Part 4 (1/2)
Another says he is sure he saw one of the wings fold upwards and the machine swing and fall. And so on. It is extremely difficult, even for a technical eye-witness, to be sure of what he sees when things happen quickly and at a distance from him; while the statements of non-technical people, who are not trained in observation, are generally so unreliable as to be useless.
It has happened often therefore, far too often, in aeroplane fatalities that have happened from time to time, that the cause of such accidents has, even after the most careful investigation, had to be written down a mystery. But in more than a few cases, though the evidence has been far from conclusive, it has been considered that a pilot has been guilty of some error of judgment. There were puzzling instances, notably in the early days of flying, when airmen began first to make cross-country flights, of engines being heard to fail suddenly, and machines seen to fall to destruction. That engines should break down was not surprising; they were doing so constantly; but there was no reason why, even if they did fail, a machine should fall helplessly instead of gliding. But what was thought to have happened, in more than one of these cases, was that the pilot, through an error of judgment, had failed to get down the bow of his machine when his motor gave signs of stopping. The craft concerned were, it should be mentioned, ”pusher” biplanes; and the same rule applied to them, in cases of engine failure, as has been explained in a previous chapter, and as is emphasised nowadays in the instruction of the novice. But in those days the beginner had frequently to learn, not from wise tuition, but from bitter experience; and he was lucky, often, if he learned his lesson and still retained his life. On certain early-type biplanes, for instance, machines with large tail-planes, and engined as a rule by a motor which was giving less than its proper amount of power, it was most dangerous for a pilot if, on observing any signs of failing in his engine, he sought to fly on in the hope that the motor would ”pick up” again, and continue its work. Directly there was a tendency of the motor to miss-fire, or lessen in the number of its revolutions per minute, the consequent reduction of the propeller draught, as it acted on the tail of the machine, would cause this tail to droop, and the machine to a.s.sume very quickly a dangerous position. And when once it began to get tail-down, as pilots found to their cost, there was nothing to be done. The machine lost what little forward speed it had, and either fell tail-first, or slipped down sideways. Such risks as these, which were very real, were rendered worse owing to the fact that, in much of the cross country flying of the early days, pilots flew too low. They lacked the confidence of those who followed them, and were too p.r.o.ne to hug the earth, instead of attaining alt.i.tude. It was not realised clearly then, as it is now, that in height lies safety. And so when a machine lost headway through engine failure, and was not put quickly enough into a glide, it happened often that it had come in contact with the earth, and had been wrecked, before there was any chance for the pilot to regain control, or for the machine itself to exhaust its side-slip, and come back to anything like a normal position.
But the failure of the human factor in flying, the lack of skill of a pilot that may lead to disaster, is shown by statistics to play no more than a small part, when accidents are studied in numbers and in detail. Some time before the war, in an a.n.a.lysis of the accidents that had befallen aviators in France--accidents concerning which there was adequate data--it was shown that only 15 per cent. of them could be attributed to a failure in judgment or skill on the part of the pilot.
Apart from errors, however, in what may be called legitimate piloting, there have been regrettable accidents due to trick or fancy flying.
Putting a machine through a series of evolutions, to interest and amuse spectators, is not of course in itself to be condemned. In such flying, and notably for instance in ”looping the loop,” facts were learnt concerning the navigation of the air, and as to the apparently hopeless positions from which an aeroplane would extricate itself, which were of very high value, from both a scientific and practical standpoint. Public interest in aviation was increased also by such displays; and it is very necessary that there should be public interest in flying, seeing that it is the public which is asked to pay for the development of our air-fleets. But the man who undertakes exhibition flying needs not only to be a highly-skilled pilot, but a man also of an exceptional temperament--a man whose familiarity with the air never leads him into a contempt for its hidden dangers; a man who will not, even though he is called on to repeat a feat time after time, abate in any way the precautions which may be necessary for his safety. In looping the loop, for instance, or in upside-down flying, it is necessary always that the aeroplane should be at a certain minimum height above the ground. Then, should anything unexpected happen, and the pilot lose command temporarily over his machine, he knows he has a certain distance which he may fall, before striking the ground; and during this fall the natural stability of his machine, aided by his own operation of the guiding surfaces, may bring it back again within control. But if he has been tempted to fly too near the ground, and has ignored for the moment this vital precaution, and if something happens for which he is not prepared, then the impact may come before he can do anything to save himself.
In the early days of flying, when aviators attempted an acrobatic feat, they ran a far heavier risk than would be the case to-day; and for the simple reason that their machines, not having a strength sufficient to withstand any abnormal stresses, were likely to collapse in the air if they were made to dive too rapidly, or placed suddenly at any angle which threw a heavy strain on their planes. A machine for exhibition flying needs to be constructed specially; but this was not realised till accidents had taught their lesson.
It is a regrettable fact, one which emerges directly from a study of aeroplane accidents, that many of them might have been avoided had men been content to follow warily in the footsteps of the pioneers, and not run heavy risks till they themselves, and the machines they controlled, had been prepared, by a long period of steady flying, to meet such greater dangers. The first men who flew realised fully the risks they ran. But when flying became more general, and men found machines ready to their hands, machines which it was a simple matter to learn to fly, this early spirit of caution was forsaken, and feats were attempted which brought fatalities in their train, and which seemed to emphasise the risks of aviation, and did it the very bad service that they fixed in the public mind a notion of its dangers, and prevented men from coming forward to take up flying as a sport.
CHAPTER VIII
FACTORS THAT MAKE FOR SAFETY
It has been calculated that nearly half the aeroplane disasters of the early days were due to a structural weakness in machines, or to mistakes either in their design, or in such details as the position, shape, and size of their surfaces. To-day, thanks to science, and to the growing skill and experience of aeroplane designers and constructors, this risk of the collapse of a machine in the air, or of its failure to respond to its controls at some critical moment through an error in design, has been to a large extent eliminated. That such risks should be eliminated wholly is, as yet, too much to expect.
One of the factors making for safety has been the steady growth in the general efficiency of aircraft: in the curve of their wings which, as a result largely of scientific research, has been made to yield a greater lift for a given surface and to offer a minimum of resistance to their pa.s.sage through the air; in the power and reliability of their engines; in the efficiency of their propellers; and in the shaping of the fusilage of a machine, and in the placing and ”stream-lining” of such parts as meet the air, so as to reduce the head resistance which is encountered at high speeds. Such gains in efficiency, which give constructors more lat.i.tude in the placing of weight and strength where experience show they are needed, have gone far to produce an airworthy machine. In the old days, when machines were inefficient, a few revolutions more or less per minute in the running of an engine meant all the difference between an ascent and merely pa.s.sing along the ground. But nowadays, through the all-round increase in efficiency that has been obtained, a machine will still fly upon its course without losing alt.i.tude, and respond to its controls, even should the number of revolutions per minute of its engine be reduced considerably.
When given a greater efficiency in lifting surfaces and power-plants--and profiting also from the lessons that had been learnt in the piloting of machines--constructors were able to devote their attention, and to do so with certainty instead of in a haphazard way, to the provision of factors of safety when a craft was in flight. With a machine of any given type, if driven through the air at a certain speed, it is possible to estimate with accuracy what the normal strains will be to which it is subjected. But even if such data are obtained, and the machine given the strength indicated, this factor of safety is insufficient. It is not so much the normal strains, as those which are abnormal, that must be guarded against in flight. A high-speed machine, if piloted on a day when the air is turbulent, may be subjected to extraordinarily heavy strains; rising many feet in the air one moment, falling again the next, and being met suddenly by vicious gusts of wind--in much the same way that a fast-moving s.h.i.+p, when fighting its way through a rough sea, is beaten and buffeted by the waves. Air waves have not of course the weight, when they deliver a blow, that lies behind a ma.s.s of water; but that these wind-waves attain sometimes an abnormal speed, and have a tremendous power of destruction, is shown in the havoc that is caused by hurricanes.
It seems astonis.h.i.+ng to many people that such a frail machine as the aeroplane, with its outspread wings containing nothing stronger often than wooden spars and ribs, covered by a cotton fabric, should be capable of being driven through the air at such a speed, say, as 100 miles an hour, encountering not only the pressure of the air, but resisting also the fluctuations to which it may be subjected. But, underlying the lightness and apparent frailty of such a wing, when one sees it in the workshop in its skeleton form, before it has been clothed in fabric, there is a skill in construction, and an experience in the choice, selection, and working of woods, that produces a structure which, for all its fragile appearance, is amazingly strong.
And the same applies, nowadays, to all the other parts of an aeroplane. That it should have taken years to gain such strength, and to reduce so largely the risk of breakage, is not in itself surprising. Men had to devise new methods in construction--always with the knowledge that weight must be saved--and to create new factors of safety, before they could build an airworthy craft.
To-day, when a man flies, he need have no lurking fear, as had the pioneers, that his craft may break in the air. Even when it is driven through a gale, plunging in the rushes of the wind, yet held straining to its task by the power of its motor, the modern aeroplane can be relied upon; and not in one detail of its construction, but in every part. Experience, the researches of science, and the growing skill with which aircraft are built, stand between the airman and many of his previous dangers. The aeroplane to-day, one of the structural triumphs of the world in its lightness and its strength, has a factor of safety which is sufficient to meet, and to withstand, not merely ordinary strains, but any such abnormal stresses as it may encounter--and which may be many times greater than the strains of normal flight.
The aviator knows also that his engine, as it gives him power to combat successfully his treacherous enemy, the wind, represents the fruit of many tests and of many failures, and of the spending of hundreds of thousands of pounds. Many of its defects have revealed themselves, and been rectified; it is no longer light where it should have weight of metal, nor weak where it should be strong. So far as any piece of mechanism can be made reliable, consisting as it does of a large number of delicate parts, operating at high speed, the aeroplane motor has been made reliable. But, so long as one motor is used, there must always, as we have said, remain a risk of breakdown.
It is for this reason that, thanks largely to the stimulus of the war--which has created a practical demand for such machines--aeroplanes are now being built, and flown with success, which are fitted with duplicate motors. With such machines, which give us a first insight as to the aircraft of the future, engine failure begins to lose its perils--particularly in regard to war. More than once during the great campaign, when flying a single-engine machine, an aviator has found his motor fail him, and has been obliged to land on hostile soil; with the result that he has been made prisoner. But with dual-engine machines it has been found that, when one motor has failed mechanically, or has been put out of action by shrapnel, the remaining unit has been sufficient--though the machine has flown naturally at a reduced rate--to enable the pilot to regain his own lines.
In peace flying, too, as well as in war, the multiple-engined aeroplane brings a new factor of safety. If one of his motors fails, and he is over country which offers no suitable landing-place, the pilot with a duplicate power-plant need not be concerned. His remaining unit or units will carry him on. There are problems with duplicate engines which remain to be solved--problems of a technical nature--which involve general efficiency, transmission gear, and the number and the placing of propellers; but already, though this new stride in aviation is in its earliest infancy, results that are most promising have been obtained.
To those who study aviation, and have done so constantly, say from the year 1909, one of the most striking signs of progress lies in the fact that, though unable at first to fly even in the lightest winds, the aviator of to-day will fight successfully against a 60 miles-an-hour wind, and will do battle if need be, once he is well aloft, with a gale which has a velocity of 90 miles an hour. He will ascend indeed, and fly, in any wind that permits him to take his machine from the ground into the air, or which the motor of his craft will allow it to make headway against. And here, though machines are still experimental, there is removed at one stroke the earliest and the most positive objection of those who criticised a man's power to fly. When the first aeroplanes flew the sceptics said: ”You have still to conquer the wind, and that you will never do. Aeroplanes will be built to fly only in favourable weather, and this will limit their use so greatly that they will have no significance.” But to-day the aviator has ceased, one might almost say, to be checked or hampered by the wind. If the need is urgent, as it often is in war, then it will be nothing less than a gale that will keep a pilot to the ground, provided he has a sufficiently powerful machine, and a suitable ground from which to rise--and granted also that he has no long distance to fly.
Wind-flying resolves itself into a question of having ample engine-power, of being able to launch a machine without accident, and get it to earth again without mishap; and of being able to make a reasonable headway against the wind when once aloft; and these difficulties should solve themselves, as larger and heavier machines are built.
Apart from the growing skill of the aviator, which has been bought dearly, science can now give him a machine, when he is in a wind, that needs no exhausting effort to hold it in flight. Craft are built, as a matter of certainty and routine, which have an automatic stability.
Science has made it possible indeed, by a mere shaping and placing of surfaces, and without the aid of mechanical devices, to give an aeroplane such a natural and inherent stability that, when it is a.s.sailed by wind gusts in flight, it will exercise itself an adequate correcting influence. To understand what this means it should be realised that, when such a machine is in flight say in war on a strategical reconnaissance, and carries pilot and pa.s.senger, the former can take it to a suitable alt.i.tude and then set and lock his controls, and afterwards devote his time, in common with that of his pa.s.senger, to the making of observations or the writing of notes. The machine meanwhile flies itself, adapting itself automatically to all the differences of wind pressure which, if it had not this natural stability, would need a constant action of the pilot to overcome. All he need do is to maintain it on its course by an occasional movement of the rudder. With such a machine, even on a day when there is a rough and gusty wind, it is possible for an airman to fly for hours without fatigue; whereas with a machine which is not automatically stable, and needs a ceaseless operation of its controls, the physical exhaustion of a pilot, after hours of flight, is very severe.
So, already, one sees these factors of safety emerge and take their place. There is no longer a grave peril of machines breaking in the air; there need be no longer, with duplicate power-plants, the constant risk of engine failing; while that implacable and treacherous foe, the wind, is being robbed daily of its perils.
CHAPTER IX
A STUDY OF THE METHODS OF GREAT PILOTS
The masters of flying, and this is a fact the novice should ponder well, have been conspicuous almost invariably for their prudence. No matter how great has been their personal skill, they have never lost their respect for the air; and this is why so many of the great flyers, after running the heaviest of risks in their pioneer work, have managed to escape with their lives. What patience and sound judgment can accomplish, when pitted even against such dangers as must be faced by an experimenter when he seeks to fly, is shown by an incident from the early career of the Wright brothers. With one of their gliders, a necessarily frail machine, and in tests made when they were both complete novices, they managed to make nearly 1000 glides; and not once in all those flights, during which they were learning the rudiments of balance and control, did they have a mishap which damaged at all seriously their machine.