 | CHAPTER XII
EXPERIMENTAL WORK IN FLYING Aeroplanes |  |
12. CHAPTER XII
EXPERIMENTAL WORK IN FLYING
THE novice about to take his first trial trip in an automobile will soon learn that the great task in his mind is to properly start the machine. He is conscious of one thing, that it will be an easy matter to stop it by cutting off the fuel supply and applying the brakes.
CERTAIN CONDITIONS IN FLYING.—In an aeroplane conditions are reversed. Shutting off the fuel supply and applying the brakes only bring on the main difficulty. He must learn to stop the machine after all this is done, and this is the great test of flying. It is not the launching,—the ability to get into the air, but the landing, that gives the pupil his first shock.
Man is so accustomed to the little swirls of air all about him, that he does not appreciate what they mean to a machine which is once free to glide along in the little currents which are so unnoticeable to him as a pedestrian.
The contour of the earth, the fences, trees, little elevations and other natural surroundings, all
HEAT IN AIR.—Heat is transmitted through the air by what is called convection, that is, the particles of the air transmit it from one point to the next. If a room is closed up tight, and a little aperture provided so as to let in a streak of sunlight, it will give some idea of the unrest of the atmosphere. This may be exhibited by smoke along the line of the sun's rays, which indicates that the particles of air are constantly in motion, although there may be absolutely nothing in the room to disturb it.
MOTION WHEN IN FLIGHT.—If you can imagine a small airship floating in that space, you can readily conceive that it will be hurled hither and thither by the motion which is thus apparent to the eye.
This motion is greatly accentuated by the surface of the earth, independently of its uneven contour. If a ball is thrown through the air, its dynamic force is measured by its impact. So with light, and heat. In the space between the planets it is very cold. The sunlight, or the rays
Unless the rays come into contact with something, they produce no effect. When the beams from the sun come into contact with the atmosphere a dynamic force is exerted, just the same as when the ball struck an object. When the rays reach the earth, reflection takes place, and these reflected beams act on the air under different conditions.
CHANGING ATMOSPHERE.—If the air is full of moisture, as it may be at some places, while comparatively dry at other points, the reflection throughout the moist area is much greater than in the dry places, hence evaporation will take place and whenever a liquid vaporizes it means heat.
On the other hand, when the vapor is turning to a liquid, condensation takes place, and that means cooling. If the air should be of the same degree of saturation throughout,—that is, have the same amount of moisture everywhere, there would be few winds. These remarks apply to conditions which exist over low altitudes all over the earth.
But at high altitudes the conditions are entirely different. As we ascend the air becomes rarer. It has less moisture, because a wet atmosphere, being heavier, lies nearer the surface of the earth.
All these conditions—the contour of the earth; the uneven character of the moisture in the air; the inequalities of the convection currents; and the unstable, tenuous, elastic nature of the atmosphere, make the trials of the aviator a hazardous one, and it has brought out numerous theories connected with bird flight. One of these assumes that the bird, by means of its finely organized sense, is able to detect rising air currents, and it selects them in its flight, and by that means is enabled to continue in flight indefinitely, by soaring, or by flapping its wings.
ASCENDING CURRENTS.—It has not been explained how it happens that these particular "ascending currents" always appear directly in the line of the bird flight; or why it is that when, for instance, a flock of wild geese which always fly through space in an A-shaped formation, are able to get ascending air currents over the wide scope of space they cover.
ASPIRATE CURRENTS.—Some years ago, in making experiments with the outstretched wings of one of the large soaring birds, a French sailor
It is known that if a ball is suspended by a string, and a jet of air is directed against it, in a particular way, the ball will move toward the jet, instead of being driven away from it. A well known spraying device, called the "ball nozzle," is simply a ball on the end of a nozzle, and the stream of water issuing is not effectual to drive the ball away.
From the bird incident alluded to, a new theory was propounded, namely, that birds flew because of the aspirated action of the air, and the wings and body were so made as to cause the moving air current to act on it, and draw it forwardly.
OUTSTRETCHED WINGS.—This only added to the "bird wing" theory a new argument that all flying things must have outstretched wings, in order to fly, forgetting that the ball, which has no outstretched wings, has also the same "aspirate" movement attributed to the wings of the bird.
The foregoing remarks are made in order to impress on the novice that theories do not make flying machines, and that speculations, or analogies of what we see all about us, will not make an aviator. A flying machine is a question of dynamics,
THE STARTING POINT.—Before the uninitiated should attempt to even mount a machine he should know what it is composed of, and how it is made. His investigation should take in every part of the mechanism; he should understand about the plane surface, what the stresses are upon its surface, what is the duty of each strut, or brace or wire and be able to make the proper repairs.
THE VITAL PART OF THE MACHINE.—The motor, the life of the machine itself, should be like a book to him. It is not required that he should know all the theories which is necessary in the building, as to the many features which go to make up a scientifically-designed motor; but he must know how and why it works. He should understand the cam action, whereby the valves are lifted at the proper time; what the effect of the spark advance means; the throttling of the engine; air admission and supply; the regulation of the carbureter; its mechanism and construction; the propeller should be studied, and its action at various speeds.
STUDYING THE ACTION OF THE MACHINE.—Then comes the study on the seat of the machine itself.
It is not enough to know that a lever or a wheel when moved a certain way will move a plane a definite direction. He should learn to know instinctively, how far a movement to make to get a certain result in the plane itself, and under running conditions, as well.
Suppose we have an automobile, running at the rate of ten miles an hour, and the chauffeur turns the steering wheel ten degrees. He can do so with perfect safety; but let the machine be going forty miles an hour, and turn the wheel ten degrees, and it may mean an accident. In one case the machine is moving 14½ feet a second, and in the other instance 58 feet.
If the airship has a lever for controlling the angle of flight, he must study its arrangement, and note how far it must be moved to assume the proper elevating angle. Then come the means for controlling the lateral stability of the machine. All these features should be considered and studied over and over, until you have made them your friends.
While thus engaged, you are perfectly sure that you can remember and act on a set of complicated movements. You imagine that you are skimming over the ground, and your sense tells you that you have sufficient speed to effect a launching. In your mind the critical time has come.
ELEVATING THE MACHINE.—Simply give the elevator lever the proper angle, sharp and quick and up you go. As the machine responds, and you can feel the cushioning motion, which follows, as it begins to ride the air, you are aware of a sensation as though the machine were about to turn over to one side; you think of the lateral control at once, but in doing so forget that the elevator must be changed, or you will go too high.
You forget about the earth; you are too busy thinking about several things which seem to need your attention. Yes, there are a variety of matters which will crowd upon you, each of which require two things; the first being to get the proper lever, and the second, to move it just so far.
In the early days of aeroplaning, when accidents came thick and fast, the most usual explanation which came from the pilot, when he recovered, was: "I pushed the lever too far."
Hundreds of trial machines were built, when man learned that he could fly, and in every instance, it is safe to say, the experimenter made the
It is a wonder that accidents were not recorded by the hundreds, instead of by the comparatively few that were heard from. It was very discouraging, no doubt, that the machines would not fly, but that all of them, if they had sufficient power, would fly, there can be no doubt.
HOW TO PRACTICE.—Absolute familiarity with every part of the machine and conditions is the first thing. The machine is brought out, and the engine tested, the machine being held in leash while this is done. It is then throttled down so that the power of the engine will be less than is necessary to raise the machine from the ground.
THE FIRST STAGE.—Usually it will require over 25 miles an hour to raise the machine. The engine is set in motion, and now, for the first time a new sensation takes possession of you, for the reason that you are cut off from communication with those around you as absolutely as though they were a hundred miles away.
This new dependence on yourself is, in itself, one of the best teachers you could have, because it begins to instill confidence and control. As the machine darts forward, going ten or fifteen miles an hour, with the din of the engine behind you, and feeling the rumbling motion of the wheels
The newness of the first sensation, which is always under those conditions very much augmented in the mind, wears away as the machine goes back and forth. There is only one control that requires your care, namely, to keep it on a straight course. This is easy work, but you are learning to make your control a reflex action,—to do it without exercising a distinct will power.
PATIENCE THE MOST DIFFICULT THING.—If you have the patience, as you should, to continue this running practice, until you absolutely eliminate the right and left control, as a matter of thought, occasionally, if the air is still turning the machine, and eventually, bringing it back, by turning it completely around, while skimming the ground, you will be ready for the second stage in the trials.
THE SECOND STAGE.—The engine is now arranged so that it will barely lift, when running at its best. After the engine is at full speed, and you are sure the machine is going fast enough, the elevator control is turned to point the machine in the air. It is a tense moment. You are on the alert.
The elevator is turned, and the forward end changes its relation with the ground before you.
With a calm air the machine is turned while running, by means of the vertical rudders. This is an easy matter, because while going at twenty miles an hour, the weight of the machine on the surface of the ground is less than one-tenth of its weight when at rest.
Thus the trial spins, half the time in the air, in little glides of fifty to a hundred feet, increasing in length, give practice, practice, PRACTICE, each turn of the field making the sport less exciting and fixing the controls more perfectly in the mind.
THE THIRD STAGE.—Thus far you have been turning on the ground. You want to turn in the air. Only the tail control was required while on the ground. Now two things are required after you leave the ground in trying to make a turn: namely, putting the tail at the proper angle, and taking charge of the stabilizers, because in making the turn in the air, the first thing which will arrest the attention will be the tendency of the machine to turn over in the direction that you are turning.
After going back and forth in straight-away glides, until you have perfect confidence and full control, comes the period when the turns should be practiced on. These should be long, and tried only on that portion of the field where you have plenty of room.
OBSERVATIONS WHILE IN FLIGHT.—If there are any bad spots, or trees, or dangerous places, they should be spotted out, and mentally noted before attempting to make any flight. When in the air during these trials you will have enough to occupy your mind without looking out for the hazardous regions at the same time.
Make the first turns in a still air. If you should attempt to make the first attempts with a wind blowing you will find a compound motion that will very likely give you a surprise. In making the first turn you will get the sensation of trying to fly against a wind. Assuming that you are turning to the left, it will have the sensation of a wind coming to you from the right.
FLYING IN A WIND.—Suppose you are flying directly in the face of a wind, the moment you begin to turn the action, or bite of the wind, will cause the ends of the planes to the right to be unduly elevated, much more so than if the air should be calm. This raising action will be liable to startle
While flying around at the part of the circle where the wind strikes you directly on the right side the machine has a tendency to climb, and you try to depress the forward end, but as soon as you reach that part of the circle where the winds begin to strike on your back, an entirely new thing occurs.
As the machine is now traveling with the wind, its grip on the air is less, and since the planes were set to lower the machine, at the first part of the turn, the descent will be pretty rapid unless the angle is corrected.
FIRST TRIALS IN QUIET ATMOSPHERE.—All this would be avoided if the first trials were made in a quiet atmosphere. Furthermore, you will be told that in making a turn the machine should be pointed downwardly, as though about to make a glide. This can be done with safety, in a still air, although you may be flying low, but it would be exceedingly dangerous with a wind blowing.
MAKING TURNS.—When making a turn, under no circumstances try to make a landing. This should never be done except when flying straight, and then safety demands that the landing should be made against the wind and not with it. There
By greater speed is meant relative to the earth. If the machine has a speed of thirty miles an hour, in still air, the speed would be forty miles an hour going with the wind, but only twenty miles against the wind. Second, the banking of the planes against the air is more effective when going into the wind than when traveling with it, and, therefore, the speed at which you contact with the earth is lessened to such an extent that a comparatively easy landing is effected.
THE FOURTH STAGE.—After sufficient time has been devoted to the long turns shorter turns may be made, and these also require the same care, and will give an opportunity to use the lateral controls to a greater extent. Begin the turns, not by an abrupt throw of the turning rudder, but bring it around gently, correcting the turning movement to a straight course, if you find the machine inclined to tilt too much, until you get used to the sensation of keeling over. Constant practice at this will soon give confidence, and assure you that you have full control of the machine.
THE FIGURE 8.—You are now to increase the height of flying, and this involves also the ability to turn in the opposite direction, so that you may
This is a test which is required in order to obtain a pilot's license. It means that you shall be able to show the ability to turn in either direction with equal facility. To keep an even flying altitude while describing this figure in a wind, is the severest test that can be exacted.
THE VOLPLANE.—This is the technical term for a glide. Many accidents have been recorded owing to the stopping of the motor, which in the past might have been avoided if the character of the glide had been understood. The only thing that now troubles the pilot when the engine "goes dead," is to select a landing place.
The proper course in such a case is to urge the machine to descend as rapidly as possible, in order to get a headway, for the time being. As there is now no propelling force the glide is depended upon to act as a substitute. The experienced pilot will not make a straight-away glide, but like the vulture, or the condor, and birds of that class, soar in a circle, and thus, by passing over and over the same surfaces of the earth, enable him to select a proper landing place.
THE LANDING.—The pilot who can make a good landing is generally a good flyer. It requires nicety of judgment to come down properly. One thing which will appear novel after the first altitude flights are attempted is the peculiar sensation of the apparently increased speed as the earth comes close up to the machine.
At a height of one hundred feet, flying thirty miles an hour, does not seem fast, because the surface of the earth is such a distance away that particular objects remain in view for some moments; but when within ten feet of the surface the same object is in the eye for an instant only.
This lends a sort of terror to the novice. He imagines a great many things, but forgets some things which are very important to do at this time. One is, that the front of the machine must be thrown up so as to bank the planes against the wind. The next is to shut off the power, which is to be done the moment the wheels strike the ground, or a little before.
Upon his judgment of the time of first touching the earth depends the success of safely alighting. He may bank too high, and come down on the tail with disastrous results. If there is plenty of field room it is better to come down at a less angle, or even keep the machine at an even keel, and the elevator can then depress the tail while running
Frequently, when about to land the machine will rock from side to side. In such a case it is far safer to go up into the air than to make the land, because, unless the utmost care is exercised, one of the wing tips will strike the earth and wreck the machine.
Another danger point is losing headway, as the earth is neared, due to flying at too flat an angle, or against a wind that happens to be blowing particularly hard at the landing place. If the motor is still going this does not make so much difference, but in a volplane it means that the descent must be so steep, at the last moment of flight, that the chassis is liable to be crushed by the impact.
FLYING ALTITUDE.—It is doubtful whether the disturbed condition of the atmosphere, due to the contour of the earth's surface, reaches higher than 500 feet. Over a level area it is certain that it is much less, but in some sections of the country, where the hill ranges extend for many miles, at altitudes of three and four hundred feet, the upper atmosphere may be affected for a thousand feet above.
Prof. Lowe, in making a flight with a balloon, from Cincinnati to North Carolina, which lasted a day and all of one night, found that during the
Before it began to ascend, he was on the western side of the great mountain range which extends south from Pennsylvania and terminates in Georgia. He was actually climbing the mountain in a drift of air which was moving eastwardly, and at no time was he within four thousand feet of the earth during that period, which shows that air movements are of such a character as to exert their influence vertically to great heights.
For cross country flying the safest altitude is 1000 feet, a distance which gives ample opportunity to volplane, if necessary, and it is a height which enables the pilot to make observations of the surface so as to be able to judge of its character.
But explanations and statements, and the experiences of pilots might be detailed in pages, and still it would be ineffectual to teach the art of flying. The only sure course is to do the work on an actual machine.
Many of the experiences are valuable to the learner, some are merely in the nature of cautions, and it is advisable for the beginner to learn what the experiences of others have been, although they may never be called upon to duplicate them.
All agree that at great elevations the flying conditions are entirely different from those met with near the surface of the ground, and the history of accidents show that in every case where a mishap was had at high altitude it came about through defect in the machine, and not from gusts or bad air condition.
On the other hand, the uptilting of machines, the accidents due to the so-called "Holes in the air," which have dotted the historic pages with accidents, were brought about at low altitudes.
At from two to five thousand feet the air may be moving at speeds of from twenty to forty miles an hour,—great masses of winds, like the trade stream, which are uniform over vast areas. To the aviator flying in such a field, with the earth hidden from him, there would be no wind to indicate that he was moving in any particular direction.
He would fly in that medium, in any direction, without the slightest sense that he was in a gale. It would not affect the control of the machine, because the air, though moving as a mass, would be the same as flying in still air. It is only when he sees fixed objects that he is conscious of the movement of the wind.
| CHAPTER XII
EXPERIMENTAL WORK IN FLYING Aeroplanes | |