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 have their effect on a slight moving air current, and these inequalities affect the air and disturb it to a still greater extent as the wind increases. Even in a still air, with the sun shining, there are air eddies, caused by the uneven heating of the air in space.

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 from the sun are there, just the same as on the earth.

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. Being rarer the action of sunlight on the particles is less intense. Reflection and refraction of the rays acting on the light atmosphere do not produce such a powerful effect as on the air near the ground.

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 was surprised to experience a peculiar pulling motion, when the bird's wings were held at a certain angle, so that the air actually seemed to draw it into the teeth of the current.

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, just as surely as the action of the sun on the air, and the movements of the currents, and the knowledge of applying those forces in the flying machine makes the aviator.

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 will be a novel sensation. Before him is the steering wheel, if it should be so equipped. Turning it to the right, swings the vertical tail plane so the machine will turn to the right. Certainly, he knows that; but how far must he turn the wheel to give it a certain angle.

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 14 1/2 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 most strenuous exertion to get up in the air the first time the machine was put on the trial ground.

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 over the uneven surface of the earth, you have the sensation of going forty miles an hour.

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. There was a slight lift, but your caution induces you to return the planes to their normal running angle. You try it again. You are now certain that the machine made a leap and left the ground. This is the exhilarating moment.

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 you, because up to this time you have been accustomed to flying along in a straight line.

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 are two reasons for this: First, when flying with the wind the speed must be greater than when flying against it.

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 be able to experience the sensation of using the stabilizers in the opposite direction. You will find in this practice that the senses must take in the course of the wind from two quarters now, as you attempt to describe the figure 8.

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 over the ground, and thus bring the machine to rest.

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 early morning the balloon, for some reason, began to ascend, and climbed nearly five thousand feet in a few hours, and as unaccountably began to descend several hours before he landed.

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 XIII

THE PROPELLER

BY far the most difficult problem connected with aviation is the propeller. It is the one great vital element in the science and art pertaining to this subject which has not advanced in the slightest degree since the first machine was launched.

The engine has come in for a far greater share of expert experimental work, and has advanced most rapidly during the past ten years. But, strange to say, the propeller is, essentially, the same with the exception of a few small changes.

PROPELLER CHANGES.—The changes which have been made pertaining to the form of structure, principally, and in the use of new materials. The kind of wood most suitable has been discovered, but the lines are the same, and nothing has been done to fill the requirement which grows out of the difference in speed when a machine is in the act of launching and when it is in full flight.

PROPELLER SHAPE.—It cannot be possible that the present shape of the propeller will be its ultimate form. It is inconceivable that the propeller is so inefficient that only one sixty-fifth of the power of the engine is available. The improvement in propeller efficiency is a direction which calls for experimental work on the part of inventors everywhere.

The making of a propeller, although it appears a difficult task, is not as complicated as would appear, and with the object in view of making the subject readily understood, an explanation will be given of the terms "Diameter," and "Pitch," as used in the art.

The Diameter has reference to the length of the propeller, from end to end. In calculating propeller pull, the diameter is that which indicates the speed of travel, and for this reason is a necessary element.

Thus, for instance, a propeller three feet in diameter, rotating 500 times a minute, has a tip speed of 1500 feet, whereas a six foot propeller, rotating at the same speed, moves 3000 feet at the tips.

PITCH.—This is the term which is most confusing, and is that which causes the most frequent trouble in the mind of the novice. The term will be made clear by carefully examining the accompanying illustration and the following description:

In Fig. 76 is shown a side view of a propeller A, mounted on a shaft B, which is free to move longitudinally. Suppose we turn the shaft so the tip will move along on the line indicated by the arrow C.

Now the pitch of the blade at D is such that it will be exactly in line with the spirally-formed course E, for one complete turn. As the propeller shaft has now advanced, along the line E, and stopped after one turn, at F, the measure between the points F and G represents the pitch of the propeller. Another way to express it would be to call the angle of the blade a five, or six, or a seven foot pitch, as the pitches are measured in feet.

Fig. 76. Describing the Pitch Line.

In the illustration thus given the propeller shaft, having advanced six feet, we have what is called a six foot pitch.

Now, to lay out such a pitch is an easy matter. Assume, as in Fig. 77, that A represents the end of the blank from which the propeller is to be cut, and that the diameter of this blank, or its length from end to end is seven feet. The problem now is to cut the blades at such an angle that we shall have a six foot pitch.

Fig. 77. Laying out the Pitch.

LAYING OUT THE PITCH.—First, we must get the circumference of the propeller, that is, the distance the tip of the propeller will travel in making one complete turn. This is done by multiplying 7 by 3.1416. This equals 21.99, or, practically, 22 feet.

A line B is drawn, extending out horizontally along one side of the blank A, this line being made on a scale, to represent 22 feet. Secondly, at the end of this line drawn a perpendicular line C, 6 feet long. A perpendicular line is always one which is at right angles to a base line. In this case B is the base line.

Line C is made 6 feet long, because we are trying to find the angle of a 6 foot pitch. If, now, a line D is drawn from the ends of the two lines B, C, it will represent the pitch which, marked across the end of the blank A, will indicate the line to cut the blade.

PITCH RULE.—The rule may, therefore, be stated as follows: Multiply the diameter (in feet) of the propeller by 3.1416, and draw a line the length indicated by the product. At one end of this line draw a perpendicular line the length of the pitch requirement (in feet), and join the ends of the two lines by a diagonal line, and this line will represent the pitch angle.

Propellers may be made of wood or metal, the former being preferred for the reason that this material makes a lighter article, and is stronger, in some respects, than any metal yet suggested.

LAMINATED CONSTRUCTION.—All propellers should be laminated,—that is, built up of layers of wood, glued together and thoroughly dried, from which the propeller is cut.

A product thus made is much more serviceable than if made of one piece, even though the laminated parts are of the same wood, because the different strips used will have their fibers overlapping each other, and thus greatly augment the strength of the whole.

Generally the alternate strips are of different materials, black walnut, mahogany, birch, spruce, and maple being the most largely used, but mahogany and birch seem to be mostly favored.

LAYING UP A PROPELLER FORM.—The first step necessary is to prepare thin strips, each, say, seven feet long, and five inches wide, and three- eighths of an inch thick. If seven such pieces are put together, as in Fig. 78, it will make an assemblage of two and five-eighth inches high.

Fig. 78. A Laminated Blank.

Bore a hole centrally through the assemblage, and place therein a pin B. The contact faces of these strips should be previously well painted over with hot glue liberally applied. When they are then placed in position and the pin is in place, the ends of the separate pieces are offset, one beyond the other, a half inch, as shown, for instance, in Fig. 79.

This will provide ends which are eight and a half inches broad, and thus furnish sufficient material for the blades. The mass is then subjected to heavy pressure, and allowed to dry before the blades are pared down.

Fig. 79. Arranging the Strips.

MAKING WIDE BLADES.—If a wider blade is desired, a greater number of steps may be made by adding the requisite number of strips; or, the strips may be made thicker. In many propellers, not to exceed four different strips are thus glued together. The number is optional with the maker.

An end view of such an assemblage of strips is illustrated in Fig. 80. The next step is to lay off the pitch, the method of obtaining which has been explained.

Fig. 80. End view of Blank.

Before starting work the sides, as well as the ends, should be marked, and care observed to place a distinctive mark on the front side of the propeller.

Around the pin B, Fig. 81, make S-shaped marks C, to indicate where the cuts on the faces of the blades are to begin. Then on the ends of the block; scribe the pitch angle, which is indicated by the diagonal line D, Fig. 80.

Fig. 81. Marking the Side.

This line is on the rear side of the propeller, and is perfectly straight. Along the front of this line is a bowline E, which indicates the front surface of the propeller blade.

PROPELLER OUTLINE.—While the marks thus given show the angles, and are designed to indicate the two faces of the blades, there is still another important element to be considered, and that is the final outline of the blades.

Fig. 82. Outlining.

It is obvious that the outline may be varied so that the entire width at 1, Fig. 82, may be used, or it may have an outline, as represented by the line 2, in this figure, so that the widest part will be at or near the dotted line 3, say two-thirds of the distance from the center of the blade.

This is the practice with most of the manufacturers at the present time, and some of them claim that this form produces the best results.

FOR HIGHER SPEEDS.—Fig. 83 shows a propeller cut from a blank, 4" x 6" in cross section, not laminated.

Fig. 83. Cut from a 4" x 6" Single Blank.

It should be borne in mind that for high speeds the blades must be narrow. A propeller seven feet in diameter with a six foot pitch, turning 950 revolutions per minute, will produce a pull of 350 pounds, if properly made.

Such a propeller can be readily handled by a forty horse power motor, such as are specially constructed for flying machine purposes.

INCREASING PROPELLER EFFICIENCY.—Some experiments have been made lately, which, it is claimed, largely increase the efficiency of propellers. The improvement is directed to the outline shape of the blade.

The typical propeller, such as we have illustrated, is one with the wide part of the blade at the extremity. The new type, as suggested, reverses this, and makes the wide part of the blade near the hub, so that it gradually tapers down to a narrow tip.

Such a form of construction is shown in Fig. 84. This outline has some advantages from one standpoint, namely, that it utilizes that part of the blade near the hub, to produce a pull, and does not relegate all the duty to the extreme ends or tips.

Fig. 84. A Suggested Form.

To understand this more fully, let us take a propeller six feet in diameter, and measure the pull or thrust at the tips, and also at a point half way between the tip and the hub.

In such a propeller, if the blade is the same width and pitch at the two points named, the pull at the tips will be four times greater than at the intermediate point.

CHAPTER XIV

EXPERIMENTAL GLIDERS AND MODEL AEROPLANES

AN amusing and very instructive pastime is afforded by constructing and flying gliding machines, and operating model aeroplanes, the latter being equipped with their own power.

Abroad this work has been very successful as a means of interesting boys, and, indeed, men who have taken up the science of aviation are giving this sport serious thought and study.

When a machine of small dimensions is made the boy wonders why a large machine does not bear the same relation in weight as a small machine. This is one of the first lessons to learn.

THE RELATION OF MODELS TO FLYING MACHINES. —A model aeroplane, say two feet in length, which has, we will assume, 50 square inches of supporting surface, seems to be a very rigid structure, in proportion to its weight. It may be dropped from a considerable height without injuring it, since the weight is only between two and three ounces.

An aeroplane twenty times the length of this model, however strongly it may be made, if dropped the same distance, would be crushed, and probably broken into fragments.

If the large machine is twenty times the dimensions of the small one, it would be forty feet in length, and, proportionally, would have only seven square feet of sustaining surface. But an operative machine of that size, to be at all rigid, would require more than twenty times the material in weight to be equal in strength.

It would weigh about 800 pounds, that is, 4800 times the weight of the model, and instead of having twenty times the plane surface would require one thousand times the spread.

It is this peculiarity between models and the actual flyers that for years made the question of flying a problem which, on the basis of pure calculation alone, seemed to offer a negative; and many scientific men declared that practical flying was an impossibility.

LESSONS FROM MODELS.—Men, and boys, too, can learn a useful lesson from the model aeroplanes in other directions, however, and the principal thing is the one of stability.

When everything is considered the form or shape of a flying model will serve to make a large flyer. The manner of balancing one will be a good criterion for the other in practice, and experimenting with these small devices is, therefore, most instructive.

The difference between gliders and model aeroplanes is, that gliders must be made much lighter because they are designed to be projected through the air by a kick of some kind.

FLYING MODEL AEROPLANES.—Model aeroplanes contain their own power and propellers which, while they may run for a few seconds only, serve the purpose of indicating how the propeller will act, and in what respect the sustaining surfaces are efficient and properly arranged.

It is not our purpose to give a treatise on this subject but to confine this chapter to an exposition of a few of the gliders and model forms which are found to be most efficient for experimental work.

AN EFFICIENT GLIDER.—Probably the simplest and most efficient glider, and one which can be made in a few moments, is to make a copy of the deltoid kite, previously referred to.

This is merely a triangularly-shaped piece of paper, or stiff cardboard A, Fig. 84, creased in the middle, along the dotted line B, the side wings C, C, being bent up so as to form, what are called diedral angles. This may be shot through the air by a flick of the finger, with the pointed end foremost, when used as a glider.

Fig. 85. Deltoid Glider.

THE DELTOID FORMATION.—This same form may be advantageously used as a model aeroplane, but in that case the broad end should be foremost.

Fig. 86. The Deltoid Racer.

Fig. 86 shows the deltoid glider, or aeroplane, with three cross braces, A, B, C, in the two forward braces of which are journaled the propeller shaft D, so that the propeller E is at the broad end of the glider.

A short stem F through the rear brace C, provided with a crank, has its inner end connected with the rear end of the shaft D by a rubber band G, by which the propeller is driven.

A tail may be attached to the rear end, or at the apex of the planes, so it can be set for the purpose of directing the angle of flight, but it will be found that this form has remarkable stability in flight, and will move forwardly in a straight line, always making a graceful downward movement when the power is exhausted.

It seems to be a form which has equal stabilizing powers whether at slow or at high speeds, thus differing essentially from many forms which require a certain speed in order to get the best results.

RACING MODELS.—Here and in England many racing models have been made, generally of the A-shaped type, which will be explained hereinafter. Such models are also strong, and able to withstand the torsional strain required by the rubber which is used for exerting the power.

It is unfortunate that there is not some type of cheap motor which is light, and adapted to run for several minutes, which would be of great value in work of this kind, but in the absence of such mechanism rubber bands are found to be most serviceable, giving better results than springs or bows, since the latter are both too heavy to be available, in proportion to the amount of power developed.

Unlike the large aeroplanes, the supporting surfaces, in the models, are at the rear end of the frames, the pointed ends being in front.

Fig. 87. A-Shaped Racing Glider.

Fig. 87 shows the general design of the A- shaped gliding plane or aeroplane. This is composed of main frame pieces A, A, running fore and aft, joined at their rear ends by a cross bar B, the ends of which project out slightly beyond their juncture with the side bars A, A. These projecting ends have holes drilled therein to receive the shafts a, a, of the propeller D, D.

A main plane E is mounted transversely across this frame at its rear end, while at its forward end is a small plane, called the elevator. The pointed end of the frame has on each side a turnbuckle G, for the purpose of winding up the shaft, and thus twisting the propeller, although this is usually dispensed with, and the propeller itself is turned to give sufficient twist to the rubber for this purpose.

THE POWER FOR MODEL AEROPLANES.—One end
of the rubber is attached to the hook of the shaft
C, and the other end to the hook or to the turnbuckle
G, if it should be so equipped.

The rubbers are twisted in opposite directions, to correspond with the twist of the propeller blades, and when the propellers are permitted to turn, their grip on the air will cause the model to shoot forwardly, until the rubbers are untwisted, when the machine will gradually glide to the ground.

MAKING THE PROPELLER.—These should have the pitch uniform on both ends, and a simple little device can be made to hold the twisted blade after it has been steamed and bent. Birch and holly are good woods for the blades. The strips should be made thin and then boiled, or, what is better still, should be placed in a deep pan, and held on a grid above the water, so they will be thoroughly steamed.

They are then taken out and bent by hand, or secured between a form specially prepared for the purpose. The device shown in Fig. 88 shows a base board which has in the center a pair of parallel pins A, A, slightly separated from each other.

Fig. 88. Making the Propeller.

At each end of the base board is a pair of holes C, D, drilled in at an angle, the angles being the pitch desired for the ends of the propeller. In one of these holes a pin E is placed, so the pins at the opposite ends project in different directions, and the tips of the propeller are held against the ends of these pins, while the middle of the propeller is held between the parallel pins A, A.

The two holes, at the two angles at the ends of the board, are for the purpose of making right and left hand propellers, as it is desirable to use two propellers with the A-shaped model. Two propellers with the deltoid model are not so necessary.

After the twist is made and the blade properly secured in position it should be allowed to thoroughly dry, and afterwards, if it is coated with shellac, will not untwist, as it is the changing character of the atmosphere which usually causes the twisted strips to change their positions. Shellac prevents the moist atmosphere from affecting them.

MATERIAL FOR PROPELLERS.—Very light propellers can also be made of thin, annealed aluminum sheets, and the pins in that case will serve as guides to enable you to get the desired pitch. Fiber board may also be used, but this is more difficult to handle.

Another good material is celluloid sheets, which, when cut into proper strips, is dipped in hot water, for bending purposes, and it readily retains its shape when cooled.

RUBBER—Suitable rubber for the strips are readily obtainable in the market. Experiment will soon show what size and lengths are best adapted for the particular type of propellers which you succeed in making.

PROPELLER SHAPE AND SIZE.—A good proportion of propeller is shown in Fig. 89. This also shows the form and manner of connecting the shaft. The latter A has a hook B on one end to which the rubber may be attached, and its other end is flattened, as at C, and secured to the blade by two-pointed brads D, clinched on the other side.

Fig. 89. Shape and Size.

The collar E is soldered on the shaft, and in practice the shaft is placed through the bearing hole at the end of the frame before the hook is bent.

SUPPORTING SURFACES.—The supporting surfaces may be made perfectly flat, although in this particular it would be well to observe the rules with respect to the camber of large machines.

CHAPTER XV

THE AEROPLANE IN THE GREAT WAR

DURING the civil war the Federal forces used captive balloons for the purpose of discovering the positions of the enemy. They were of great service at that time, although they were stationed far within the lines to prevent hostile guns from reaching them.

BALLOON OBSERVATIONS.—Necessarily, observations from balloons were and are imperfect. It was found to be very unsatisfactory during the Russian-Japanese war, because the angle of vision is very low, and, furthermore, at such distances the movements, or even the location of troops is not observable, except under the most favorable conditions.

Balloon observation during the progress of a battle is absolutely useless, because the smoke from the firing line is, necessarily, between the balloon and the enemy, so that the aerial scout has no opportunity to make any observations, even in detached portions of the fighting zone, which are of any value to the commanders.

CHANGED CONDITIONS OF WARFARE.—Since our great war, conditions pertaining to guns have been revolutionized. Now the ranges are so great that captive balloons would have to be located far in the rear, and at such a great distance from the firing line that even the best field glasses would be useless.

The science of war has also evolved another condition. Soldiers are no longer exposed during artillery attacks. Uniforms are made to imitate natural objects. The khaki suits were designed to imitate the yellow veldts of South Africa; the gray-green garments of the German forces are designed to simulate the green fields of the north.

THE EFFORT TO CONCEAL COMBATANTS.—The French have discarded the historic red trousers, and the elimination of lace, white gloves, and other telltale insignias of the officers, have been dispensed with by special orders.

In the great European war armies have burrowed in the earth along battle lines hundreds of miles in length; made covered trenches; prepared artificial groves to conceal batteries, and in many ingenious ways endeavored to make the battlefield an imitation field of nature.

SMOKELESS POWDER.—While smokeless powder has been utilized to still further hide a fighting force, it has, in a measure, uncovered itself, as the battlefield is not now, as in olden times, overspread with masses of rolling smoke.

Nevertheless, over every battlefield there is a haze which can be penetrated only from above, hence the possibilities of utilizing the aeroplane in war became the most important study with all nations, as soon as flying became an accomplished fact.

INVENTIONS TO ATTACK AERIAL CRAFT.—Before any nation had the opportunity to make an actual test on the battlefield, inventors were at work to devise a means whereby an aerial foe could be met. In a measure the aerial gun has been successful, but months of war has shown that the aeroplane is one of the strongest arms of the service in actual warfare.

It was assumed prior to the European war that the chief function of the aeroplane would be the dropping of bombs,—that is for service in attacking a foe. Actual practice has not justified this theory. In some places the appearance of the aeroplane has caused terror, but it has been found the great value is its scouting advantages.

FUNCTION OF THE AEROPLANE IN WAR.—While bomb throwing may in the future be perfected, it is not at all an easy problem for an aviator to do work which is commensurate with the risk involved. The range is generally too great; the necessity of swift movement in the machine too speedy to assure accuracy, and to attack a foe at haphazard points can never be effectual. Even the slowly-moving gas fields, like the Zeppelin, cannot deliver bombs with any degree of precision or accuracy.

BOMB-THROWING TESTS.—It is interesting, however, to understand how an aviator knows where or when to drop the bomb from a swiftly-moving machine. Several things must be taken into consideration, such as the height of the machine from the earth; its speed, and the parabolic curve that the bomb will take on its flight to the earth.

When an object is released from a moving machine it will follow the machine from which it is dropped, gradually receding from it, as it descends, so that the machine is actually beyond the place where the bomb strikes the earth, due to the retarding motion of the atmosphere against the missile.

The diagram Fig. 90 will aid the boy in grasping the situation. A is the airship; B the path of its flight; a the course of the bomb after it leaves the airship; and D the earth. The question is how to determine the proper movement when to release the bomb.

METHOD FOR DETERMINING MOVEMENT OF A BOMB.—Lieut. Scott, U. S. A., of the Coast Survey Artillery, suggested a method for determining these questions. It was necessary to ascertain, first, the altitude and speed. While the barometer is used to determine altitudes, it is obvious that speed is a matter much more difficult to ascertain, owing to the wind movements, which in all cases make it difficult for a flier to determine, even with instruments which have been devised for the purpose.

Fig. 90. Course of a Bomb.

Instead, therefore, of relying on the barometer, the ship is equipped with a telescope which may be instantly set at an angle of 45 degrees, or vertically.

Thus, Fig 91 shows a ship A, on which is mounted a telescope B, at an angle of 45 degrees. The observer first notes the object along the line of 45 degrees, and starts the time of this observation by a stop watch.

The telescope is then turned so it is vertical, as at C, and the observer watches through the telescope until the machine passes directly over the object, when the watch is stopped, to indicate the time between the two observations.

Fig. 91. Determining Altitude and Speed.

The height of the machine along the line D is thus equal to the line E from B to C, and the time of the flight from B to a being thus known, as well as the height of the machine, the observer consults specially-prepared tables which show just what kind of a curve the bomb will make at that height and speed.

All that is necessary now is to set the sighter of the telescope at the angle given in the tables, and when the object to be hit appears at the sight, the bomb is dropped.

THE GREAT EXTENT OF MODERN BATTLE LINES.— The great war brought into the field such stupendous masses of men that the battle lines have extended over an unbroken front of over 200 miles.

In the battle of Waterloo, about 140,000 men were engaged on both sides, and the battle front was less than six miles. There were, thus massed, along the front, over 20,000 men every mile of the way, or 10,000 on each side.

In the conflict between the Allies and the Germans it is estimated that there were less than 7500 along each mile. It was predicted in the earlier stages of the war that it would be an easy matter for either side to suddenly mass such an overwhelming force at one point as to enable the attacking party to go through the opposing force like a wedge.

Such tactics were often employed by Napoleon and other great masters of war; but in every effort where it has been attempted in the present conflict, it was foiled.

The opposing force was ready to meet the attack with equal or superior numbers. The eye of the army, the aeroplane, detected the movements in every instance.

THE AEROPLANE DETECTING THE MOVEMENTS OF ARMIES.—In the early stages of the war, when the Germans drove the left of the French army towards Paris, the world expected an investment of that city. Suddenly, and for no apparent reason, the German right was forced back and commenced to retreat.

It was not known until weeks afterwards that the French had assembled a large army to the west and northwest of Paris, ready to take the Germans in flank the moment an attempt should be made to encircle the Paris forts.

The German aviators, flying over Paris, discovered the hidden army, and it is well they did so, for it is certain if they had surrounded the outlying forts, it would have been an easy matter for the concealed forces to destroy their communications, and probably have forced the surrender of a large part of the besiegers.

The aeroplane in warfare, therefore, has constantly noted every disposition of troops, located the positions and judged the destination of convoys; the battery emplacements; and the direction in which large forces have been moved from one part of the line to the other, thus keeping the commanders so well informed that few surprises were possible.

THE EFFECTIVE HEIGHT FOR SCOUTING.—It has been shown that aeroplane scouting is not effective at high altitudes. It is not difficult for aviators to reach and maintain altitudes of five thousand feet and over, but at that elevation it is impossible to distinguish anything but the movement of large forces.

SIZES OF OBJECTS AT GREAT DISTANCES.—At a distance of one mile an automobile, twenty feet in length, is about as large as a piece of pencil one inch long, viewed at a distance of thirty-five feet. A company of one hundred men, which in marching order, say four abreast, occupies a space of eight by one hundred feet, looks to the aviator about as large as an object one inch in length, four and a half feet from the eye.

The march of such a body of men, viewed at that distance, is so small as almost to be imperceptible to the eye of an observer at rest. How much more difficult it is to distinguish a movement if the observer is in a rapidly-moving machine.

For these reasons observations must be made at altitudes of less than a mile, and the hazard of these enterprises is, therefore, very great, since the successful scout must bring himself within range of specially designed guns, which are effective at a range of 3000 yards or more, knowing that his only hope of safety lies in the chance that the rapidly-moving machine will avoid the rain of bullets that try to seek him out.

SOME DARING FEATS IN WAR.—It would be impossible to recount the many remarkable aerial fights which have taken place in the great war. Some of them seem to be unreal, so startling are the tales that have been told. We may well imagine the bravery that will nerve men to fight thousands of feet above the earth.

One of the most thrilling combats took place between a Russian aeroplane and a Zeppelin, over Russian Poland, at the time of the first German invasion. The Zeppelin was soaring over the Russian position, at an altitude of about a mile. A Russian aviator ascended and after circling about, so as to gain a position higher than the airship, darted down, and crashed into the great gas field.

The aviator knew that it meant death to him, but his devotion led him to make the sacrifice. The Zeppelin, broken in two, and robbed of its gas, slowly moved toward the earth, then gradually increased the speed of its descent, as the aeroplane clung to its shattered hulk, and by the time it neared the earth its velocity was great enough to assure the destruction of all on board, while the ship itself was crushed to atoms.

One of the most spectacular fights of the war occurred outside Paris, when one of the German Taubes attempted to make its periodical tour of observation. One of the French aeroplanes, which had the advantage of greater speed, mounted to a greater altitude, and circled about the Taube.

The latter with its machine gun made a furious attack, during these maneuvers, but the French ship did not reply until it was at such an elevation that it could deliver the attack from above. Then its machine gun was brought into play. As was afterwards discovered, the wings and body of the Taube were completely riddled, and it was a marvel how it was possible for the German aviator to remain afloat as long as he did.

Soon the Taube was noticed to lurch from side to side, and then dart downwardly. The monoplane, in the pursuit, gradually descended, but it was not able to follow the destroyed Taube to the earth, as the latter finally turned over, and went swirling to destruction.

The observer, as well as the aviator, had both been killed by the fire from the monoplane.

In the trenches on the Marne, to the northeast of Paris, where the most stubborn conflict raged for over a week, the air was never clear of aeroplanes. They could be seen in all directions, and almost all types of machines were represented. The principal ones, however, were monoplanes.

THE GERMAN TAUBE.—The German Taube is a monoplane, its main supporting surfaces, as well as the tail planes, are so constructed that they represent a bird. Taube means dove. It would have been more appropriate to call it a hawk.

On the other hand, the French monoplane, of which the Bleriot is the best known example, has wings with well rounded extremities, and flaring tail, so that the two can be readily distinguished.

On one occasion, during the lull in the battle, two of the Taubes approached the area above the French lines, and after ascending to a great height, began the volplane toward their own lines. Such a maneuver was found to be the most advantageous, as it gave the scouting aeroplane the advantage of being able to discover the positions and movements with greater ease, and at the same time, in case of accident to the machine, the impetus of the flight would be to their own lines.

Three of the French aeroplanes at once began their circling flight, mounting higher and higher, but without attempting to go near the Taubes. When the French ships had gained the proper altitude, they closed in toward the German ships, before the latter could reach their own lines in their volplaning act.

This meant that they must retreat or fight, and the crack of the guns showed that it meant a struggle. The monoplanes circled about with incredible skill, pouring forth shot after shot. Soon one of the Taubes was seen to flutter. This was the signal for a more concentrated attack on her.

The army in the trenches, and on the fields below, witnessed the novel combat. The flying ships were now approaching the earth, but the gunners below dared not use their guns, because in the maneuvers they would be as likely to strike friend as foe.

The wounded Taube was now shooting to the earth, and the two monoplanes began to give their attention to the other ship, which was attempting to escape to the north. The flash of the guns of all the fliers could be plainly seen, but the sounds were drowned by the roar of the great conflict all about them.

The Taube could not escape the net around her. She, too, was doomed. A shot seemed to strike the gasoline tank, and the framework was soon enveloped in flames. Then she turned sidewise, as the material on one side burned away, and skidding to the left she darted to the earth, a shapeless mass.

It was found that the aviator was not hurt by the shot, but was, undoubtedly, killed by the impact with the earth. The observer was riddled with bullets, and was likely dead before the ship reached the earth.

In the western confines of Belgium, near Ypres, the British employed numerous aircraft, many of them biplanes, and at all times they were in the air, reporting observations. Many of the flying fights have been recorded, and the reports when published will be most thrilling reading.

HOW AEROPLANES REPORT OBSERVATIONS.—It may be of some interest to know how aeroplanes are able to report observations to the commanders in the field, from the airship itself. Many ingenious devices have been devised for this purpose.

SIGNAL FLAGS.—The best known and most universally used method is by the use of signaling flags. Suppose the commander of a force is desirous of getting the range of a hidden battery, or a massed force in his front. The observer in the aeroplane will sail over the area at an understood altitude, say one mile in height.

The officer in charge of the battery, knowing the height of the airship, is able, by means of the angle thus given him, to get the distance between his battery and the concealed point beneath the airship. The observer in the airship, of course, signals the engineer officer, the exact point or time when the airship is directly above, and this gives him the correct angle.

The guns of the battery are then directed and fired so as to reach the concealed point. It is now important to be able to send intelligible signals to the officer in charge of the battery. If the shot goes beyond the mark, the observer in the airship raises the flag above his head, which indicates that it was too high.

HOW USED.—If the shot fell short he would lower the flag. If the shot landed too far to the right, this would be indicated by the flag, and if too far to the left, the signal would, in like manner, be sufficient to enable the gunners to correct the guns.

When the exact range is obtained the observer in the ship waves the flag about his head, in token of approval. All this work of noting the effect of the shots must be taken while the airship is under fire, and while circling about within visual range of the concealed object below.

The officer in charge of the battery, as well as the observer on the flying craft, must be equipped with powerful glasses, so the effect of the shots may be noted on the one hand, and the signals properly read by the officer on the other hand.

It may be said, however, that air battles have not been frequent and that they have been merely incidents of the conditions under which they were operated. The mission of the aeroplane is now conceded to be purely one of observation, such as we have described.

Both French and German reports are full of incidents showing the value of observations, and also concerning the effects of bombs. Extracts from the diaries of prisoners gave many interesting features of the results of aeroplane work.

CASUALTIES DUE TO AEROPLANES.—In the diary of one was found the remark: "I was lucky to escape the bomb thrown by a French aviator at Conrobet, which killed eight of my companions."

Another says: "The Seventh Company of the Third Regiment of the Guard had eight killed and twenty-two wounded by bomb from a French aeroplane."

Another: "An officer showed us a torn coat taken from one of sixty soldiers wounded by a bomb from an aeroplane."

A prisoner says: "Near Neuville an aeroplane bomb dropped on a supply train, killed four men, wounded six, and killed a considerable number of horses."

The Belgians, after their defeat and the capture of Antwerp, were forced to the west along the coast. In some way they learned that the Kaiser was about to occupy a chateau near Dixmunde. Several aviators flew above the position and dropped a number of bombs on the building, completely wrecking it, and it was fortunate that the Emperor left the building only twenty minutes before, as several of his aides and soldiers on duty were killed.

On numerous occasions the headquarters of the different commanders have been discovered and had to be moved to safer places.

During all these wonderful exploits which will live in history because men had the opportunity during the war to use them for the first time in actual conflict, the official reports have not mentioned the aviators by name. The deaths of the brave men have brought forth the acknowledgments of their services. During the first three months of the war it is estimated that over sixty aviators and aides had lost their lives in the conflict on the two great battle lines. This does not take into account those who met death on the Zeppelins, of which five had been destroyed during that time.

THE END

GLOSSARY OF WORDS USED IN TEXT OF THIS VOLUME

Where a word has various meanings, that definition is given which will express the terms used by the author in explaining the mechanism or subject to which it refers.

Aviation. The art of flying.

Altitude. Height; a vertical distance above any point.

Attraction. The art or process of drawing towards.

Allusion. Referring to a certain thing.

Assume. Taking it for granted.

Accentuated. To lay great stress upon a thing.

Angle of Movement. Any direction which is upwardly or downwardly, as distinguished from the direction of movement which is either to the right or to the left.

Acquire. To obtain; to recover; to procure.

Analogous. Corresponding to or resembling some other thing or object.

Air Hole. A term used to express a condition in flying where the machine while in horizontal flight takes a sudden drop, due to counter currents.

Ailerons. Literally, small planes. Used to designate the small planes which are designed to stabilize a machine.

Angle. A figure, or two straight lines which start at the same point. The sides of these lines are termed the angle.

Analysis. To separate; to take apart and examine the various parts or elements of a thing.

Aeroplane. Any form of machine which has planes, and is heavier than air. Usually a flying structure which is propelled by some motive power.

Accumulation. Adding to; bringing together the same or unlike articles.

Ascribable. A reference to some antecedent source.

Aeronautics. The science of flying.

Anterior. Meaning the front or forward margin or portion of a body.

Artifices. Any artificial product, or workmanship.

Axially. Through the central portion. Thus, the shaft which goes through a cylinder is axially arranged.

Automatic. A thing which operates by its own mechanism; a contrivance which is made in such a manner that it will run without manual operation or care.

Alertness. Quick; being active.

Apex. The point at which two lines meet; also the extreme pointed end of a conical figure.

Ascension. Moving upwardly.

Accessories. The parts of a machine, or artielee which may ha used in connection therewith.

Anemometer. An instrument for measuring the force or the velocity of wind.

Anemograph. An instrument that usually traces a curved line OH paper to make a record of the force or direction, or velocity of the wind.

Anemometrograph. A device which determines the force, velocity and direction of the wind.

Accretion. Adding to little by little.

Accelerated. Quiekening; hurrying the process.

Abridged. Partly taken away from; shortened.

Abrogate. To dispense with; to set aside.

Abnormal Not in the usual manner; not in a regular way.

Alternate. First one and then another; going from one side to the other.

Ancient Lights. An old English law which prevents a neighbor from shutting off sunlight.

Angularly. A line which runs out from another so that the two are not parallel.

Aneroid. Not wet. Applied to the type of barometer where the medium for determ,ining the pressure is not made of mercury.

Aspirate. A term given by the French to that peculiar action of wing, or other body, which, when placed in certain positions, relative to a current of air, will cause it to be drawn into the current.

Assemblage. The bringing together of the parts or elements of a machine.

Augment. To aid; to add to or increase.

Banked. The term used in aviation which indicates that the machine is turned up so that its supporting surfaces rest against the air, as in alighting.

Barometer. An instrument for determining the air pressure, and thereby indicating altitudes.

Bevel Pinion. A toothed wheel driven by a larger wheel.

Bi-Plane. Two planes. In aviation that type which has two planes, similar in size, usually, and generally placed one above the other so they are separated the same distance from each other, as the width of each of the planes.

Bulge. A hump; an enlargement beyond the normal at any point.

Camber, also Cambre. The upward curve in a plane.

Catapult. A piece of mechanism for projecting or throwing a missile.

Carbureter. The device which breaks up the fuel oil, and mixes the proper quantity of air with it before it is drawn into the engine.

Catastrophe. A calamity; a sad ending; loss of life or of property.

Cellular. Made up of small hollows, or compartments; filled with holes.

Celestial. Pertaining to the heavens.

Centrifugal. That force which throws outwardly from a rotating body.

Centripetal. That force, like the attraction of gravity, which draws a body to the center.

Characteristic. Striking; that which is peculiar to some thing or object.

Commensurate. Sufficient; in proper proportion; sufficient for the occasion.

Commercially. Pertaining to the nature of trade; the making of money.

Complicated. Not easily explainable; not easy to separate.

Comparatively. Judged by something else; taken with reference to another object or thing.

Compression. The drawing together; forcing into a smaller compass, or space.

Composition. Made up of different elements, or things.

Conceivable. Made up from the imagination.

Concaved. Hollowed: In aviation it has reference to the underside of the plane, which is usually provided, structurally, with a hollow or trough formation.

Conforming. To make alike in form; to bring into harmony.

Conjunction. In eonneetion with; joining together.

Convex. A rounded surface; a bulging out.

Conclusion. The end; a finding in law; a reasoning from a certain condition.

Conductivity. The property of materials whereby they will transmit heat along from one part to another, also electricity.

Concentrated. Brought together; assembled in a smaller space.

Conclusive. A positive ending; decisive of the matter at issue.

Concentrically. A line which is at all points at the same distance from one point.

Condensation. The act or process of making denser, or being brought together.

Contemplate. To consider; to judge.

Convoys. A protecting force which aeeompanies the transfer of property.

Convection. The diffusion of heat through a liquid or gas.

Consistent. A state of harmony; the same at &11 times.

Constant. In mathematics, a figure which never changes; or a figure used as a fixed valuation in a problem.

Controllable. Held within bounds; that which can be within the power to accomplish.

Correctional. The means whereby a fault may be made right.

Consequence. The result; that which flows from a preceding action.

Counterforce. An action contrary or opposite to the main force.

Counter-balance. Any power equally opposing another.

Counteract. A force acting in opposition to another.

Countercurrent. An air current which sets up in an opposite direction in the path of a moving aeroplane.

Cushioned. An action which takes place against a moving aeroplane, by a sudden gust of air or countercurrent.

Dedicated. To set apart for some special purpose.

Degree. An interval; a grade; a stage; a certain proportion.

Deltoid. Shaped like the Greek letter delta.

Density. Closeness of parts.

Demonstration. Making clear; showing up; an exhibition or expression.

Deceptive. The power or tendency to give a false impression.

Deterrent. To hold back; to prevent action.

Detracting. The tendency to take away; to belittle.

Depressed. To move downwardly.

Destination. The place set for the end of the journey.

Despoiling. To take away from; robbing or taking from another by force or by stealth.

Dependant. Hanging below; projecting from the lower side.

Dexterity. Agility; smartness in action.

Deranged. Put out of order; wrongly arranged.

Develop. Brought out; to put into a correct shape or form.

Deferred. Put over to another time.

Designedly. With a direct purpose.

Diagonal. Across an object at an angle to one or more aides.

Diametrically. Across an object through or near the center thereof.

Diagram. A mechanical plan or outline of an object.

Dimension. The distance across an object. The measurement, for instance, of a propeller from tip to tip.

Dynamically. Pertaining to motion as a result of force.

Dispossessed. A term used to indicate the act which removes a person from the possession of property.

Diameter. The measurement across an object.

Divest. Taken away from; removed out of.

Disregard. Deliberate lack of attention.

Diversity. The state wherein one is unlike another; dissimilarity.

Drift. The term used to indicate the horizontal motion, or the pull of an aeroplane.

Dragon. A fabulous monster, usually in the form of a serpent.

Duplicate. Two; made in exact imitation of an original.

Easement. A legal phrase to designate that right which man possesses, irrespective of any law, to gain access to his property.

Effrontery. Boldness with insolence; rashness without propriety.

Effective. To be efficient.

Element. One part of a whole.

Elasticity. Material which will go back to its original form after being distorted, is said to be elastic.

Eliminate. To take away from; to remove a part, or the whole.

Elliptical. Oblong with rounded ends.

Elusive. Capable of escaping from; hard to hold.

Elevator. The horizontal planes in front or rear, or in both front and rear of the supporting surfaces of an aeroplane.

Emergency. A sudden occurrence calling for immediate action.

Emplacement. A spot designed to hold heavy field pieces in intrenchments.

Enactment. The formulation of a law; the doing of a special thing.

Enunciated. Announced; setting forth of an act or a condition.

Energy. That quality by reason of which anything tends to move or act.

Equidistant. Two points or objects at equal distance from a common point.

Equilibrinm. A balance produced by the action of two or more forces.

Equalizing, One made equal to the other; one side the same as the other.

Equipped. Armed; provided with the proper material, or in the same condition.

Essential. The important part or element.

Essence The real charaeter or element of the thing itself.

External. The outermost portion.

Evolution. A gradual change or building up; from a lower to a higher order.

Evolved. Brought out from a crude condition to a better form.

Expression. The art of explaining or setting forth.

Expansion. Growing larger; to occupy a greater space.

Exerted. To work to the utmost; to put forth in action.

Exhilaratiorn. A lively, pleasing or happy sensation.

Exploited. To fully examine and consider, as well as carry out.

Extremity. The end; as far as ean be considered.

Facility. Ease of management; to do things without difficulty.

Factor. One of the elements in a problem, or in mechanical action.

Fascination, Attraetiveness that is pleasing.

Flexure. The capacity to bend and yield, and return to its original position.

Flexible, That which will yield; springy.

Fore and Aft. Lengthwise, as from stem to stern of a ship.

Formation. The shape or arrangement of an article or thing.

Formulated. Put into some eonerete form, or so arranged that it may be understood.

Frictionless. Being without a grinding or retarding aotion.

Fulcrumed. A resting place for a lever.

Function. The duty or sphere of action in a person, or object.

Glider. An aeroplane, without power, adapted to be operated by an aviator.

Governing. An element which is designed to control a machine in a regular manner.

Graduated. A marked portion, which is regularly laid off to indicate measurements or quantities.

Gravity. The attraction of mass for mass. The tendency of bodies to move toward the earth.

Gravitatior The force with which all bodies attract each other.

Gyratory. Having a circular and wheeling as well as a rotary motion.

Gyroscope. A wheel, designed to illustrate the laws of motion, which freely revolves in gimbals within a ring, and when set into motion, objects to change its plane of rotation.

Hemispherical. The half of a sphere. The half of an apple would be hemispherical.

Hazardous. That which is doubtful; accompanied by danger.

Helicopter. A type of flying machine which has a large propeller, or more than one, revolubly fixed on vertical shafts, by means of which the machine is launched and projected through the air.

Horizontal. Level, like water.

Hydroplane. A term used to designate an aeroplane which is provided with pontoons, whereby it may alight on the water, and be launched from the surface. The term hydroaeroplane is most generally used to indicate this type of machine.

Impact. The striking against; the striking force of one body against another.

Immersed. Placed under water below the surface.

Impinge. To strike against; usually applied where air strikes a plane or a surface at an angle.

Imitation. Similarity; the same in appearance.

Incompatible. Without harmony; incapable of existing together.

Incurved. Applied to a surface formation where there is a depression, or hollow.

Inequalities. Not smooth, or regular; uneven.

Infinitely, Boundless; in great number, or quality; without measure.

Initial. The first; that which is at the beginning.

Indestructibility. Not capable of being injured or destroyed.

Influenced. Swayed; to be induced to change.

Inherent. That which is in or belongs to itself.

Initiating. To teach; to instill; to give an insight.

Indicator. A term applied to mechanism which shows the results of certain operations and enables the user to read the measure, quantity, or quality shown.

Inconceivable. Not capable of understanding; that which cannot be understood by the human mind.

Institute. To start; to bring into operation.

Insignias. Things which are significant of any particular calling or profession.

Instinct. That quality in man or animals which prompts the doing of things independently of any direct knowledge or understanding.

Intermediate. Between; that which may be within or inside the scope of the mind, or of certain areas.

Intervening. The time between; also applied to the action of a person who may take part in an affair between two or more persons.

Interval. A time between.

Investigator. One who undertakes to find out certain things.

Incidence. In physics this is a term to indicate the line which falls upon or strikes another at an angle.

Inverted. Upside down.

Invest. To give to another thing something that it lacked before.

Kinetic. Consisting in or depending upon motion.

Laminated. Made up of a plurality of parts. When wooden strips, of different or of the same kinds are glued and then laid together and put under heavy pressure until thoroughly dried, the mass makes a far more rigid structure than if cut out of a single piece.

Launchiug. The term applied to the raising, or starting of a boat, or of a flying object.

Lateral. In mining this is a term to indicate the drifts or tunnels which branch out from the main tunnel. Generally it has reference to a transverse position or direction,—that is, at right angles to a fore and aft direction.

Lift. The vertical motion, or direction in an airship; thus the lift may be the load, or the term used to designate what the ship is capable of raising up.

Ligament. The exceedingly strong tendons or muscles of birds and animals, usually of firm, compact tissues.

Limitations. Within certain bounds; in a prescribed scope.

Longitudinally. Usually that direction across the longest part.

Majestically. Grand; exalted dignity; the quality which inspires reverence or fear.

Manipulate. To handle; to conduct so that it will result in a certain way.

Maneuver. A methodical movement or change in troops.

Manually. To perform by hand.

Manifestations. The act of making plain to the eye or to the understanding.

Manually-operated. With the hands; a term applied to such machines as have the control planes operated by hand.

Maintained. Kept up; to provide for; to sustain.

Material. The substance, or the matter from which an article is made; also the important thing, or element.

Mass. In physics it is that which in an article is always the same. It differs from weight in the particular that the mass of an article is the same, however far it may be from the center of the earth, whereas weight changes, and becomes less and less as it recedes from the center of the earth.

Margin. The edge; the principal differecee between this word and edge, is, that margin has reference also to a border, or narrow strip along the edge, as, for instance, the blank spaces at the edges of a printed page.

Medievral. Belonging to the Middle Ages.

Mercury. A silver-white liquid metal, usually called quicksilver, and rather heavy. It dissolves most metals, and this process is called amalgamation.

Militate. In determining a question, to have weight, or to influence a decision.

Mobility. Being freely movable; capable of quick change.

Modifieation. A change; making a difference.

Monitor. Advising or reproving. Advising or approving by way of caution.

Monstrosities. Anything which is huge, or distorted, or wrong in structure.

Monorail. A railway with a single track, designed to be used by a bicycle form of carriage, with two wheels, fore and aft of each other, and depending for its stability upon gyroscopes, mounted on the carriage.

Momentum. That which makes a moving body difficult to stop. It is the weight of a moving body, multiplied by its speed.

Monoplane. The literal meaning is one plane. As monoplane machines are all provided with a fore and aft body, and each has a wing or plane projecting out from each side of this body, it is obvious that it has two planes instead of one. The term, however, has reference to the fact that it has only one supporting surface on the same plane. Biplanes have two supporting surfaces, one above the other.

Multiplicity. Frequently confounded with plurality. The latter means more than one, whereas multiplicity has reference to a great number, or to a great variety.

Muscular. Being strong; well developed.

Negative. The opposite of positive; not decisive.

Neutralize. From the word neuter, which means neither, hence the term may be defined as one which is not a part of either, or does not take up with either side.

Normal Pressure. Normal means the natural or usual, and when applied to air it would have reference to the condition of the atmosphere at that particular place. If the pressure could change from its usual condition, it would be an abnormal pressure.

Notoriously. Generally known, but not favorably so; the subject of general remark; or unfavorably known.

Obscurity. Not well known; in the background; without clear vision; hidden from view.

Obliquely. That which differs from a right angle; neither obtuse nor acute; deviating from a line by any angle except a right angle.

Obvious. That which is readily observed and understood.

Orthopter. That type of flying machine which depends on flapping wings to hold it in space, and to transport it, in imitation of the motion of the wings of birds in flying.

Oscillate. Moving to and fro; the piston of a steam engine has an oscillating motion.

Outline. Describing a marginal line on a drawing; setting forth the principal features of an argument, or the details of a story, or the like.

Overlapping. One placed over the other.

Parabolic. A form of curve somewhat similar to an ellipse.

Pedestal. A standard or support; an upright to hold machinery.

Pertinent. Appropriate; pertaining to the subject.

Pectoral. The bone which forms the main rib or support at the forward edge of a bird's wing.

Persistent. Keeping at it; determination to proceed.

Perpendicular. At right angles to a surface. This term is sometimes wrongly applied in referring to an object, particularly to an object which is vertical, meaning up and down. The blade of a square is perpendieular to the handle at all times, but the blade is vertical only when it points to the center of the earth.

Pernicious. Bad; not having good features or possessing wrong attributes.

Pendulum. A bar or body suspended at a point and adapted to swing to and fro.

Perpetual. For all time; unending or unlimited time.

Phenomena. Some peculiar happening, or event, or object.

Pitch. In aviation this applies to the angle at which the blades of a propeller are cut. If a propeller is turned, and it moves forwardly in the exact path made by the angle, for one complete turn, the distance traveled by the propeller axially indicates the pitch in feet.

Placement. When an object is located at any particular point, so that it is operative the location is called the placement.

Plane. A flat surface for supporting a flying machine in the air. Plane of movement pertains to the imaginary surface described by a moving body. A bicycle wheel, for instance, when moving forwardly in a straight line, has a plane of movement which is vertical; but when the machine turns in a circle the upper end of the wheel is turned inwardly, and the plane of rhovement is at an angle.

Pliant. Easily yielding; capable of being bent; liable to be put out of shape.

Plurality. See multiplicity. More than one.

Poise. Held in suspension; disposed in a particular way.

Pontoon. Applied to a series of boats ranged side by side to support a walk laid thereon. In aviation it has reference to a float for supporting an aeroplane.

Ponderous. Large; heavy; difficult to handle.

Posterior. The rear end; the opposite of anterior.

Principles. The very nature or essence of a thing; the source or cause from which a thing springs.

Proportion. The relation that exists between different parts or things.

Propounded. Questioned; stated; to state formally for consideration

Proprietary. A right; the ownership of certain property.

Primitive. The beginning or early times; long ago.

Prelude. A statement or action which precedes the main feature to be presented.

Proximity. Close to; near at hand.

Prototype. That which is used as the sample from, which something is made or judged.

Propeller. The piece of meebanism, with screw shaped blade, designed to be rapidly rotated in order to drive a vessel forwardly. It is claimed by some that the word Impeller would be the more proper term.

Primarily. At the first; the commencement.

Precedes. Goes ahead; forward of all.

Propulsive. The force which gives motion to an object.

Projected. Thrown forward; caused to fly through the air.

Radially. Out from the center; projecting like the spokes of a wheel.

Ratio. The relation of degree, number, amount; one with another.

Reaction. A counterforce; acting against.

Recognize. To know; seeing, hearing, or feeling, and having knowledge therefrom.

Reflection. Considering; judging one thing by the examination of another. A beam of light, or an object, leaving a surface.

Refraction. That peculiarity in a beam of light, which, in passing through water at an angle, bends out of its course and again assumes a direct line after passing through.

Reflex. Turned back on itself, or in the direction from which it came.

Requisite. Enough; suffieient for all purposes.

Relegate. To put back or away.

Rectangular. Having one or more right angles.

Reservations. Land which is held by the Government for various purposes.

Resistance. That which holds back; preventing movement.

Retarding. Preventing a free movement.

Revoluble. The turning or swinging motion of a body like the earth in its movement around the sun. See Rotative. To cause to move as in an orbit or circle.

Resilient. Springy; having the quality of elasticity.

Reversed. Changed about; turned front side to the rear.

Rotative. That which turns, like a shaft. The movement of the earth on its axis is rotative.

Saturation. Putting one substance into another until it will hold no more. For instance, adding salt to water until the water cannot take up any more.

Security. Safety, assuredness that there will be no danger.

Segment. A part eut off from a circle. Distinguished from a sector, which might be likened to the form of one of the sections of an orange.

Sexagonal. Six-sided.

Sine of the Angle. The line dropped from the highest point of an
angle to the line which runs out horizontally.

Sinuous. Wavelike; moving up and down like the waves of the ocean.

Simulates. To pattern or copy after; the making of the like.

Skipper. A thin flat stone.

Spirally-formed. Made like an auger; twisted.

Stability. In airships that quality which holds the ship on an even and unswerving course, and prevents plunging and side motions.

Structural. Belonging to the features of eonstruetion.

Strata. Two or more layers; one over or below the other.

Stream line. In expressing the action of moving air, or an aeroplane transported through air, every part is acted upon by the air. Stream lines are imaginary lines which act upon the planes at all points, and all in the same direction, or angle.

Stupendous. Great; important; above the ordinary.

Substitute. One taken for another; replacing one thing by something else.

Supporting. Giving aid; helping another.

Synchronous. Acting at the same time, and to the same extent. Thus if two wheels, separated from each other at great distances, are so arranged that they turn at exactly the same speed, they are said to turn synchronously.

Tactics. The art of handling troops in the presence of an enemy. It differs from strategy in the particular that the latter word is used to explain the movements or arrangement of forces before they arrive at the battle line.

Tandem. One before the other; one after the other.

Tangent. A line drawn from a circle at an angle, instead of radially.

Technically. Pertaining to some particular trade, science or art.

Tenuous. Thin, slender, willowy, slight.

Tetrahedral. This has reference to a form which is made up of a multiplicity of triangularly shaped thin blades, so as to form numerous cells, and thus make a large number of supporting surfaces. Used as a kite.

Theories. Views based upon certain consideration.

Theoretical. Where opinions are founded on certain information, and expressed, not from the standpoint of actual knowledge, but upon conclusions derived from such examinations.

Torsion. A twist; a circular motion around a body.

Transmitted. Sent out; conveyed from one point to another.

Transformed. Changed; entirely made over from one thing to another.

Transverse. When a body is shorter from front to rear than from side to side its longest dimension is transversely. Distinguish from lateral, which has reference only to the distance at right angles from the main body.

Translation. The transportation of a body through the air.

Trajectory. The path made by a body projected through the air.

Triangular. A form or body having three sides and three angles.

Typical. In the form of; a likeness to.

Ultimate. The end; the finality; the last that can be said.

Uninitiated. Not having full knowledge; withont information.

Unique. Peculiar; something that on account of its peculiar construction or arrangements stands out beyond the others.

Universal. Everywhere; all over the world.

Undulate. To move up and down; a wave-like motion.

Utility. Of use; to take advantageous use of.

Unstable. Not having anything permanent; in a ship in flight one that will not ride on an even keel, and is liable to pitch about.

Vacuum. Where air is partly taken away, or rendered rarer.

Valved. A surface which has a multiplicity of openings with valves therein, or, through which air can move in one direction.

Vaunted. To boast concerning; to give a high opinion.

Velocity. Speed; the rate at which an object can move from place to place.

Vertical. A line running directly to the center of the earth; a line at right angles to the surface of water.

Vibratory. Moving from side to side; a regular motion.

Volplane. The glide of a machine without the use of power.

Warping. The twist given to certain portions of planes, so as to cause the air to aet against the warped portions.

Weight. The measure of the force which gravity exerts on all objects.