Spurred on by the success attained by the more experienced and better known aviators numerous inventors of lesser fame are almost daily producing practical flying machines varying radically in construction from those now in general use.
One of these comparatively new designs is the Van Anden biplane, made by Frank Van Anden of Islip, Long Island, a member of the New York Aeronautic Society. While his machine is wholly experimental, many successful short flights were made with it last fall (1909). One flight, made October 19th, 1909, is of particular interest as showing the practicability of an automatic stabilizing device installed by the inventor. The machine was caught in a sudden severe gust of wind and keeled over, but almost immediately righted itself, thus demonstrating in a most satisfactory manner the value of one new attachment.
Features of Van Anden Model.
In size the surfaces of the main biplane are 26 feet in spread, and 4 feet in depth from front to rear. The upper and lower planes are 4 feet apart. Silkolene coated with varnish is used for the coverings. Ribs (spruce) are curved one inch to the foot, the deepest part of the curve (4 inches) being one foot back from the front edge of the horizontal beam. Struts (also of spruce, as is all the framework) are elliptical in shape. The main beams are in three sections, nearly half round in form, and joined by metal sleeves.
There is a two-surface horizontal rudder, 2x2x4 feet, in front. This is pivoted at its lateral center 8 feet from the front edge of the main planes. In the rear is another two-surface horizontal rudder 2x2x2 1/2 feet, pivoted in the same manner as the front one, 15 feet from the rear edges of the main planes.
Hinged to the rear central strut of the rear rudder is a vertical rudder 2 feet high by 3 feet in length.
The Method of Control.
In the operation of these rudders—both front and rear—and the elevation and depression of the main planes, the Curtiss system is employed. Pushing the steering-wheel post outward depresses the front edges of the planes, and brings the machine downward; pulling the steering-wheel post inward elevates the front edges of the planes and causes the machine to ascend.
Turning the steering wheel itself to the right swings the tail rudder to the left, and the machine, obeying this like a boat, turns in the same direction as the wheel is turned. By like cause turning the wheel to the left turns the machine to the left.
Automatic Control of Wings.
There are two wing tips, each of 6 feet spread (length) and 2 feet from front to rear. These are hinged half way between the main surfaces to the two outermost rear struts. Cables run from these to an automatic device working with power from the engine, which automatically operates the tips with the tilting of the machine. Normally the wing tips are held horizontal by stiff springs introduced in the cables outside of the device.
It was the successful working of this device which righted the Van Anden craft when it was overturned in the squall of October 19th, 1909. Previous to that occurrence Mr. Van Anden had looked upon the device as purely experimental, and had admitted that he had grave uncertainty as to how it would operate in time of emergency. He is now quoted as being thoroughly satisfied with its practicability. It is this automatic device which gives the Van Anden machine at least one distinctively new feature.
While on this subject it will not be amiss to add that Mr. Curtiss does not look kindly on automatic control. "I would rather trust to my own action than that of a machine," he says. This is undoubtedly good logic so far as Mr. Curtiss is concerned, but all aviators are not so cool-headed and resourceful.
Motive Power of Van Anden.
A 50-horsepower "H-F" water cooled motor drives a laminated wood propeller 6 feet in diameter, with a 17 degree pitch at the extremities, increasing toward the hub. The rear end of the motor is about 6 inches back from the rear transverse beam and the engine shaft is in a direct line with the axes of the two horizontal rudders. An R. I. V. ball bearing carries the shaft at this point. Flying, the motor turns at about 800 revolutions per minute, delivering 180 pounds pull. A test of the motor running at 1,200 showed a pull of 250 pounds on the scales.
Still Another New Aeroplane.
Another new aeroplane is that produced by A. M. Herring (an old-timer) and W. S. Burgess, under the name of the Herring-Burgess. This is also equipped with an automatic stability device for maintaining the balance transversely. The curvature of the planes is also laid out on new lines. That this new plan is effective is evidenced by the fact that the machine has been elevated to an altitude of 40 feet by using one-half the power of the 30-horsepower motor.
The system of rudder and elevation control is very simple. The aviator sits in front of the lower plane, and extending his arms, grasps two supports which extend down diagonally in front. On the under side of these supports just beneath his fingers are the controls which operate the vertical rudder, in the rear. Thus, if he wishes to turn to the right, he presses the control under the fingers of his right hand; if to the left, that under the fingers of his left hand. The elevating rudder is operated by the aviator's right foot, the control being placed on a foot-rest.
Motor Is Extremely Light.
Not the least notable feature of the craft is its motor. Although developing, under load, 30-horsepower, or that of an ordinary automobile, it weighs, complete, hardly 100 pounds. Having occasion to move it a little distance for inspection, Mr. Burgess picked it up and walked off with it—cylinders, pistons, crankcase and all, even the magneto, being attached. There are not many 30-horsepower engines which can be so handled. Everything about it is reduced to its lowest terms of simplicity, and hence, of weight. A single camshaft operates not only all of the inlet and exhaust valves, but the magneto and gear water pump, as well. The motor is placed directly behind the operator, and the propeller is directly mounted on the crankshaft.
This weight of less than 100 pounds, it must be remembered, is not for the motor alone; it includes the entire power plant equipment.
The "thrust" of the propeller is also extraordinary, being between 250 and 260 pounds. The force of the wind displacement is strong enough to knock down a good-sized boy as one youngster ascertained when he got behind the propeller as it was being tested. He was not only knocked down but driven for some distance away from the machine. The propeller has four blades which are but little wider than a lath.
Machine Built by Students.
Students at the University of Pennsylvania, headed by Laurence J. Lesh, a protege of Octave Chanute, have constructed a practical aeroplane of ordinary maximum size, in which is incorporated many new ideas. The most unique of these is to be found in the steering gear, and the provision made for the accommodation of a pupil while taking lessons under an experienced aviator.
Immediately back of the aviator is an extra seat and an extra steering wheel which works in tandem style with the front wheel. By this arrangement a beginner may be easily and quickly taught to have perfect control of the machine. These tandem wheels are also handy for passengers who may wish to operate the car independently of one another, it being understood, of course, that there will be no conflict of action.
Frame Size and Engine Power.
The frame has 36 feet spread and measures 35 feet from the front edge to the end of the tail in the rear. It is equipped with two rear propellers operated by a Ramsey 8-cylinder motor of 50 horsepower, placed horizontally across the lower plane, with the crank shaft running clear through the engine.
The "Pennsylvania I" is the first two-propeller biplane chainless car, this scheme having been adopted in order to avoid the crossing of chains. The lateral control is by a new invention by Octave Chanute and Laurence J. Lesh, for which Lesh is now applying for a patent. The device was worked out before the Wright brothers' suit was begun, and is said to be superior to the Wright warping or the Curtiss ailerons. The landing device is also new in design. This aeroplane will weigh about 1,500 pounds, and will carry fuel for a flight of 150 miles, and it is expected to attain a speed of at least 45 miles an hour.
There are others, lots of them, too numerous in fact to admit of mention in a book of this size.
As a commercial proposition the manufacture and sale of motor-equipped aeroplanes is making much more rapid advance than at first obtained in the similar handling of the automobile. Great, and even phenomenal, as was the commercial development of the motor car, that of the flying machine is even greater. This is a startling statement, but it is fully warranted by the facts.
It is barely more than a year ago (1909) that attention was seriously attracted to the motor-equipped aeroplane as a vehicle possible of manipulation by others than professional aviators. Up to that time such actual flights as were made were almost exclusively with the sole purpose of demonstrating the practicability of the machine, and the merits of the ideas as to shape, engine power, etc., of the various producers.
Results of Bleriot's Daring.
It was not until Bleriot flew across the straits of Dover on July 25th, 1909, that the general public awoke to a full realization of the fact that it was possible for others than professional aviators to indulge in aviation. Bleriot's feat was accepted as proof that at last an absolutely new means of sport, pleasure and research, had been practically developed, and was within the reach of all who had the inclination, nerve and financial means to adopt it.
From this event may be dated the birth of the modern flying machine into the world of business. The automobile was taken up by the general public from the very start because it was a proposition comparatively easy of demonstration. There was nothing mysterious or uncanny in the fact that a wheeled vehicle could be propelled on solid, substantial roads by means of engine power. And yet it took (comparatively speaking) a long time to really popularize the motor car.
Wonderful Results in a Year.
Men of large financial means engaged in the manufacture of automobiles, and expended fortunes in attracting public attention to them through the medium of advertisements, speed and road contests, etc. By these means a mammoth business has been built up, but bringing this business to its present proportions required years of patient industry and indomitable pluck.
At this writing, less than a year from the day when Bleriot crossed the channel, the actual sales of flying machines outnumber the actual sales of automobiles in the first year of their commercial development. This may appear incredible, but it is a fact as statistics will show.
In this connection we should take into consideration the fact that up to a year ago there was no serious intention of putting flying machines on the market; no preparations had been made to produce them on a commercial scale; no money had been expended in advertisements with a view to selling them.
Some of the Actual Results.
Today flying machines are being produced on a commercial basis, and there is a big demand for them. The people making them are overcrowded with orders. Some of the producers are already making arrangements to enlarge their plants and advertise their product for sale the same as is being done with automobiles, while a number of flying machine motor makers are already promoting the sale of their wares in this way.
Here are a few actual figures of flying machine sales made by the more prominent producers since July 25th, 1909.
Santos Dumont, 90 machines; Bleriot, 200; Farman, 130; Clemenceau-Wright, 80; Voisin, 100; Antoinette, 100. Many of these orders have been filled by delivery of the machines, and in others the construction work is under way.
The foregoing are all of foreign make. In this country Curtiss and the Wrights are engaged in similar work, but no actual figures of their output are obtainable.
Larger Plants Are Necessary.
And this situation exists despite the fact that none of the producers are really equipped with adequate plants for turning out their machines on a modern, business-like basis. The demand was so sudden and unexpected that it found them poorly prepared to meet it. This, however, is now being remedied by the erection of special plants, the enlargement of others, and the introduction of new machinery and other labor-saving conveniences.
Companies, with large capitalization, to engage in the exclusive production of airships are being organized in many parts of the world. One notable instance of this nature is worth quoting as illustrative of the manner in which the production of flying machines is being commercialized. This is the formation at Frankfort, Germany, of the Flugmaschine Wright, G. m. b. H., with a capital of $119,000, the Krupps, of Essen, being interested.
Prices at Which Machines Sell.
This wonderful demand from the public has come notwithstanding the fact that the machines, owing to lack of facilities for wholesale production, are far from being cheap. Such definite quotations as are made are on the following basis:
Santos Dumont—List price $1,000, but owing to the rush of orders agents are readily getting from $1,300 to $1,500. This is the smallest machine made.
Bleriot—List price $2,500. This is for the cross-channel type, with Anzani motor.
Antoinette—List price from $4,000 to $5,000, according to size.
Wright—List price $5,600.
Curtiss—List price $5,000.
There is, however, no stability in prices as purchasers are almost invariably ready to pay a considerable premium to facilitate delivery.
The motor is the most expensive part of the flying machine. Motor prices range from $500 to $2,000, this latter amount being asked for the Curtiss engine.
Systematic Instruction of Amateurs.
In addition to the production of flying machines many of the experienced aviators are making a business of the instruction of amateurs. Curtiss and the Wrights in this country have a number of pupils, as have also the prominent foreigners. Schools of instruction are being opened in various parts of the world, not alone as private money-making ventures, but in connection with public educational institutions. One of these latter is to be found at the University of Barcelona, Spain.
The flying machine agent, the man who handles the machines on a commission, has also become a known quantity, and will soon be as numerous as his brother of the automobile. The sign "John Bird, agent for Skimmer's Flying Machine," is no longer a curiosity.
Yes, the Airship Is Here.
From all of which we may well infer that the flying machine in practical form has arrived, and that it is here to stay. It is no exaggeration to say that the time is close at hand when people will keep flying machines just as they now keep automobiles, and that pleasure jaunts will be fully as numerous and popular. With the important item of practicability fully demonstrated, "Come, take a trip in my airship," will have more real significance than now attaches to the vapid warblings of the vaudeville vocalist.
As a further evidence that the airship is really here, and that its presence is recognized in a business way, the action of life and accident insurance companies is interesting. Some of them are reconstructing their policies so as to include a special waiver of insurance by aviators. Anything which compels these great corporations to modify their policies cannot be looked upon as a mere curiosity or toy.
It is some consolation to know that the movement in this direction is not thus far widespread. Moreover it is more than probable that the competition for business will eventually induce the companies to act more liberally toward aviators, especially as the art of aviation advances.
Successful aviation has evoked some peculiar things in the way of legal action and interpretation of the law.
It is well understood that a man's property cannot be used without his consent. This is an old established principle in common law which holds good today.
The limits of a man's property lines, however, have not been so well understood by laymen. According to eminent legal authorities such as Blackstone, Littleton and Coke, the "fathers of the law," the owner of realty also holds title above and below the surface, and this theory is generally accepted without question by the courts.
Rights of Property Owners.
In other words the owner of realty also owns the sky above it without limit as to distance. He can dig as deep into his land, or go as high into the air as he desires, provided he does not trespass upon or injure similar rights of others.
The owner of realty may resist by force, all other means having failed, any trespass upon, or invasion of his property. Other people, for instance, may not enter upon it, or over or under it, without his express permission and consent. There is only one exception, and this is in the case of public utility corporations such as railways which, under the law of eminent domain, may condemn a right of way across the property of an obstinate owner who declines to accept a fair price for the privilege.
Privilege Sharply Confined.
The law of eminent domain may be taken advantage of only by corporations which are engaged in serving the public. It is based upon the principle that the advancement and improvement of a community is of more importance and carries with it more rights than the interests of the individual owner. But even in cases where the right of eminent domain is exercised there can be no confiscation of the individual's property.
Exercising the right of eminent domain is merely obtaining by public purchase what is held to be essential to the public good, and which cannot be secured by private purchase. When eminent domain proceedings are resorted to the court appoints appraisers who determine upon the value of the property wanted, and this value (in money) is paid to the owner.
How It Affects Aviation.
It should be kept in mind that this privilege of the "right of eminent domain" is accorded only to corporations which are engaged in serving the public. Individuals cannot take advantage of it. Thus far all aviation has been conducted by individuals; there are no flying machine or airship corporations regularly engaged in the transportation of passengers, mails or freight.
This leads up to the question "What would happen if realty owners generally, or in any considerable numbers, should prohibit the navigation of the air above their holdings?" It is idle to say such a possibility is ridiculous—it is already an actuality in a few individual instances.
One property owner in New Jersey, a justice of the peace, maintains a large sign on the roof of his house warning aviators that they must not trespass upon his domain. That he is acting well within his rights in doing this is conceded by legal authorities.
Hard to Catch Offenders.
But, suppose the alleged trespass is committed, what is the property owner going to do about it? He must first catch the trespasser and this would be a pretty hard job. He certainly could not overtake him, unless he kept a racing aeroplane for this special purpose. It would be equally difficult to identify the offender after the offense had been committed, even if he were located, as aeroplanes carry no license numbers.
Allowing that the offender should be caught the only recourse of the realty owner is an action for damages. He may prevent the commission of the offense by force if necessary, but after it is committed he can only sue for damages. And in doing this he would have a lot of trouble.
Points to Be Proven.
One of the first things the plaintiff would be called upon to prove would be the elevation of the machine. If it were reasonably close to the ground there would, of course, be grave risk of damage to fences, shrubbery, and other property, and the court would be justified in holding it to be a nuisance that should be suppressed.
If, on the other hand; the machine was well up in the air, but going slowly, or hovering over the plaintiff's property, the court might be inclined to rule that it could not possibly be a nuisance, but right here the court would be in serious embarrassment. By deciding that it was not a nuisance he would virtually override the law against invasion of a man's property without his consent regardless of the nature of the invasion. By the same decision he would also say in effect that, if one flying machine could do this a dozen or more would have equal right to do the same thing. While one machine hovering over a certain piece of property may be no actual nuisance a dozen or more in the same position could hardly be excused.
Difficult to Fix Damages.
Such a condition would tend to greatly increase the risk of accident, either through collision, or by the carelessness of the aviators in dropping articles which might cause damages to the people or property below. In such a case it would undoubtedly be a nuisance, and in addition to a fine, the offender would also be liable for the damages.
Taking it for granted that no actual damage is done, and the owner merely sues on account of the invasion of his property, how is the amount of compensation to be fixed upon? The owner has lost nothing; no part of his possessions has been taken away; nothing has been injured or destroyed; everything is left in exactly the same condition as before the invasion. And yet, if the law is strictly interpreted, the offender is liable.
Right of Way for Airships.
Somebody has suggested the organization of flying-machine corporations as common carriers, which would give them the right of eminent domain with power to condemn a right of way. But what would they condemn? There is nothing tangible in the air. Railways in condemning a right of way specify tangible property (realty) within certain limits. How would an aviator designate any particular right of way through the air a certain number of feet in width, and a certain distance from the ground?
And yet, should the higher courts hold to the letter of the law and decide that aviators have no right to navigate their craft over private property, something will have to be done to get them out of the dilemma, as aviation is too far advanced to be discarded. Fortunately there is little prospect of any widespread antagonism among property owners so long as aviators refrain from making nuisances of themselves.
Possible Solution Offered.
One possible solution is offered and that is to confine the path of airships to the public highways so that nobody's property rights would be invaded. In addition, as a matter of promoting safety for both operators and those who may happen to be beneath the airships as they pass over a course, adoption of the French rules are suggested. These are as follows:
Aeroplanes, when passing, must keep to the right, and pass at a distance of at least 150 feet. They are free from this rule when flying at altitudes of more than 100 feet. Every machine when flying at night or during foggy weather must carry a green light on the right, and a red light on the left, and a white headlight on the front.
These are sensible rules, but may be improved upon by the addition of a signal system of some kind, either horn, whistle or bell.
Responsibility of Aviators.
Mr. Jay Carver Bossard, in recent numbers ofFly, brings out some curious and interesting legal points in connection with aviation, among which are the following:
"Private parties who possess aerial craft, and desire to operate the same in aerial territory other than their own, must obtain from land owners special permission to do so, such permission to be granted only by agreement, founded upon a valid consideration. Otherwise, passing over another's land will in each instance amount to a trespass.
"Leaving this highly technical side of the question, let us turn to another view: the criminal and tort liability of owners and operators to airship passengers. If A invites B to make an ascension with him in his machine, and B, knowing that A is merely an enthusiastic amateur and far from being an expert, accepts and is through A's innocent negligence injured, he has no grounds for recovery. But if A contracts with B, to transport him from one place to another, for a consideration, and B is injured by the poor piloting of A, A would be liable to B for damages which would result. Now in order to safeguard such people as B, curious to the point of recklessness, the law will have to require all airship operators to have a license, and to secure this license airship pilots will have to meet certain requirements. Here again is a question. Who is going to say whether an applicant is competent to pilot a balloon or airship?
Fine for an Aeronaut.
"An aeroplane while maneuvering is suddenly caught by a treacherous gale and swept to the ground. A crowd of people hasten over to see if the aeronaut is injured, and in doing so trample over Tax-payer Smith's garden, much to the detriment of his growing vegetables and flowers. Who is liable for the damages? Queer as it may seem, a case very similar to this was decided in 1823, in the New York supreme court, and it was held that the aeronaut was liable upon the following grounds: 'To render one man liable in trespass for the acts of others, it must appear either that they acted in concert, or that the act of the one, ordinarily and naturally produced the acts of the others, Ascending in a balloon is not an unlawful act, but it is certain that the aeronaut has no control over its motion horizontally, but is at the sport of the wind, and is to descend when and how he can. His reaching the earth is a matter of hazard. If his descent would according to the circumstances draw a crowd of people around him, either out of curiosity, or for the purpose of rescuing him from a perilous situation, all this he ought to have foreseen, and must be responsible for.'
Air Not Really Free.
"The general belief among people is, that the air is free. Not only free to breathe and enjoy, but free to travel in, and that no one has any definite jurisdiction over, or in any part of it. Now suppose this were made a legal doctrine. Would a murder perpetrated above the clouds have to go unpunished? Undoubtedly. For felonies committed upon the high seas ample provision is made for their punishment, but new provisions will have to be made for crimes committed in the air.
Relations of Owner and Employee.
"It is a general rule of law that a master is bound to provide reasonably safe tools, appliances and machines for his servant. How this rule is going to be applied in cases of aeroplanes, remains to be seen. The aeroplane owner who hires a professional aeronaut, that is, one who has qualified as an expert, owes him very little legal duty to supply him with a perfect aeroplane. The expert is supposed to know as much regarding the machine as the owner, if not more, and his acceptance of his position relieves the owner from liability. When the owner hires an amateur aeronaut to run the aeroplane, and teaches him how to manipulate it, even though the prescribed manner of manipulation will make flight safe, nevertheless if the machine is visibly defective, or known to be so, any injury which results to the aeronaut the owner is liable for.
As to Aeroplane Contracts.
"At the present time there are many orders being placed with aeroplane manufacturing companies. There are some unique questions to be raised here under the law of contract. It is an elementary principle of law that no one can be compelled to complete a contract which in itself is impossible to perform. For instance, a contract to row a boat across the Atlantic in two weeks, for a consideration, could never be enforced because it is within judicial knowledge that such an undertaking is beyond human power. Again, contracts formed for the doing of acts contrary to nature are never enforcible, and here is where our difficulty comes in. Is it possible to build a machine or species of craft which will transport a person or goods through the air? The courts know that balloons are practical; that is, they know that a bag filled with gas has a lifting power and can move through the air at an appreciable height. Therefore, a contract to transport a person in such manner is a good contract, and the conditions being favorable could undoubtedly be enforced. But the passengers' right of action for injury would be very limited.
No Redress for Purchasers.
"In the case of giving warranties on aeroplanes, we have yet to see just what a court is going to say. It is easy enough for a manufacturer to guarantee to build a machine of certain dimensions and according to certain specifications, but when he inserts a clause in the contract to the effect that the machine will raise itself from the surface of the earth, defy the laws of gravity, and soar in the heavens at the will of the aviator, he is to say the least contracting to perform a miracle.
"Until aeroplanes have been made and accepted as practical, no court will force a manufacturer to turn out a machine guaranteed to fly. So purchasers can well remember that if their machines refuse to fly they have no redress against the maker, for he can always say, 'The industry is still in its experimental stage.' In contracting for an engine no builder will guarantee that the particular engine will successfully operate the aeroplane. In fact he could never be forced to live up to such an agreement, should he agree to a stipulation of that sort. The best any engine maker will guarantee is to build an engine according to specifications."
5There is a wonderful performance daily exhibited in southern climes and occasionally seen in northerly latitudes in summer, which has never been thoroughly explained. It is the soaring or sailing flight of certain varieties of large birds who transport themselves on rigid, unflapping wings in any desired direction; who in winds of 6 to 20 miles per hour, circle, rise, advance, return and remain aloft for hours without a beat of wing, save for getting under way or convenience in various maneuvers. They appear to obtain from the wind alone all the necessary energy, even to advancing dead against that wind. This feat is so much opposed to our general ideas of physics that those who have not seen it sometimes deny its actuality, and those who have only occasionally witnessed it subsequently doubt the evidence of their own eyes. Others, who have seen the exceptional performances, speculate on various explanations, but the majority give it up as a sort of "negative gravity."
Soaring Power of Birds.
The writer of this paper published in the "Aeronautical Annual" for 1896 and 1897 an article upon the sailing flight of birds, in which he gave a list of the authors who had described such flight or had advanced theories for its explanation, and he passed these in review. He also described his own observations and submitted some computations to account for the observed facts. These computations were correct as far as they went, but they were scanty. It was, for instance, shown convincingly by analysis that a gull weighing 2.188 pounds, with a total supporting surface of 2.015 square feet, a maximum body cross-section of 0.126 square feet and a maximum cross-section of wing edges of 0.098 square feet, patrolling on rigid wings (soaring) on the weather side of a steamer and maintaining an upward angle or attitude of 5 degrees to 7 degrees above the horizon, in a wind blowing 12.78 miles an hour, which was deflected upward 10 degrees to 20 degrees by the side of the steamer (these all being carefully observed facts), was perfectly sustained at its own "relative speed" of 17.88 miles per hour and extracted from the upward trend of the wind sufficient energy to overcome all the resistances, this energy amounting to 6.44 foot-pounds per second.
Great Power of Gulls.
It was shown that the same bird in flapping flight in calm air, with an attitude or incidence of 3 degrees to 5 degrees above the horizon and a speed of 20.4 miles an hour was well sustained and expended 5.88 foot-pounds per second, this being at the rate of 204 pounds sustained per horsepower. It was stated also that a gull in its observed maneuvers, rising up from a pile head on unflapping wings, then plunging forward against the wind and subsequently rising higher than his starting point, must either time his ascents and descents exactly with the variations in wind velocities, or must meet a wind billow rotating on a horizontal axis and come to a poise on its crest, thus availing of an ascending trend.
But the observations failed to demonstrate that the variations of the wind gusts and the movements of the bird were absolutely synchronous, and it was conjectured that the peculiar shape of the soaring wing of certain birds, as differentiated from the flapping wing, might, when experimented upon, hereafter account for the performance.
Mystery to be Explained.
These computations, however satisfactory they were for the speed of winds observed, failed to account for the observed spiral soaring of buzzards in very light winds and the writer was compelled to confess: "Now, this spiral soaring in steady breezes of 5 to 10 miles per hour which are apparently horizontal, and through which the bird maintains an average speed of about 20 miles an hour, is the mystery to be explained. It is not accounted for, quantitatively, by any of the theories which have been advanced, and it is the one performance which has led some observers to claim that it was done through 'aspiration.' i, e., that a bird acted upon by a current, actually drew forward into that current against its exact direction of motion."
Buzzards Soar in Dead Calm.
A still greater mystery was propounded by the few observers who asserted that they had seen buzzards soaring in a dead calm, maintaining their elevation and their speed. Among these observers was Mr. E. C. Huffaker, at one time assistant experimenter for Professor Langley. The writer believed and said then that he must in some way have been mistaken, yet, to satisfy himself, he paid several visits to Mr. Huffaker, in Eastern Tennessee and took along his anemometer. He saw quite a number of buzzards sailing at a height of 75 to 100 feet in breezes measuring 5 or 6 miles an hour at the surface of the ground, and once he saw one buzzard soaring apparently in a dead calm.
The writer was fairly baffled. The bird was not simply gliding, utilizing gravity or acquired momentum, he was actually circling horizontally in defiance of physics and mathematics. It took two years and a whole series of further observations to bring those two sciences into accord with the facts.
Results of Close Observations.
Curiously enough the key to the performance of circling in a light wind or a dead calm was not found through the usual way of gathering human knowledge, i. e., through observations and experiment. These had failed because I did not know what to look for. The mystery was, in fact, solved by an eclectic process of conjecture and computation, but once these computations indicated what observations should be made, the results gave at once the reasons for the circling of the birds, for their then observed attitude, and for the necessity of an independent initial sustaining speed before soaring began. Both Mr. Huffaker and myself verified the data many times and I made the computations.
These observations disclosed several facts:
1st.—That winds blowing five to seventeen miles per hour frequently had rising trends of 10 degrees to 15 degrees, and that upon occasions when there seemed to be absolutely no wind, there was often nevertheless a local rising of the air estimated at a rate of four to eight miles or more per hour. This was ascertained by watching thistledown, and rising fogs alongside of trees or hills of known height. Everyone will readily realize that when walking at the rate of four to eight miles an hour in a dead calm the "relative wind" is quite inappreciable to the senses and that such a rising air would not be noticed.
2nd.—That the buzzard, sailing in an apparently dead horizontal calm, progressed at speeds of fifteen to eighteen miles per hour, as measured by his shadow on the ground. It was thought that the air was then possibly rising 8.8 feet per second, or six miles per hour.
3rd.—That when soaring in very light winds the angle of incidence of the buzzards was negative to the horizon—i. e., that when seen coming toward the eye, the afternoon light shone on the back instead of on the breast, as would have been the case had the angle been inclined above the horizon.
4th.—That the sailing performance only occurred after the bird had acquired an initial velocity of at least fifteen or eighteen miles per hour, either by industrious flapping or by descending from a perch.
An Interesting Experiment.
5th.—That the whole resistance of a stuffed buzzard, at a negative angle of 3 degrees in a current of air of 15.52 miles per hour, was 0.27 pounds. This test was kindly made for the writer by Professor A. F. Zahm in the "wind tunnel" of the Catholic University at Washington, D. C., who, moreover, stated that the resistance of a live bird might be less, as the dried plumage could not be made to lie smooth.
This particular buzzard weighed in life 4.25 pounds, the area of his wings and body was 4.57 square feet, the maximum cross-section of his body was 0.110 square feet, and that of his wing edges when fully extended was 0.244 square feet.
With these data, it became surprisingly easy to compute the performance with the coefficients of Lilienthal for various angles of incidence and to demonstrate how this buzzard could soar horizontally in a dead horizontal calm, provided that it was not a vertical calm, and that the air was rising at the rate of four or six miles per hour, the lowest observed, and quite inappreciable without actual measuring.
Some Data on Bird Power.
The most difficult case is purposely selected. For if we assume that the bird has previously acquired an initial minimum speed of seventeen miles an hour (24.93 feet per second, nearly the lowest measured), and that the air was rising vertically six miles an hour (8.80 feet per second), then we have as the trend of the "relative wind" encountered:
6— = 0.353, or the tangent of 19 degrees 26'.17
which brings the case into the category of rising wind effects. But the bird was observed to have a negative angle to the horizon of about 3 degrees, as near as could be guessed, so that his angle of incidence to the "relative wind" was reduced to 16 degrees 26'.
The relative speed of his soaring was therefore:
Velocity = square root of (17 squared + 6 squared) = 18.03 miles per hour.
At this speed, using the Langley co-efficient recently practically confirmed by the accurate experiments of Mr. Eiffel, the air pressure would be:
18.03 squared X 0.00327 = 1.063 pounds per square foot.
If we apply Lilienthal's co-efficients for an angle of 6 degrees 26', we have for the force in action: