Aeroplanes - Zerbe
AEROPLANESBY J. S. ZERBE
NEW YORK, CUPPLES & LEON COMPANY, 1915,
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INTRODUCTORY
In preparing this volume on Flying Machines the aim has been to present the subject in such a manner as will appeal to boys, or beginners, in this field of human activity.
The art of aviation is in a most primitive state. So many curious theories have been brought out that, while they furnish food for thought, do not, in any way, advance or improve the structure of the machine itself, nor are they of any service in teaching the novice how to fly.
The author considers it of far more importance to teach right principles, and correct reasoning than to furnish complete diagrams of the details of a flying machine. The former teach the art, whereas the latter merely point out the mechanical arrangements, independently of the reasons for making the structures in that particular way.
Relating the history of an art, while it may be interesting reading, does not even lay the foundations of a knowledge of the subject, hence that field has been left to others.
The author knows from practical experience, while experimenting with and building aeroplanes, how eagerly every boy inquires into details. They want the reasons for things.
It is not the aim of the book to teach the art of flying, but rather to show how and why the present machines fly. The making and the using are separate and independent functions, and of the two the more important is the knowledge how to make a correct machine.
Hundreds of workmen may contribute to the building of a locomotive, but one man, not a builder, knows better how to handle it. To manipulate a flying machine is more difficult to navigate than such a ponderous machine, because it requires peculiar talents, and the building is still more important and complicated, and requires the exercise of a kind of skill not necessary in the locomotive.
The art is still very young; so much is done which arises from speculation and theories; too much dependence is placed on the aviator; the desire in the present condition of the art is to exploit the man and not the machine ; dare-devil exhibitions seem to be more important than perfecting the mechanism; and such useless attempts as flying upside down, looping the loop, and characteristic displays of that kind, are of no value to the art.
CONTENTS
- INTRODUCTORY
- THEORIES AND FACTS ABOUT FLYING
- PRINCIPLES OF AEROPLANE FLIGHT
- THE FORM OR SHAPE OF FLYING MACHINES
- FORE AND AFT CONTROL
- DIFFERENT MACHINE TYPES AND THEIR CHARACTERISTICS
- THE LIFTING SURFACES OF AEROPLANES
- ABNORMAL FLYING STUNTS AND SPEEDS
- KITES AND GLIDERS
- AEROPLANE CONSTRUCTION
- POWER AND ITS APPLICATION
- FLYING MACHINE ACCESSORIES
- EXPERIMENTAL WORK IN FLYING
- THE PROPELLER
- EXPERIMENTAL GLIDERS AND MODEL AEROPLANES
- THE AEROPLANE IN THE GREAT WAR
- GLOSSARY
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 here in after.
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.
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.
CHAPTER VI - THE LIFTING SUKFACES OF AEROPLANES
This subject includes the form, shape and angle of planes, used in flight. It is the direction in which most of the energy has been expended in developing machines, and the true form is still involved in doubt and uncertainty.
RELATIVE SPEED AND ANGLE. The relative speed and angle, and the camber, or the curved formation of the plane, have been considered in all their aspects, so that the art in this respect has advanced with rapid strides.
NARROW PLANES MOST EFFECTIVE. It was learned, in the early stages of the development by practical experiments, that a narrow plane, fore and aft, produces a greater lift than a wide one, so that, assuming the plane has 100 square feet of sustaining surface, it is far better to make the shape five feet by twenty than ten by ten.
However, it must be observed, that to use the narrow blade effectively, it must be projected through the air with the long margin forwardly.
Its sustaining power per square foot of surface is much less if forced through the air lengthwise. Experiments have shown why a narrow blade has proportionally a greater lift, and this may be more clearly understood by examining the illustrations which show the movement of planes through the air at appropriate angles.
STREAM LINES ALONG A PLANE. In Fig. 22, A is a flat plane, which we will assume is 10 feet from the front to the rear margin. For convenience seven stream lines of air are shown, which contact with this inclined surface. The first line, after the contact at the forward end,, is driven downwardly along the surface, so that it forms what we might term a moving film.
The second air stream 2, strikes the first stream, followed successively by the other streams, 3, 4, and so on, each succeeding stream being compelled to ride over, or along on the preceding mass of cushioned air, the last lines, near the lower end, being, therefore, at such angles, and contacting with such a rapidly-moving column, that it produces but little lift in comparison with the 1st, 2d and 3d stream lines. These stream lines are taken by imagining that the air approaches and contacts with the plane only along the lines indicated in the sketch, although they also in practice are active against every part of the plane.
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.
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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 here in after.
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.
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.
CHAPTER VI - THE LIFTING SUKFACES OF AEROPLANES
This subject includes the form, shape and angle of planes, used in flight. It is the direction in which most of the energy has been expended in developing machines, and the true form is still involved in doubt and uncertainty.
RELATIVE SPEED AND ANGLE. The relative speed and angle, and the camber, or the curved formation of the plane, have been considered in all their aspects, so that the art in this respect has advanced with rapid strides.
NARROW PLANES MOST EFFECTIVE. It was learned, in the early stages of the development by practical experiments, that a narrow plane, fore and aft, produces a greater lift than a wide one, so that, assuming the plane has 100 square feet of sustaining surface, it is far better to make the shape five feet by twenty than ten by ten.
However, it must be observed, that to use the narrow blade effectively, it must be projected through the air with the long margin forwardly.
Its sustaining power per square foot of surface is much less if forced through the air lengthwise. Experiments have shown why a narrow blade has proportionally a greater lift, and this may be more clearly understood by examining the illustrations which show the movement of planes through the air at appropriate angles.
STREAM LINES ALONG A PLANE. In Fig. 22, A is a flat plane, which we will assume is 10 feet from the front to the rear margin. For convenience seven stream lines of air are shown, which contact with this inclined surface. The first line, after the contact at the forward end,, is driven downwardly along the surface, so that it forms what we might term a moving film.
The second air stream 2, strikes the first stream, followed successively by the other streams, 3, 4, and so on, each succeeding stream being compelled to ride over, or along on the preceding mass of cushioned air, the last lines, near the lower end, being, therefore, at such angles, and contacting with such a rapidly-moving column, that it produces but little lift in comparison with the 1st, 2d and 3d stream lines. These stream lines are taken by imagining that the air approaches and contacts with the plane only along the lines indicated in the sketch, although they also in practice are active against every part of the plane.
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.
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