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5. CHAPTER V
DIFFERENT MACHINE TYPES AND THEIR CHARACTERISTICS

THERE are three distinct types of heavier-than-air machines, which are widely separated in all their characteristics, so that there is scarcely a single feature in common.

Two of them, the aeroplane, and the orthopter, have prototypes in nature, and are distinguished by their respective similarities to the soaring birds, and those with flapping wings.

The Helicopter, on the other hand, has no antecedent type, but is dependent for its raising powers on the pull of a propeller, or a plurality of them, constructed, as will be pointed out hereinafter.

AEROPLANES.—The only form which has met with any success is the aeroplane, which, in practice, is made in two distinct forms, one with a single set of supporting planes, in imitation of birds, and called a monoplane; and the other having two wings, one above the other, and called the bi-plane, or two-planes.

All machines now on the market which do not depend on wing oscillations come under those types.

THE MONOPLANE.—The single plane type has some strong claims for support. First of these is the comparatively small head resistance, due to the entire absence of vertical supporting posts, which latter are necessary with the biplane type. The bracing supports which hold the outer ends of the planes are composed of wires, which offer but little resistance, comparatively, in flight.

ITS ADVANTAGES.—Then the vertical height of the machine is much less than in the biplane. As a result the weight, which is farther below the supporting surface than in the biplane, aids in maintaining the lateral stability, particularly since the supporting frame is higher.

Usually, for the same wing spread, the monoplane is narrower, laterally, which is a further aid to prevent tilting.

ITS DISADVANTAGES.—But it also has disadvantages which must be apparent from its structure. As all the supporting surface is concentrated in half the number of planes, they must be made of greater width fore and aft, and this, as we shall see, later on, proves to be a disadvantage.

It is also doubted whether the monoplane can

be made as strong structurally as the other form, owing to the lack of the truss formation which is the strong point with the superposed frame. A truss is a form of construction where braces can be used from one member to the next, so as to brace and stiffen the whole.

THE BIPLANE.—Nature does not furnish a type of creature which has superposed wings. In this particular the inventor surely did not follow nature. The reasons which led man to employ this type may be summarized as follows:

In experimenting with planes it is found that a broad fore and aft surface will not lift as much as a narrow plane. This subject is fully explained in the chapter on The Lifting Surfaces of Planes. In view of that the technical descriptions of the operation will not be touched upon at this place, except so far as it may be necessary to set forth the present subject.

This peculiarity is due to the accumulation of a mass of moving air at the rear end of the plane, which detracts from its lifting power. As it would be a point of structural weakness to make the wings narrow and very long, Wenham many years ago suggested the idea of placing one plane above the other, and later on Chanute, an engineer, used that form almost exclusively, in experimenting with his gliders.

It was due to his influence that the Wrights adopted that form in their gliding experiments, and later on constructed their successful flyers in that manner. Originally the monoplane was the type generally employed by experimenters, such as Lilienthal, and others.

STABILITY IN BIPLANES.—Biplanes are not naturally as stable laterally as the monoplane. The reason is, that a downward tilt has the benefit of only a narrow surface, comparable with the monoplane, which has broadness of wing.

To illustrate this, let us assume that we have a biplane with planes five feet from front to rear, and thirty-six feet in length. This would give two planes with a sustaining surface of 360 square feet. The monoplane would, probably, divide this area into one plane eight and a half feet from front to rear, and 42 feet in length.

In the monoplane each wing would project out about three feet more on each side, but it would have eight and a half feet fore and aft spread to the biplane's five feet, and thus act as a greater support.

THE ORTHOPTER.—The term orthopter, or ornithopter, meaning bird wing, is applied to such flying machines as depend on wing motion to support them in the air.

Unquestionably, a support can be obtained by

beating on the air but to do so it is necessary to adopt the principle employed by nature to secure an upward propulsion. As pointed out elsewhere, it cannot be the concaved type of wing, or its shape, or relative size to the weight it must carry.

As nature has furnished such a variety of data on these points, all varying to such a remarkable degree, we must look elsewhere to find the secret. Only one other direction offers any opportunity, and that is in the individual wing movement.

NATURE'S TYPE NOT UNIFORM.—When this is examined, the same obscurity surrounds the issue. Even the speeds vary to such an extent that when it is tried to differentiate them, in comparison with form, shape, and construction, the experimenter finds himself wrapt in doubt and perplexity.

But birds do fly, notwithstanding this wonderful array of contradictory exhibitions. Observation has not enabled us to learn why these things are so. High authorities, and men who are expert aviators, tell us that the bird flies because it is able to pick out ascending air currents.

THEORIES ABOUT FLIGHT OF BIRDS.—Then we are offered the theory that the bird has an instinct which tells it just how to balance in the air when its wings are once set in motion. Frequently,

what is taken for instinct, is something entirely different.

It has been assumed, for instance, that a cyclist making a turn at a rapid speed, and a bird flying around a circle will throw the upper part of the body inwardly to counteract the centrifugal force which tends to throw it outwardly.

Experiments with the monorail car, which is equipped with a gyroscope to hold it in a vertical position, show that when the car approaches a curve the car will lean inwardly, exactly the same as a bird, or a cyclist, and when a straight stretch is reached, it will again straighten up.

INSTINCT.—Now, either the car, so equipped possesses instinct, or there must be a principle in the laws of nature which produces the similarity of action.

In like manner there must be some principle that is entirely independent of the form of matter, or its arrangement, which enables the bird to perform its evolutions. We are led to believe from all the foregoing considerations that it is the manner or the form of the motion.

MODE OF MOTION.—In this respect it seems to be comparable in every respect to the great and universal law of the motions in the universe. Thus, light, heat and electricity are the same, the

manifestations being unlike only because they have different modes of motion.

Everything in nature manifests itself by motion. It is the only way in which nature acts. Every transformation from one thing to another, is by way of a movement which is characteristic in itself.

Why, then, should this great mystery of nature, act unlike the other portions of which it is a part?

THE WING STRUCTURE.—The wing structure of every flying creature that man has examined, has one universal point of similarity, and that is the manner of its connection with the body. It is a sort of universal joint, which permits the wing to swing up and down, perform a gyratory movement while doing so, and folds to the rear when at rest.

Some have these movements in a greater or less degree, or capable of a greater range; but the joint is the same, with scarcely an exception. When the stroke of the wing is downwardly the rear margin is higher than the front edge, so that the downward beat not only raises the body upwardly, but also propels it forwardly.

THE WING MOVEMENT.—The moment the wing starts to swing upwardly the rear end is depressed,

and now, as the bird is moving forwardly, the wing surface has a positive angle of incidence, and as the wing rises while the forward motion is taking place, there is no resistance which is effective enough to counteract the momentum which has been set up.

The great problem is to put this motion into a mechanical form. The trouble is not ascribable to the inability of the mechanic to describe this movement. It is an exceedingly simple one. The first difficulty is in the material that must be used. Lightness and strength for the wing itself are the first requirements. Then rigidity in the joint and in the main rib of the wing, are the next considerations.

In these respects the ability of man is limited. The wing ligatures of flying creatures is exceedingly strong, and flexible; the hollow bone formation and the feathers are extremely light, compared with their sustaining powers.

THE HELICOPTER MOTION.—The helicopter, or helix-wing, is a form of flying machine which depends on revolving screws to maintain it in the air. Many propellers are now made, six feet in length, which have a pull of from 400 to 500 pounds. If these are placed on vertically-disposed shafts they would exert a like power to raise a machine from the earth.

Obviously, it is difficult to equip such a machine with planes for sustaining it in flight, after it is once in the air, and unless such means are provided the propellers themselves must be the mechanism to propel it horizontally.

This means a change of direction of the shafts which support the propellers, and the construction is necessarily more complicated than if they were held within non-changeable bearings.

This principle, however, affords a safer means of navigating than the orthopter type, because the blades of such an instrument can be forced through the air with infinitely greater speed than beating wings, and it devolves on the inventor to devise some form of apparatus which will permit the change of pull from a vertical to a horizontal direction while in flight.