rise and fall by this means there must be a limit to the time it can remain in the air. The continual releaseof gas diminishes the rese rve of lifting power until finally, when all the extra weight has been thrown away and the balloon is made to descend, it cannot be made to rise again ; or the descent be checked, because the lifting power is not sufficient to sustain the load.

When the balloon ascends the atmospheric pressure diminishes, becoming less the higher the elevation attained. This permits the gas inside

INTK0DTJCTI0N. 15

the balloon to expand, the effect being that as the pressure outside decreases that inside increases, and, unless a means of escape is provided, the envelope would burst with disastrous results to the occupants of the car. A loss of gas thus takes place additional to that required to regulate the buoyancy, and it is intensified by the effect of shadow and sunshine, which causes the gas to expand as it becomes heated by the sun's rays and to cool when they are obscured by cloud. Apart from the object of seeking suitable air currents at different altitudes the aeronaut who is merely voyaging from one place to another would preferably keep his balloon at a fairly constant moderate altitude. This can be done where the nature of the ground permits without sacrificing the reserve of lifting power by using what is called a guide rope, an invention of immense value in ballooning and due to a celebrated English aeronaut, Charles Green. The arrangement consists of along heavy rope attached to the car of the balloon and allowed to hang vertically downwards so that it touches the ground. It forms a part of the extra weight but, unlike the loose sand or paper, is not thrown away. Whilst this rope is suspended away from the ground its entire weight is acting against the lifting effort of the balloon. If the buoyancy decreases the rope will touch the ground and as the balloon descends an increasing amount of its length will rest upon the ground. The balloon will obviously be relieved of the weight of this portion and therefore its buoyancy will be increased accordingly, the descent will be checked and a state of equilibrium produced. In fact as the balloon rises and falls due to variations in the buoyancy so will the guide rope rest with more or less of its weight upon the ground and act as an automatic regulator of the lifting effort.

The shape of a balloon is determined by the use to which it will be put. If it is to be used as a drifting balloon the shape will be approximately spherical, as the work which it will do is merely to float in the currents of air. But if it is to be a dirigible balloon the shape will be elongated in the direction of its horizontal axis, because the shape should be such as to offer the smallest practicable amount of resistance when proceeding against the direction of flow of an air current. The shape which gives best results in this respect is somewhat similar to that adopted for the Whitehead torpedo, and agrees with the experiments of Captain Eenard, in France, who found that an elongated balloon which is larger in diameter at the forward end and smaller at the rear end, requires less power to drive it through the air than if it had ends of equally pointed shape.

The envelope of a drifting balloon only has to bear the strain of supporting the car and its load, except under abnormal circumstances. The shape, therefore, does not tend to become distorted. A dirigible balloon, however, is subjected to the pressure of the air current against which it may be moving ; its envelope must therefore be able to withstand this strain as well as that due to the effort required for lifting and sustaining the car and load. This is one of the difficulties which the designer of a dirigible balloon has to deal with. If the aeronaut releases some of the gas for the purpose of descending he is depriving the envelope of its internal support, and may come to disaster by reason of the distortion of the shape of his balloon. According to M. Santos Dumont, the successful dirigible balloon must be able to descend without losing gas and ascend without sacrificing ballast ; in fact, you must not interfere with the reserve of lifting power.

This can be effected by an ingenious device which was suggested at the end of the eighteenth century by General Mensuir and used by Dupuy de Lome in his balloon, as well as by Santos Dumont himself. It consists of a small balloon or pocket fixed inside the main envelope, and filled with air, which is kept at pressure by means of a fan. The gas can thus expand without unduly straining the envelope by pressing against the pocket which collapses, losing more or less of the contained air, and making more space for the gas inside the main envelope. If the gas contracts the pump inflates the pocket again with air, so that the reduction in bulk of the gas is compensated. Escape valves are provided for the air, a regular stream flowing through the pocket under normal conditions. The balloon is elevated and

B descends by the action of its propeller, the envelope being tilted to point upwards or downwards by an alteration of balance. M. Santos Dumont uses his guide rope for this purpose, shifting its position so that the weight pulls at front, rear, or centre, according to the angle at which he desires the balloon to go.

Attempts have been made to direct airships by means of sails, but without much success. There are two other methods which have been used, namely, by screw propellers and by vibrating planes or wings. Neither of these has yet been proved to be the superior one. Mr. Laurence Hargrave, in Australia, has made models propelled by both methods, each flying well. Sir Hiram Maxim and Mr. Horatio Phillips in England, Messrs. Santos Dumont, Tissandier, Captains Eenard and Krebs in France, and others have done well with screw propellers driven by steam, petrol, electric, and compressed-air engines, though the two first-named inventors did not permit their machines to have free flight.

The problem of aerial navigation by machines heavier than air resolves itself into two main components, viz., power of sustaining a load in air and power of maintaining a proper balance. If these can be achieved, the factor of propulsion is comparatively easy to deal with. One of the most able of scientific experimenters in this art, Otto Lilienthai of Berlin, who commenced his trials of flight at 13 years of age, and continued

INTBODTTCTION. 19

them for 25 years, eliminated the question of motive power, and confined himself entirely with the problem of balance. He decided that soaring birds ascend by skilful use of the pressure produced by currents of air, and that no external source of power is needed to imitate them, all the apparatus required being sustaining surfaces correctly designed and constructed, with of course an acquired art in using them properly. His investigations were published in 1889 as a book, called " Der Vogelflug als Grundlage der Fiiegekunst " (" Bird Flight as the Basis of the Flying Art ") and his opinion was that birds fly by dexterity alone ; there is no mysterious upward force or kind of reversed gravity.

Making some experiments whilst suspended from a support by means of a rope, he actually succeeded in raising himself about 30 ft. from the ground by means of wings, which he vibrated by his own power, his weight and that of the machine being, however, partly counterbalanced. The majority of his experiments consisted in gliding flights taken from the top of a hill having a moderate slope. These trials were taken so often that he regarded them as a sport, in which his mechanic assistant also participated. The apparatus consisted of fixed aeroplanes, to which he attached himself, always facing the wind. Notwithstanding the proficiency and experience thus gained, Lilienthal met his death whilst engaging in the attempt to make a flight of greatest possible length in the capacity of his apparatus. A sudden gust of wind appears to have been too heavy for him to adjust his equilibrium to meet it, and the soundness of his opinions upon this point were unluckily proved by the aeroplanes being thrown backwards from their proper angle. The apparatus thus deprived of the supporting effect of the wind fell rapidly to the ground, and the accident proved fatal to the enthusiastic and able experimenter.

Professor Langley, another very clever worker at this problem in the United States, constructed a model machine which would travel against the wind and yet keep at an average horizontal level. He considers that a machine can be designed and made which w r ould carry out this principle of soaring bird flight by utilising the fluctuations of w r ind velocity, which, according to his ideas, occurred between very much smaller intervals of time than generally supposed. To satisfy himself that this was so, he made some accurate experiments by using a very sensitive anemometer, which recorded as well as indicated the velocity and fluctuations of wind during short intervals of time. An account of these experiments is given in the Proceedings of the Smithsonian Institute, July, 1904, entitled "The Internal Work of the Wind,'' showing graphic curves of wind velocities plotted against intervals of time. They show that changes take place with great rapidity and to an extraordinary extent. Existing records as taken by an ordinary anemometer, registering at long intervals of time, showed wind velocity variation only from 20 to 27 miles per hour ; but the true fluctuations as recorded by the special anemometer were enormously more than this, and occurred with great suddenness. As an example, the velocity would vary within the space of one minute from about 30 miles per hour to zero, then to 14 miles per hour, and regain its former velocity within the space of two minutes, including some intermediate fluctuations of 12 miles per hour or so occurring in between. Some of these curves are to be found in Engineering for July 13th, 1S84, page 51.

A pioneer experimenter in this idea of the principle of bird flight was Le Bris, who made some actual flights in France. He was a sea captain; and seems to have had a very good grasp of the problem. From observations on soaring birds made by him during his voyages, he came to the conclusion that when the current of air strikes the forward edge of the bird's wing an aspirating action is produced, by which the bird is actually drawn into the wind without any effort on its own part. He shot an albatross, and having spread its wings, presented the forward edges to the wind, just as the bird would do in flight. He states that as a result he felt the bird pulled forward into the wind as he had anticipated. His soaring machines consisted of aeroplanes of concave shape, similar to a bird's wing, to which he attached himself.

To start his flight he obtained an initial velocity by being driven in a cart or glided from a convenient height. A very interesting account is given at length of these trials in Chanute's book, " Progress in Flying Machines/' page 104, &c. Le Bris seems to have abandoned his experiments through financial straits and bad luck, also loss of energy due to advancing age, rather than to failure of his ideas. That lifting effort can be produced by the action of an air current upon the edge of a curved surface, as distinct from the lifting effect produced by an air current moving against an inclined flat surface, has been demonstrated by Mr. Horatio Phillips in England. He does not, however, appear to have experienced or relied upon the aspirating effect mentioned by Le Bris. His ideas seem to have been confined to producing a lifting effect, and rather to the contrary he shows that the lift of his planes was accompanied with some amount of backward thrust or drift. Nevertheless, his principle is quite a distinct and novel one. He states as a result of his experiments, extending for 27 years, that anything approaching a flat surface is useless for supporting heavy loads in the air. His idea consists in the use of a narrow surface, curved both above and underneath. When such a plane encounters a current of air directly against its forward edge there is produced a difference of pressure between the upper and under surfaces, and the plane tends to rise. By multiplying the number of planes any desired amount of lifting effect should be produced. He proved that this idea was correct by experiments upon a variety of shapes of plane, and constructed a machine which actually flew round an experimental track. The advocates of each system, "lighter than air," or " heavier than air," have scored a partial success, and including, as they do, men of undoubted ability on either side, have removed the stigma which at one time attached itself to every experimenter in the art of aerial navigation.

In Germany, at Berlin, Otto Lilienthal has devoted his attention to most painstaking study and experiments with soaring apparatus. He convinced himself that flat surfaces present undue resistance, his final aeroplanes being of the concavo-convex form. The trials were made on hilly country against the wind, the experimenter launching himself and his apparatus from the top of a hill itself, or from the roof of a tower constructed for the purpose on the hill. He was successful in soaring to heights of 65 to 82 feet. Daring 1891 he tried aeroplane wings, having an area of 172 square ft., the apparatus weighing 53 lbs. Including himself the total weight raised was 229 lbs., which shows that the aeronlane would sustain and lift a weight of 1'33 lbs. per square foot of area, the wind velocity being calculated as 23 miles per hour. A tail having vertical and horizontal planes was necessary to keep the apparatus steady. Lilienthal generally proportioned his aeroplanes to have three-quarter square foot of surface per pound weight to be raised and sustained. The propelling power calculated (furnished by the wind) was at the rate of 6 h.-p. approximate, to every 1,000 square feet of surface. Lilienthal was killed by a fall when making one of his flights on August 9th, 1896 ; the cause was apparently due to a sudden gust of wind striking the aeroplanes and overbalancing the apparatus in a backward direction.

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PLATE VI.— The Wellman Airship.

An'end view of the Car with Mr. Wellman on board (see extreme right of Car).

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PLATE VIII.— An Earlier Deutsch Dirigible.

CHAPTER II. Dirigible Balloons*

Henry Giffard.

A name which is well known amongst engineers is that of Henry Giffard, the inventor of the injector apparatus for feeding water into steam

Fig. 1.— GiffarcTs Dirigible Balloon.

boilers, an invention which is in use all over the world at the present day. This engineer devoted his attention to aerial navigation in 1850 and constructed a dirigible balloon (Fig. 1) . It was of elongated shape, 39 ft. in diameter at the largest part and 144 ft. in length over all. Motive power was provided by a steam engine driving a screw propeller having two blades and a diameter of 11 ft. To avoid risk of fire the funnel of the boiler was bent downwards and draught produced by a steam blast. Steering depended upon a rudder of sail construction. Mr. Giffard ascended from Paris on 24th September, 1852, obtaining a speed of 4J to 6f miles per hour with a screw speed of 110 revolutions per minute.

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Dupuy de Lome.

Another engineer of repute, Mr. Dupuy de L6me, a French naval architect, commenced upon the design and construction of a dirigible balloon during the siege of Paris in 1870, it was however not completed until 1872. He dealt with his experiments in a very thorough manner and applied his knowledge and experience of navigation in water to navigation in air. The balloon of elongated shape (Fig. 2), had a maximum diameter of 48ft. and a total length of 118 ft., the capacity for containing gas, was 120,000 cubic ft. It was propelled by a screw made of sails 29 J ft. diameter, 26 ft. pitch, driven by 8 men at 27J revolutions per minute. The surface of the propeller blades was 160 square ft., total and slip ratio 23 per cent., the balloon advancing 20 ft. for each revolution of the propeller. In the trials a speed of about 6J miles per hour was obtained and it was considered that the rudder had enabled the course to be altered

DIRIGIBLE BALLOONS.

by 12 degrees approximately, the day being windy. This balloon had an available ascending power of 5,515 lbs. The weight of the structure was 3,885 lbs. The men who worked the propeller weighed together 1,325 lbs., and are supposed to have produced ^ h.-p. Apparently the trial was

Fig. 2.— Dnpuy de Ldme's Dirigible Balloon.

satisfactory, the calculated and observed velocities being almost identical.

Gaston Tissandier.

Some experiments were made in 1881 by Gaston Tissandier, in France, who also used a screw propeller to drive his balloon (Fig. 3). But practical

FLYING MACHINES.

electric motors having come into existence, he applied electricity to drive the propeller, partly because there was less risk of fire than with a steam engine. Another advantage is that an electric motor does not give out products of combustion, which disturb the ballasting of the balloon. Ex-

Fig. 3. — Tissandier'a Dirigible Balloon.

periments were first made with a model, the large balloon being constructed afterwards with the assistance of the information gained. This experimental model balloon- was of elongated form, about 11 ft. in length by 4 ft. 6 ins. diameter at the largest part. It had a capacity of 77£ cubic feet, pure hydrogen being used to inflate it, giving