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 a.s.serted, 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 a.s.sumed the vertical, as in position 3, the tail is again reversed to a.s.sume 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 s.p.a.ce, 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 ill.u.s.trated by a.s.suming 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 a.s.sume 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 ill.u.s.tration that at high velocities supporting surfaces are not necessary.

Commercial uses require safety as the first element, and reliability as the next essential. For pa.s.senger service there must be an a.s.surance 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 ill.u.s.tration 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, j.a.pan, 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 pa.s.sing 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 s.e.xagonal 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._