THE CENTER OF PRESSURE.—In such a plane the center of pressure is near its upper end, probably near the line 3, so that the greater portion of the lift is exerted by that part of the plane above line 3.

AIR LINES ON THE UPPER SIDE OF THE PLANE.— Now, another factor must be considered, namely, the effect produced on the upper side of the plane, over which a rarefied area is formed at certain points, and, in practice, this also produces, or should be utilized to effect a lift.

RAREFIED AREA.—What is called a rarefied area, has reference to a state or condition of the atmosphere which has less than the normal pressure or quantity of air. Thus, the pressure at sea level, is about 14 3/4 per square inch

As we ascend the pressure grows less, and the air is thus rarer, or, there is less of it. This is a condition which is normally found in the atmosphere. Several things tend to make a rarefied condition. One is altitude, to which we have just referred.

Then heat will expand air, making it less dense, or lighter, so that it will move upwardly, to be replaced by a colder body of air. In aeronautics neither of these conditions is of any importance in considering the lifting power of aeroplane surfaces.

RAREFACTION PRODUCED BY MOTION.—The third rarefied condition is produced by motion, and generally the area is very limited when brought about by this means. If, for instance, a plane is held horizontally and allowed to fall toward the earth, it will be retarded by two forces, namely, compression and rarefaction, the former acting on the under side of the plane, and the latter on the upper side.

Of the two rarefaction is the most effectual, and produces a greater effect than compression. This may be proven by compressing air in a long pipe, and noting the difference in gauge pressure between the ends, and then using a suction pump on the same pipe.

When a plane is forced through the air at any angle, a rarefied area is formed on the side which is opposite the one having the positive angle of incidence.

If the plane can be so formed as to make a large and effective area it will add greatly to the value of the sustaining surface.

Unfortunately, the long fiat plane does not lend any aid in this particular, as the stream line flows down along the top, as shown in Fig. 23, without being of any service.

Fig. 23. Air lines on the upper side of a Plane.

THE CONCAVED PLANE.—These considerations led to the adoption of the concaved plane formation, and for purposes of comparison the diagram, Fig. 24, shows the plane B of the same length and angle as the straight planes.

In examining the successive stream lines it will be found that while the 1st, 2d and 3d lines have a little less angle of impact than the corresponding lines in the straight plane, the last lines, 5, 6 and 7, have much greater angles, so that only line 4 strikes the plane at the same angle.

Such a plane structure would, therefore, have its center of pressure somewhere between the lines 3 and 4, and the lift being thus, practically, uniform over the surface, would be more effective.

THE CENTER OF PRESSURE.—This is a term used to indicate the place on the plane where the air acts with the greatest force. It has reference to a point between the front and rear margins only of the plane.

Fig. 24. Air lines below a concaved Plane.

UTILIZING THE RAREFIED AREA.—This structure, however, has another important advantage, as it utilizes the rarefied area which is produced, and which may be understood by reference to Fig. 25.

The plane B, with its upward curve, and at the same angle as the straight plane, has its lower end so curved, with relation to the forward movement, that the air, in rushing past the upper end, cannot follow the curve rapidly enough to maintain the same density along C, hence this exerts

an upward pull, due to the rarefied area, which serves as a lifting force, as well as the compressed mass beneath the plane.

CHANGING CENTER OF PRESSURE.—The center of pressure is not constant. It changes with the angle of the plane, but the range is considerably less on a concave surface than on a flat plane.

Fig. 25. Air lines above a convex Plane.

In a plane disposed at a small angle, A, as in Fig. 26, the center of pressure is nearer the forward end of the plane than with a greater positive angle of incidence, as in Fig. 27, and when the plane is in a normal flying angle, it is at the center, or at a point midway between the margins.

PLANE MONSTROSITIES.—Growing out of the idea that the wing in nature must be faithfully copied, it is believed by many that a plane with a pronounced thickness at its forward margin is one of the secrets of bird flight.

Accordingly certain inventors have designed types of wings which are shown in Figs. 28 and 29.

Fig. 28 Changing centers of Pressures.

Fig 29. Bird-wing structures.

Both of these types have pronounced bulges, designed to "split" the air, forgetting, apparently, that in other parts of the machine every effort is made to prevent head resistance.

THE BIRD WING STRUCTURE.—The advocates of such construction maintain that the forward edge of the plane must forcibly drive the air column apart, because the bird wing is so made, and that while it may not appear exactly logical, still there is something about it which seems to do the work, and for that reason it is largely adopted.

WHY THE BIRD'S WING HAS A PRONOUNCED BULGE.—Let us examine this claim. The bone which supports the entire wing surface, called the (pectoral), has a heavy duty to perform. It is so constructed that it must withstand an extraordinary torsional strain, being located at the forward portion of the wing surface. Torsion has reference to a twisting motion.

In some cases, as in the bat, this primary bone has an attachment to the rear of the main joint, where the rear margin of the wing is attached to the leg of the animal, thus giving it a support and the main bone is, therefore, relieved of this torsional stress.

THE BAT'S WING.—An examination of the bat's wing shows that the pectoral bone is very small and thin, thus proving that when the entire wing support is thrown upon the primary bone it must be large enough to enable it to carry out its functions. It is certainly not so made because it is a necessary shape which best adapts it for flying.

If such were the case then nature erred in the case of the bat, and it made a mistake in the housefly's wing which has no such anterior enlargement to assist (?) it in flying.

AN ABNORMAL SHAPE.—Another illustration is shown in Fig. 30, which has a deep concave directly behind the forward margin, as at A, so that when the plane is at an angle of about 22 degrees, a horizontal line, as B, passing back from the nose, touches the incurved surface of the plane at a point about one-third of its measurement back across the plane.

Fig. 30. One of the Monstrosities

This form is an exact copy of the wing of an actual bird, but it belongs, not to the soaring, but to the class which depends on flapping wings, and as such it cannot be understood why it should be used for soaring machines, as all aeroplanes are.

The foregoing instances of construction are cited to show how wildly the imagination will roam when it follows wrong ideals.

THE TAIL AS A MONITOR.—The tendency of the center of pressure to change necessitates a correctional means, which is supplied in the tail of the machine, just as the tail of a kite serves to hold it at a correct angle with respect to the wind and the pull of the supporting string.



CHAPTER VII

ABNORMAL FLYING STUNTS AND SPEEDS

"PEQUOD, a Frenchman, yesterday repeatedly performed the remarkable feat of flying with the machine upside down. This exhibition shows that the age of perfection has arrived in flying machines, and that stability is an accomplished fact."—News item.

This is quoted to show how little the general public knows of the subject of aviation. It correctly represents the achievement of the aviator, and it probably voiced the sentiment of many scientific men, as well as of the great majority of aviators.

A few days afterwards, the same newspaper published the following:

"Lieutenant ——, while experimenting yesterday morning, met his death by the overturning of his machine at an altitude of 300 meters. Death was instantaneous, and the machine was completely destroyed."

The machines used by the two men were of the same manufacture, as Pequod used a stock machine which was strongly braced to support the inverted weight, but otherwise it was not unlike the well known type of monoplane.

Beachy has since repeated the experiment with a bi-plane, and it is a feat which has many imitators, and while those remarkable exhibitions are going on, one catastrophe follows the other with the same regularity as in the past.

Let us consider this phase of flying. Are they of any value, and wherein do they teach anything that may be utilized,

LACK OF IMPROVEMENTS IN MACHINES.—It is remarkable that not one single forward step has been taken to improve the type of flying machines for the past five years. They possess the same shape, their stabilizing qualities and mechanism for assuring stability are still the same.

MEN EXPEDITED, AND NOT THE MACHINE.—The fact is, that during this period the man has been exploited and not the machine. Men have learned, some few of them, to perform peculiar stunts, such as looping the loop, the side glide, the drop, and other features, which look, and are, hazardous, all of which pander to the sentiments of the spectators.

ABNORMAL FLYING OF NO VALUE.—It would be too broad an assertion to say that it has absolutely no value, because everything has its use in a certain sense, but if we are to judge from the progress of inventions in other directions, such exhibitions will not improve the art of building the device, or make a fool-proof machine.

Indeed, it is the very thing which serves as a deterrent, rather than an incentive. If machines can be handled in such a remarkable manner, they must be, indeed, perfect! Nothing more is needed! They must represent the highest structural type of mechanism!

That is the idea sought to be conveyed in the first paragraph quoted. It is pernicious, instead of praiseworthy, because it gives a false impression, and it is remarkable that even certain scientific journals have gravely discussed the perfected (?) type of flying machine as demonstrated by the experiments alluded to.

THE ART OF JUGGLING.—We may, occasionally, see a cyclist who understands the art of balancing so well that he can, with ease, ride a machine which has only a single wheel; or he can, with a stock bicycle, ride it in every conceivable attitude, and make it perform all sorts of feats.

It merely shows that man has become an expert at juggling with a machine, the same as he manipulates balls, and wheels, and other artifices, by his dexterity.

PRACTICAL USES THE BEST TEST.—The bicycle did not require such displays to bring it to perfection. It has been the history of every invention that improvements were brought about, not by abnormal experiments, but by practical uses and by normal developments.

The ability of an aviator to fly with the machine in an inverted position is no test of the machine's stability, nor does it in any manner prove that it is correctly built. It is simply and solely a juggling feat—something in the capacity of a certain man to perform, and attract attention because they are out of the ordinary.

CONCAVED AND COXVEX PLANES:—They were performed as exhibition features, and intended as such, and none of the exponents of that kind of flying have the effrontery to claim that they prove anything of value in the machine itself, except that it incidentally has destroyed the largely vaunted claim that concaved wings for supporting surfaces are necessary.

HOW MOMENTUM IS A FACTOR IN INVERTED FLYING.— When flying "upside down," the convex side of the plane takes the pressure of the air, and maintains, so it is asserted, the weight of the machine. This is true during that period when the loop is being made. The evolution is made by first darting down, as shown in Fig. 31, from the horizontal position, 1, to the position 2, where the turn begins.

Fig. 31. Flying upside down.

TURNING MOVEMENT.—Now note the characteristic angles of the tail, which is the controlling factor. In position 1 the tail is practically horizontal. In fact, in all machines, at high flight, the tail is elevated so as to give little positive angle of incidence to the supporting planes.

In position No. 2, the tail is turned to an angle of incidence to make the downward plunge, and when the machine has assumed the vertical, as in position 3, the tail is again reversed to assume the angle, as in 1, when flying horizontally.

At the lower turn, position 4, the tail is turned similar to the angle of position 2, which throws the rear end of the machine down, and as the horizontal line of flight is resumed, in an inverted position, as in position 4, the tail has the same angle, with relation to the frame, as the supporting planes.

During this evolution the engine is running, and the downward plunge develops a tremendous speed, and the great momentum thus acquired, together with the pulling power of the propeller while thus in flight, is sufficient to propel it along horizontally, whatever the plane surface curve, or formation may be.

It is the momentum which sustains it in space, not the air pressure beneath the wings, for reasons which we have heretofore explained. Flights of sufficient duration have thus been made to prove that convex, as well as concave surfaces are efficient; nevertheless, in its proper place we have given an exposition of the reasoning which led to the adoption of the concaved supporting surfaces.

WHEN CONCAVED PLANES ARE DESIRABLE.— Unquestionably, for slow speeds the concaved wing is desirable, as will be explained, but for high speeds, surface formation has no value. That is shown by Pequod's feat.

THE SPEED MANIA.—This is a type of mania which pervades every field of activity in the building of aeroplanes. Speed contests are of more importance to the spectators on exhibition grounds than stability or durability. Builders pander to this, hence machines are built on lines which disregard every consideration of safety while at normal flight.

USES OF FLYING MACHINES.—The machine as now constructed is of little use commercially. Within certain limitations it is valuable for scouting purposes, and attempts have been made to use it commercially. But the unreliable character of its performances, due to the many elements which are necessary to its proper working, have operated against it.

PERFECTION IN MACHINES MUST COME BEFORE SPEED.—Contrary to every precept in the building of a new article, the attempt is made to make a machine with high speed, which, in the very nature of things, operates against its improvement. The opposite lack of speed—is of far greater utility at this stage of its development.

THE RANGE OF ITS USE.—The subject might be illustrated by assuming that we have a line running from A to Z, which indicates the range of speeds in aeroplanes. The limits of speeds are fairly stated as being within thirty and eighty- five miles per hour. Less than thirty miles are impossible with any type of plane, and while some have made higher speeds than eighty-five miles it may be safe to assume that such flights took place under conditions where the wind contributed to the movement.

Fig. 32. Chart showing Range of Uses

COMMERCIAL UTILITY.—Before machines can be used successfully they must be able to attain slower speeds. Alighting is the danger factor. Speed machines are dangerous, not in flight or at high speeds, but when attempting to land. A large plane surface is incompatible with speed, which is another illustration that at high velocities supporting surfaces are not necessary.

Commercial uses require safety as the first element, and reliability as the next essential. For passenger service there must be an assurance that it will not overturn, or that in landing danger is not ever-present. For the carrying of freight interrupted service will militate against it.

How few are the attempts to solve the problem of decreased speed, and what an eager, restless campaign is being waged to go faster and faster, and the addition of every mile above the record is hailed as another illustration of the perfection (?) of the flying machine.

To be able to navigate a machine at ten, or fifteen miles an hour, would scarcely be interesting enough to merit a paragraph; but such an accomplishment would be of far more value than all of Pequod's feats, and be more far-reaching in its effects than a flight of two hundred miles per hour.



CHAPTER VIII

KITES AND GLIDERS

KITES are of very ancient origin, and in China, Japan, and the Malayan Peninsula, they have been used for many years as toys, and for the purposes of exhibiting forms of men, animals, and particularly dragons, in their periodical displays.

THE DRAGON KITE.—The most noted of all are the dragon kites, many of them over a hundred feet in length, are adapted to sail along majestically, their sinuous or snake-like motions lending an idea of reality to their gorgeously-colored appearance in flight.

ITS CONSTRUCTION.—It is very curiously wrought, and as it must be extremely light, bamboo and rattan are almost wholly used, together with rice paper, in its construction.

Fig. 33 shows one form of the arrangement, in which the bamboo rib, A, in which only two sections are shown, as B, B, form the backbone, and these sections are secured together with pivot pins C. Each section has attached thereto a hoop, or circularly-formed rib, D, the rib passing through the section B, and these ribs are connected together loosely by cords E, which run from one to the other, as shown.

These circular ribs, D, are designed to carry a plurality of light paper disks, F, which are attached at intervals, and they are placed at such angles that they serve as small wing surfaces or aeroplanes to hold the structure in flight.

Fig. 33. Ribs of Dragon Kite

THE MALAY KITE.—The Malay kite, of which Fig. 34 shows the structure, is merely made up of two cross sticks, A, B, the vertical strip, A, being bent and rigid, whereas the cross stick, B, is light and yielding, so that when in flight it will bend, as shown, and as a result it has wonderful stability due to the dihedral angles of the two surfaces. This kite requires no tail to give it stability.

Fig. 34. The Malay Kite.

DIHEDRAL ANGLES.—This is a term to designate a form of disposing of the wings which has been found of great service in the single plane machines. A plane which is disposed at a rising angle, as A, A, Fig. 35, above the horizontal line, is called dihedral, or diedral.

Fig. 35. Dihedral Angle.

This arrangement in monoplanes does away with the necessity of warping the planes, or changing them while in flight. If, however, the angle is too great, the wind from either quarter is liable to raise the side that is exposed.

THE COMMON KITE.—While the Malay kite has only two points of cord attachment, both along the vertical rib, the common kite, as shown in Fig. 36, has a four-point connection, to which the flying cord is attached. Since this form has no dihedral angle, it is necessary to supply a tail, which thus serves to keep it in equilibrium, while in flight.

Fig. 36. Common Kite.

Various modifications have grown out of the Malay kite. One of these forms, designed by Eddy, is exactly like the Malay structure, but instead of having a light flexible cross piece, it is bent to resemble a bow, so that it is rigidly held in a bent position, instead of permitting the wind to give it the dihedral angle.

THE BOW KITE.—Among the different types are the bow kite, Fig. 37, and the sexagonal structure, Fig. 38, the latter form affording an especially large surface.

_Fig. 37. Bow Kite.-

Fig. 38. Hexagonal Kite.

THE BOX KITE.—The most marked improvement in the form of kites was made by Hargreaves, in 1885, and called the box kite. It has wonderful stability, and its use, with certain modifications, in Weather Bureau experiments, have proven its value.

It is made in the form of two boxes, A, B, open at the ends, which are secured together by means of longitudinal bars, C, that extends from one to the other, so that they are held apart a distance, approximately, equal to the length of one of the boxes.

Fig. 39. Hargreave Kite.

Their fore and aft stability is so perfect that the flying cord D is attached at one point only, and the sides of the boxes provide lateral stability to a marked degree.

THE VOISON BIPLANE.—This kind of kite furnished the suggestion for the Voison biplane, which was one of the earlier productions in flying machines.

Fig. 40 shows a perspective of the Voison plane, which has vertical planes A, A, at the ends, and also intermediate curtains B, B. This was found to be remarkably stable, but during its turning movements, or in high winds, was not satisfactory, and for that reason was finally abandoned.

LATERAL STABILITY IN KITES NOT CONCLUSIVE AS TO PLANES.—This is instanced to show that while such a form is admirably adapted for kite purposes, where vertical curtains are always in line with the wind movement, and the structure is held taut by a cord, the lateral effect, when used on a machine which does not at all times move in line with the moving air current. A condition is thus set up which destroys the usefulness of the box kite formation.

Fig. 40. Voison Biplane.

THE SPEAR KITE.—This is a novel kite, with remarkable steadiness and is usually made with the wings on the rear end larger than those on the forward end (Fig. 41), as thereby the cord A can be attached to the spear midway between the two sets of wings.

Fig. 41. Spear Kite.

THE CELLULAR KITE.—Following out the suggestion of the Hargreaves kite, numerous forms embodying the principle of the box structure were made and put on the market before the aeroplane became a reality.

Fig. 42. Cellular Kite.

A structure of this form is illustrated in Fig. 42. Each box, as A, B, has therein a plurality of vertical and horizontal partitions, so that a number of cells are provided, the two cell-like boxes being held apart by a bar C, axially arranged.

This type is remarkably stable, due to the small cells, and kites of this kind are largely used for making scientific experiments.

THE TETRAHEDRAL KITE.—Prof. Bell, inventor of the telephone, gave a great deal of study to kites, which resulted in the tetrahedral formation, as shown in Fig. 43.

Fig. 43. Tetrahedral Kite.

The structure, apparently, is somewhat complicated, but an examination of a single pair of blades, as shown at A, shows that it is built up of triangularly-formed pieces, and that the openings between the pieces are equal to the latter, thereby providing a form of kite which possesses equilibrium to a great degree.

It has never been tried with power, and it is doubtful whether it would be successful as a sustaining surface for flying machines, for the same reasons that caused failure with the box-like formation of the Voison Machine.

THE DELTOID.—The deltoid is the simplest, and the most easily constructed of all the kites. It is usually made from stiff cardboard, A-shaped in outline, as shown in Figs. 44 and 45, and bent along a central line, as at A, forming two wings, each of which is a right-angled triangle.

Fig. 44. and 45. Deltoid Formation.

The peculiarity of this formation is, that it has remarkable stability when used as a kite, with either end foremost. If a small weight is placed at the pointed end, and it is projected through the air, it will fly straight, and is but little affected by cross currents.

THE DUNNE FLYING MACHINE.—A top view of this biplane is shown in Fig. 46. The A-shaped disposition of the planes, gives it good lateral stability, but it has the disadvantage under which all aeroplanes labor, that the entire body of the machine must move on a fore and aft vertical plan in order to ascend or descend.

Fig. 46. The Dunne Bi-plane.

This is a true deltoid formation, as the angle of incidence of the planes is so disposed that when the planes are horizontal from end to end, the inclination is such as to make it similar to the deltoid kite referred to.

ROTATING KITE.—A type of kite unlike the others illustrated is a rotating structure, which gives great stability, due to the gyroscopic action on the supporting surfaces.

Fig. 47 shows a side view with the top in section. The supporting surface is umbrella-shaped. In fact, the ordinary umbrella will answer if not dished too much. An angularly-bent piece of wire A, provided with loops B, B, at the ends, serve as bearings for the handle of the umbrella.

At the bend of the wire loop C, the cord D is attached. The lower side of the umbrella top has cup-shaped pockets E, near the margin, so arranged that their open ends project in the same direction, and the wind catching them rotates the circular plane.

Fig. 47. Rotable Umbrella Kite.

KITE PRINCIPLES.—A careful study of the examples here given, will impress the novice with one important fact, which, in its effect has a more important bearing on successful flight, than all the bird study and speculations concerning its mysteries.

This fact, in essence, is, that the angle of the kite is the great factor in flight next to the power necessary to hold it. Aside from this, the comparison between kites and aeroplanes is of no practical value.

Disregarding the element of momentum, the drift of a machine against a wind, is the same, dynamically, as a plane at rest with the wind moving past it. But there is this pronounced difference: The cord which supports the kite holds it so that the power is in one direction only.

When a side gust of wind strikes the kite it is moved laterally, in sympathy with the kite, hence the problem of lateral displacement is not the same as with the aeroplane.

LATERAL STABILITY IN KITES.—In the latter the power is definitely fixed with relation to the machine itself, and if we should assume that a plane with a power on it sufficient to maintain a flight of 40 miles an hour, should meet a wind moving at the same speed, the machine would be stationary in space.

Such a condition would be the same, so far as the angles of the planes are concerned, with a kite held by a string, but there all similarity in action ends.

The stabilizing quality of the kite may be perfect, as the wind varies from side to side, but the aeroplane, being free, moves to the right or to the left, and does not adjust itself by means of a fixed point, but by a movable one.

SIMILARITY OF FORE AND AFT CONTROL.—Fore and aft, however, the kite and aeroplane act the same. Fig. 48 shows a diagram which illustrates the forces which act on the kite, and by means of which it adjusts its angle automatically.

Let us assume that the kite A is flown from a cord B, so that its angle is 22 1/2 degrees, the wind being 15 miles per hour to maintain the cord B at that angle. When the wind increases to 20 miles an hour there is a correspondingly greater lift against the kite.

Fig. 48. Action of Wind forces on Kite.

As its angle is fixed by means of the loop C, it cannot change its angle with reference to the cord, or independently of it, and its only course is to move up higher and assume the position shown by the figure at D, and the angle of incidence of the kite is therefore changed to 15 degrees, or even to 10 degrees.

In the case of the aeroplane the effect is similar from the standpoint of power and disposition of the planes. If it has sufficient power, and the angle of the planes is not changed, it will ascend; if the planes are changed to 15 degrees to correspond with the kite angle it will remain stationary.

GLIDING FLIGHT.—The earliest attempt to fly by gliding is attributed to Oliver, a Monk of Malmesbury who, in 1065 prepared artificial wings, and with them jumped from a tower, being injured in the experiment.

Nearly 700 years later, in 1801, Resnier, a Frenchman, conducted experiments with varying results, followed by Berblinger, in 1842, and LeBris, a French sailor, in 1856.

In 1884, J. J. Montgomery, of California, designed a successful glider, and in 1889 Otto and Gustav Lilienthal made the most extended tests, in Germany, and became experts in handling gliders.

Pilcher, in England, was the next to take up the subject, and in 1893 made many successful glides, all of the foregoing machines being single plane surfaces, similar to the monoplane.

Long prior to 1896 Octave Chanute, an engineer, gave the subject much study, and in that year made many remarkable flights, developing the double plane, now known as the biplane.

He was an ardent believer in the ability of man to fly by soaring means, and without using power for the purpose.

It is doubtful whether gliders contributed much to the art in the direction of laterally stabilizing aeroplanes. They taught useful lessons with respect to area and fore and aft control.

The kite gave the first impulse to seek out a means for giving equilibrium to planes, and Montgomery made a kite with warping wings as early as 1884.

Penaud, a Frenchman, in 1872, made a model aeroplane which had the stabilizing means in the tail. All these grew out of kite experiments; and all gliders followed the kite construction, or the principles involved in them, so that, really, there is but one intervening step between the kite and the flying machine, as we know it, the latter being merely kites with power attached, as substitutes for the cords.

ONE OF THE USES OF GLIDER EXPERIMENTS.— There is one direction in which gliders are valuable to the boy and to the novice who are interested in aviation. He may spend a lifetime in gliding and not advance in the art. It is questionable whether in a scientific way it will be of any service to him; but experiments of this character give confidence, the ability to quickly grasp a situation, and it will thus teach self reliance in emergencies.

When in a glider quick thinking is necessary. The ability to shift from one position to another; to apply the weight where required instantaneously; to be able during the brief exciting moment of flight to know just what to do, requires alertness.

Some are so wedded to the earth that slight elevation disturbs them. The sensation in a glider while in flight is unlike any other experience. It is like riding a lot of tense springs, and the exhilaration in gliding down the side of a hill, with the feet free and body suspended, is quite different from riding in an aeroplane with power attached.

HINTS IN GLIDING.—It seems to be a difficult matter to give any advice in the art of gliding. It is a feat which seems to necessitate experiment from first to last. During the hundreds of tests personally made, and after witnessing thousands of attempts, there seems to be only a few suggestions or possible directions in which caution might be offered.

First, in respect to the position of the body at the moment of launching. The glider is usually so made that in carrying it, preparatory to making the run and the leap required to glide, it is held so that it balances in the hands.

Now the center of air pressure in gliding may not be at the same point as its sustaining weight when held by the hand, and furthermore, as the arm-pits, by which the body of the experimenter are held while gliding, are not at the same point, but to the rear of the hands, the moment the glider is launched too great a weight is brought to the rear margin of the planes, hence its forward end lifts up.

This condition will soon manifest itself, and be corrected by the experimenter; but there is another difficulty which is not so easy to discover and so quick to remedy, and that is the swing of the legs the moment the operator leaves the ground.

The experimenter learns, after many attempts, that gliding is a matter of a few feet only, and he anticipates landing too soon, and the moment he leaps from the ground the legs are swung forwardly ready to alight.

This is done unconsciously, just as a jumper swings his legs forwardly in the act of alighting. Such a motion naturally disturbs the fore and aft stability of the gliding machine, by tilting up the forward margin, and it banks against the air, instead of gliding.

The constant fear of all gliders is, that the machine will point downwardly, and his motion, as well as the position of the body, tend to shoot it upwardly, instead.



CHAPTER IX

AEROPLANE CONSTRUCTION

As may be inferred from the foregoing statements, there are no definite rules for the construction of either type of flying machine, as the flying models vary to such an extent that it is difficult to take either of them as a model to represent the preferred type of construction.

LATERAL, AND FORE AND AFT.—The term lateral should be understood, as applied to aeroplanes. It is always used to designate the direction at right angles to the movement of the machine. Fore and aft is a marine term meaning lengthwise, or from front to rear, hence is always at right angles to the lateral direction.

The term transverse is equivalent to lateral, in flying machine parlance, but there is this distinction: Transverse has reference to a machine or object which, like the main planes of an aeroplane, are broader, (that is,—from end to end) than their length, (from front to rear).

On the other hand, lateral has reference to side branches, as, for instance, the monoplane wings, which branch out from the sides of the fore and aft body.

STABILITY AND STABILIZATION.—These terms constantly appear in describing machines and their operations. If the flying structure, whatever it may be, has means whereby it is kept from rocking from side to side, it has stability, which is usually designated as lateral stability. The mechanism for doing this is called a stabilizer.

THE WRIGHT SYSTEM.—The Wright machine has reference solely to the matter of laterally controlling the flying structure, and does not pertain to the form or shape of the planes.

In Fig. 49 A designates the upper and lower planes of a Wright machine, with the peculiar rounded ends. The ends of the planes are so arranged that the rear margins may be raised or lowered, independently of the other portions of the planes, which are rigid. This movement is indicated in sketch 1, where the movable part B is, as we might say, hinged along the line C.

The dotted line D on the right hand end, shows how the section is depressed, while the dotted lines E at the left hand end shows the section raised. It is obvious that the downturned ends, as at D, will give a positive angle at one end of the planes, and the upturned wings E at the other end will give a negative angle, and thus cause the right hand end to raise, and the other end to move downwardly, as the machine moves forwardly through the air.

CONTROLLING THE WARPING ENDS.—Originally the Wrights controlled these warping sections by means of a cradle occupied by the aviator, so that the cradle would move or rock, dependent on the tilt of the machine. This was what was termed automatic control. This was found to be unsatisfactory, and the control has now been placed so that it connects with a lever and is operated by the aviator, and is called Manually-operated control.

In all forms of control the wings on one side are depressed on one side and correspondingly elevated on the other.

THE CURTIS WINGS.—Curtis has small wings, or ailerons, intermediate the supporting surfaces, and at their extremities, as shown in sketch 2. These are controlled by a shoulder rack or swinging frame operated by the driver, so that the body in swinging laterally will change the two wings at the same time, but with angles in different directions.

THE FARMAN AILERONS.—Farman's disposition is somewhat different, as shown in sketch 3. The wings are hinged to the upper planes at their rear edges, and near the extremities of the planes. Operating wires lead to a lever within reach of the aviator, and, by this means, the wings are held at any desired angle, or changed at will.

The difficulty of using any particular model, is true, also, of the arrangement of the fore and aft control, as well as the means for laterally stabilizing it. In view of this we shall submit a general form, which may be departed from at will.

FEATURES WELL DEVELOPED.—Certain features are fairly well developed, however. One is the angle of the supporting plane, with reference to the frame itself; and the other is the height at which the tail and rudder should be placed above the surface of the ground when the machine is at rest.

DEPRESSING THE REAR END.—This latter is a matter which must be taken into consideration, because in initiating flight the rear end of the frame is depressed in order to give a sufficient angle to the supporting planes so as to be able to inaugurate flight.

In order to commence building we should have some definite idea with respect to the power, as this will, in a measure, determine the area of the supporting surfaces, as a whole, and from this the sizes of the different planes may be determined.

DETERMINING THE SIZE.—Suppose we decide on 300 square feet of sustaining surface. This may require a 30, a 40 or a 50 horse power motor, dependent on the speed required, and much higher power has been used on that area.

However, let us assume that a forty horse power motor is available, our 300 square feet of surface may be put into two planes, each having 150 square feet of surface, which would make each 5' by 30' in size; or, it may be decided to make the planes narrower, and proportionally longer. This is immaterial. The shorter the planes transversely, the greater will be the stability, and the wider the planes the less will be the lift, comparatively.

RULE FOR PLACING THE PLANES.—The rule for placing the planes is to place them apart a distance equal to the width of the planes themselves, so that if we decide on making them five feet wide, they should be placed at least five feet apart. This rule, while it is an admirable one for slow movements or when starting flight, is not of any advantage while in rapid flight.

If the machine is made with front and rear horizontally-disposed rudders, or elevators, they also serve as sustaining surfaces, which, for the present will be disregarded.

Lay off a square A, Fig. 49a, in which the vertical lines B, B, and the horizontal lines C, C, are 5' long, and draw a cross D within this, the lines running diagonally from the corners.

Now step off from the center cross line D, three spaces, each five feet long, to a point E, and join this point by means of upper and lower bars F, G, with the upper and lower planes, so as to form the tail frame.

Fig. 49a. Rule for spacing Planes.

As shown in Fig. 50, the planes should now be indicated, and placed at an angle of about 8 degrees angle, which are illustrated, H being the upper and I the lower plane. Midway between the forward edges of the two planes, is a horizontal line J, extending forwardly, and by stepping off the width of two planes, a point K is made, which forms the apex of a frame L, the rear ends of the bars being attached to the respective planes H, I, at their forward edges.

Fig. 50. Frame of Control Planes.

Fig. 51. and Fig. 52.

ELEVATING PLANES.—We must now have the general side elevation of the frame, the planes, their angles, the tail and the rudder support, and the frame for the forward elevator.

To this may be added the forward elevating plane L, the rear elevator, or tail M, and the vertical steering rudder N.

The frame which supports the structure thus described, may be made in a variety of ways, the object being to provide a resilient connection for the rear wheel O.

Fig. 52 shows a frame which is simple in construction and easily attached. The lower fore and aft side bars P have the single front wheel axle at the forward end, and the aft double wheels at the rear end, a flexible bar Q, running from the rear wheel axle to the forward end of the lower plane.

A compression spring R is also mounted between the bar and rear end of the lower plane to take the shock of landing. The forward end of the bar P has a brace S extending up to the front edge of the lower plane, and another brace T connects the bars P, S, with the end of the forwardly- projecting frame.

Fig. 53. Plan view.

The full page view, Fig. 53, represents a plan view, with one of the wings cut away, showing the general arrangement of the frame, and the three wheels required for support, together with the brace bars referred to.

The necessity of the rear end elevation will now be referred to. The tail need not, necessarily, be located at a point on a horizontal line between the planes. It may be higher, or lower than the planes, but it should not be in a position to touch the ground when the machine is about to ascend.

Fig. 54. Alighting.

The angle of ascension in the planes need not exceed 25 degrees so the frame does not require an angle of more than 17 degrees. This is shown in Fig. 54, where the machine is in a position ready to take the air at that angle, leaving ample room for the steering rudder.

ACTION IN ALIGHTING.—Also, in alighting, the machine is banked, practically in the same position thus shown, so that it alights on the rear wheels O.

The motor U is usually mounted so its shaft is midway between the planes, the propeller V being connected directly with the shaft, and being behind the planes, is on a medial line with the machine.

The control planes L, M, N, are all connected up by means of flexible wires with the aviator at the set W, the attachments being of such a character that their arrangement will readily suggest themselves to the novice.

THE MONOPLANE.—From a spectacular standpoint a monoplane is the ideal flying machine. It is graceful in outline, and from the fact that it closely approaches the form of the natural flyer, seems to be best adapted as a type, compared with the biplane.

THE COMMON FLY.—So many birds have been cited in support of the various flying theories that the house fly, as an example has been disregarded. We are prone to overlook the small insect, but it is, nevertheless, a sample which is just as potent to show the efficiency of wing surface as the condor or the vulture.

The fly has greater mobility than any other flying creature. By the combined action of its legs and wings it can spring eighteen inches in the tenth of a second; and when in flight can change its course instantaneously.

If a sparrow had the same dexterity, proportionally, it could make a flight of 800 feet in the same time. The posterior legs of the fly are the same length as its body, which enable it to spring from its perch with amazing facility.

Fig. 55. Common Fly. Outstretched Wings.

The wing surface, proportioned to its body and weight, is no less a matter for wonder and consideration.

In Fig. 55 is shown the outlines of the fly with outstretched wings. Fig. 56 represents it with the wing folded, and Fig. 57 is a view of a wing with the relative size of the top of the body shown in dotted lines.

Fig. 56. Common Fly. Folded Wings.

The first thing that must attract attention, after a careful study is the relative size of the body and wing surface. Each wing is slightly smaller than the upper surface of the body, and the thickness of the body is equal to each wing spread.

Fig. 57. Relative size of wing and body.

The weight, compared with sustaining surface, if expressed in understandable terms, would be equal to sixty pounds for every square foot of surface.

STREAM LINES.—The next observation is, that what are called stream lines do not exist in the fly. Its head is as large in cross section as its body, with the slightest suggestion only, of a pointed end. Its wings are perfectly flat, forming a true plane, not dished, or provided with a cambre, even, that upward curve, or bulge on the top of the aeroplane surface, which seems to possess such a fascination for many bird flight advocates.

It will also be observed that the wing connection with the body is forward of the line A, which represents the point at which the body will balance itself, and this line passes through the wings so that there is an equal amount of supporting surface fore and aft of the line.

Again, the wing attachment is at the upper side of the body, and the vertical dimension of the body, or its thickness, is equal to four-fifths of the length of he wing.

The wing socket permits a motion similar to a universal joint, Fig. 55 showing how the inner end of the wing has a downward bend where it joins the back, as at B.

THE MONOPLANE FORM.—For the purpose of making comparisons the illustrations of the monoplane show a machine of 300 square feet of surface, which necessitates a wing spread of forty feet from tip to tip, so that the general dimensions of each should be 18 1/2 feet by 8 1/2 feet at its widest point.

First draw a square forty feet each way, as in Fig. 58, and through this make a horizontal line 1, and four intermediate vertical lines are then drawn, as 2, 3, 4, 5, thus providing five divisions, each eight feet wide. In the first division the planes A, B, are placed, and the tail, or elevator C, is one-half the width of the last division.

Fig. 58. Plan of Monoplane.

The frame is 3 1/2 feet wide at its forward end, and tapers down to a point at its rear end, where the vertical control plane D is hinged, and the cross struts E, E, are placed at the division lines 3, 4, 5.

The angles of the planes, with relation to the frame, are usually greater than in the biplane, for the reason that the long tail plane requires a greater angle to be given to the planes when arising; or, instead of this, the planes A, B, are mounted high enough to permit of sufficient angle for initiating flight without injuring the tail D.

Some monoplanes are built so they have a support on wheels placed fore and aft. In others the tail is supported by curved skids, as shown at A, Fig. 59, in which case the forward supporting wheels are located directly beneath the planes. As the planes are at about eighteen degrees angle, relative to the frame, and the tail plane B is at a slight negative angle of incidence, as shown at the time when the engine is started, the air rushing back from the propeller, elevates the tail, and as the machine moves forwardly over the ground, the tail raises still higher, so as to give a less angle of incidence to the planes while skimming along the surface of the ground.

Fig. 59. Side Elevation, Monoplane.

In order to mount, the tail is suddenly turned to assume a sharp negative angle, thus swinging the tail downwardly, and this increases the angle of planes to such an extent that the machine leaves the ground, after which the tail is brought to the proper angle to assure horizontal flight.

The drawing shows a skid at the forward end, attached to the frame which carries the wheels. The wheels are mounted beneath springs so that when the machine alights the springs yield sufficiently to permit the skids to strike the ground, and they, therefore, act as brakes, to prevent the machine from traveling too far.



CHAPTER X

POWER AND ITS APPLICATION

THIS is a phase of the flying machine which has the greatest interest to the boy. He instinctively sees the direction in which the machine has its life,—its moving principle. Planes have their fascination, and propellers their mysterious elements, but power is the great and absorbing question with him.

We shall try to make its application plain in the following pages. We have nothing to do here with the construction and operation of the motor itself, as, to do that justice, would require pages.

FEATURES IN POWER APPLICATION.—It will be more directly to the point to consider the following features of the power and its application:

1. The amount of power necessary.

2. How to calculate the power applied.

3. Its mounting.

WHAT AMOUNT OF POWER IS NECESSARY.—In the consideration of any power plant certain calculations must be made to determine what is required. A horse power means the lifting of a certain weight, a definite distance, within a specified time.

If the weight of the vehicle, with its load, are known, and its resistance, or the character of the roadway is understood, it is a comparatively easy matter to calculate just how much power must be exerted to overcome that resistance, and move the vehicle a certain speed.

In a flying machine the same thing is true, but while these problems may be known in a general way, the aviator has several unknown elements ever present, which make estimates difficult to solve.

THE PULL OF THE PROPELLER.—Two such factors are ever present. The first is the propeller pull. The energy of a motor, when put into a propeller, gives a pull of less than eight pounds for every horse power exerted.

FOOT POUNDS.—The work produced by a motor is calculated in Foot Pounds. If 550 pounds should be lifted, or pulled, one foot in one second of time, it would be equal to one horse power.

But here we have a case where one horse power pulls only eight pounds, a distance of one foot within one second of time, and we have utilized less than one sixty-fifth of the actual energy produced.

SMALL AMOUNT OF POWER AVAILABLE.—This is due to two things: First, the exceeding lightness of the air, and its great elasticity; and, second, the difficulty of making a surface which, when it strikes the air, will get a sufficient grip to effect a proper pull.

Now it must be obvious, that where only such a small amount of energy can be made available, in a medium as elusive as air, the least change, or form, of the propeller, must have an important bearing in the general results.

HIGH PROPELLER SPEED IMPORTANT.—Furthermore, all things considered, high speed is important in the rotation of the propeller, up to a certain point, beyond which the pull decreases in proportion to the speed. High speed makes a vacuum behind the blade and thus decreases the effective pull of the succeeding blade.

WIDTH AND PITCH OF BLADES.—If the blade is too wide the speed of the engine is cut down to a point where it cannot exert the proper energy; if the pitch is very small then it must turn further to get the same thrust, so that the relation of diameter, pitch and speed, are three problems far from being solved.

It may be a question whether the propeller form, as we now know it, is anything like the true or ultimate shape, which will some day be discovered.

EFFECT OF INCREASING PROPELLER PULL.—If the present pull could be doubled what a wonderful revolution would take place in aerial navigation, and if it were possible to get only a quarter of the effective pull of an engine, the results would be so stupendous that the present method of flying would seem like child's play in comparison.

It is in this very matter,—the application of the power, that the bird, and other flying creatures so far excel what man has done. Calculations made with birds as samples, show that many of them are able to fly with such a small amount of power that, if the same energy should be applied to a flying machine, it would scarcely drive it along the ground.

DISPOSITION OF THE PLANES.—The second factor is the disposition or arrangement of the planes with relation to the weight. Let us illustrate this with a concrete example:

We have an aeroplane with a sustaining surface of 300 square feet which weighs 900 pounds, or 30 pounds per square foot of surface.

DIFFERENT SPEEDS WITH SAME POWER.—Now, we may be able to do two things with an airship under those conditions. It may be propelled through the air thirty miles an hour, or sixty miles, with the expenditure of the same power.

An automobile, if propelled at sixty, instead of thirty miles an hour, would require an additional power in doing so, but an airship acts differently, within certain limitations.

When it is first set in motion its effective pull may not be equal to four pounds for each horse power, due to the slow speed of the propeller, and also owing to the great angle of incidence which resists the forward movement of the ship.

INCREASE OF SPEED ADDS TO RESISTANCE.—Finally, as speed increases, the angle of the planes decrease, resistance is less, and up to a certain point the pull of the propeller increases; but beyond that the vacuum behind the blades becomes so great as to bring down the pull, and there is thus a balance,—a sort of mutual governing motion which, together, determine the ultimate speed of the aeroplane.

HOW POWER DECREASES WITH SPEED.—If now, with the same propeller, the speed should be doubled, the ship would go no faster, because the bite of the propeller on the air would be ineffective, hence it will be seen that it is not the amount of power in itself, that determines the speed, but the shape of the propeller, which must be so made that it will be most effective at the speed required for the ship.

While that is true when speed is the matter of greatest importance, it is not the case where it is desired to effect a launching. In that case the propeller must be made so that its greatest pull will be at a slow speed. This means a wider blade, and a greater pitch, and a comparatively greater pull at a slow speed.

No such consideration need be given to an automobile. The constant accretion of power adds to its speed. In flying machines the aviator must always consider some companion factor which must be consulted.

HOW TO CALCULATE THE POWER APPLIED.—In a previous chapter reference was made to a plane at an angle of forty-five degrees, to which two scales were attached, one to get its horizontal pull, or drift, and the other its vertical pull, or lift.

PULLING AGAINST AN ANGLE.—Let us take the same example in our aeroplane. Assuming that it weighs 900 pounds, and that the angle of the planes is forty-five degrees. If we suppose that the air beneath the plane is a solid, and frictionless, and a pair of scales should draw it up the incline, the pull in doing so would be one-half of its weight, or 450 pounds.

It must be obvious, therefore, that its force, in moving downwardly, along the surface A, Fig. 60, would be 450 pounds.

The incline thus shown has thereon a weight B, mounted on wheels a, and the forwardly-projecting cord represents the power, or propeller pull, which must, therefore, exert a force of 450 pounds to keep it in a stationary position against the surface A.

In such a case the thrust along the diagonal line E would be 900 pounds, being the composition of the two forces pulling along the lines D, F.

THE HORIZONTAL AND VERTICAL PULL.—Now it must be obvious, that if the incline takes half of the weight while it is being drawn forwardly, in the line of D, if we had a propeller drawing along that line, which has a pull of 450 pounds, it would maintain the plane in flight, or, at any rate hold it in space, assuming that the air should be moving past the plane.

Fig. 60. Horizontal and Vertical pull.

The table of lift and drift gives a fairly accurate method of determining this factor, and we refer to the chapter on that subject which will show the manner of making the calculations.

THE POWER MOUNTING.—More time and labor has been wasted, in airship experiments, in poor motor mounting, than in any other direction. This is especially true where two propellers are used, or where the construction is such that the propeller is mounted some distance from the motor.

SECURING THE PROPELLER TO THE SHAFT.—But even where the propeller is mounted on the engine shaft, too little care is exercised to fix it securely. The vibratory character of the mounting makes this a matter of first importance. If there is a solid base a poorly fixed propeller will hold much longer, but it is the extreme vibration that causes the propeller fastening to give way.

VIBRATIONS.—If experimenters realized that an insecure, shaking, or weaving bed would cause a loss of from ten to fifteen per cent. in the pull of the propeller, more care and attention would be given to this part of the structure.

WEAKNESSES IN MOUNTING.—The general weaknesses to which attention should be directed are, first, the insecure attachment of the propeller to the shaft; second, the liability of the base to weave; or permit of a torsional movement; third, improper bracing of the base to the main body of the aeroplane.

If the power is transferred from the cylinder to the engine shaft where it could deliver its output without the use of a propeller, it would not be so important to consider the matter of vibration; but the propeller, if permitted to vibrate, or dance about, absorbs a vast amount of energy, while at the same time cutting down its effective pull.

Aside from this it is dangerous to permit the slightest displacement while the engine is running. Any looseness is sure to grow worse, instead of better, and many accidents have been registered by bolts which have come loose from excessive vibration. It is well, therefore, to have each individual nut secured, or properly locked, which is a matter easily done, and when so secured there is but little trouble in going over the machine to notice just how much more the nut must be taken up to again make it secure.

THE GASOLINE TANK.—What horrid details have been told of the pilots who have been burned to death with the escaping gasoline after an accident, before help arrived. There is no excuse for such dangers. Most of such accidents were due to the old practice of making the tanks of exceedingly light or thin material, so that the least undue jar would tear a hole at the fastening points, and thus permit the gasoline to escape.

A thick copper tank is by far the safest, as this metal will not readily rupture by the wrench which is likely in landing.

WHERE TO LOCATE THE TANK.—There has been considerable discussion as to the proper place to locate the tank. Those who advocate its placement overhead argue that in case of an accident the aeroplane is likely to overturn, and the tank will, therefore, be below the pilot. Those who believe it should be placed below, claim that in case of overturning it is safer to have the tank afire above than below.

DANGER TO THE PILOT.—The great danger to the pilot, in all cases of accidents, lies in the overturning of the machine. Many have had accidents where the machine landed right side up, even where the fall was from a great height, and the only damage to the aviator was bruises. Few, if any, pilots have escaped where the machine has overturned.

It is far better, in case the tank is light, to have it detached from its position, when the ship strikes the earth, because in doing so, it will not be so likely to burn the imprisoned aviator.

In all cases the tank should be kept as far away from the engine as possible. There is no reason why it cannot be placed toward the tail end of the machine, a place of safety for two reasons: First, it is out of the reach of any possible danger from fire; and, second, the accidents in the past show that the tail frame is the least likely to be injured.

In looking over the illustrations taken from the accidents, notice how few of the tails are even disarranged, and in many of them, while the entire fore body and planes were crushed to atoms, the tail still remained as a relic, to show its comparative freedom from the accident.

In all monoplanes the tail really forms part of the supporting surface of the machine, and the adding of the weight of the gasoline would be placing but little additional duty on the tail, and it could be readily provided for by a larger tail surface, if required.

THE CLOSED-IN BODY.—The closed-in body is a vast improvement, which has had the effect of giving greater security to the pilot, but even this is useless in case of overturning.

STARTING THE MACHINE.—The direction in which improvements have been slow is in the starting of the machine. The power is usually so mounted that the pilot has no control over the starting, as he is not in a position to crank it.

The propeller being mounted directly on the shaft, without the intervention of a clutch, makes it necessary, while on the ground, for the propeller to be started by some one outside, while others hold the machine until it attains the proper speed.

This could be readily remedied by using a clutch, but in the past this has been regarded as one of the weight luxuries that all have been trying to avoid. Self starters are readily provided, and this with the provision that the propeller can be thrown in or out at will, would be a vast improvement in all machines.

PROPELLERS WITH VARYING PITCH.—It is growing more apparent each day, that a new type of propeller must be devised which will enable the pilot to change the pitch, as the speed increases, and to give a greater pitch, when alighting, so as to make the power output conform to the conditions.

Such propellers, while they may be dangerous, and much heavier than the rigid type, will, no doubt, appear in time, and the real improvement would be in the direction of having the blades capable of automatic adjustment, dependent on the wind pressure, or the turning speed, and thus not impose this additional duty on the pilot.



CHAPTER XI

FLYING MACHINE ACCESSORIES

THE ANEMOMETER.—It requires an expert to judge the force or the speed of a wind, and even they will go astray in their calculations. It is an easy matter to make a little apparatus which will accurately indicate the speed. A device of this kind is called an Anemometer.

Two other instruments have grown out of this, one to indicate the pressure, and the other the direction of the moving air current.

THE ANEMOGRAPH.—While these instruments indicate, they are also made so they will record the speed, the pressure and the direction, and the device for recording the speed and pressure is called a Anemograph.

All these instruments may be attached to the same case, and thus make a handy little device, which will give all the information at a glance.

THE ANEMOMETROGRAPH.—This device for recording, as well as indicating the speed, pressure and direction, is called an Anemometrograph, The two important parts of the combined apparatus, for the speed and pressure, are illustrated, to show the principle involved. While the speed will give the pressure, it is necessary to make a calculation to get the result while the machine does this for you.

Fig. 61. Speed Indicator.

THE SPEED INDICATOR.—Four hemispherical cups A are mounted on four radiating arms B, which are secured to a vertical stem C, and adapted to rotate in suitable bearings in a case, which, for convenience in explaining, is not shown.

On the lower end of the stem C, is a small bevel pinion, which meshes with a smaller bevel pinion within the base. This latter is on a shaft which carries a small gear on its other end, to mesh with a larger gear on a shaft which carries a pointer D that thus turns at a greatly reduced speed, so that it can be easily timed.

Fig. 62. Air Pressure Indicator.

AIR PRESSURE INDICATOR.—This little apparatus is readily made of a base A which is provided with two uprights B, C, through the upper ends of which are holes to receive a horizontally-disposed bar D. One end of the bar is a flat plane surface E, which is disposed at right angles to the bar, and firmly fixed thereto.

The other end of the bar has a lateral pin to serve as a pivot for the end of a link F, its other end being hinged to the upper end of a lever G, which is pivoted to the post C, a short distance below the hinged attachment of the link F, so that the long end of the pointer which is constituted by the lever G is below its pivot, and has, therefore, a long range of movement.

A spring I between the upper end of the pointer G and the other post B, serves to hold the pointer at a zero position. A graduated scale plate J, within range of the pointer will show at a glance the pressure in pounds of the moving wind, and for this purpose it would be convenient to make the plane E exactly one foot square.

DETERMINING THE PRESSURE FROM THE SPEED.— These two instruments can be made to check each other and thus pretty accurately enable you to determine the proper places to mark the pressure indicator, as well as to make the wheels in the anemometer the proper size to turn the pointer in seconds when the wind is blowing at a certain speed, say ten miles per hour.

Suppose the air pressure indicator has the scale divided into quarter pound marks. This will make it accurate enough for all purposes.

CALCULATING PRESSURES FROM SPEED.—The following table will give the pressures from 5 to 100 miles per hour:

Velocity of wind in Pressure Velocity of wind in Pressure miles per hour per sq. ft. miles per hour per sq ft 5 .112 55 15.125 10 .500 60 18.000 15 1.125 65 21.125 20 2.000 70 22.500 25 3.125 75 28.125 30 4.600 80 32.000 35 6.126 86 36.126 40 8.000 90 40.500 45 10.125 95 45.125 50 12.5 100 50.000

HOW THE FIGURES ARE DETERMINED.—The foregoing figures are determined in the following manner: As an example let us assume that the velocity of the wind is forty-five miles per hour. If this is squared, or 45 multiplied by 45, the product is 2025. In many calculations the mathematician employs what is called a constant, a figure that never varies, and which is used to multiply or divide certain factors.

In this case the constant is 5/1000, or, as usually written, .005. This is the same as one two hundredths of the squared figure. That would make the problem as follows:

45 X 45 = 2025 / 200 = 10.125; or, 45 X 45 - 2025 X .005 = 10.125.

Again, twenty-five miles per hour would be 25 X 25 = 625; and this multiplied by .005 equals 2 pounds pressure.

CONVERTING HOURS INTO MINUTES.—It is sometimes confusing to think of miles per hour, when you wish to express it in minutes or seconds. A simple rule, which is not absolutely accurate, but is correct within a few feet, in order to express the speed in feet per minute, is to multiply the figure indicating the miles per hour, by 8 3/4.

To illustrate: If the wind is moving at the rate of twenty miles an hour, it will travel in that time 105,600 feet (5280 X 20). As there are sixty minutes in an hour, 105,600 divided by 60, equals 1760 feet per minute. Instead of going through all this process of calculating the speed per minute, remember to multiply the speed in miles per hour by 90, which will give 1800 feet.

This is a little more then two per cent. above the correct figure. Again; 40 X 90 equals 3600. As the correct figure is 3520, a little mental calculation will enable you to correct the figures so as to get it within a few feet.

CHANGING SPEED HOURS TO SECONDS.—As one- sixtieth of the speed per minute will represent the rate of movement per second, it is a comparatively easy matter to convert the time from speed in miles per hour to fraction of a mile traveled in a second, by merely taking one-half of the speed in miles, and adding it, which will very nearly express the true number of feet.

As examples, take the following: If the wind is traveling 20 miles an hour, it is easy to take one-half of 20, which is 10, and add it to 20, making 30, as the number of feet per second. If the wind travels 50 miles per hour, add 25, making 75, as the speed per second.

The correct speed per second of a wind traveling 20 miles an hour is a little over 29 feet. At 50 miles per hour, the correct figure is 73 1/3 feet, which show that the figures under this rule are within about one per cent. of being correct.

With the table before you it will be an easy matter, by observing the air pressure indicator, to determine the proper speed for the anemometer. Suppose it shows a pressure of two pounds, which will indicate a speed of twenty miles an hour. You have thus a fixed point to start from.

PRESSURE AS THE SQUARE OF THE SPEED.—Now it must not be assumed that if the pressure at twenty miles an hour is two pounds, that forty miles an hour it is four pounds. The pressure is as the square of the speed. This may be explained as follows: As the speed of the wind increases, it has a more effective push against an object than its rate of speed indicates, and this is most simply expressed by saying that each time the speed is doubled the pressure is four times greater.

As an example of this, let us take a speed of ten miles an hour, which means a pressure of one- half pound. Double this speed, and we have 20 miles. Multiplying one-half pound by 4, the result is 2 pounds. Again, double 20, which means 40 miles, and multiplying 2 by 4, the result is 8. Doubling forty is eighty miles an hour, and again multiplying 8 by 4, we have 32 as the pounds pressure at a speed of 80 miles an hour.

The anemometer, however, is constant in its speed. If the pointer should turn once a second at 10 miles an hour, it would turn twice at 20 miles an hour, and four times a second at 40 miles an hour.

GYROSCOPIC BALANCE.—Some advance has been made in the use of the gyroscope for the purpose of giving lateral stability to an aeroplane. While the best of such devices is at best a makeshift, it is well to understand the principle on which they operate, and to get an understanding how they are applied.

THE PRINCIPLE INVOLVED.—The only thing known about the gyroscope is, that it objects to changing the plane of its rotation. This statement must be taken with some allowance, however, as, when left free to move, it will change in one direction.

To explain this without being too technical, examine Fig. 63, which shows a gyroscopic top, one end of the rim A, which supports the rotating wheel B, having a projecting finger C, that is mounted on a pin-point on the upper end of the pedestal D.

Fig. 63. The Gyroscope.

When the wheel B is set in rotation it will maintain itself so that its axis E is horizontal, or at any other angle that the top is placed in when the wheel is spun. If it is set so the axis is horizontal the wheel B will rotate on a vertical plane, and it forcibly objects to any attempt to make it turn except in the direction indicated by the curved arrows F.

The wheel B will cause the axis E to swing around on a horizontal plane, and this turning movement is always in a certain direction in relation to the turn of the wheel B, and it is obvious, therefore, that to make a gyroscope that will not move, or swing around an axis, the placing of two such wheels side by side, and rotated in opposite directions, will maintain them in a fixed position; this can also be accomplished by so mounting the two that one rotates on a plane at right angles to the other.

Fig. 64. Application of the Gyroscope.

THE APPLICATION OF THE GYROSCOPE.—Without in any manner showing the structural details of the device, in its application to a flying machine, except in so far as it may be necessary to explain its operation, we refer to Fig. 64, which assumes that A represents the frame of the aeroplane, and B a frame for holding the gyroscopic wheel C, the latter being mounted so it rotates on a horizontal plane, and the frame B being hinged fore and aft, so that it is free to swing to the right or to the left.

For convenience in explaining the action, the planes E are placed at right angles to their regular positions, F being the forward margin of the plane, and G the rear edge. Wires H connect the ends of the frame B with the respective planes, or ailerons, E, and another wire I joins the downwardly-projecting arms of the two ailerons, so that motion is transmitted to both at the same time, and by a positive motion in either direction.

Fig. 65. Action of the Gyroscope.

In the second figure, 65, the frame of the aeroplane is shown tilted at an angle, so that its right side is elevated. As the gyroscopic wheel remains level it causes the aileron on the right side to change to a negative angle, while at the same time giving a positive angle to the aileron on the left side, which would, as a result, depress the right side, and bring the frame of the machine back to a horizontal position.

FORE AND AFT GYROSCOPIC CONTROL.—It is obvious that the same application of this force may be applied to control the ship fore and aft, although it is doubtful whether such a plan would have any advantages, since this should be wholly within the control of the pilot.

Laterally the ship should not be out of balance; fore and aft this is a necessity, and as the great trouble with all aeroplanes is to control them laterally, it may well be doubted whether it would add anything of value to the machine by having an automatic fore and aft control, which might, in emergencies, counteract the personal control of the operator.

ANGLE INDICATOR.—In flight it is an exceedingly difficult matter for the pilot to give an accurate idea of the angle of the planes. If the air is calm and he is moving over a certain course, and knows, from experience, what his speed is, he may be able to judge of this factor, but he cannot tell what changes take place under certain conditions during the flight.

For this purpose a simple little indicator may be provided, shown in Fig. 66, which is merely a vertical board A, with a pendulum B, swinging fore and aft from a pin a which projects out from the board a short distance above its center.

The upper end of the pendulum has a heart- shaped wire structure D, that carries a sliding weight E. Normally, when the aeroplane is on an even keel, or is even at an angle, the weight E rests within the bottom of the loop D, but should there be a sudden downward lurch or a quick upward inclination, which would cause the pendulum below to rapidly swing in either direction, the sliding weight E would at once move forward in the same direction that the pendulum had moved, and thus counteract, for the instant only, the swing, when it would again drop back into its central position.

Fig. 66. Angle Indicator.

With such an arrangement, the pendulum would hang vertically at all times, and the pointer below, being in range of a circle with degrees indicated thereon, and the base attached to the frame of the machine, can always be observed, and the conditions noted at the time the changes take place.

PENDULUM STABILIZER.—In many respects the use of a pendulum has advantages over the gyroscope. The latter requires power to keep it in motion. The pendulum is always in condition for service. While it may be more difficult to adjust the pendulum, so that it does not affect the planes by too rapid a swing, or an oscillation which is beyond the true angle desired, still, these are matters which, in time, will make the pendulum a strong factor in lateral stability.

Fig. 67. Simple Pendulum Stabilizer.

It is an exceedingly simple matter to attach the lead wires from an aileron to the pendulum. In Fig. 67 one plan is illustrated. The pendulum A swings from the frame B of the machine, the ailerons a being in this case also shown at right angles to their true positions.

The other, Fig. 68, assumes that the machine is exactly horizontal, and as the pendulum is in a vertical position, the forward edges of both ailerons are elevated, but when the pendulum swings both ailerons will be swung with their forward margins up or down in unison, and thus the proper angles are made to right the machine.

STEERING AND CONTROLLING WHEEL.—For the purpose of concentrating the control in a single wheel, which has not alone a turning motion, but is also mounted in such a manner that it will oscillate to and fro, is very desirable, and is adapted for any kind of machine.

Fig. 68. Pendulum Stabilizers.

Fig. 69 shows such a structure, in which A represents the frame of the machine, and B a segment for the stem of the wheel, the segment being made of two parts, so as to form a guideway for the stem a to travel between, and the segment is placed so that the stem will travel in a fore and aft direction.

The lower end of the stem is mounted in a socket, at D, so that while it may be turned, it will also permit this oscillating motion. Near its lower end is a cross bar E from which the wires run to the vertical control plane, and also to the ailerons, if the machine is equipped with them, or to the warping ends of the planes.

Fig. 69. Steering and Control Wheel.

Above the cross arms is a loose collar F to which the fore and aft cords are attached that go to the elevators, or horizontal planes. The upper end of the stem has a wheel G, which may also be equipped with the throttle and spark levers.

AUTOMATIC STABILIZING WINGS.—Unquestionably, the best stabilizer is one which will act on its own initiative. The difficulty with automatic devices is, that they act too late, as a general thing, to be effective. The device represented in Fig. 70 is very simple, and in practice is found to be most efficient.

In this Fig. 70 A and B represent the upper and the lower planes, respectively. Near the end vertical standards a, D, are narrow wings E E, F F, hinged on a fore and aft line close below each of the planes, the wings being at such distances from the standards C D that when they swing outwardly they will touch the standards, and when in that position will be at an angle of about 35 degrees from the planes A B.

Fig. 70. Automatic Stabilizing Wings.

Fig. 71. Action of Stabilizing Wings.

Inwardly they are permitted to swing up and lie parallel with the planes, as shown in Fig. 71 where the planes are at an angle. In turning, all machines skid,—that is they travel obliquely across the field, and this is also true when the ship is sailing at right angles to the course of the wind.

This will be made clear by reference to Fig. 72, in which the dart A represents the direction of the movement of the aeroplane, and B the direction of the wind, the vertical rudder a being almost at right angles to the course of the wind.

Fig. 72. Into the Wind at an Angle.

In turning a circle the same thing takes place as shown in Fig. 73, with the tail at a different angle, so as to give a turning movement to the plane. It will be seen that in the circling movement the tendency of the aeroplane is to fly out at a tangent, shown by the line D, so that the planes of the machine are not radially-disposed with reference to the center of the circle, the line E showing the true radial line.

Referring now to Fig. 71, it will be seen that this skidding motion of the machine swings the wings E F inwardly, so that they offer no resistance to the oblique movement, but the wings E E, at the other end of the planes are swung outwardly, to provide an angle, which tends to raise up the inner end of the planes, and thereby seek to keep the planes horizontal.

Fig. 73. Turning a Circle.

BAROMETERS.—These instruments are used for registering heights. A barometer is a device for measuring the weight or pressure of the air. The air is supposed to extend to a height of 40 miles from the surface of the sea. A column of air one inch square, and forty miles high, weighs the same as a column of mercury one inch square and 30 inches high.

Such a column of air, or of mercury, weighs 14 3/4 pounds. If the air column should be weighed at the top of the mountain, that part above would weigh less than if measured at the sea level, hence, as we ascend or descend the pressure becomes less or more, dependent on the altitude.

Mercury is also used to indicate temperature, but this is brought about by the expansive quality of the mercury, and not by its weight.

Fig. 74. Aneroid Barometer.

ANEROID BAROMETER.—The term Aneroid barometer is frequently used in connection with air- ship experiments. The word aneroid means not wet, or not a fluid, like mercury, so that, while aneroid barometers are being made which do use mercury, they are generally made without.

One such form is illustrated in Fig. 74, which represents a cylindrical shell A, which has at each end a head of concentrically formed corrugations. These heads are securely fixed to the ends of the shell A. Within, one of the disk heads has a short stem C, which is attached to the short end of a lever D, this lever being pivoted at E. The outer end of this lever is hinged to the short end of another lever F, and so by compounding the levers, it will be seen that a very slight movement of the head B will cause a considerable movement in the long end of the lever F.

This end of the lever F connects with one limb of a bell-crank lever G, and its other limb has a toothed rack connection with a gear H, which turns the shaft to which the pointer I is attached.

Air is withdrawn from the interior of the shell, so that any change in the pressure, or weight of the atmosphere, is at once felt by the disk heads, and the finger turns to indicate the amount of pressure.

HYDROPLANES.—Hydro means water, hence the term hydroplane has been given to machines which have suitable pontoons or boats, so they may alight or initiate flight from water.

There is no particular form which has been adopted to attach to aeroplanes, the object generally being to so make them that they will sustain the greatest amount of weight with the least submergence, and also offer the least resistance while the motor is drawing the machine along the surface of the water, preparatory to launching it.

SUSTAINING WEIGHT OF PONTOONS.—A pontoon having within nothing but air, is merely a measuring device which determines the difference between the weight of water and the amount placed on the pontoon. Water weighs 62 1/2 pounds per cubic foot. Ordinary wood, an average of 32 pounds, and steel 500 pounds.

It is, therefore, an easy matter to determine how much of solid matter will be sustained by a pontoon of a given size, or what the dimensions of a pontoon should be to hold up an aeroplane which weighs, with the pilot, say, 1100 pounds.

As we must calculate for a sufficient excess to prevent the pontoons from being too much immersed, and also allow a sufficient difference in weight so that they will keep on the surface when the aeroplane strikes the surface in alighting, we will take the figure of 1500 pounds to make the calculations from.

If this figure is divided by 62 1/2 we shall find the cubical contents of the pontoons, not considering, of course, the weight of the material of which they are composed. This calculation shows that we must have 24 cubic feet in the pontoons.