How It Flies; or, The Conquest of the Air. Richard Ferris
Renard and Krebs airship La France, at Chalais-Meudon.
Nor has the influence of the gasoline motor been much less upon that other great class of aircraft, the dirigible balloon. After 1885, when Renard and Krebs’ airship La France made its two historic voyages from Chalais-Meudon to Paris, returning safely to its shed, under the propulsion of an electric motor, the problem of the great airship lay dormant, waiting for the discovery of adequate motive power. If the development of the dirigible balloon seems less spectacular than that of the aeroplane, it is because the latter had to be created; the dirigible, already in existence, had only to be revivified.
Confronted with these new and strange shapes in the sky, some making stately journeys of hundreds of miles, others whirring hither and thither with the speed of the whirlwind, wonder quickly gives way to the all-absorbing question: How do they fly? To answer fully and satisfactorily, it seems wise, for many readers, to recall in the succeeding chapters some principles doubtless long since forgotten.
As with every great advance in civilization, this expansion of the science of aeronautics has had its effect upon the language of the day. Terms formerly in use have become restricted in application, and other terms have been coined to convey ideas so entirely new as to find no suitable word existent in our language. It seems requisite, therefore, first to acquaint the reader with clear definitions of the more common terms that are used throughout this book.
Aeronautics is the word employed to designate the entire subject of aerial navigation. An aeronaut is a person who sails, or commands, any form of aircraft, as distinguished from a passenger.
Aviation is limited to the subject of flying by machines which are not floated in the air by gas. An aviator is an operator of such machine.
A free balloon, with parachute.
Both aviators and aeronauts are often called pilots.
A balloon is essentially an envelope or bag filled with some gaseous substance which is lighter, bulk for bulk, than the air at the surface of the earth, and which serves to float the apparatus in the air. In its usual form it is spherical, with a car or basket suspended below it. It is a captive balloon if it is attached to the ground by a cable, so that it may not rise above a certain level, nor float away in the wind. It is a free balloon if not so attached or anchored, but is allowed to drift where the wind may carry it, rising and falling at the will of the pilot.
A dirigible balloon.
A dirigible balloon, sometimes termed simply a dirigible, usually has its gas envelope elongated in form. It is fitted with motive power to propel it, and steering mechanism to guide it. It is distinctively the airship.
Aeroplanes are those forms of flying machines which depend for their support in the air upon the spread of surfaces which are variously called wings, sails, or planes. They are commonly driven by propellers actuated by motors. When not driven by power they are called gliders.
A biplane glider.
Aeroplanes exist in several types: the monoplane, with one spread of surface; the biplane, with two spreads, one above the other; the triplane, with three spreads, or decks; the multiplane, with more than three.
The tetrahedral plane is a structure of many small cells set one upon another.
Ornithopter is the name given to a flying machine which is operated by flapping wings.
A parachute descending.
Helicopter is used to designate machines which are lifted vertically and sustained in the air by propellers revolving in a horizontal plane, as distinguished from the propellers of the aeroplane, which revolve in vertical planes.
A parachute is an umbrella-like contrivance by which an aeronaut may descend gently from a balloon in mid-air, buoyed up by the compression of the air under the umbrella.
For the definition of other and more technical terms the reader is referred to the carefully prepared Glossary toward the end of the book.
Chapter II.
THE AIR.
Intangibility of air—Its substance—Weight—Extent—Density—Expansion by heat—Alcohol fire—Turbulence of the air—Inertia—Elasticity—Viscosity—Velocity of winds—Aircurrents—Cloud levels—Aerological stations—High altitudes—Practical suggestions—The ideal highway.
The air about us seems the nearest approach to nothingness that we know of. A pail is commonly said to be empty—to have nothing in it—when it is filled only with air. This is because our senses do not give us any information about air. We cannot see it, hear it, touch it.
When air is in motion (wind) we hear the noises it makes as it passes among other objects more substantial; and we feel it as it blows by us, or when we move rapidly through it.
We get some idea that it exists as a substance when we see dead leaves caught up in it and whirled about; and, more impressively, when in the violence of the hurricane it seizes upon a body of great size and weight, like the roof of a house, and whisks it away as though it were a feather, at a speed exceeding that of the fastest railroad train.
In a milder form, this invisible and intangible air does some of our work for us in at least two ways that are conspicuous: it moves ships upon the ocean, and it turns a multitude of windmills, supplying the cheapest power known.
That this atmosphere is really a fluid ocean, having a definite substance, and in some respects resembling the liquid ocean upon which our ships sail, and that we are only crawling around on the bottom of it, as it were, is a conception we do not readily grasp. Yet this conception must be the foundation of every effort to sail, to fly, in this aerial ocean, if such efforts are to be crowned with success.
As a material substance the air has certain physical properties, and it is the part of wisdom for the man who would fly to acquaint himself with these properties. If they are helpful to his flight, he wants to use them; if they hinder, he must contrive to overcome them.
In general, it may be said that the air, being in a gaseous form, partakes of the properties of all gases—and these may be studied in any text-book on physics, Here we are concerned only with those qualities which affect conditions under which we strive to fly.
Of first importance is the fact that air has weight. That is, in common with all other substances, it is attracted by the mass of the earth exerted through the force we call gravity. At the level of the sea, this attraction causes the air to press upon the earth with a weight of nearly fifteen pounds (accurately, 14.7 lbs.) to the square inch, when the temperature is at 32° F. That pressure is the weight of a column of air one inch square at the base, extending upward to the outer limit of the atmosphere—estimated to be about 38 miles (some say 100 miles) above sea-level. The practical fact is that normal human life cannot exist above the level of 15,000 feet, or a little less than three miles; and navigation of the air will doubtless be carried on at a much lower altitude, for reasons which will appear as we continue.
The actual weight of a definite quantity of dry air—for instance, a cubic foot—is found by weighing a vessel first when full of air, and again after the air has been exhausted from it with an air-pump. In this way it has been determined that a cubic foot of dry air, at the level of the sea,