Chapter XXV The Aerial Lifeboat
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.
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.