The inventor of one of the devices described later on in this book modestly claims that he did not invent it but it invented itself. What he means is that he worked step by step, from simple beginnings, each step when complete suggesting the next. To put it another way, many inventions grow in the inventor's mind, sometimes from unpromising beginnings, the most unlikely start often resulting in the most successful ending.
Who has not heard of the "tanks" which made such a name for themselves when they suddenly appeared in Northern France? The British Commander-in-Chief simply mentioned that a new type of armoured car had come into use with good results, but the newspaper men set the whole non-Teutonic world laughing with droll stories of huge monsters suggestive of prehistoric animals which suddenly began to crawl through the slime and mud of the battle-field, pouring death and destruction upon the astounded Germans.
How they came to be called tanks no one seems to know clearly but that is how they will be known for all time. It has been suggested that they were so named because tank is one of the things which they certainly are not, the intention being thereby to add to the mystification of the enemy. That is by the way, however, for we are more concerned with the things than with their name.
Their precise origin is wrapped in mystery but we have it on excellent authority that they grew out of the peaceful "tractor," originally intended to drag a plough to and fro across a field in the service of the farmer. An illustration of one of these interesting machines will be seen in this book which will well repay a little study.
It consists of a steel frame or platform upon which is mounted a four-cylinder petrol engine with a reservoir above to carry the supply of fuel and with a radiator in front to cool the water which keeps the engine from becoming too hot. Towards the back of the vehicle is what is called by engineers a worm-gear, the function of which is to reduce the one thousand revolutions per minute of the engine to somewhere near the slow speed required of the wheels of the tractor.
This worm-gear is simply a wheel with suitable teeth on its edge in conjunction with a screw so made that its thread can engage comfortably with the teeth. This latter, because of the wriggling appearance which it presents when it is revolving is called a worm, which name it gives to the whole apparatus. Both wheel and worm are mounted in bearings which form part of a case enclosing the whole so that dirt is excluded while, the case being filled with oil, ample lubrication is assured. The shafts of both wheel and worm emerge through holes in the case.
It will easily be seen that each single turn of the worm will propel the wheel one tooth, so that if the wheel have fifty teeth, for example, the worm will turn fifty times to the wheel's once. Thus a great reduction in speed is attainable with this device and what is equally valuable, a great increase of power also results. Thus a small engine, working at a high speed, is able by means such as this to pull very heavy loads at a slow speed.
It is evident, however, that the reduction necessary in this case cannot be attained even by a worm-gear, for there are other wheels visible which show that ordinary tooth gearing is also employed to reduce the speed even further before it is applied to driving the tractor along. Practically all the other gear which we see in the picture, above the platform, consists of the controlling apparatus.
The object with a screw-like appearance just behind the engine is not really a screw but is a flexible coupling joining the engine to the worm-gear, its "flexibility" enabling the two to work sweetly together even though by chance they may get just a little out of line with each other.
But by far the most interesting part of the machine is that which is underneath the frame. At one end we see a pair of ordinary-looking wheels and between them the gear for swinging them to right or left for steering purposes, but even they are somewhat unusual, since they will be seen to have flanges or rims round the edge for the purpose of biting into the earth, so that they may be able to guide the machine the better in soft ground.
The back wheels, however, are quite peculiar, for there is a pair on each side and round each pair is a chain somewhat after the fashion of a huge bicycle chain. The links of this chain are made of tough steel and they are two feet wide, so that each chain forms a broad track upon which the machine moves. The links of this track-chain will be seen to be tooth-shaped so that they grip or bite deeply into the yielding ground. The teeth, moreover, are shaped like those of a saw and they are so placed as best to help the tractor forward.
Between the two chain-wheels will be noticed a row of smaller wheels and it is these which largely support the weight of the machine, the chains forming tracks upon which they run.
The wheels actually turned by the power of the engine are the chain-wheels, and their action is such as to keep on laying down and then taking up again two broad firm tracks along which, at the same time, they keep propelling the other wheels which carry the weight above. The effect, really, is just as if the machine had a pair of driving wheels two feet wide and of enormous diameter, of such diameter, in fact, that the part in contact with the ground is almost flat. Thus there is always a broad bearing surface to prevent sinking in soft earth, while the tooth-like shape of the links gives a firm hold even under very adverse conditions.
This form of construction has been used for some few years now under the name of "caterpillar" or "centipede" traction. A glance at the picture will explain those names, particularly if the chain-driven part of the vehicle be imagined to be a little longer than it is in the particular machine shown.
The idea of armouring a vehicle with bullet-proof plates is also a fairly old conception. Armoured trains were used again and again during the South African War, and armoured motor-cars became familiar to most people. In the case of cars, however, the armour could only be very light and the guns carried were limited practically to a single machine-gun and some rifles. Moreover, the operations of a car are very largely confined to such places as are blessed with good roads or smooth plains. An armoured car of the older type would have cut a poor figure amid the shell-holes and mine-craters of Northern France. It would have had to keep to the roads and so it was little used.
But the idea of an armoured vehicle was good and a good idea is never entirely lost. Sooner or later some genius puts it to good use. Thus the idea of an armoured vehicle came to be associated with the idea represented in the centipede tractor and the result was the tank.
Why not armour a large centipede, said someone? Make it very big and strong. It will trample down the barb-wire entanglements as if they were grass. If made long enough and rightly balanced it will pass over the trenches like a moving bridge. Nothing but a direct hit from a heavy gun will do it much harm. For, observe, the mechanism can be entirely covered up, all the vital parts can be well protected, and the chain tracks can be so strong as to be almost undamageable.
By permission of Messrs. Foster and Co.
The Parent of the Tank.
Here we see an innocent agricultural tractor with caterpillar hind wheels. It is out of such a machine that the idea of the formidable tank was evolved.
Thus we get a glimpse of the growth of this simple peaceful agricultural machine into one of the most striking mechanical achievements of the Great War.
Another thing which seems to have grown more or less of itself is the bomb or grenade. Before the time of modern accurate fire-arms hand-grenades were quite a recognized weapon. The "Grenadier" Guards owe their title to this fact and carry the design of a bursting grenade upon their uniforms. Yet until a few years ago everyone thought that such things were done with for ever: that with modern rifles soldiers would seldom get near enough together to use grenades and that if they did the bayonet would be the weapon to be used.
When, however, the Germans were driven back at the battle of the Marne and found themselves compelled to entrench in order to avoid further disaster, it soon became evident that neither rifle nor bayonet nor both together entirely filled the needs of the infantryman.
Since the Allies were not powerful enough to drive the Germans from their trenches forthwith, they, too, had to entrench. Gradually the trenches drew nearer and nearer together and at the same time skill in entrenching increased. Thus a time soon arrived when both rifle and bayonet were largely useless for purposes of offence. Then the hand-grenade came into its own again, for the men could throw it from the depths of their own trench high into the air in the hope that it would fall into the trenches of the enemy. The call for these quickly produced the supply. There is little need to describe them here, for who among us has not intimate friends who used them again and again? This much may be said, however. They were little hollow balls of cast iron, sometimes chequered so that when they burst they flew into many fragments. Inside was a charge of explosive with a suitable fuse or firing mechanism. Some were fixed to the end of a stick for convenience in throwing, while others were simply handled like a cricket-ball.
They serve to show us, however, how an old idea may under fresh conditions be revived into what is practically a new invention.
Another example of the same sort is the revival of chain mail. Who, but a few years ago, would have thought it possible that modern soldiers would go to battle sheathed in shirts consisting of little metal plates cunningly connected by wire links and so overlapping each other as to form a perfect shield for all the more vital parts of the body? To what extent these were worn I do not know, for the British soldier is a very shy fellow in some ways and there are few who would not be a trifle ashamed to let their comrades see them thus garbed. They would feel that it was a confession of fear, and however afraid an Englishman may be he will never admit it. He is really a pious fraud, for the more he is really afraid inwardly the more courageously will he act just to hide his fear.
Since, however, the bullet-proof helmet is worn officially nowadays there seems no reason whatever why the bullet-proof waistcoat should not be adopted officially too. It is very light and very flexible and it is claimed that it is quite effectual in stopping rifle and machine-gun bullets.
Thus we see in what different ways inventions grow. Some are warlike from first to last, like the gun and the torpedo, but we find a vast range of peaceful things growing into implements of warfare, as the farmer's tractor has been developed into the tank, while not less interesting are the old ideas revived and adapted to modern needs, exemplified by the hand-grenade and the chain armour.
Of all the great inventions perhaps the most striking because of the suddenness with which they have come upon us are those relating to the navigation of the air. Until a few years ago "to fly" was taken to typify the impossible. Now we see men flying every day and there is scarcely anyone who has not had a friend or relative in the Flying Corps.
Recent experience, too, has shown that this one invention has revolutionized warfare in several important departments, particularly in the use of very heavy long-range artillery. Huge guns, hidden in a hollow or behind a hill, have been set to throw shells on to an unseen target, while a man in an aeroplane above watches the result and signals back by wireless. Thus by the aid of aircraft the power of artillery has been immensely increased.
Again, aircraft have superseded cavalry for reconnaissance purposes, that is to say, for finding out the enemy's strength and preparedness. Only a few years ago a General who needed information as to his foe would send forward a screen of cavalrymen who would cautiously creep forward until, judging by what they could see and by what sort of a reception they got, they were able to form some idea of the foe's arrangements. Nowadays, however, the airmen sail over his head and take photographs of him and his positions. A careful commander to-day not only screens his men and his guns from view along the land but he also tries his best to make them invisible from above. And, speaking of inventions, the soldiers have shown a degree of ingenuity in making themselves and their guns invisible which almost merits a volume to itself.
The airman, therefore, goes up and sails over the enemy. He may be simply observing for some particular unit of artillery, or he may be sent to find out things generally—nothing in particular, but anything which seems likely to be of use. He looks out intently and carefully, moreover he not only looks with his own eyes: as has just been mentioned, he takes photographs, which can be developed on his return and studied minutely at leisure. He may, or may not, according to circumstances, send back reports of an urgent nature by wireless telegraphy.
In some cases these duties are all carried out by one man, but in others there are two: one the pilot who looks after the working of the machine, and the other the observer whose whole attention can thus be devoted to scrutinizing the enemy.
Of course, when aeroplanes go on scouting expeditions like this they are apt to be attacked by the enemy both by anti-aircraft guns and also by other aeroplanes. The former can only be met by high speed and the steering of a somewhat erratic course so as to confuse the gunners and prevent them from taking good aim.
The other aeroplanes, however, must be met by actual fighting. The only way to defeat them is to go for them and attack them, a machine-gun being the most usual weapon.
Besides those who go up for definite scouting operations or to "spot," as it is termed, for the artillery, there are other machines whose sole duty is fighting. These go up for the purpose of driving off those machines of the enemy which may come prying, or to keep the ground, so to speak, for the scouting machines and enable them to do their work unmolested.
Then there are, of course, still others whose function is to carry out bombing expeditions.
All these different duties call for different types of machine, but I do not propose to go into the differences here since changes are so rapid in this particular field that only the general principles remain unchanged for any length of time. What has just been hinted, however, as to the different kinds of work which the aeroplane is called upon to do will enable the reader to see why different kinds of machines are needed.
So far we have only spoken of aeroplanes. There is a kind of machine sometimes called a hydroplane but which we are gradually getting to call a sea-plane. The latter term is much to be preferred, since the former is also in use to denote a special kind of high-speed boat.
Now a sea-plane only differs from an aeroplane in that it has floats instead of wheels. The aeroplane has wheels to enable it to alight upon and arise from the ground: the sea-plane has floats by which it can alight upon the water and arise from the water also.
In some instances this float idea is made so pronounced a feature of the machine that it becomes a flying boat.
Sea-planes are therefore really only aeroplanes specially adapted for a certain purpose. They are really just as much aeroplanes as those machines which go by that name. It is somewhat unfortunate, therefore, that a separate term is used to describe them. But there it is: names grow in a very curious way, not always in a logical way, and a name having once stuck to a thing in the mind of the public it is very difficult to make any alteration.
Aeroplanes, then, may be said to include a subdivision known as sea-planes, and for the rest of this chapter what is said of aeroplanes will apply to sea-planes also.
Without doubt, these are the fastest vehicles in existence. Many of them can exceed a speed of a hundred miles an hour. Consequently, the pilot lives while he is aloft in the equivalent of a furious gale, and it would seem as if that must produce such a degree of cold as to be almost unendurable. Moreover, it appears that this cold is almost as bad in summer as in winter, for the temperature high up in the air is much the same all the year round. The consequent muffling up with thick clothes and gloves, while it mitigates the cold, must add greatly to the pilot's difficulties in managing his machine. The protection for his eyes and ears which is made necessary by the same conditions must likewise add to his difficulties or at any rate to his discomfort. On the other hand, the effect of gliding at a very high speed over a perfectly smooth track, for that is in effect what it is, is very exhilarating, which to some extent compensates for the other drawbacks.
Moreover, the handling of such a machine in the air, particularly if a fight is included in the programme, appeals strongly to the sporting instincts of young men, so much so that during the War, in spite of the dangers and hardships, and the continual loss of life, there was never a dearth of men anxious to become pilots.
Owing to these considerations, too, it follows that the best aviators are to be found in those lands where the people are most devoted to sports. Hence, as we have it on excellent authority, the young men of Great Britain and the United States, with their love of adventure and their strong sporting instincts, make better men in the air than the Germans.
But really we are more concerned here with the machines than with the men, so let us get back to our subject.
The aeroplane consists of one or more "planes" or surfaces which, on being held at a certain slant and then pushed forward rise or remain supported in the air. Therefore the plane or planes need to be supplemented by first a tail and horizontal rudder to hold them at the correct slant, and an engine and propeller to drive them forward.
It is not necessary, here, to go over the history of the aeroplane, as that has been told so often. It is not of much interest, moreover, except to those who are particularly concerned with small details of construction, for in a general way the machine of to-day is very little different from one pictured by Sir George Cayley a hundred years ago. It is only the perfecting of the details which has transformed a dream into a very real thing.
So we will look only at the construction of the aeroplane in a general way, to do which we must first consider why it flies at all. It is due to the well-established law that action is always accompanied by a reaction equally strong and in the opposite direction. When a gun is fired the explosion not only drives the shell forward but equally drives the gun itself backward. The backward energy of the recoil is precisely equal to the forward energy of the shell. The two are equal but in opposite directions. In like manner a rocket ascends because the hot gases from the paper cylinder blow forcibly downwards, thereby producing an equal reaction upwards.
Now the plane of a flying machine is held with its forward edge a little higher than its rear edge, so that as it is pushed along it tends to catch the air and throw it downwards. Hence the reaction tends to lift the plane upwards. When the machine starts the reaction is not sufficient to overcome gravity, which is trying to hold the machine down upon the ground, but as the speed increases and the air is thrust down with more and more violence the point is ultimately reached when the reaction is able to overcome gravity and the machine ascends.
When a sufficient height is reached, the pilot alters the position of his horizontal rudder or "elevator" so as to make the position of the plane more flat, with the result that it throws the air downwards to a less extent, and the reaction is thereby reduced until it is only just sufficient to keep the machine at the same height. To descend, the position of the plane is made still flatter, the reaction is reduced still more and gravity has its way once again, bringing the machine to earth.
In other words, the machine acts under the influence of two forces: the downward pull of gravity and the upward reaction due to the action of the machine in throwing the air downward. The former never varies, the latter can be varied by the pilot at will: he can increase it by increasing the speed or by increasing the tilt of his plane or planes: he can reduce it by diminishing the speed or the tilt. Since generally speaking the speed of his engine will remain constant, he rises, remains at the same height or falls, at will, by the simple manipulation of the elevator through which he can change the tilt or inclination.
Most machines have a fixed tail as well as a horizontal rudder or elevator, the same being so set that it tends to keep the plane in a certain normal inclination, the elevator being called in to increase that or diminish it as may be required.
In addition to the elevator there is also another rudder of the ordinary kind, such as every ship and boat has, for guiding the machine to right or left. The elevator steers up and down, the rudder steers to either hand.
Provision is also made for balancing the machine. This is sometimes in the form of two small planes hinged to the main plane, one at either end, connected together and to a controlling lever by wires, so that by their use the pilot can steer the right-hand side of his machine upwards and the left-hand downward, or vice versa, if through any cause he finds a tendency to capsize.
In some machines the same effect is produced not by separate planes but by pulling the main plane itself somewhat out of shape, but precisely the same principle is involved.
The planes are usually made with a slight curve in them, so that they may the better catch the air and "scoop" it downwards, so to speak. They usually consist of fabric specially made for the purpose, stretched upon a light wooden framework. The whole framework is usually of wood with metal fittings frequently made of aluminium for the sake of lightness.
The engines have been mentioned in another chapter. The propeller which is almost invariably fixed directly upon the shaft of the engine has two blades only and not three as is usual with those of ships. Precisely why this should be so is not clear, but experience shows that two-bladed propellers are preferable for this work. They are made of wood, several layers being glued together under pressure, the resulting log being then carved out to the required shape. This makes a stronger thing than it would be if cut out of a single piece of wood.
All parts, engine, elevator, rudder and balancing arrangement, are controlled by very simple means from the pilot's seat.
In monoplanes there is but one main plane, resembling a pair of bird's wings. Or if we care to look upon it as two planes, one each side of the "body," then we must call it a pair. Since the name "mono" indicates one it is best to think of it as one plane although it may be in two parts. The biplane has, as its name implies, two planes, but in that case there can be no doubt, since they are placed one above the other. Machines have been made with three planes and even with as many as five, but monoplanes and biplanes appear to hold the field.
It is not possible for an aeroplane to be in any sense armoured for protection against bullets: for defence the pilot has to depend upon his own cunning man[oe]uvres combined with the fast speed at which he can move. For offensive purposes he usually has a machine gun mounted right in front of him with which he can pour a stream of bullets into an opponent or even, by flying low, he can attack a body of infantry. It is recorded that one German prisoner during the war, speaking of the daring of the British pilots in thus attacking men on foot, exclaimed, "They will pull the caps off our heads next."
Some of the aeroplanes have their propeller behind the pilot and some have it in front. The latter, to distinguish them, are called "Tractor" machines, since in their case the propeller pulls them along. Now it is easy to see that a difficulty arises in such cases through the best position for the gun being such that it throws its bullets right on to the propeller. But that has been overcome in a most simple yet ingenious way. The gun is itself operated by the engine with the result that a bullet can only be shot forth during those intervals when neither blade of the propeller is in the way. The propeller is moving so fast that it cannot be seen and the bullets are flying out in a continuous rattle, yet every bullet passes between the blades and not one ever touches.
It is easy to see that when an aeroplane is manned by a single man, as is often the case, he must have his hands very full indeed, what with the machine itself and the gun as well. In fact, he often has to leave the machine for a short time to look after itself while he busies himself with the gun.
Now there we see a sign of the wonderful work which has been done in the course of but a few years in the perfecting of the aeroplane, the result of a series of improvements in detail which make but a dreary story if related but which make all the difference between the risky, uncertain machine of a few years ago and the safe, reliable machine of to-day. Modern machines are inherently stable. The older ones had the elements of stability in them but they were so crudely proportioned that these inherent qualities did not have a chance to come into play.
If one drops a flat card edgewise from a height it seems as if it ought to fall straight down to the ground. Yet we all know from experience that it seldom does anything of the kind. Instead, it assumes a position somewhere near horizontal and then descends in a series of swoops from side to side. There we see the principle at work which, in a well-designed aeroplane, causes inherent stability. The explanation is as follows.
The aeroplane is sustained in the air through the upward pressure of the air resisting the downward pull of gravity. That has been fully explained already. Now gravity, as we all know, acts upon every part of a body whether it be an aeroplane or anything else. But for practical purposes, we may regard its action as concentrated at one particular point in that body, called the "centre of gravity." Likewise, the upward pressure of the air acts upon the whole of the under surface of the plane or planes, yet we may regard it as concentrated at a certain point called the "centre of pressure." Further, we all know from experience that a pendulum or other suspended body is only still when its centre of gravity is exactly under the point of suspension. If we move it to either side it will swing back again.
In just the same way, the only position in which an aeroplane will remain steady is that in which the centre of gravity is exactly under the point of suspension or, in other words, the centre of pressure. For the centre of pressure in the aeroplane is precisely similar to the point of suspension of a pendulum.
Let us, then, picture to ourselves an aeroplane flying along on a horizontal course with this happy state of things prevailing. Something we will suppose occurs to upset it with the result that it begins to dive downwards. It is then in the position of sliding downhill and instantly its speed increases in consequence. That increase of speed causes the air to press a little more strongly than it did before upon the front edge of the planes. In other words, the centre of pressure shifts forward a little, with the result that the centre of gravity is then a little to the rear of the centre of pressure.
A moment's reflection will show that with the centre of pressure (or point of suspension) in advance of the centre of gravity there is a tendency for the machine to turn upwards again, or, in other words, to right itself.
If, on the other hand, the initial upset causes it to shoot upwards the speed instantly falls off and the centre of pressure retreats, turning the machine downwards once more. And the same principle applies whatever the disturbance may be. Instantly and automatically a turning force comes into play which tends to check and ultimately to correct what has gone wrong.
This principle explains the behaviour of the card dropped from an upstairs window and, no doubt, as has been said, it operated also in the early flying machines, but in their case other factors caused disturbing elements with which the self-righting tendency was not strong enough to cope. As time went on, however, experience taught the makers how to avoid these disturbing factors until at last the self-righting tendency was able to act effectively, thus producing the aeroplane which is inherently stable and which will, for short periods at all events, fly safely without attention from its pilot.
Each little improvement in this direction was an invention. Of course, there were certain men whose names stand out prominently in the history of the aeroplane, notable among whom are the Wright brothers, but the final result is due to innumerable inventions, many of them by unknown men.
But perhaps someone will say, how can you possibly talk about final results in a matter which is still in its infancy?
The answer to that is that so far as the safe, "flyable" machine is concerned, it has arrived. Little now remains to be done in that direction. Further improvements there will, of course, be, but the great fundamental problems of flight have been solved.
Balloons had not long been invented when the idea arose of a device by means of which an aeronaut who found himself in difficulties might be able to reach the ground in safety. In other words, the need was felt for something which should play towards the balloon the part which the lifeboat does to the ship.
The original idea of a parachute was even older than that, since we are told of a man away back in the seventeenth century who amused the King of Siam by jumping from a height and steadying his descent by means of a couple of umbrellas. It was not, however, until the very end of the eighteenth century or the beginning of the nineteenth that descents were made from really considerable heights from balloons.
The usual arrangement then was to have the parachute hanging at full length fastened below the basket, or tied to one side of the balloon in such a manner that it could be detached by cutting the cords that held it up. When the parachute was carried below the balloon basket the man was already in the cradle or seat of the parachute ready to be dropped, but when the seat was tied to the side of the car of the balloon the aeronaut, when he wished to make a descent, first got from the car into the seat, and, casting himself adrift from the car, swung out from under the centre of the balloon so that when he was hanging clear another man in the balloon cut the cords or pulled a slip-knot which set the parachute free. There were different ways of doing this and when a man was by himself he had to get into the sling of the parachute and, on finding himself clear of everything, he would give a tug to a cord which would release a catch holding up the parachute and allow it to drop to earth.
The parachute, at the very first, was but a simple affair, being little more than a circular sheet of cotton or similar fabric, but it was very soon found necessary to make it a bag or it would not properly hold the air. Cords were attached at regular intervals all around the edge of this bag, these cords being gathered together and attached to the edge of a basket which carried the man. Sometimes only a sling was used, or a simple light seat after the fashion of the "bosun's chair" upon which a sailor is sometimes hauled to the top of an unclimbable mast, or a steeplejack to the top of a chimney.
Thus, when it was dropped, the weight of the man, pulling upon all the cords simultaneously, drew down the edge of the bag, which, catching the air in its fall, acted as a powerful brake and reduced the rate of falling to such an extent that if all went well the man alighted in safety if not comfort.
As has already been remarked in another chapter, air, which seems to us sometimes to be so exceedingly light as to have practically no weight at all, really has weight and also the property which we call inertia, by virtue of which things at rest prefer to stay at rest.
Now when this open air-bag, of considerable area, is pulled downwards it causes a very considerable disturbance in the air. As it descends the air inside and beneath it is first pushed downwards and compressed a little, then it commences to move outwards, towards the edge, round which it finally escapes to fill the slight vacuum in the space just above the descending parachute. All this the air objects to do because of its inertia. The parachute has to force it to act thus and in that way it uses up some of the force of gravity which all the time is pulling the man earthwards. In other words, that force, instead of dragging the man downwards at such a speed as to dash him to pieces, is so far employed in churning up the air that what is left only brings him down quite slowly and ends with just a gentle bump. That is the scientific explanation of what happens, although expressed in somewhat homely language.
To anyone who thinks of this matter it will be clear that a relatively heavy weight like a man, suspended from a parachute, is like a very delicately poised pendulum, and consequently it is not surprising to hear that the early parachutes oscillated very considerably from side to side, so much so, indeed, that this oscillation became a decided danger, for before the proper shape of the air-bag was found out they sometimes skidded and even turned inside out. It was found, however, at quite an early stage that this instability could be to some extent cured by making a hole right in the centre or crown of the parachute through which the air compressed inside could blow upwards in a powerful jet. At first sight it seems as if this would much weaken the parachute and cause it to descend too quickly, but quite a large hole can be safely made, and to make such a hole is only the same thing as slightly reducing the area and that can be easily remedied by slightly increasing the diameter.
Reading of this many years ago, I have often been puzzled as to why the presence of the hole should have this steadying effect, the explanation given in the old scientific textbook from which I learnt it being obviously very unsatisfactory. Of recent years, however, this subject of parachutes has been very deeply studied by an eminent engineer of London, Mr. E. R. Calthrop, the inventor of the "Guardian Angel" parachute to which these remarks are leading up, and he has hit upon what is undoubtedly the explanation. He says that the big jet of air shooting upwards through the crown of the parachute forms in effect a rudder which steers the parachute in a straight downward course, just as the rudder guides a boat upon the surface of the water.
It is quite possible that thus far the impression conveyed to the reader's mind is that the parachute and its use are very simple, straightforward matters. One may be inclined to think that it is only necessary to get a circular sheet of fabric, to fasten the cords to it, to connect them to a suitable seat and then to descend from any height at any time in perfect safety. If you make a model from a flat sheet of cotton, then one made like a bag, and drop them with little weights attached from the top window of your house you will see what funny things the air can do. After having tried these little ones, you will begin to suspect that the big parachute is full of waywardness: and, as a matter of fact, until recent years, it has been very largely a delusion and a snare. By its refusal to act and open at the right moment it has sacrificed many lives. Although apparently so simple, there were conditions existing and forces at work which for a century or more had never been properly considered and investigated, and it is only now that we have arrived at a parachute whose certainty of action and general trustworthiness entitle it to be called the "lifeboat of the air."
The troubles with the older parachutes were two. First, although often it opened quite quickly, and carried its load as perfectly as could be desired, it sometimes had the habit of delaying its opening, and unless the fall were from a very great height it was unsafe to take the risk, indeed, it sometimes refused to open at all, and the poor parachutist suffered a fearful death. It had to be carried in a more or less folded-up state. Often it was hung up by its centre to the side of a balloon, when it was very like a shut-up umbrella. Consequently the power of opening quickly and certainly was of the first importance, and the lack of that power and the uncertainty of its action were a very serious defect. It has always suffered from an ill reputation as to reliability.
The second fault lay with the cords. They would persist in getting entangled. Everyone knows how a dozen cords hanging near together will get entangled with each other on the slightest provocation. Such cords if blown about by a strong wind would be much worse even than when still, and if, as must often be the case with parachutes, they be coiled up, we all know from our own experience that some of them would be almost sure to get knotted and tangled together when, in a sudden emergency, the attempt was made to pull them all out of their coils in a second or two. Just picture to yourself what it means: a dozen coiled cords all close together, themselves all coiled up in loops, suddenly pulled. Something awkward appears almost inevitable. And the result of even one rope going awry may be fatal, for it may prevent the parachute opening out fully, probably giving it a "lop-sided" form incapable of gripping the air effectually and consequently allowing the unfortunate man to fall with a velocity which means certain death. This second cause of failure to open, through entanglement of cordage, has happened in a number of cases, with fatal results.
So much for the faults of the old primitive parachute. Now let us consider for a moment the urgent need for a parachute which is free from such faults. The man who goes up in a balloon on a Saturday afternoon feels so sure of his "craft" that he thinks he needs no "lifeboat," yet men in ordinary free balloons have been killed for want of them. The spectators at country fairs no longer appreciate a parachute descent as a great and extraordinary spectacle. But in warfare, with kite balloons by the dozen, with dirigible balloons by the score and aeroplanes by the hundred, the call for parachutes is urgent and irresistible. At all events, Mr. Calthrop found an irresistible call to devote years of close study, unceasing toil and considerable sums of money to the task of perfecting an improved parachute which would always open and open quickly, and whose cords would never get entangled. He has the satisfaction of knowing that by so doing he has provided an appliance that in the air is as reliable as a lifeboat is at sea, and that at all times, and from every kind of aircraft, can be depended upon in case of accident to save the lives of gallant airmen who but for his work would be dashed to death. The Great War has taught us to regard life somewhat cheaply. For years we were more concerned with taking life than with saving it, yet surely to save the life of one's own men is equivalent to taking the lives of one's opponents, so that even from the point of view of warfare the saving of life may be a help towards victory. This is particularly so when the lives saved are those of the choicest spirits, and among the most highly trained. It has been reckoned that to make a fully-trained pilot costs as much as £1500, so that to save but a few, even in their preparatory nights on the training-grounds where so many accidents happen, makes quite an appreciable difference in the cost of a war, without considering the main question of the men's lives.
Many inventions arise through a man thinking of an idea and then seeking and finding some application for it. Elsewhere in this book, I give examples of such cases. Here we have an instance of the opposite, for Mr. Calthrop found his thoughts strongly directed in this direction by the death of a personal friend, the Hon. C. S. Rolls, one of the early martyrs in the cause of aviation, not to mention others who shared the same risks and in some cases the same fate. His interest thus aroused, he first studied all the records which could be found relating to parachute accidents, so as to ascertain, if possible, what were the causes of failure. Then he commenced a long series of experiments with a view to removing these causes. Improvement after improvement was tried, unexpected difficulties were discovered and grappled with, the kinematograph was called in to record the movements of the falling objects, a task for which it is far better fitted than the human eye, and after years of this there emerged the finished parachute, automatic in its action, perfectly reliable and a true safeguard, which I am about to describe.
The parachute's body consists of the finest quality silk carefully cut into gussets of such a shape that when sewn together somewhat after the manner of the cover of an umbrella, they form a shallow bag, parabolic in section, of that particular shape which the material would assume naturally were it perfectly elastic when enclosing its resisting body of compressed air.
At intervals round the edge are fastened twenty-four V-shaped tapes. These are only a few feet long and the lower end of each V-shaped pair is attached to a long main tape. There are twelve of these main tapes, and their lower ends unite in a metal disc from which is suspended the sling and harness by which the man is supported.
The "Guardian Angel" Parachute.
(1) Shows the airman in the harness by which he is attached to the parachute. By means of the star-shaped buckle he can instantly release himself. (2) Shows the parachute two seconds after the airman has jumped from the aeroplane. In (3) he is seen nearing the ground.
(By permission of E. R. Calthrop, Esq.)
So the twenty-four short tapes form twelve V's to the points of which are attached the twelve long tapes which support the man. The reason why tapes are used in this particular parachute and not cords will be referred to later.
In the crown of the silk body there is the usual hole for the purpose of forming the air-rudder to steady the parachute in its descent.
And now we can consider the first great feature of this wonderful invention and ask ourselves these questions: "By what means is it made to open?" "What makes it more reliable than others?"
To answer that we must first see why the others sometimes refused to open. In whatever way an ordinary parachute may be packed it must, when coming into use, assume the state of a shut umbrella with a hole in the top.
In this condition it is assumed that as it falls the air will find a way in through the lower end and will blow the parachute open in precisely the same way that a strong wind will sometimes blow out the folds of an umbrella.
But, as a matter of fact, the loose folds of a parachute, when the edge of the gussets is gathered in, are sure to overlap and enfold each other more or less. Thus, when in the shut-umbrella state, it sometimes happens that air which is inside can escape upwards through the hole more easily than fresh air can get in from below. The parachute, in such a state, is, let us imagine, falling rapidly through the air. The result is just the same as if it were still and the air were rushing upwards past it. And the upward rush past the top hole tends to suck air out through the hole faster than fresh air can find a way in at the bottom.
This is the principle of the ejector, which engineers have put to many uses. For example, the vacuum brakes employed on many large railways owe all their power to stop a train to a vacuum caused by an ejector. There is a short tube or nozzle, placed in the centre of another tube through which steam blows. The action of the steam in the outer tube as it rushes past the end of the inner tube drags after it the air which is in the inner tube so effectively as to produce quite a good vacuum. And in precisely the same way, the upward rush of air past the parachute, or what is just the same, the falling of the parachute through stationary air, can suck the air from inside the latter and create a vacuum in it if the gussets gathered together at the mouth unfortunately overlap one another and are thus locked together by the pressure of the air striving to get in. Thus, instead of the downward fall causing the ordinary parachute to open, as in most cases it will do quite well, the fall under these particular conditions actually binds its folds together and prevents it from opening. It is true this does not often happen, but the risk is always present at every drop, and this unreliability has cost the lives of brave men and women, and the knowledge of this constant risk has led others to write down the parachute a failure, by reason of its known unreliability to open instantly. Even when it does open the depth it falls before it opens is so variable, by reason of the fight between vacuum and pressure, that it may be one hundred feet one time and one thousand feet next time with the same parachute.
Now the "Guardian Angel" is designed so that those conditions cannot occur. Its silken covering is first laid out on the ground and into the centre is introduced a beautifully-designed disc of aluminium, somewhat like a large inverted saucer, of exceeding lightness but of ample strength for what it has to do. Then the silk body is pleated and folded back over the upper part of this launching-disc and gradually packed so that it occupies but a very small space upon the upper surface of the disc. It is so folded that its edge comes in the topmost layer and also in such a manner that on the tapes being pulled the silk unfolds easily and regularly, flowing down as it were over the edge of the disc almost as water flows if allowed to fall from a tap upon the centre of an inverted saucer. After the folding is complete another aluminium disc is placed above the packed silk body which shields it from the enormous air pressure when it is being released from an aeroplane flying at top speed. The upper and lower fabric covers are then superimposed and sealed and the "Guardian Angel" parachute is ready for use.
The tapes, likewise, are folded up, in a special way upon the bottom cover, which is sprung over the bottom of the disc. The bottom cover with the tapes upon it, is pulled away by the weight of the airman as he makes his jump to safety, and the tapes are so arranged that a pull upon them causes them to draw out steadily and smoothly, almost like water falling from a height.
If we regard the silk as forming a shallow bag inverted, we may say that it is folded upon the disc inside out and the function of the disc is to cause it to spread and enclose a wide column of air as it is pulled from its folds. To commence with it is nothing more than so much folded-up silk, but from the first moment of action it becomes a bag with a wide-open mouth, for its open mouth cannot be smaller than the disc. Therefore, from the first instant it begins to grip the air and the ejector action never gets a chance to commence. The pressure of air inside is from the very commencement of the fall greater than that of the surrounding air. Moreover, the disc covers the hole until the parachute is actually open, thereby making ejector action doubly impossible.
The widely-opened mouth of the air-bag (I cannot help repeating that term for it is so expressive) swallows up more and more air as the thing falls rapidly, with the result that the air inside is instantly compressed and the increasing pressure as the silk is more and more fully drawn out causes it to expand until the whole is fully extended like a huge umbrella. The instant compression of the enclosed column of air is what causes it always to open automatically.
When once it is pointed out it is easy to see what a difference the presence of this disc makes. It is so simple that it cannot fail to act and having once produced that open mouth all the rest is due to the action of natural forces which can be absolutely relied upon. The ordinary parachute with its hopeless irregularities has, in fact, been converted into a machine whose action can never fail.
The disc is fastened to the balloon or aeroplane and is left behind when the parachute falls, having done its work.
And now let us consider the tapes. As has already been remarked, a series of coiled cords cannot be relied upon to pull out straight without possibility of entanglement, but a tape, if folded to and fro like a Chinese cracker, will invariably do so. So packed tapes have been substituted for coiled corded rigging, with the certainty that they cannot be entangled in the fiercest air current.
And now we come to another interesting feature. The man is not suspended directly from the small disc to which the tapes are attached but by a non-spinning sling which contains a shock absorber. This latter consists of a number of strands of rubber and it is owing to its action that the aviator who trusts his life to the parachute suffers little or no shock; even when the instant opening of the parachute begins to arrest his fall. And not only does it save him from shock, but it also avoids the possibility of too great a stress coming suddenly upon the parachute or its rigging of tapes.
The aviator himself is attached to the parachute through the shock-absorber sling, by means of a harness which he wears constantly throughout his flight, so that in the event of trouble he only has to jump overboard and the parachute automatically does the rest. This harness consists of two light but strong aluminium tubular rings through which he places his arms, combined with a series of straps which can be so adjusted that the stress of carrying him comes upon those parts of his body best adapted to bear it.
This improved parachute is the only one which is capable of being used instantly and without preparation for descent from an aeroplane flying at top speed. It is easy to see that it is one thing to drop from a stationary or nearly stationary balloon and quite another to dive from an aeroplane at one hundred miles per hour. The latter is equivalent to suddenly trusting oneself to a parachute during the strongest gale. It has been found, by experiment, however, that high speed is no bar to the use of this parachute since it only causes the parachute to open a little more quickly than usual, which means that it can be used with safety from an even lower height.
Under the worst conditions this wonderful parachute can be relied upon always to open and carry its load at a height of only one hundred feet, and its use is safe in all circumstances when dropped from two hundred feet above the ground. After it has once got into operation and taken charge of affairs, so to speak, the man descends at the rate of only fifteen feet per second, which is just about the same as dropping from a height of a little over three feet. In other words, he will arrive on the ground with no worse bump than you would get by jumping off the dining-room table.
But suppose that there were a wind blowing: would not the parachute come down in a slanting direction and then drag the man along? Or may he not alight upon a tree or the roof of a house, only to be pulled off again and flung headlong? Quite true he might, were not proper provision made for such occurrences. Embodied in the harness is a lock which can be instantly undone, by a simple movement of a lever in the hand, and by its aid the man on touching earth or on alighting upon anything solid can release himself instantly, after which the parachute can sail away whither it will, but he will be safe and sound.
What Mr. Calthrop has accomplished by the invention of his "Guardian Angel" parachute may be summarised briefly by saying that he has reduced the minimum height from which a parachute could be dropped from two thousand to two hundred feet, and that he has made it possible to launch a parachute, with the certainty of safety, from any kind of aircraft flying at the slowest or highest speed of which they are capable.
You are only a boy now, but when in years to come you are quite old and have grey hair you may become a Member of the Air Board and—who knows—it may become your duty to decide that this great invention shall be always used on the training grounds to save the lives of the young men, not yet born, who are then learning to fly. During the War, one was killed every day, 365 in a year, many of whom might have been saved had more "Guardian Angels" been in use.