I L 545 H73 CORNELL UNIVERSITY LIBRARY BOUGHT WITH THE INCOME OF THE SAGE ENDOWMENT FUND GIVEN IN 1891 BY HENRY WILLIAMS SAGE HOW TO FLY AS A BIRD BY JOHN P. HOLLAND Those who desire to travel like the !riird5_ through Nature's great, high- [jvay, the atmosphere, must not be l-liscouraged by the wise ones who 'idvise them to attempt to do only vhat is practicable, telling them l:hat the problem of flight is in the same [rategory as perpetual motion, the search tor the philosopher's stone and for the pabled fountain of perpetual youth. Practically the same thing was said |-egarding a proposition I made over l:hirty years ago to our Government to Ijuild an experimental submarine boat. Irhe late Commodore Simpson reporting iin that suggestion to the Navy Depart- |ment said it would be of no use, be- cause no one could be found to operate |it, and because it could not bfe directed under water. The attempt to do so, he added, would be practically an aggra- Ivated case of a man trying to find his Iway in a fog. A few years before his victory over the Spanish fleet at Santiago, the late lAdmiral Sampson, in a spirit of cour- jteous kindness, advised me to discon- Itinue my efforts to persuade our' Navy iDepartment to experiment with subma- trine boats as my time would surely be Iwasted. He. assured me that even though Isuch a boat could do everything that I jhad proved to be practicable with my {second submarine boat in 1881, yet he fcould see no use for them in the Navy. Still another high authority, Herr Bus- lley, the head of a German Imperial {School for some division of that naval [service, asserted that no man of experi- [ence in marine design or construction, fno naval architect, had ever been foolish {enough to waste his time on the con- Istruction of submarine boats, and that [only unsuccessful medical doctors, school {teachers and other outsiders, ever made [attempts in that direction. He fairly hit the mark in that obser- Ivation as I happen to be an ex-school [teacher. Even with this criticism of [submarines they are now included in {the building program of all important [maritime countries and they already have [■had influence in the designs of their new i ships. They are no longer laughed at I 3r ridiculed. And what is still more re- 1 tnarkable, I a'm credibly informed that Herr Busley himself now favors the 'only real thing" in submarines, a Ger- nan invention. This remarkable change in the views Df naval departments, of boards of admi- ralty and other officials connected with the! management of naval affairs, in this country and in Europe, was not due to any striking improvement in principle, orgain in efficiency of this type of boat, between the date of the successful ex- periments made with my second boat in 1881 and the exhibition of the Holland to Admiral Dewey, on the Potomac, in April, igoi, but simply and solely to the unbiased opinion that emine:it sea cap- tains frankly- expressed, which carried universal conviction and was absolutely beyond question. Although it has bsen remarked that professional persons are generally con- servative, that is, opposed to the accept- ance of new ideas, and that many of them even manifest a tendency to run in a rut and to keep running there per- sistently, yet, in this particular, they are no different from the rest of humanity. Since the very beginning of things the simplest and most rapid mode of animal locomotion has been daily exhibited be- fore their faces, as if to provoke them to imitate it, yet nothing worthy of no- tice has ever been done towards its ac- complishment. It is true that men have always desired to be able to fly like the birds, and in cases of dire necessity, as in cities reduced to extremity by beleag- uering armies, or travelers dying of hun- ger or thirst in the desert, that po'tver was even rttore ardently but fruitlessly desired. From very ancient times men vainly attempted to fly with crude imitations of wings operated bv their arms. Those who happened to survive their experi- ments might be pardoned for believing that the power of levitation was mys- terious because it proved to be beyond their reach, but the general tendency of humanity, even at the present day, to at- tribute obscure natural phenomena to some occult power, or to accept the de- cision of some "authorities" that it is mysterious, saves them the trouble of in- vestigation, and they are satisfied. Wit- ness the belief in the work of Pluto and of Jove in the thunder and lightning, amongst the Ancient Greeks, and of the Thunder bird amongst the modern Zulus and Hottentots. But the most astonishing exhibition of that kind is to hear educated men, in- vestigators of natural phenomena, at the present day, talk about the mysteries of flight and soaring, or attributing super- human intelligence to birds in the art Cc ^ {-["J^ai balancing, selecting favoring currents, etc., instead of openly confessing that there must be some simple functions of the natural apoaratus for flight that they have mistaken or misunderstood, or which until now, they have failed to no- tice. Why do they propose explanations of bird flight that cannot possibly account for even one-half of the support .re- quired in certain plain cases and yet not inform us regarding what is lacking thereto? Even though they would not wish to be credited with belief in the occult, equalling that of the ancient Greeks, or the Modern Zulus, yet they afford us no alternative explana- tion. It is unfortunate that the net result of the investigations of those who have studied bird flight is that it is far be- yond human reach if they are not greatly - mistaken. Almost without exception they main- tain absurd theories that cannot in the nature of things be true, that are re- futed before their faces every day by every flying thing, and that are far from being reasonable and simple as are the natural functions regarding which they dogmatize. We have been assured by conscientious and zealous workers in this field that air reaction due to down-beating wings must be competent to balance the bird's weight. This takes account only of the sup- port afforded while a bird is making its down stroke. The source of support during the elevation of the wings, they generally credit to the mystery account, although Mr. O. Chanute, who is proba- bly the most painstaking and industrious of them all, asserts that aeroplane action must be credited with giving great as- sistance. The utter inadequacy of air reaction from down beating as a means of sup- port during steady flight must also be credited to the mystery account. StilJ another mystery is thus formu- lated by Mr. O. Chanute in his valuable and interesting work, "Progress in Fly- ing Machines," page 251. "There is good reason to believe that the output of energy appertaining to the motor mus- cles of birds in proportion to their weight, which, as we have seen there is good reason to believe develop work in ordinary flight at the rate of one horse power to 20 pounds of weight, and can for a brief period, in rising, give out en- ergj' at such a rate as to represent an engine of only 5 or 6 pounds weight de- veloping one horse power." That is, a 20 pound bird develops one horse power during steady flight, and a S pound bird develops one horse power when rising, say from the level, and also when alighting. Maintaining this proportion a man who is ambitious to fly by his own mus- cular energy must be able to develop 150 divided by 20, equals 754 horse power, continuously during steady flight, and 150 divided by S) equals 30 horse power, when rising from the level and alight- ing. We need not delay longer over the mystery account as it is quite a long one, as will be apparent later.' With this encouragement in mind, we should act wisely in quitting the study of flying for good, in case we find that the authorities are not in error, or else follow it up to an actual demonstration if we find that by a common sense appli- cation of the laws of physics, and by comparisons with the perfect examples afforded by Nature, that they are mis- taken. For this purpose we may study a pro- posed design for a machine to be oper- ated by muscular energy alone. We shall then encounter the ordinary "mysteries" of the case and see how Nature treats them, ,as well as determine whether a man can operate it himself even though he possesses less than one one-hundred and twentieth part of the muscular pow- er that the authorities assure us is quite essential. What we shall most assuredly dis- cover from our study is the extreme denseness of human stupidity in failing through all past ages to understand the simplest and most rapid mode of animal locomotion, although man was ingenious enough to cloak over his laziness of mind and neglect and rest satisfied by assur- ing himself that the whole subject was an impenetrable mystery. No one needs to excuse himself be- cause we are all together in the same boat and in very good company. Some very distinguished scientific gentleman and great inventors, amongst whom may be named Thomas A. Edison, Professor Melville Bell, the late Professor Lang- ley, O. Chanute and many others in this country, as well as very many equally distinguished scientists in Europe, have devoted much study, although vainly, to this interesting subject. My first design was made in 1863, shortly before I began the study of sub- marines, but I had no suspicion of the influence of the chief, almost the only, natural force employed by every flying animal until it occurred to me, not as the result of ?tudy or industry, but purely by accident a few years ago. Therefore, this discovery is not an in- vention, and I have great pleasure in thus describing it publicly in order that some one may be stimulated to lead the way Into what will be practically, a new order of existence. Individual Flying Machine Designed to be Operated Solely by Mus- cular Energy. It may consist of two transverse wing arms at the operator's back, one of them at the level of his neck, the other one being set about four or five inches below his hips. These wing arms are fastened on short tubular shafts provided with ball bearings at each end of each shaft. These shafts are carried by bearings on a foundation plate, or substitute for the bird's backbone, which is provided with rigid metal carriers at its sides, near the middle of its length, that extend around the operator's sides for the purpose of holding the treadle guides and a frame carrying a diaphragm on which his body rests in a nearly horizontal position, face downward, when he is in full flight. Carried on bearings fastened on the foundation plate are also placed two short, transverse tubular shafts opposite to one another, their approaching ends carrying mitre gears, which gear into two corresponding gears placed on the inner ends of the tubular shafts that have their outer ends fastened to the transverse wing arms. The short trans- verse shafts carry near their outer ends each a grooved metal arc, carrying a small wire rope, which extends back- wards, or downwards, from where one end of each is fastened to each arc ra- dius to a treadle at each side, at the lower end of the apparatus. It is evident that when the short shafts are connected by mitre wheels and the treadles are pushed alter- nately, the operator's body being in- clined forward,' or nearly horizontal, that the two wing arms will vibrate in oppo- site directions. The wing sails are set on pieces of wood bent to the proper curvature and attached to metal rings through which the wing arms pass. Pins passing through the arms limit the swing of the cross pieces around them to about 45 de- grees in order to provide that the sails may automatically feather, that, is, change their ' inclination, when the ma- chine is starting in a calm and before it has attained sufficient velocity to ren- der feathering unnecessary. Provision is made in the wing arm bearings to , permit of the arms being revolved simultaneously around their axis with the object of controlling the inclination of the sails. This is accom- plished by means of two light handles depending one on either side, from the forward wing arm and by a connection between both arms. By means of handles referred to, the machine can be operated by the hands, or it may be driven by the feet by means of the treadles, or, both means of op- eration may be employed together when the hard work of starting or alighting in a calm, from the level, happens to be necessary. The inertia of all the moving parts is cushioned by a device attached to the radial arms of the arcs carrying the wire rope on each side. The effect of cush- ioning is to reverse the direction of mo- tion of the wings without shock and thus economize power and facilitate speed. It is evident that each half of each wing arm, with its sail balances the other half with its sail, and that com- pensation to obtain balance is therefore unnecessary. The wing arms in the machine illus- trated on page — , are made of No. 22, one and one-quarter inch steel tubes in the middle, tapering to three-eighths inch diameter at the ends. These tubes wi|ll be strong enough to dispense with truss- ing, which is inadmissible. The weight of the machine illustrated will be, when it is completed, 35 pounds, but with more suitable material and bet- ter workmanship that weight can be re- duced to IS pounds.. This figure shall be taken as the weight of effective machine; although it may weigh more. It is evident that the mysteries of sta- bilit}' and balancing will be eliminated in this machine, because the centre of grav- ity of apparatus and operator together will, be about 15 inches under the centre of support, which is unchangeable and effective at the crossing of two diagonal lines joining the centre of effort of the wings that are situated diagonally. T-he centre of resistance will be on the same plane as the centre of thrust, or propulsion, and there can, therefore, exist no tendency to tip upwards or downwards. The anterior edges of the wings being thick and convexed eliminates the ri^ to the operator, of ■ meeting the fate of Lillienthal. With the fore-and-aft sec- tion of his planes or wings nearly corre- sponding with the plane of his direction of motion and his apparatus moving at comparatively slow speed, there is little wonder that, owing to a slight move- ment of the operator, or to a vertical current of low speed, that their upper forward surfaces took the wind, or in nautical phraseolos'y were taken aback. This apparatus is designed to imitate, as closely as possible the mechanism ex- isting in Nature for the attainment of flight through the air, because the un- numbered failures of attempts that aimed at employing only crude substitutes for natural means 'and methods, prove that Its plans are the best and that the de- gree of success of devices for these purposes will depend on the exactness with which its perfect examples are fol- lowed. It will be shown herein that the mech- anism of natural flight has never here- tofore been properly understood. Until within the last decade it was generally believed that the necessary aerial sup- port of flying animals was afforded sole- ly by the reaction of air against the de- scending wings, and that during its flight a bird produces a reaction at the centre of effort of each wing competent to support at least one-half of the bird's weight. A bird's wing during beating, or row- ing flight, is a lever of the third order, having the fulcrum at one end, the weight or working point, towards the other end, and the power applied at some point between them. The inner, joint, at which the wing is attached to the body, is the fulcrum. The power is applied at the point of attachment of the pectoral muscles to the Wing arm. The working point at which the power is utilized being taken . as the centre of effort of each wing, the distance from the fulcrum to the centre of effort is from four to nine times greater than the distance from the fulcrum to the point of attachment of the pectoral mus- cles, depending on the species of bird. This ratio generally increases with the size of the species, being greatest with so_arers, and abopt nine in the case of the great wandering albatross, the infor- mation regarding which is sufficiently definite for purposes of comparison. If the reaction equal-to-weight theory is correct then the pectoral muscles must contract, at each wing stroke, 'with a force equal to nine times , the bird's weight in order that reaction equal to the weight may exist at the centres of effort, leaving the question of support during the intermission, while the wings- are rising, entirely out of consideration or rather crediting it to the mystery ac- count. The same bird makes wing beats at the rate of no per minute, through about 90 degrees of arc, when rising from the water. Therefore, if the pressure at the centres of effort must be equal to the weight, twenty pounds, it must be ex- erted at the rate of no beats per min- ute, the vertical speed of the centres of effort being 21.5985 feet per second, 2ox 21.5985, divided by 550, equals 0.7854 horse power. The force, actually required for sup- port by air reaction alone during one down beat is equal to the bird's weight divided by the ratio of the levers in the wings 9; 20 divided by 9 equals 2 2-g pounds at the centres of effort. Reaction 2 2-9x21.59, divided by 550, equals 0.0872 horse power, equals 43.96 foot pounds per second and this force is exerted only when the bird begins to rise from smooth 'water or when alighting. The source of support during the ele- vation of the wings will be pointed out later. Another reference to Nature will re- veal the source of the supporting power during flight. An albatross flying, in calm weather, beating its wings and not soaring, supports its 20 pound weight with very little apparent effort. The wing spread is 10.5 feet, the radius of the centre of effort of each wing is about 3.75 feet, total wing surface 5.5 square . feet, and the vertical speed of the centre of effort of each wing is at the leisurely rate of 5.5 feet per second. The wing reaction to direct down beat- ing is, in this case, 0.0703 pounds per square foot, and the total direct reaction is 5.5x0.0703, equals 0.386 pounds. Thus it falls short of adequate support, and it is in action only while the wings are descending. Nor can aeroplan action of the wings, as it is at present believed to be employed in steady flight, afford any satisfactory explanation of the bird's means of support. Suppose that, as is commonly believed, the wings do work as aeroplanes during their elevation. The speed in this kind of flight is from 30 to 35 miles per hour. The pressure on a flat surface, of a wind blowing 35 miles per hour is 6.125 pounds per square foot. The inclination of the wings when acting as aeroplanes during flight IS generally calculated to be about 6 degrees. The normal pressure of the, wing surface due to this inclination is 0.207 of the pressure at no inclination, the vertical, or lifting component is 0.206, and the horizontal component is 0.0217 of the same. The lifting force due to aeroplane action under these con- ditions should therefore be S.SXI.125X 0.206, equals 6.939 pounds.. Mr. O. Chanute believes that 30 per cent, should be added to this amount because of the greater efficiency of con-' caved surfaces than of the flat plane sur- faces : 6.939x1.3, equals 9.02 pounds. These results are surprising in view of the consensus of opinion of the auth- orities cited by Mr. Chanute. Instead of the 7.5 horse power that the albatross should develop in order to be in agree- ment with their theories, we find only 0.386x5.5 feet per second, divided by 550, equals 0.00396 horse power, equals 2.178 foot pounds per second, developed as the result of direct reaction in steady flight. Because the wings act, in this case, as a vibrating propeller, 60 per cent, of this power is expended as propulsive force and there remains as direct lift, during down beating, only O.1544 pounds, and no help whatever from this source while the wings are rising. On the supposition that aeroplane ac- tion is effective during the elevation of the wings, we find that the resulting lift can be no more than 9.02 pounds, less than one-half of the bird's weight, and this help caniiot exist during the descent of the wings. It is evident; therefore, that if the bird's support is to depend on direct re- action during the down beating, and to aeroplane action during wing elevation, there must be 60 times more elevating power developed during the rise of the wings than during their descent. But the maximum lifting power exerted, dur- ing one-half the time is less than one- half of what is required and of what most certainly exists. This is all that existing theories sug- gest or permit in explanation of the con- nundrum of how the 20 pound albatross supports its weight during beating or row- inp- flight, but it is very much less than one-half of what is wanted and of what is actually provided and employed in Nature even though the source of the remainder has thus far escaped obser- vation. I It is certain that there can be nothing occult in the performance of the alba- tross described above, and it is probable that the failure thus far to explain it, and to solve the mystery of soaring, is owing mainly to the influence of incor- rect theories and to omissions and over- sights in observing the results of experi- ments and the natural function referred to above. Yet the bird moves through the air like a thing without weight and not merely as a floating object that rests on something else. It is remarkable also that it moves in circles, curves and re- verse curves, and that it descends to the surface of the water and rises again as if there were no such thing as gravita- tion to hinder it. As soon as it acquires a certain horizontal speed it is imme- diately endowed with the hitherto in- comprehensible power of levitation. Its weight is certainly supported, and sup- ported constantly no matter whether the wings are beating downward, rising, or extended in soaring. The bird's support cannot be due to aeroplane action, that is, compression of air under the advancing wings, which it is calculated, must carry their anterior . edges about six degrees higher than the posterior edges in order to produce suf- ficient effect as aeroplanes. We have seen that with six degrees inclination, the support afforded is less than one- half of what is required even during one-half the time it is flying. But we also have incontestible evidence that the albatross soars horizontally with the un- der surfaces of the wings held quite flat in the fore-and-aft direction. We have equally good evidence that the turkey buzzard generally soars horizontally with its wings similarly held flat. In neither of these cases can what is commonly known as aeroplane action exist. Neither can the concaving of the un- der wing surfaces afford any help al- though so much has been attributed to is efficiency. It will be apparent to any person that examines the wing of an albatross preserved in any museum of natural history that the surface under the primary feathers is quite flat, and that if a flat card or board is held, fore- and aft, under the secondary and ter- tiary wing feathers, that a pressure rep- resenting what actually exists there during flight, viz., one-fortieth of one pound per square inch of surface sup- ported that that part will lie perfectly flat, thus establishing the correctness of the observations quoted above and com- pelling us to reject all explanations of bird flight thus far proposed. Very costly and careful experiments were made with inclined planes by the late Professor Langley, Sir Hiram S. Maxim, Mr. O. Chanute, and others, in this field, as it appeared to be the most promising of affording light on the mys- teries of flight and soaring. They de- termined the varying degrees of reac- tion from pressure of air on surfaces of various sizes and of varying degrees of inclination, and they found how many pounds weight could be lifted per sauare foot of inclined plane, and per horse power applied to moving it hori- zontally. But the vitally important mat- ter, the agent that every flying thing employs to sustain its weight, defective, or minus pressure or air rarefaction over the wings and tail, remained almost en- tirely unnoticed, and certainly was never defined as the important factor in pro- ducing levitation. A study of the transverse, vertical sectioiyof a bird's wing when it is ex- tended in flight will render it clear that defective pressure must exist, during flight, over the greater part of its upper surface when a certain speed is attained. The wing, in this case, moves approxi- mately edgewise through the air at good speed, and the air may eitlier impinge on the under surface or move parallel with It. The air stream is divided by the wmg's anterior edge, the body of the stream represented by the wing's thick- ness at each transverse section being de- flected upward and oyer the u.pper sur- face by the wing's curved forward sec- tion, the extreme forward edge of which is nearly on the same plane as the under surface of the wing. 'The air thrown up- ward by the wing's curved edge cannot recurve instantly and get into close con- tact with the upper surface on account of Its inertia. The air pressure, there- fore, drops below atmosphere between the passing current of air and the wing's upper surface, the space between them being probably filled by eddying currents at a pressure below that existing in the free air depending on the relative speeds of the air current and the wing and on the degree of their inclination to each other. How very small may be the propor- tion, or degree, of defective pressure over the wings required for support in the case of the flying albatross consid- ered above may be easily ascertained. The total wing surface is 5.5 square feet— 792 square inches, to which add 8 square inches for the tail, total 800 square inches. It was shown above that the vertical component of the direct reaction due to the down beat of the wings was only 0.IS44 pounds, and this is so small, con- sidering the bird's weight, that it may be neglected. The bird's 20 pounds' weight will therefore be supposed to be entirely sup- ported by the defective pressure over the wings. Bird's weight, 20 pounds. Divided by supporting surface, 800 square inches'. Equals 1-40 pound. The effect of negative, of defective pressure on one side of a plane exposed to the wind being equivalent to just as much positive pressure on its other or exposed side, the one-fortieth pound defective, or negative, pressure per square inch on the wing's upper surface IS equivalent to one-fortieth pound posi- tive pressure on each square inch of their under surface. The surface being 800 square inches, 800 x 1-40 equals 20 pounds, the bird's weight. This helps to explain the increasing lifting efficiency of inclined planes with increasing inclination. The solution of the problem of flight was near, when, in 1880, it was proved that a ship's propeller, in most cases, moved the ship as much by pumping water from ahead as by pushing it directly backward. It was still nearer when Hargreaves invented the box kite, but his apparently satisfactory explanation of reasons for its efficiency prevented a search for the true one. Any person can readily satisfy him- self of the usefulness of defective pres- sure by taking an ordinary box kite, measuring its lifting power and weight against an ordinary kite having the same lifting surface, then continuing the sides of the. box kite vertically over the upper lifting planes until they project above them a few inches in front, at the edges of the sides, and have the upper edges of the lengthened sides made horizontal when the kite is flying. The gain over the original box kite will be clearly apparent. The lower plane in the box kite fully exploys defective pressure because the vertical side planes joined to its edges prevent the outer air from flowing in- ward over the upper surface of the lower plane to destroy the defective pressure existing there and thus mar its efii- ciencJ^ Now if a rectangular portion of each of the side vertical planes and of nearly the full fore-and-aft length of the lower plane be removed from their lower ends so as to permit the outer air to be drawn in by the rarefaction existing over the lower planes, and if the side projections over the vertical planes be removed, it will be found that the effi- ciency of the box kite will be destroyed and that it will require a much stronger wind to cause it to rise while it is in this condition, although its steadiness will not be noticeably impaired. If convexed planes be substituted for the flat planes in the kite the mystery of bird levitation will be quickly solved to the experimenter's satisfaction. There are good reasons for believing that the still deeper mystery of soaring flight IS capable of an equally simple ex- planation. In the case cited above, of an albatross flying in calm weather, it was shown that the propelling, or drift force was only 0.2316 pounds; that is, about one-eighty-sixth part of the bird's weight applied as propelling force suf- fices to overcome the frictional resist- ance of the air, which must be very little indeed against the exceedingly srnooth surface of the bird's body and wings, and it maintains speed enough to preserve a suitable degree of defective pressure over the wings and tail to afford necessary support. A study of Mr. O.'Chanute's table of lift and drift force for aeroplanes pro- pelled through air while inclined to the horizon indicates that the inclination of the albatross's wings should be about 45 minutes of arc if they were flat planes. But as they are thick edged, convex surfaces, their action may differ considerably from the performance of flat planes. The chief difference is that the angle of inclination may vary a good deal from zero, or even minus, to a con- siderable positive angle without notably affecting the degree of minus pressure above them. To employ nautical phrase- ology, the bird may sail even into the wind's eye and still have support and steerage way. It is also very doubtful whether the inner halves of the wings that are chiefly effective as supports have, dur- ing flight, any inclination to the air streams they encounter. If they have no inclination air resistance must be re- duced to a minimum and the proportion of power expended in propulsion, al- ready shown to be very small indeed, must be still further reduced; Propulsion is done by the outer halves, or rather about two-fifths, of the wings, which are much less rigid than the inner parts that are held stiff, enough to sup- port the weight steadily while flying. The outer parts indeed do their pro- portion of supporting, but being more flexible, they yield to the extra pres- sure during the down beat. The posterior edge is forced upward and the wing thus forms half of a vi- brating screw propeller that wastes no power in indirect action, such as hap- pens with the best propdler designed by man. Referring again to the case of the albatross employing beating flight m calm weather. The speed of the centres of effort of its wings was 5.5 feet per second, and the radius of the centres of effort was 3.7S feet. When the wmg stroke was made through 90 degrees, the down beat therefore occupied more than one second, and when the stroke was through J20 degrees nearly i.J seconds were required to complete it, and just as much more time to raise them. This is leisurely work indeed. It is plainly per- ceptible that during steady flight no variation of the supporting power is vis- ible, although if it varied much the bird should certainly drop by gravity through a considerable distance during the ij^ seconds required to elevate the wings if support depended on the reaction due to the previous stroke. Again, because their under surfaces are held flat in the fore-and-aft direction, there can be no air compression under the wings and there- fore no support from that source. It has been shown above that considerable air rarefaction must exist over the wings while the bird is moving at good speed, and it has also been shown that the de- gree of rarefaction required for com- plete support is that required to produce a compensating pressure under the wings of only one-fortieth pound per square inch, equal to only sixty-nine one- hundredths of one inch water pressure. This evidence clearly leads to the con- viction that the chief and almost the only source of support during steady flight is air rarefaction over the bird's wings and tajl. ' This support is constant during flight whether the wings are rising, descend- ing, or extended in soaring. There is very little less lift from rare- faction of air when the wings are rising than while they are descending, because the bird's horizontal speed is about 9 times greater than the vertical speed of the centres of effort. ' It has been observed that in windy weather the bird seldom beats its wings, but swings in curves and circles, the plane of the wings, or rather the trans- verse axis through the body and wing tips, constantly changing its -inclination to the horizon in every direction, chiefly sidewise. It is evident that the descend- ing wing can always exert propelling force when the tail and risins wing are employed to throw the bird's momentum on the descending wing, which will probably be fouiid to be the outer wing in the curve around which the bird is circling. Some observers notice that in a wind requiring close reefed topsails, that is, in a gale, the albatross does not soar continuously, but makes an ^ occasional wing beat, evidently to maintain the speed necessary to hold tlie minus pres- sure or rarefaction that affords sup- port. A captured albatross liberated in mid- ocean from the stern of a steamer ex- tended its wings in its descent and, not touching the water, soared away without making a single wing beat while it re- mained visible. The available energy for this performance was obtained from the bird's weight of say 20 pounds, falling possibly 30 feet, 20 x 30 equals 600 foot pounds. It may be noted that the angle of in- clination of the wings during beating flight must not be considered in refer- ence to the horizon, but to the result- ant direction of air streams intercepted at any point in the wing in connection with the wing's motion. ' All soaring birds are admirably fitted for the development and maintenance of minus pressure over their wings. They have to do little else during flight than to keep the air pumped out that happens to leak upward through their wings, or endwise from their inner ends, into the places where defective pressure must be maintained. The work of propulsion is, on account of their practically perfect shape and surface, reduced to the work of over- coming air friction against their bodies and wings, and that is almost below calculation. Humboldt, Darwin and other natural- ists noticed that the large vultures gen- erally began their flight by launching themselves from an elevated • position, extending their wings during a short descent evidently made to acquire the velocity necessary to establish defective pressure, and then soar in circles, curves and reverse curves until they disap- peared beyond some neighboring eleva- tion, or by gradually rising until they passed beyond the range of vision. The reverse method was adopted when alighting. The bird approached its rest- ing place at a lower level. When it came near enough it turned upward and arose until its energy of motion was nearly absorbed. If any remained when alighting it was checked by u few vigor- ous wing beats against the direction of motion. An interesting observation of spar- rows trying to rise vertically in a fence corner will help support the views set forth above regarding the forces utilized in bird flight. The bird's body was vertical in each case and the wings vibrated almost hori- zontally, but at much higher speed than in ordinary flight. It was very plain in the shape of the blurred stroke made by the rapidly mov- ing wings that the tips of the primary feathers reached nearly two inches higher at the ends of the strokes than they did at half-way when moving for- ward and backward. Fanning the air they were for certain, and fanning it hard, with the fronts and backs of the wings alternately, having positive pressure on one side and de- fective pressure or rarefaction on the other, and the secondary feathers ap- peared to be doing most of the work. The higher speed of beating, when ris- in<^ vertically, is rendered possible by the' shortening of the radia of inertia due to moving the ends of the primaries forward. By raising the wings in this way nearly double power is exerted in equal time, because there is no inter- mission and on account of the increased speed of beating. It is interesting to notice that the sparrow when thus rising vertically moves upward very slowly, certainly not faster than one foot per second, and it is very clear that he is exerting his utmost strength. Yet he often gives up the attempt, especially if the fence hap- pens to be much over S feet in height, and he takes risks by attempting to es- cape in some other direction rather than face the work that he knows is beyond his strength. Now if a vertical rise of say 8 feet is beyond the sparrow's strength when he is producing an air reaction on one side of his wings, which, plus the rarefaction on their other sides is only a trifle more than can lift his weight, how very much less must be his work when he is flying horizontally? Very clearly the lift due to compres- sion of air under his wings can never come anywhere near equaling his weight. It does not do so when he is making a supreme eff^ort to get oyer a fence, and in his horizontal flight it can amount to only a small fraction of the equivalent of his weight. Operation of Flying Machine. It will be perceived that in the ma- chine illustrated there can be no in- termission in the development of direct reaction, even though that is a matter of little importance, excepting at the times of starting and stopping, when, owing to the want of horizontal speed, the intensity of air rarefaction over the wings is much reduced. Determining the Particulars op the Machine. Suppose the machine weighs 15 lbs. and that the operator weighs... 140 " ISS " If we took the albatross as our model, the great wing spread of the correspond- ing machine, more than 20 feet, would render it too unwieldy to be conveniently handled by an individual. As we are free to take any other soar- er than the albatross for a model, sup- pose we take the 30 pound California vulture of 8 feet 10 inches wing spread. The cube root of 155 divided by 30 equals about 1.72 and this is the dimen- sion ratio. 8.83x1.72 equals 15.1876, say 15 feet 2 Jnches wing spread. Proportionate speed for our machine would be as the square root of the di- mension ratio, 1.72 equals 1.31. Suppose the speed of the vulture is 30 miles. 30x1.3 equals would be 39 miles per hour. But because the friction of our machine will be much greater in proportion than the vultures, we must be content with much lower speed, say 30 miles per hour. Its wing surface will be in the pro- portion of the square of the dimension ratio, 1.72 D. R. 1.72 squared equals 2.9584x7 square feet surface of the vul- ture's wings 20.7088 square feet for the wing sail area.' The spread of our wings being IS feet 2 inches, we shall make them 1.25 feet wide, narrower in proportion than the vulture's, which will give about 18 square feet surface per pair and 36 square feet surface in two sets of wings. The radius of the centre of effort of each wing will be 5.687 feet. The weight divided by the radius of the centre of effort, 155 divided by 5.687 feet equals 27.25 lbs. at the two centres of effort of the two descending wings, and say 13.6 lbs. at the centre effort of each wing. To Ascertain the Speed of Wing Beat Necessary to Balance the Total Weight. Weight 155, divided by radius of cen- tre of effort, 5.687, equals 27.25 lbs. pres- sure to be exerted at both centres of effort together, and 13.6 lbs. on each sail. The area of each sail is 9 square feet. 13.6 divided by 9 equals 1.51 pqunds per square foot. Square root of 1.51x200 equals wind speed to give this pressure, 1.51x200 equals 17-38 miles per hour, equals nearly 25.5 feet per second. This 25.5 feet per second is the speed of the centre of effort during the initial strokes when the machine is starting. The length of the circular arc de- scribed by each centre of effort durmg the first down beats is 11.9 feet. 11. 9 divided by 25.5 equals 0.46 second per down beat. That is, the first down beat should be made in a trifle less than one- half second. This is the same as the work that a man would perform in running up a short stairway at the rate of 4.48 feet per second and carrying a weight of 15 pounds on his back. This is nearly equal to running up eight steps per second, taking two steps at a time. But this hard work would continue for only a very few seconds because air rarefaction over the wings due to speed of trans- lation begins immediately and increases very rapidly until only propelling force is required, the weight of the machine and operator being taken by the positive pressure due to air rarefaction, as in the case of the albatross cited above. This also represents the work to be done in starting from the level, the most difficult condition. Should the start be made from an elevation so that a descent for the purpose of acquiring speed would be possible, the initial work would be greatly reduced. Starting in a 20 mile head wind would take 72 pounds off the total weight to begin vvith. In a very few seconds the speed would increase to 29.3 miles, when rarefaction would support the total weight. It was shown above that in the case of the albatross travelling 35 miles per hour, equals 51.33 feet per second, that the total energy exerted by the bird in order to support its weight and to main- tain its speed was represented by a total air reaction of 0.386 foot pounds per sec- ond.. It is reasonable to assume that the vul- ture, being as clever a soarer as the alba- tross, will require to develop energy at the same rate power only in proportion to its weight. Its weight being 50 per cent, greater than that of the albatross by that proportion. 0.386x1^ equals 0.552 feet pounds per second. This represents the work of the vulture during ordinary flight. Our machine being 1.72 times larger lineally, will require 1.72 cubed times more power for steady flight. 1.72 cubed equals 5.166. But even though we may be able to construct the wings of our machine so that they may be almost as frictionless as those of the vulture, yet it does not ap- pear to be possible to provide that both the operator and the body of the ma- chine can be so arranged and covered by smooth surfaces that their friction can be reduced to anything near what would compare with that of the bird, bearing in mind that if they were equally friction- less the proportion would be as the square of the lineal dimensions, that is, 2.9 times, say 3 times greater. It will be reasonable and safe there- fore to provide that the operator must develop say lo times more work per second than the preceeding calculations call for. . 2.8s feet pounds per second x 10, equals 28.5 feet pounds per second. Let us compare this with the ordi- nary work of a laborer working 10 hours per day. He exerts continuously, while working, one-eighth to one-tenth horse power. One-eighth horse power equals SSo divided by 8 equals 68.7 foot pounds per second, and one-tenth horse power equals 55 foot pounds per second. But our machine should require only 28.5 foot pounds per second, that is, about one-half the work of a laborer. A man walking at a moderate rate of speed, say 3 miles per hour, does work equal to lifting his weight through one- twentieth of the distance he travels in any given time. At 3 miles per hour he travels 4.5 feet per second. 4.5 divided by 20 equals 0.225 feet per second. 0.225x155 pounds equals 34.875 foot pounds per second. But the work of propelling our ma- chine through the air at a speed of 30 miles per hour cannot exceed 28.5 foot pounds per second, which is much less than the work a 155 pound man does in walking 3 miles per hour. It appears to be clear that both the weight of our machine as well as its speed may be greatly increased before we reach the limit of work done for 10, hours daily by an ordinary day laborer. Of the two kinds of apparatus which thus far have been proposed for me- chanical flight, viz., individual flying machines, operated by muscular energy, and aeroplane machine operated by some kind of engine, or motor, the individual flying machine has been considered wor- thy of consideration before the other kind, because even though it will be much inferior to engine driven aero- plane machine in speed, radius and car- rying power, yet it will be incomparably more important because neither machin- erv nor fuel will be required, thus elimi- nating the risks of disabled engines and failure of fuel supply. It will also be safe and simple in construction and op- eration, smaller and lighter, always available because it will require no sup- plies and always ready for instant use. After the first necessarily crude and imperfect machine has demonstrated its practicability, we may look for their rapid development in simplicity and effi- ciency, as well as reduction of cost that will place them at everybody's service. It is evident that a machine constructed of Krupp steel in suitable forms can be built of equal strength and of much less than one-half of the weight of an effec- tive machine of the materials now avail- able. For example, the 36 pound machine re- ferred to above employs heavy cast iron gears, steel parts that in places are much too heavy, and aluminum in unsuitable sizes in many cases. As practicable machines of both kinds would be invaluable in warfare, it is only simple justice to humanity to prevent any military power from "cornering," or monopolizing their use by thus placing it in every one's power to construct and develop them unhindered. Having practically emptied the bag of mysteries that for ages have hindered the development of winged flying ma- chines we shall now consider the much simpler problem of engine operated aero- planes. This is a simple matter in comparison with winged flight, because there are practically no mysteries to be encoun- tered, nothing in fact in the shape of a serious difficulty, not even excepting the "serious problems of stability and bal- ancing," of which we are warned by some investigators, especially in the case of our machine encountering vertical air currents. Regarding the difficulties of stability and balancing, there is no difference in these things between aerial machines and submarine boats. Both cases are exactly' similar in the essential requirments that the centre of gravity must be maintained unchangeably in one position and that it must be held unalterably under the cen- tre of support, or buoyancy. The centre of resistance must also be approximately opposite the point at which the propulsive power is applied, although when rudders are employed, this matter is not of much importance. But it is essential that the relative posi- tions of tl},ese centres have no tendency to change unexpectedly. Regarding the dangers of vertical cur- rents. They exist in water as well as in air, yet in the hundreds of dives I made in my first four submarine boats in the Passaic river, and at many points in New York harbor between Hoboken and Sandy Hook, in all kinds of weather and in all stages of the tides, I never noticed any disturbance of movement, or other perceptible effect, from them. In fact while closed up in the moving boat there was no evidence of their exist- ence. The reason is clear. The horizontal speed of the] moving boat is so much greater than ' the vertical speed of the current that the latter makes no impres- sion on the trim, or on the direction of motion. Why should there be any difference in the case of machines floating and mov- ing in air? This objection cannot be dignified by calling it a mystery. It is merely one of the "ghosts" conjured up by some people by way of excuse for failing to understand the case. This will be rendered clearer by con- sidering the cases of instability cited by those who believe that both aerial ma- chines and submarines are equally liable to dive uncontrollably. The case of Lillienthal has already been explained. The case of the aeronaut who was killed last summer in San Francisco by falling with his broken aeroplane some 2,000 feet was in no way similar to Lill- ienthal's case. The San Franciscan aer- onaut caused his aeroplane to dive down- ward edgewise, at a very steep angle in order to acquire the velocity necessary for manoeuvering. After having acquired high velocity in his descent of some hundreds of feet hev steered his machine to move horizontal- ly. The great moving inertia due to the velocity of his descent was thus suddenly thrown on his wing arms, and because they were very far from being strong enough to endure the excessive sudden strain, they gave way, and the aero- naut with his broken machine was pre- cipitated to the earth. The submarine catastrophies cited are those of the English A.8 and the French Farfadet. It is remarkable that the eminent gen- tlemen who discoursed before the Eng- lish Society of Naval Architects, last summer, on the cause of the loss of these vessels attributed it to the untimely and improper use of the diving rudder instead of noticing what was clear to almost everybody else. These same gen- tlemen alluded to the fact that in the case of A.8 the main water ballast tank, of IS tons capacity, was practically filled at that time by 9 tons of water, leaving 6 tons volume of empty space. The captain of the trawler — to avoid ramming, which at high speed the A.8 turned rapidly to pass under the trawl- er's stern — testified that as the submarine moved around the curve she laid down on her side forcing her conning tower under water, through the open hatch, on the top of which the water poured, causing the boat to go down by the head and disappear. The centrifugal force due to the boat's rapid motion in a circular curve caused the water in the tank to move to the outside of the curve and upset the boat. The Case of the French Submarine. Farfadet was practically similar, ex- cepting that in her case there occurred a change of speed or inclination that caused the water in her partially filled tank to move to its forward end, thus causing the common centre of gravity of the boat, and the water in its tanks, to move far enough forward to force the forward part of the boat under water. This unexpected manceuvre, combined with her speed, forced the top of her tur- ret under and she took enough water on board to send her to the bottom. Evidently it is an important, yet a very- simple matter, that the centre of gravity of both aerial machines and submarines should be held immovably in one place, and that these centres should be at a suf- ficient distance beneath, exactly beneath the centre of support or buoyancy. It will surprise most people interested in aeronautics to learn that the practica- bility of flight with engine-driven aero- planes was demonstrated beyond ques- tion over 13 years ago by Mr. Phillips, a distinguished English military officer, al- though for some reason he did not ap- pear to appreciate his own work nor follow the plain course which his success clearly indicated. As far as my knowledge extends he was the first, or one of the first, to at- tach importance to air rarefaction over a bird's wings, and to direct attention to the fact that the albatross's wings are held flat in the fore-and-aft direction when it soars horizontally. See Engi- neering, London, August 14, 1885, and March 10, and May S, 1903. Mr. H. C. Vogt explained the function of air rarefaction on the lee side of ship's sails, and the forward faces of the blades of air propellers, in Bngineering, Eon- don, August 14, 1885, and September 22, 1888, but no one, so far as I am aware, even suspected that air rarefaction over a bird's wings, instead of being merely a help or even a considerable help, as Phillips believed, was the main factor, in fact almost the only source of sup- port for all flying animals, when they are in full flight. Thirteen years have passed since Mr. PhilHps proved the practicability of aer- oplane flight, not by causing his appara- tus to lift itself with a man to direct it, but by proving that a certain area of aeroplane surface, even though unsuita- bly arranged, did actually lift about 39 per cent, more total weight than anybody up to that time, including all the author- ities, would admit to be within the range of possibility. His machine was not quite large enough and the power was inadequate. Nor is it probable that he expected that it would also lift himself, but that same machine would have given much better results had there not existed certain de- fects in the design that prevented the presence of the degree of rarefaction, and consequent, lifting power that would have been attainable had these defects been eliminated. The .vertical supports for his aeroplanes were nicely arranged to conduct air from above into the places where, with proper precautions, a much more intense degree of rarefaction would have existed. The important point that his experi- ment developed was that, with suitable conditions, some other force besides those recognized by the authorities was in action, and in effective action, al- though he failed to fully appreciate it. Had his machine been a little larger, with about double the power provided, even of the same unsuitable, heavy kind, he could certainly have flown in the air, and he would not have been compelled to wait as long as I did, 20 years, after providing the first successful submarine boat, before the value of his invention was even partially recognized. Mr. Phillips's machine is described in Engineering, London, March 10 and May S, 1893. It consists of a Venetian bUnd shaped frame containing 50 slats or "sustainers" i^ inches wide and 22 feet long, fitted 2 inches apart in a frame 22 feet broad and 9 feet S inches high. The sustainers had a combined area of 136 square feet ; they are convex on the upper surface, and concave below, the hollow being about one-sixteenth inch deep. The frame holding the sustainers is set up in a light canoe-shaped carriage, composed principally of two bent planks like the two top streaks of a whale boat, and being 25 feet long and 18 inches wide, mounted on three wheels i foot in diameter, one in front and two at the rear. This vehicle carries a small boiler with a compound engine, which works a two-bladed aerial screw propeller re- volving about 400 times per minute. The fuel is Welsh coal. There is said to be no attempt to provide exceptionally light machinery. The weights of the various parts of the machine are, ap- proximately, carriage and wheels, 60 pounds. Machinery with water in boiler and fire in grate, 200 pounds ; sustainers. 70 pounds ; total weight, 330 pounds. The machine was run on a circular path of wood with a circumference, of 628 inches (200 inches diameter), and to keep it in position (preventing er- ratic flight) wires were carried from various parts of the machine to a cen- tral pole. I Still further to control the flight, which there is no means of guiding, the machine is not of sufficient size to carry a man, the forward wheel is so balanced that it never leaves the track, and there- fore serves as a guide, carrying some 17 pounds of the weight, the remainder be- ing on the hind wheels. On the first run 72 pounds dead weight were added, making the total lift 402 pounds. As soon as speed was gotten up and when the machine faced the wind, the hind wheels rose some two or three feet clear of the track, thus showing that the weight was carried by the air upon the Venetian blind sustainers. A second trial was made with the dead weight re- duced to 16 pounds and the circuit was made at a speed of about 28 miles per hour (2,464 feet per minute), with the wheels clear of the ground for about three-fourths of the distance. That the machine can not only sustain itself, but an added weight. Was demonstrated be- yond all doubt, even under the disadvan- tages of. proceeding in a circle, with the wind blowing pretty stiffly. It is possible that Mr. Phillips was dis- couraged by the opinions of those per- sons who "proved" that for successful mechanical flight an engine was required which, with its supply of coal and water for even a very- brief performance, should weigh no more than 5 pounds per horse power, whereas available en- gines weighed many times more than 5 pounds per horse power, and more prob- ably 60 pounds, but apparently he was not aware of the existence, at the time he made his experiment, of internal com- bustion, hydrocarbon engines that need not have weighed more than one-fifth of the wfeight of his motor, with its sup- plies. A specially designed Brayton en- gine would have suited the work fairly well. At the present day we can avail ourselves of "the wonderful development of automobile engines, due chiefly 0»S6EB CO., PRINT SHOP woo SECTION OF PLAt^E.,FOLL Size.. I ^ SECT ION ^VIEW OF 1 I CP ANE SLAT, FULL SIZE SECTION SHOEING A 3 fl A N 3 E VI E ^T FOR Ur'R'GHT POSTS -pLAN OF MACHINE. 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