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 ill.u.s.trated in Fig.

42. Each box, as A, B, has therein a plurality of vertical and horizontal part.i.tions, 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 ill.u.s.trated 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 p.r.o.nounced 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 a.s.sume 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 s.p.a.ce.

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 ill.u.s.trates the forces which act on the kite, and by means of which it adjusts its angle automatically.

Let us a.s.sume 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 a.s.sume 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 subst.i.tutes 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 antic.i.p.ates 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.