Lecture on Artificial Flight Part 2

XIV.--SURFACE.

The next of the three properties necessary for flight, is the extension of the locomotive organs in winged beings--the planes. Although the wings in the different animals differ much in their form, texture, construction, number, and the matter which composes them, yet they resemble one another in the expansion and development of their surfaces, being stretched on each side of the body, and playing the part of a parachute. The animal, therefore, cannot fall like a stone, in obedience to the accelerated force of gravity, but it descends with a slow velocity; constant regular, and considerably abated.

This influence, then, exercised by the flat surface on the fall of ma.s.ses, is seen in a sheet of paper of the same weight as a grain of lead, it will fall much more slowly. But if we make the paper a compact ball, and flatten the lead into a broad, thin sheet, the reverse result will be produced, and the paper reach the ground before the lead.

Therefore, bodies in the air are light or heavy in proportion to their surfaces, and the heaviest may become light by an alteration of form.

For successful flight, then, a just proportion of surface and weight is necessary; because, as stated, the air being elastic, its resistance is much more effectual with light bodies than heavy ones; and this proportion is such that the extent of surface is always in an inverse ratio to the weight of the winged animal.

The principle in the fall of flat surfaces is strictly applicable to the bird. Its weight, tending downwards, and being situated below the plain of suspension, keeps it well balanced, so that it cannot fall head over heels, nor rapidly. If the wings are inclined at an angle with the horizon, the bird will not descend vertically, but glide along an inclined plane with much greater swiftness, because the vertical distance remains unaltered in the same s.p.a.ce of time. Hence their immense horizontal velocity, without comparatively any effort. This is in obedience to two forces--gravity, or weight, and resistance of surface.

XV.--POWER.

But for actual flight a third force is required--the propelling power, the necessary amount of which has greatly been overrated by many mathematicians.

Borelli estimated the power of a three pound bird to be over one hundred and thirty horses relatively. But, Navier, more reasonably, calculated a force of five horses sufficient for the flight of a pigeon. Coulomb, again, offset this "great liberality" by demonstrating that the surface to support a man must be two miles long and two hundred feet wide, with the power of a "Corliss engine" to propel such a "fifty acre ranch."

Now, facts prove that man can, without danger, descend from an high elevation under a surface of much less than fifteen feet diameter; and the force to lift himself, as will be shown hereafter, is also comparatively small. He can walk up stairs, and likewise mount upon air, which, properly manipulated, becomes sufficiently solid.

It has been demonstrated beyond a doubt, that the heaviest flying animals require the smallest amount of surface and power in proportion.

The surface is less, because the resistance of the atmosphere is much greater toward one unbroken body than all the parts thereof if detached.

Hence a stork, weighing eight times as much as a pigeon, needs only five square feet of surface, while the eight pigeons, with nearly one square foot each, possess together over seven square feet; and the common fly, if magnified to the size of the crane, would show a surface sixty times as large.

The heaviest flyers require the least amount of power, because weight, as stated before, itself is power, which increases in a certain ratio.

Hence we find the muscular force of the smaller beings, who possess little weight, to be enormous; this is particularly so with insects, who are the strongest in creation. A stag-beetle, of which two hundred weigh only one pound, can lift fourteen ounces; crickets leap eighty times their own length, and the "lively flea" can jump through s.p.a.ce estimated at even two hundred times the length of its body--which accounts for the difficulty of catching it. If a mouse would simply reproduce the gait of a horse, its progress would be about twenty inches per minute only, and cats would soon find themselves out of employment.

Nature has wisely established a compensation to make amends for the diminutiveness of organs by rapidity of movement, and has, consequently, furnished the animal with the necessary power to produce this rapidity.

The force necessary for lifting in all winged beings is not near so great as is generally supposed. The fall of a body, continually accelerating, is seventeen feet per second, and a very great force would be necessary indeed to offset this gravitation, if that second were allowed to expire without a counter-movement; but when that body is provided with a parachute-like arrangement, there is no such rapid fall of seventeen feet per second; and when, besides, the force is applied constantly, thereby counteracting even a fraction of the fall, the power needed to accomplish this is but a trifle; it is the principle, to use a homely phrase, that "a st.i.tch in time saves nine." What extra strength the animal possesses has to be used in pursuit or escape, from the powerful eagle to the minutest insect; they must be prepared to exert at a given moment all the strength that nature has given to them in store.

Their strength is no greater than that of fishes or quadrupeds; all possess surplus power greatly above the need of their average use, and the strength exhibited therefore by flying creatures shows only that but a small portion of it is used for lifting and propelling purposes.

Eagles have been known to carry off small deer, lambs, hares, and even young children. Many of the fishing birds, as pelicans and herons, can likewise carry considerable loads, while the smaller birds are capable of transporting comparatively large twigs for building purposes. A swallow can traverse 1000 miles at a single journey, and the swift, the fastest of all, is known to have made nearly 180 miles an hour. The albatross, despising compa.s.s and land-mark, trusts himself boldly for weeks together to the mercy or fury of the mighty ocean; and the huge condor of the Andes, as Humboldt, Darwin, Orton, and others inform us, lifts himself to a hight where no sound is heard, and from an unseen point surveys, in solitary grandeur, the wide range of plain and mountain below. He has been seen flying over the Chimborazo, and attains, on occasions, an alt.i.tude of six miles.

XVI.--FLYING CREATURES, THEIR PROPORTIONS, MOVEMENTS.

The great common characteristic of the different winged beings are the same throughout all the modifications of detail. These are, as stated, weight, extension of surface, and the mechanical application of the propelling force; so that the animal is a gliding plane, part of which is fixed and the other moveable, and the whole being maintained in stable equilibrium by the weight of the body, placed a little below the plane of suspension.

By comparing the different species it is found, by M. de Lucy and others, that the extent of surface is in inverse ratio to the weight, the determination of this ratio being based upon certain considerations.

The proof of this is overwhelming. Supposing all flying creatures of the same weight, say one pound, it is found that the:

Gnat possesses 50 Common fly 22 Bee 5 Beetle 4 Sparrow 3 Pigeon 1-2/3 Stork nearly 1 Vulture 3/4 Crane nearly 1/2

Square feet of surface per pound.

Thus we find the gnat, of which 160,000 make one pound, and which weighs four hundred and sixty times less than the beetle, has thirteen times more surface, comparatively. The sparrow weighs about ten times less than the pigeon, and has twice as much surface in proportion. The Australian crane--one of the heaviest birds, it weighs over twenty pounds, or almost three million times as much as the gnat--possesses the least surface--not quite ten square feet, or one hundred and twenty times less than that insignificant but formidable animal. Yet its flight is, gliding softly on the air, without effort or fatigue, with but little exertion, the longest maintained, and it can, with few exceptions, elevate itself the highest.

In regard to the movements of the wings, there is a similar ratio; for, while the mosquito makes over two hundred wing strokes per second, the sparrow makes only thirteen, the buzzard three, and so on, continually decreasing with heavier bodies.

A word about bats and flying fish. Although bats present no real resemblance whatever to birds or insects, but are much more like ourselves, they must be cla.s.sed amongst the creatures of the air, because they are constantly moving in it, and governed by the same laws.

Their flight, being somewhat fluttering, but otherwise powerful, true and perfect, is undoubtedly caused, particularly in the early part of the night, when feeding, by their darting right and left after the almost invisible numerous insects, which they devour at once.

The wing of the bat is, like that of the bird, concavo-convex, and also more or less twisted upon itself, but it differs in so far that its arm is not covered with feathers, but a very delicate membrane, which forms the parachute-like wing.

Their nocturnal, and therefore disreputable habits, with our dislike for the blood-sucking propensity of a large specie, the vampire, has kept our interest in these otherwise harmless and clean creatures at rather freezing point. But they can be tamed easily, and are capable of giving considerable pleasure.

The flight of a shoal of flying-fish as they shoot forth from the dark green wave in a glittering throng, gleaming brightly in the sunshine, is a charming sight. But these fish can scarcely be cla.s.sed with the creatures of the air, because true flight, that is the manipulation of the wings, is lacking. They are mentioned because they represent, like the kite, the first step toward that true flight which all other creatures in the air possess.

They are capable of moving through the air from 500 to 600 feet, and as much as 20 feet above the water. The fish first acquires initial velocity by a preliminary rush through the water, when it throws itself suddenly into the air, and, at the same moment, spreads out, kite-like, at a slight inclination upwards, its extraordinarily large pectoral fins. It keeps up the great speed until its momentum is exhausted, when the same performance is repeated.

The fact in favor of mechanical flight is certainly incontrovertible that less surface and less power is required and flight maintained the longest, in proportion to heavier bodies.

It must be convincing, therefore, that it is possible for man to apply the laws of flight to industrial purposes in the same manner as he has been able, in these days, to apply all the other grand physical laws that he has taken the trouble to study and fathom. The law of surface and force reigns in the most absolute and exact manner over all flying animals. It does not stop here. Nature, whose laws are general and universal, has not created this one only for the restricted compa.s.s of the winged animate beings. The law which sustains on the water the leaf and the straw is the same for the gigantic Great Eastern; and the mechanical law of the forces which drives the wheelbarrow also conducts on its iron line the locomotive and its endless train.

XVII.--MECHANICAL PRACTICABILITY OF ARTIFICIAL FLIGHT.

Living beings have been, in every age, compared to machines, but it is only in the present day that the bearing and justice of this comparison are fully comprehensible. Modern engineers have created machines which execute more difficult and various operations than animate beings are capable of; yet it is always from nature first that man has to draw his inspirations.

Of the different functions of animal mechanism, that of locomotion is certainly one of the most important and interesting; and as we have brought this art on land and water, by successfully imitating the natural movements of walking and swimming, to quite a high state of perfection, the next great problem, equally possible, because flight is a natural movement, remains to be solved.

Of course, as different as the wheel of the locomotive is from the limb of the quadruped, and the screw of a steamship from the fin of a fish, so will the coming flying machine differ from the construction of bird, bat or insect.

Walking, swimming and flying are modifications of, and merging into, each other by insensible gradations; and the modifications, resulting therefrom, are necessitated by the amount of support afforded on, and in the different mediums--earth, water, air. Although flight is, indisputably, the finest of the different animal movements, yet it does not essentially differ from the other two, as the material and forces employed are literally the same as those in walking and swimming.

Flight is, therefore, a purely mechanical problem, and in compliance with the law of decrease, as stated before, the surface requisite to transport bodies in the air, is found to be about one-half, proportionately, to twelve times the weight.

Applying this observation to an apparatus of, say 200 [lb]s., we find that the surface of a bird of 18 [lb]s.--about one-twelfth of said 200 [lb]s.--to be 10 square feet; multiplying this by twelve, its weight, we have 120 square feet of surface, and of which one-half accordingly, 60 square feet, is enough for the support of 200 pounds. Such a machine, although possessing much less surface than parachutes generally do, is in the form of inclined planes of proper construction, fully sufficient for man to slide down safely through the air, without exertion, from an elevation at least ten times the vertical distance, that is, from the top of the Palace Hotel to the foot of Baldwin's.

As to the force required, although impossible to give datas, the law of decrease with greater weight reigns absolute here also. Man's muscular power for tolerably swift horizontal flight is far greater than necessary; and, with properly constructed contrivances, he will be able to travel, at an incline upwards of one in thirty, at least twenty miles an hour, by manual power alone. A carrier pigeon flies, for a short time, at the rate of one hundred miles an hour, and some birds much faster. But in employing any of the many excellent motive powers at command now, and with larger machines, we will be able to surpa.s.s the swiftest birds.

As for the objection, that the fury of the wind will hinder artificial flight, it is refuted by observing that even a hurricane, which, traveling over eighty miles an hour, occurs but rarely, does hardly prevent the flight of fast birds, and still less would that of a compact and solid flying machine, because of its greater weight and momentum.

And even if an occasional storm should be dangerous, the machine, by its greater swiftness, could be turned above, below or sideways, out of the path of destruction, or it need not travel at such rare times. Besides, the effect of the storm upon a body within its own medium is insignificant to what it is when that body offers resistance by being attached to another medium, as ships on the water, or houses and fences on land.