The EARLY HISTORY of the AIRPLANE

 The DAYTON-WRIGHT AIRPLANE CO. DAYTON OHIO

The Wright Brothers' Aeroplane

_By Orville and Wilbur Wright_

Though the subject of aerial navigation is generally considered new, ithas occupied the minds of men more or less from the earliest ages. Ourpersonal interest in it dates from our childhood days. Late in theautumn of 1878 our father came into the house one evening with someobject partly concealed in his hands, and before we could see what itwas, he tossed it into the air. Instead of falling to the floor, as weexpected, it flew across the room, till it struck the ceiling, where itfluttered awhile, and finally sank to the floor. It was a little toy, known to scientists as a "helicoptere, " but which we, with sublimedisregard for science, at once dubbed a "bat. " It was a light frame ofcork and bamboo, covered with paper, which formed two screws, driven inopposite directions by rubber bands under torsion. A toy so delicatelasted only a short time in the hands of small boys, but its memory wasabiding. 

Several years later we began building these helicopteres for ourselves, making each one larger than that preceding. But, to our astonishment, wefound that the larger the "bat" the less it flew. We did not know that amachine having only twice the linear dimensions of another would requireeight times the power. We finally became discouraged, and returned tokite-flying, a sport to which we had devoted so much attention that wewere regarded as experts. But as we became older we had to give up thisfascinating sport as unbecoming to boys of our ages. 

It was not till the news of the sad death of Lilienthal reached Americain the summer of 1896 that we again gave more than passing attention tothe subject of flying. We then studied with great interest Chanute's"Progress in Flying Machines, " Langley's "Experiments in Aerodynamics, "the "Aeronautical Annuals" of 1905, 1906, and 1907, and severalpamphlets published by the Smithsonian Institution, especially articlesby Lilienthal and extracts from Mouillard's "Empire of the Air. " Thelarger works gave us a good understanding of the nature of the flyingproblem, and the difficulties in past attempts to solve it, whileMouillard and Lilienthal, the great missionaries of the flying cause, infected us with their own unquenchable enthusiasm, and transformed idlecuriosity into the active zeal of workers. 

In the field of aviation there were two schools. The first, represented by such men as Professor Langley and Sir Hiram Maxim, gave chief attention to power flight; the second, represented byLilienthal, Mouillard, and Chanute, to soaring flight. Our sympathieswere with the latter school, partly from impatience at the wastefulextravagance of mounting delicate and costly machinery on wingswhich no one knew how to manage, and partly, no doubt, from theextraordinary charm and enthusiasm with which the apostles of soaringflight set forth the beauties of sailing through the air on fixedwings, deriving the motive power from the wind itself. 

The balancing of a flyer may seem, at first thought, to be a very simplematter, yet almost every experimenter had found in this one point whichhe could not satisfactorily master. Many different methods were tried. Some experimenters placed the center of gravity far below the wings, inthe belief that the weight would naturally seek to remain at the lowestpoint. It is true, that, like the pendulum, it tended to seek the lowestpoint; but also, like the pendulum, it tended to oscillate in a mannerdestructive of all stability. A more satisfactory system, especially forlateral balance, was that of arranging the wings in the shape of a broadV, to form a dihedral angle, with the center low and the wing-tipselevated. In theory this was an automatic system, but in practice it hadtwo serious defects: first, it tended to keep the machine oscillating;and second, its usefulness was restricted to calm air. 

In a slightly modified form the same system was applied to thefore-and-aft balance. The main aeroplane was set at a positive angle, and a horizontal tail at a negative angle, while the center of gravitywas placed far forward. As in the case of lateral control, there was atendency to constant undulation, and the very forces which caused arestoration of balance in calms caused a disturbance of the balance inwinds. Notwithstanding the known limitations of this principle, it hadbeen embodied in almost every prominent flying machine which had beenbuilt. 

After considering the practical effect of the dihedral principle, wereached the conclusion that a flyer founded upon it might be of interestfrom a scientific point of view, but could be of no value in a practicalway. We therefore resolved to try a fundamentally different principle. We would arrange the machine so that it would not tend to right itself. We would make it as inert as possible to the effects of change ofdirection or speed, and thus reduce the effects of wind-gusts to aminimum. We would do this in the fore-and-aft stability by giving theaeroplanes a peculiar shape; and in the lateral balance by arching thesurfaces from tip to tip, just the reverse of what our predecessors haddone. Then by some suitable contrivance, actuated by the operator, forces should be brought into play to regulate the balance. 

Lilienthal and Chanute had guided and balanced their machines, byshifting the weight of the operator's body. But this method seemedto us incapable of expansion to meet large conditions, because theweight to be moved and the distance of possible motion were limited, while the disturbing forces steadily increased, both with wing areaand with wind velocity. In order to meet the needs of large machines, we wished to employ some system whereby the operator could vary atwill the inclination of different parts of the wings, and thus obtainfrom the wind forces to restore the balance which the wind itself haddisturbed. This could easily be done by using wings capable of beingwarped, and by supplementary adjustable surfaces in the shape ofrudders. As the forces obtainable for control would necessarilyincrease in the same ratio as the disturbing forces, the methodseemed capable of expansion to an almost unlimited extent. Ahappy device was discovered whereby the apparently rigid systemof superposed surfaces, invented by Wenham, and improved byStringfellow and Chanute, could be warped in a most unexpectedway, so that the aeroplanes could be presented on the right andleft sides at different angles to the wind. This, with an adjustable, horizontal front rudder, formed the main feature of our first glider. 

The period from 1885 to 1900 was one of unexampled activity inaeronautics, and for a time there was high hope that the age of flyingwas at hand. But Maxim, after spending $100, 000, abandoned the work;the Ader machine, built at the expense of the French Government, was afailure; Lilienthal and Pilcher were killed in experiments; and Chanuteand many others, from one cause or another, had relaxed their efforts, though it subsequently became known that Professor Langley was stillsecretly at work on a machine for the United States Government. Thepublic, discouraged by the failures and tragedies just witnessed, considered flight beyond the reach of man, and classed its adherentswith the inventors of perpetual motion. 

We began our active experiments at the close of this period, in October, 1900, at Kitty Hawk, North Carolina. Our machine was designed to beflown as a kite, with a man on board, in winds from 15 to 20 miles anhour. But, upon trial, it was found that much stronger winds wererequired to lift it. Suitable winds not being plentiful, we found itnecessary, in order to test the new balancing system, to fly the machineas a kite without a man on board, operating the levers through cordsfrom the ground. This did not give the practice anticipated, but itinspired confidence in the new system of balance. 

In the summer of 1901 we became personally acquainted with Mr. Chanute. When he learned that we were interested in flying as a sport, and notwith any expectation of recovering the money we were expending on it, hegave us much encouragement. At our invitation, he spent several weekswith us at our camp at Kill Devil Hill, four miles south of Kitty Hawk, during our experiments of that and the two succeeding years. He alsowitnessed one flight of the power machine near Dayton, Ohio, in October, 1904. 

The machine of 1901 was built with the shape of surface used byLilienthal, curved from front to rear like the segment of a parabola, with a curvature 1/12 the depth of its cord; but to make doubly surethat it would have sufficient lifting capacity when flown as a kite in15 or 20-mile winds, we increased the area from 165 square feet, used in1900, to 308 square feet--a size much larger than Lilienthal, Pilcher, or Chanute had deemed safe. Upon trial, however, the lifting capacityagain fell very far short of calculation, so that the idea of securingpractice while flying as a kite had to be abandoned. Mr. Chanute, whowitnessed the experiments, told us that the trouble was not due to poorconstruction of the machine. We saw only one other explanation--that thetables of air-pressures in general use were incorrect. 

[Illustration]

We then turned to gliding--coasting downhill on the air--as the onlymethod of getting the desired practice in balancing a machine. Aftera few minutes' practice we were able to make glides of over 300 feet, and in a few days were safely operating in 27-mile winds. In theseexperiments we met with several unexpected phenomena. We found that, contrary to the teachings of the books, the center of pressure on acurved surface traveled backward when the surface was inclined, at smallangles, more and more edgewise to the wind. We also discovered that infree flight, when the wing on one side of the machine was presented tothe wind at a greater angle than the one on the other side, the wingwith the greater angle descended, and the machine turned in a directionjust the reverse of what we were led to expect when flying the machineas a kite. The larger angle gave more resistance to forward motion, andreduced the speed of the wing on that side. The decrease in speed morethan counterbalanced the effect of the larger angle. The addition of afixed vertical vane in the rear increased the trouble, and made themachine absolutely dangerous. It was some time before a remedy wasdiscovered. This consisted of movable rudders working in conjunctionwith the twisting of the wings. The details of this arrangement aregiven in specifications published several years ago. 

The experiments of 1901 were far from encouraging. Although Mr. Chanuteassured us that, both in control and in weight carried per horse-power, the results obtained were better than those of any of our predecessors, yet we saw that the calculations upon which all flying machines had beenbased were unreliable, and that all were simply groping in the dark. Having set out with absolute faith in the existing scientific data, wewere driven to doubt one thing after another, till finally, after twoyears of experiment, we cast it all aside, and decided to rely entirelyupon our own investigations. Truth and error were everywhere sointimately mixed as to be undistinguishable. Nevertheless, the timeexpended in preliminary study of books was not misspent, for they gaveus a good general understanding of the subject, and enabled us at theoutset to avoid effort in many directions in which results would havebeen hopeless. 

The standard measurements of wind-pressures is the force produced by acurrent of air of one mile per hour velocity striking square against aplane of one square foot area. The practical difficulties of obtainingan exact measurement of this force have been great. The measurements bydifferent recognized authorities vary 50 per cent. When this simplest ofmeasurements presents so great difficulties, what shall be said of thetroubles encountered by those who attempt to find the pressure at eachangle as the plane is inclined more and more edgewise to the wind? Inthe eighteenth century the French Academy prepared tables giving suchinformation, and at a later date the Aeronautical Society of GreatBritain made similar experiments. Many persons likewise publishedmeasurements and formulas; but the results were so discordant thatProfessor Langley undertook a new series of measurements, the resultsof which form the basis of his celebrated work, "Experiments inAerodynamics. " Yet a critical examination of the data upon which hebased his conclusions as to the pressures at small angles showsresults so various as to make many of his conclusions little betterthan guesswork. 

To work intelligently, one needs to know the effects of a multitudeof variations that could be incorporated in the surfaces of flyingmachines. The pressures on squares are different from those onrectangles, circles, triangles, or ellipses; arched surfaces differfrom planes, and vary among themselves according to the depth ofcurvature; true arcs differ from parabolas, and the latter differamong themselves; thick surfaces differ from thin, and surfacesthicker in one place than another vary in pressure when the positionsof maximum thickness are different; some surfaces are most efficientat one angle, others at other angles. The shape of the edge also makesa difference, so that thousands of combinations are possible in sosimple a thing as a wing. 

We had taken up aeronautics merely as a sport. We reluctantly enteredupon the scientific side of it. But we soon found the work sofascinating that we were drawn into it deeper and deeper. Two testingmachines were built, which we believed would avoid the errors to whichthe measurements of others had been subject. After making preliminarymeasurements on a great number of different-shaped surfaces, to secure ageneral understanding of the subject, we began systematic measurementsof standard surfaces, so varied in design as to bring out the underlyingcauses of differences noted in their pressures. Measurements weretabulated on nearly 50 of these at all angles from zero to 45 degrees atintervals of 2-1/2 degrees. Measurements were also secured showing theeffects on each other when surfaces are superposed, or when they followone another. 

Some strange results were obtained. One surface, with a heavy roll atthe front edge, showed the same lift for all angles from 7-1/2 to 45degrees. A square plane, contrary to the measurements of all ourpredecessors, gave a greater pressure at 30 degrees than at 45 degrees. This seemed so anomalous that we were almost ready to doubt our ownmeasurements, when a simple test was suggested. A weather-vane, with twoplanes attached to the pointer at an angle of 80 degrees with eachother, was made. According to our tables, such a vane would be inunstable equilibrium when pointing directly into the wind; for if bychance the wind should happen to strike one plane at 39 degrees and theother at 41 degrees, the plane with the smaller angle would have thegreater pressure, and the pointer would be turned still farther out ofthe course of the wind until the two vanes again secured equalpressures, which would be at approximately 30 and 50 degrees. But thevane performed in this very manner. Further corroboration of the tableswas obtained in experiments with the new glider at Kill Devil Hill thenext season. 

In September and October, 1902, nearly 1, 000 gliding flights were made, several of which covered distances of over 600 feet. Some, made againsta wind of 36 miles an hour, gave proof of the effectiveness of thedevices for control. With this machine, in the autumn of 1903, we made anumber of flights in which we remained in the air for over a minute, often soaring for a considerable time in one spot, without any descentat all. Little wonder that our unscientific assistant should think theonly thing needed to keep it indefinitely in the air would be a coat offeathers to make it light!

With accurate data for making calculations, and a system of balanceeffective in winds as well as in calms, we were now in a position, wethought, to build a successful power-flyer. The first designs providedfor a total weight of 600 lbs. , including the operator and an eighthorse-power motor. But, upon completion, the motor gave more power thanhad been estimated, and this allowed 150 lbs. To be added forstrengthening the wings and other parts. 

Our tables made the designing of the wings an easy matter, and asscrew-propellers are simply wings traveling in a spiral course, weanticipated no trouble from this source. We had thought of getting thetheory of the screw-propeller from the marine engineers, and then, byapplying our tables of air-pressures to their formulas, of designingair-propellers suitable for our purpose. But so far as we could learn, the marine engineers possessed only empirical formulas, and the exactaction of the screw-propeller, after a century of use, was still veryobscure. As we were not in a position to undertake a long series ofpractical experiments to discover a propeller suitable for our machine, it seemed necessary to obtain such a thorough understanding of thetheory of its reactions as would enable us to design them fromcalculations alone. What at first seemed a problem became more complexthe longer we studied it. With the machine moving forward, the airflying backward, the propellers turning sidewise, and nothing standingstill, it seemed impossible to find a starting-point from which to tracethe various simultaneous reactions. Contemplation of it was confusing. After long arguments we often found ourselves in the ludicrous positionof each having been converted to the other's side, with no moreagreement than when the discussion began. 

[Illustration]

It was not till several months had passed, and every phase of theproblem had been thrashed over and over, that the various reactionsbegan to untangle themselves. When once a clear understanding had beenobtained there was no difficulty in designing suitable propellers, withproper diameter, pitch, and area of blade, to meet the requirements ofthe flyer. High efficiency in a screw-propeller is not dependent uponany particular or peculiar shape; and there is no such thing as a "best"screw. A propeller giving a high dynamic efficiency when used upon onemachine may be almost worthless when used upon another. The propellershould in every case be designed to meet the particular conditions ofthe machine to which it is to be applied. Our first propellers, builtentirely from calculation, gave in useful work 66 per cent. Of the powerexpended. This was about one-third more than had been secured by Maximor Langley. 

The first flights with the power machine were made on December 17, 1903. Only five persons besides ourselves were present. These were Messrs. John T. Daniels, W. S. Dough, and A. D. Etheridge, of the Kill DevilLife-Saving Station; Mr. W. C. Brinkley, of Manteo; and Mr. John Ward, of Naghead. Although a general invitation had been extended to thepeople living within five or six miles, not many were willing to facethe rigors of a cold December wind in order to see, as they no doubtthought, another flying machine not fly. The first flight lasted only 12seconds, a flight very modest compared with that of birds, but it was, nevertheless, the first in the history of the world in which a machinecarrying a man had raised itself by its own power into the air in freeflight, had sailed forward on a level course without reduction of speed, and had finally landed without being wrecked. The second and thirdflights were a little longer, and the fourth lasted 59 seconds, coveringa distance of 852 feet over the ground against a 20-mile wind. 

After the last flight the machine was carried back to camp and set downin what was thought to be a safe place. But a few minutes later, whilewe were engaged in conversation about the flights, a sudden gust of windstruck the machine, and started to turn it over. All made a rush to stopit, but we were too late. Mr. Daniels, a giant in stature and strength, was lifted off his feet, and falling inside, between the surfaces, wasshaken about like a rattle in a box as the machine rolled over and over. He finally fell out upon the sand with nothing worse than painfulbruises, but the damage to the machine caused a discontinuance ofexperiments. 

In the spring of 1904, through the kindness of Mr. Torrence Huffman, ofDayton, Ohio, we were permitted to erect a shed, and to continueexperiments, on what is known as the Huffman Prairie, at Simms Station, eight miles east of Dayton. The new machine was heavier and stronger, but similar to the one flown at Kill Devil Hill. When it was ready forits first trial every newspaper in Dayton was notified, and about adozen representatives of the Press were present. Our only request wasthat no pictures be taken, and that the reports be unsensational, so asnot to attract crowds to our experiment grounds. There were probably 50persons altogether on the ground. When preparations had been completed awind of only three or four miles was blowing--insufficient for startingon so short a track--but since many had come a long way to see themachine in action, an attempt was made. To add to the other difficulty, the engine refused to work properly. The machine, after running thelength of the track, slid off the end without rising into the air atall. Several of the newspaper men returned the next day, but were againdisappointed. The engine performed badly, and after a glide of only 60feet, the machine came to the ground. Further trial was postponed tillthe motor could be put in better running condition. The reporters hadnow, no doubt, lost confidence in the machine, though their reports, inkindness, concealed it. Later, when they heard that we were makingflights of several minutes' duration, knowing that longer flights hadbeen made with airships, and not knowing any essential differencebetween airships and flying machines, they were but little interested. 

We had not been flying long in 1904 before we found that the problem ofequilibrium had not as yet been entirely solved. Sometimes, in making acircle, the machine would turn over sidewise despite anything theoperator could do, although, under the same conditions in ordinarystraight flight, it could have been righted in an instant. In oneflight, in 1905, while circling around a honey locust tree at a heightof about 50 feet, the machine suddenly began to turn up on one wing, andtook a course toward the tree. The operator, not relishing the idea oflanding in a thorn-tree, attempted to reach the ground. The left wing, however, struck the tree at a height of 10 or 12 feet from the groundand carried away several branches; but the flight, which had alreadycovered a distance of six miles, was continued to the starting-point. 

The causes of these troubles--too technical for explanation here--werenot entirely overcome till the end of September, 1905. The flights thenrapidly increased in length, till experiments were discontinued afterOctober 5, on account of the number of people attracted to the field. Although made on a ground open on every side, and bordered on two sidesby much-traveled thoroughfares, with electric cars passing every hour, and seen by all the people living in the neighborhood for miles around, and by several hundred others, yet these flights have been made by somenewspapers the subject of a great "mystery. "

A practical flyer having been finally realized, we spent the years 1906and 1907 in constructing new machines and in business negotiations. Itwas not till May of this year that experiments (discontinued in October, 1905) were resumed at Kill Devil Hill, North Carolina. The recentflights were made to test the ability of our machine to meet therequirements of a contract with the United States Government to furnisha flyer capable of carrying two men and sufficient fuel supplies for aflight of 125 miles, with a speed of 40 miles an hour. The machine usedin these tests was the same one with which the flights were made atSimms Station in 1905, though several changes had been made to meetpresent requirements. The operator assumed a sitting position, insteadof lying prone, as in 1905, and a seat was added for a passenger. Alarger motor was installed, and radiators and gasoline reservoirs oflarger capacity replaced those previously used. No attempt was made tomake high or long flights. 

In order to show the general reader the way in which the machineoperates, let us fancy ourselves ready for the start. The machine isplaced upon a single-rail track facing the wind, and is securelyfastened with a cable. The engine is put in motion, and the propellersin the rear whir. You take your seat at the center of the machine besidethe operator. He slips the cable, and you shoot forward. An assistantwho has been holding the machine in balance on the rail starts forwardwith you, but before you have gone 50 feet the speed is too great forhim, and he lets go. Before reaching the end of the track the operatormoves the front rudder, and the machine lifts from the rail like a kitesupported by the pressure of the air underneath it. The ground under youis at first a perfect blur, but as you rise the objects become clearer. At a height of 100 feet you feel hardly any motion at all, except forthe wind which strikes your face. If you did not take the precaution tofasten your hat before starting, you have probably lost it by thistime. The operator moves a lever: the right wing rises, and the machineswings about to the left. You make a very short turn, yet you do notfeel the sensation of being thrown from your seat, so often experiencedin automobile and railway travel. You find yourself facing toward thepoint from which you started. The objects on the ground now seem to bemoving at much higher speed, though you perceive no change in thepressure of the wind on your face. You know then that you are travelingwith the wind. When you near the starting-point the operator stops themotor while still high in the air. The machine coasts down at an obliqueangle to the ground, and after sliding 50 or 100 feet, comes to rest. Although the machine often lands when traveling at a speed of a mile aminute, you feel no shock whatever, and cannot, in fact, tell the exactmoment at which it first touched the ground. The motor close beside youkept up an almost deafening roar during the whole flight, yet in yourexcitement you did not notice it till it stopped!

Our experiments have been conducted entirely at our own expense. In thebeginning we had no thought of recovering what we were expending, whichwas not great, and was limited to what we could afford in recreation. Later, when a successful flight had been made with a motor, we gave upthe business in which we were engaged, to devote our entire time andcapital to the development of a machine for practical uses. As soon asour condition is such that constant attention to business is notrequired, we expect to prepare for publication the results of ourlaboratory experiments, which alone made an early solution of the flyingproblem possible. 

How We Made the First Flight

_By Orville Wright_

The flights of the 1902 glider had demonstrated the efficiency of oursystem of maintaining equilibrium, and also the accuracy of thelaboratory work upon which the design of the glider was based. We thenfelt that we were prepared to calculate in advance the performance ofmachines with a degree of accuracy that had never been possible with thedata and tables possessed by our predecessors. Before leaving camp in1902 we were already at work on the general design of a new machinewhich we proposed to propel with a motor. 

Immediately upon our return to Dayton, we wrote to a number ofautomobile and motor builders, stating the purpose for which we desireda motor, and asking whether they could furnish one that would developeight brake-horsepower, with a weight complete not exceeding 200 pounds. Most of the companies answered that they were too busy with theirregular business to undertake the building of such a motor for us; butone company replied that they had motors rated at 8 horse-power, according to the French system of ratings, which weighed only 135pounds, and that if we thought this motor would develop enough power forour purpose they would be glad to sell us one. After an examination ofthe particulars of this motor, from which we learned that it had but asingle cylinder of 4-inch bore and 5-inch stroke, we were afraid it wasmuch over-rated. Unless the motor would develop a full 8brake-horsepower, it would be useless for our purpose. 

Finally we decided to undertake the building of the motor ourselves. Weestimated that we could make one of four cylinders with 4-inch bore and4-inch stroke, weighing not over two hundred pounds, including allaccessories. Our only experience up to that time in the building ofgasoline motors had been in the construction of an air-cooled motor, 5-inch bore and 7-inch stroke, which was used to run the machinery ofour small workshop. To be certain that four cylinders of the size we hadadopted (4" x 4") would develop the necessary 8 horse-power, we firstfitted them in a temporary frame of simple and cheap construction. Injust six weeks from the time the design was started, we had the motor onthe block testing its power. The ability to do this so quickly waslargely due to the enthusiastic and efficient services of Mr. C. E. Taylor, who did all the machine work in our shop for the first as wellas the succeeding experimental machines. There was no provision forlubricating either cylinders or bearings while this motor was running. For that reason it was not possible to run it more than a minute or twoat a time. In these short tests the motor developed about ninehorse-power. We were then satisfied that, with proper lubrication andbetter adjustments, a little more power could be expected. Thecompletion of the motor according to drawing was, therefore, proceededwith at once. 

[Illustration]

While Mr. Taylor was engaged with this work, Wilbur and I were busy incompleting the design of the machine itself. The preliminary tests ofthe motor having convinced us that more than 8 horse-power would besecured, we felt free to add enough weight to build a more substantialmachine than we had originally contemplated. 

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For two reasons we decided to use two propellers. In the first place wecould, by the use of two propellers, secure a reaction against a greaterquantity of air, and at the same time use a larger pitch angle than waspossible with one propeller; and in the second place by having thepropellers turn in opposite directions, the gyroscopic action of onewould neutralize that of the other. The method we adopted of driving thepropellers in opposite directions by means of chains is now too wellknown to need description here. We decided to place the motor to oneside of the man, so that in case of a plunge headfirst, the motor couldnot fall upon him. In our gliding experiments we had had a number ofexperiences in which we had landed upon one wing, but the crushing ofthe wing had absorbed the shock, so that we were not uneasy about themotor in case of a landing of that kind. To provide against the machinerolling over forward in landing, we designed skids like sled runners, extending out in front of the main surfaces. Otherwise the generalconstruction and operation of the machine was to be similar to that ofthe 1902 glider. 

When the motor was completed and tested, we found that it would develop16 horse-power for a few seconds, but that the power rapidly droppedtill, at the end of a minute, it was only 12 horse-power. Ignorant ofwhat a motor of this size ought to develop, we were greatly pleased withits performance. More experience showed us that we did not get one-halfof the power we should have had. 

With 12 horse-power at our command, we considered that we could permitthe weight of the machine with operator to rise to 750 or 800 pounds, and still have as much surplus power as we had originally allowed for inthe first estimate of 550 pounds. 

Before leaving for our camp at Kitty Hawk we tested the chain drive forthe propellers in our shop at Dayton, and found it satisfactory. Wefound, however, that our first propeller shafts, which were constructedof heavy gauge steel tubing, were not strong enough to stand the shocksreceived from a gasoline motor with light fly wheel, although they wouldhave been able to transmit three or four times the power uniformlyapplied. We therefore built a new set of shafts of heavier tubing, whichwe tested and thought to be abundantly strong. 

We left Dayton, September 23, and arrived at our camp at Kill Devil Hillon Friday, the 25th. We found there provisions and tools, which had beenshipped by freight several weeks in advance. The building, erected in1901 and enlarged in 1902, was found to have been blown by a storm fromits foundation posts a few months previously. While we were awaiting thearrival of the shipment of machinery and parts from Dayton, we were busyputting the old building in repair, and erecting a new building to serveas a workshop for assembling and housing the new machine. 

Just as the building was being completed, the parts and material for themachines arrived simultaneously with one of the worst storms that hadvisited Kitty Hawk in years. The storm came on suddenly, blowing 30 to40 miles an hour. It increased during the night, and the next day wasblowing over 75 miles an hour. In order to save the tar-paper roof, wedecided it would be necessary to get out in this wind and nail down moresecurely certain parts that were especially exposed. When I ascended theladder and reached the edge of the roof, the wind caught under my largecoat, blew it up around my head and bound my arms till I was perfectlyhelpless. Wilbur came to my assistance and held down my coat while Itried to drive the nails. But the wind was so strong I could not guidethe hammer and succeeded in striking my fingers as often as the nails. 

The next three weeks were spent in setting the motor-machine together. On days with more favorable winds we gained additional experience inhandling a flyer by gliding with the 1902 machine, which we had found inpretty fair condition in the old building, where we had left it the yearbefore. 

Mr. Chanute and Dr. Spratt, who had been guests in our camp in 1901 and1902, spent some time with us, but neither one was able to remain to seethe test of the motor-machine, on account of the delays caused bytrouble which developed in the propeller shafts. 

While Mr. Chanute was with us, a good deal of time was spent indiscussion of the mathematical calculations upon which we had based ourmachine. He informed us that, in designing machinery, about 20 per cent. Was usually allowed for the loss in the transmission of power. As we hadallowed only 5 per cent. , a figure we had arrived at by some crudemeasurements of the friction of one of the chains when carrying only avery light load, we were much alarmed. More than the whole surplus inpower allowed in our calculations would, according to Mr. Chanute'sestimate, be consumed in friction in the driving chains. After Mr. Chanute's departure, we suspended one of the drive chains over asprocket, hanging bags of sand on either side of the sprocket of aweight approximately equal to the pull that would be exerted on thechains when driving the propellers. By measuring the extra amount ofweight needed on one side to lift the weight on the other, we calculatedthe loss in transmission. This indicated that the loss of power fromthis source would be only 5 per cent. , as we originally estimated. Butwhile we could see no serious error in this method of determining theloss, we were very uneasy until we had a chance to run the propellerswith the motor to see whether we could get the estimated number ofturns. 

The first run of the motor on the machine developed a flaw in one of thepropeller shafts which had not been discovered in the test at Dayton. The shafts were sent at once to Dayton for repair, and were not receivedagain until November 20, having been gone two weeks. We immediately putthem in the machine and made another test. A new trouble developed. Thesprockets which were screwed on the shafts, and locked with nuts ofopposite thread, persisted in coming loose. After many futile attemptsto get them fast, we had to give it up for that day, and went to bedmuch discouraged. However, after a night's rest, we got up the nextmorning in better spirits and resolved to try again. 

While in the bicycle business we had become well acquainted with the useof hard tire cement for fastening tires on the rims. We had once used itsuccessfully in repairing a stop watch after several watchsmiths hadtold us it could not be repaired. If tire cement was good for fasteningthe hands on a stop watch, why should it not be good for fastening thesprockets on the propeller shaft of a flying machine? We decided to tryit. We heated the shafts and sprockets, melted cement into the threads, and screwed them together again. This trouble was over. The sprocketsstayed fast. 

Just as the machine was ready for test bad weather set in. It had beendisagreeably cold for several weeks, so cold that we could scarcely workon the machine for some days. But now we began to have rain and snow, and a wind of 25 to 30 miles blew for several days from the north. Whilewe were being delayed by the weather we arranged a mechanism to measureautomatically the duration of a flight from the time the machine startedto move forward to the time it stopped, the distance traveled throughthe air in that time, and the number of revolutions made by the motorand propeller. A stop watch took the time; an anemometer measured theair traveled through; and a counter took the number of revolutions madeby the propellers. The watch, anemometer and revolution counter were allautomatically started and stopped simultaneously. From data thusobtained we expected to prove or disprove the accuracy of our propellercalculations. 

On November 28, while giving the motor a run indoors, we thought weagain saw something wrong with one of the propeller shafts. On stoppingthe motor we discovered that one of the tubular shafts had cracked!

[Illustration]

Immediate preparation was made for returning to Dayton to build anotherset of shafts. We decided to abandon the use of tubes, as they did notafford enough spring to take up the shocks of premature or missedexplosions of the motor. Solid tool-steel shafts of smaller diameterthan the tubes previously used were decided upon. These would allow acertain amount of spring. The tubular shafts were many times strongerthan would have been necessary to transmit the power of our motor if thestrains upon them had been uniform. But the large hollow shafts had nospring in them to absorb the unequal strains. 

Wilbur remained in camp while I went to get the new shafts. I did notget back to camp again till Friday, the 11th of December. Saturdayafternoon the machine was again ready for trial, but the wind was solight a start could not have been made from level ground with the run ofonly sixty feet permitted by our monorail track. Nor was there enoughtime before dark to take the machine to one of the hills, where, byplacing the track on a steep incline, sufficient speed could be securedfor starting in calm air. 

Monday, December 14, was a beautiful day, but there was not enough windto enable a start to be made from the level ground about camp. Wetherefore decided to attempt a flight from the side of the big KillDevil Hill. We had arranged with the members of the Kill Devil Hill LifeSaving Station, which was located a little over a mile from our camp, toinform them when we were ready to make the first trial of the machine. We were soon joined by J. T. Daniels, Robert Westcott, Thomas Beachem, W. S. Dough and Uncle Benny O'Neal, of the station, who helped us getthe machine to the hill, a quarter mile away. We laid the track 150 feetup the side of the hill on a 9-degree slope. With the slope of thetrack, the thrust of the propellers and the machine starting directlyinto the wind, we did not anticipate any trouble in getting up flyingspeed on the 60-foot monorail track. But we did not feel certain theoperator could keep the machine balanced on the track. 

When the machine had been fastened with a wire to the track, so that itcould not start until released by the operator, and the motor had beenrun to make sure that it was in condition, we tossed up a coin to decidewho should have the first trial. Wilbur won. I took a position at one ofthe wings, intending to help balance the machine as it ran down thetrack. But when the restraining wire was slipped, the machine startedoff so quickly I could stay with it only a few feet. After a 35 to40-foot run it lifted from the rail. But it was allowed to turn up toomuch. It climbed a few feet, stalled, and then settled to the groundnear the foot of the hill, 105 feet below. My stop watch showed that ithad been in the air just 3-1/2 seconds. In landing the left wing touchedfirst. The machine swung around, dug the skids into the sand and brokeone of them. Several other parts were also broken, but the damage to themachine was not serious. While the test had shown nothing as to whetherthe power of the motor was sufficient to keep the machine up, since thelanding was made many feet below the starting point, the experiment haddemonstrated that the method adopted for launching the machine was asafe and practical one. On the whole, we were much pleased. 

Two days were consumed in making repairs, and the machine was not readyagain till late in the afternoon of the 16th. While we had it out on thetrack in front of the building, making the final adjustments, a strangercame along. After looking at the machine a few seconds he inquired whatit was. When we told him it was a flying machine he asked whether weintended to fly it. We said we did, as soon as we had a suitable wind. He looked at it several minutes longer and then, wishing to becourteous, remarked that it looked as if it would fly, if it had a"suitable wind. " We were much amused, for, no doubt, he had in mind therecent 75-mile gale when he repeated our words, "a suitable wind!"

During the night of December 16, 1903, a strong cold wind blew from thenorth. When we arose on the morning of the 17th, the puddles of water, which had been standing about camp since the recent rains, were coveredwith ice. The wind had a velocity of 10 to 12 meters per second (22 to27 miles an hour). We thought it would die down before long, and soremained indoors the early part of the morning. But when ten o'clockarrived, and the wind was as brisk as ever, we decided that we hadbetter get the machine out and attempt a flight. We hung out the signalfor the men of the life saving station. We thought that by facing theflyer into a strong wind, there ought to be no trouble in launching itfrom the level ground about camp. We realized the difficulties of flyingin so high a wind, but estimated that the added dangers in flight wouldbe partly compensated for by the slower speed in landing. 

We laid the track on a smooth stretch of ground about one hundred feetnorth of the new building. The biting cold wind made work difficult, andwe had to warm up frequently in our living room, where we had a goodfire in an improvised stove made of a large carbide can. By the time allwas ready, J. T. Daniels, W. S. Dough and A. D. Etheridge, members ofthe Kill Devil Life Saving Station; W. C. Brinkley, of Manteo, andJohnny Moore, a boy from Nag's Head, had arrived. 

We had a "Richards" hand anemometer with which we measured the velocityof the wind. Measurements made just before starting the first flightshowed velocities of 11 to 12 meters per second, or 24 to 27 miles perhour. Measurements made just before the last flight gave between 9 and10 meters per second. One made just after showed a little over 8 meters. The records of the Government Weather Bureau at Kitty Hawk gave thevelocity of the wind between the hours of 10:30 and 12 o'clock, the timeduring which the four flights were made, as averaging 27 miles at thetime of the first flight and 24 miles at the time of the last. 

 * * * * *

Wilbur, having used his turn in the unsuccessful attempt on the 14th, the right to the first trial now belonged to me. After running the motora few minutes to heat it up, I released the wire that held the machineto the track, and the machine started forward into the wind. Wilbur ranat the side of the machine, holding the wing to balance it on the track. Unlike the start on the 14th, made in a calm, the machine, facing a27-mile wind, started very slowly. Wilbur was able to stay with it tillit lifted from the track after a forty-foot run. One of the life savingmen snapped the camera for us, taking a picture just as the machine hadreached the end of the track and had risen to a height of about twofeet. The slow forward speed of the machine over the ground is clearlyshown in the picture by Wilbur's attitude. He stayed along beside themachine without any effort. 

The course of the flight up and down was exceedingly erratic, partly dueto the irregularity of the air, and partly to lack of experience inhandling this machine. The control of the front rudder was difficult onaccount of its being balanced too near the center. This gave it atendency to turn itself when started; so that it turned too far on oneside and then too far on the other. As a result the machine would risesuddenly to about ten feet, and then as suddenly dart for the ground. Asudden dart when a little over a hundred feet from the end of the track, or a little over 120 feet from the point at which it rose into the air, ended the flight. As the velocity of the wind was over 35 feet persecond and the speed of the machine against this wind ten feet persecond, the speed of the machine relative to the air was over 45 feetper second, and the length of the flight was equivalent to a flight of540 feet made in calm air. This flight lasted only 12 seconds, but itwas nevertheless the first in the history of the world in which amachine carrying a man had raised itself by its own power into the airin full flight, had sailed forward without reduction of speed, and hadfinally landed at a point as high as that from which it started. 

 * * * * *

At twenty minutes after eleven Wilbur started on the second flight. Thecourse of this flight was much like that of the first, very much up anddown. The speed over the ground was somewhat faster than that of thefirst flight, due to the lesser wind. The duration of the flight wasless than a second longer than the first, but the distance covered wasabout seventy-five feet greater. 

Twenty minutes later the third flight started. This one was steadierthan the first one an hour before. I was proceeding along pretty wellwhen a sudden gust from the right lifted the machine up twelve tofifteen feet and turned it up sidewise in an alarming manner. It begansliding off to the left. I warped the wings to try to recover thelateral balance and at the same time pointed the machine down to reachthe ground as quickly as possible. The lateral control was moreeffective than I had imagined and before I reached the ground the rightwing was lower than the left and struck first. The time of this flightwas fifteen seconds and the distance over the ground a little over 200feet. 

Wilbur started the fourth and last flight at just 12 o'clock. The firstfew hundred feet were up and down as before, but by the time threehundred feet had been covered, the machine was under much bettercontrol. The course for the next four or five hundred feet had butlittle undulation. However, when out about eight hundred feet themachine began pitching again, and, in one of its starts downward, struckthe ground. The distance over the ground was measured and found to be852 feet; the time of the flight 59 seconds. The frame supporting thefront rudder was badly broken, but the main part of the machine was notinjured at all. We estimated that the machine could be put in conditionfor flight again in a day or two. 

While we were standing about discussing this last flight, a suddenstrong gust of wind struck the machine and began to turn it over. Everybody made a rush for it. Wilbur, who was at one end, seized it infront, Mr. Daniels and I, who were behind, tried to stop it by holdingto the rear uprights. All our efforts were vain. The machine rolled overand over. Daniels, who had retained his grip, was carried along with it, and was thrown about head over heels inside of the machine. Fortunatelyhe was not seriously injured, though badly bruised in falling aboutagainst the motor, chain guides, etc. The ribs in the surfaces of themachine were broken, the motor injured and the chain guides badly bent, so that all possibility of further flights with it for that year were atan end. 

[Illustration]

Some Aeronautical Experiments

_By Wilbur Wright_

The difficulties which obstruct the pathway to success in flying machineconstruction are of three general classes: (1) Those which relate to theconstruction of the sustaining wings. (2) Those which relate to thegeneration and application of the power required to drive the machinethrough the air. (3) Those relating to the balancing and steering of themachine after it is actually in flight. Of these difficulties two arealready to a certain extent solved. Men already know how to constructwings or aeroplanes which, when driven through air at sufficient speed, will not only sustain the weight of the wings themselves, but also thatof the engine, and of the engineer as well. Men also know how to buildengines and screws of sufficient lightness and power to drive theseplanes at sustaining speed. As long ago as 1893 a machine weighing 8, 000lbs. Demonstrated its power both to lift itself from the ground and tomaintain a speed of from 30 to 40 miles per hour; but it came to griefin an accidental free flight, owing to the inability of the operators tobalance and steer it properly. This inability to balance and steer stillconfronts students of the flying problem, although nearly ten years havepassed. When this one feature has been worked out the age of flyingmachines will have arrived, for all other difficulties are of minorimportance. 

The person who merely watches the flight of a bird gathers theimpression that the bird has nothing to think of but the flappingof its wings. As a matter of fact, this is a very small part of itsmental labour. Even to mention all the things the bird must constantlykeep in mind in order to fly securely through the air would take avery considerable treatise. If I take a piece of paper, and afterplacing it parallel with the ground, quickly let it fall, it will notsettle steadily down as a staid, sensible piece of paper ought to do, but it insists on contravening every recognized rule of decorum, turning over and darting hither and thither in the most erraticmanner, much after the style of an untrained horse. Yet this is thestyle of steed that men must learn to manage before flying can becomean everyday sport. The bird has learned this art of equilibrium, andlearned it so thoroughly that its skill is not apparent to our sight. We only learn to appreciate it when we try to imitate it. Now, thereare two ways of learning how to ride a fractious horse: one is to geton him and learn by actual practice how each motion and trick may bebest met; the other is to sit on a fence and watch the beast awhile, and then retire to the house and at leisure figure out the best way ofovercoming his jumps and kicks. The latter system is the safest; butthe former, on the whole, turns out the larger proportion of goodriders. It is very much the same in learning to ride a flying machine;if you are looking for perfect safety you will do well to sit on afence and watch the birds; but if you really wish to learn you mustmount a machine and become acquainted with its tricks by actual trial. 

 * * * * *

My own active interest in aeronautical problems dates back to the deathof Lilienthal in 1896. The brief notice of his death which appeared inthe telegraphic news at that time aroused a passive interest which hadexisted from my childhood, and led me to take down from the shelves ofour home library a book on "Animal Mechanism, " by Prof. Marey, which Ihad already read several times. From this I was led to read more modernworks, and as my brother soon became equally interested with myself, wesoon passed from the reading to the thinking, and finally to the workingstage. It seemed to us that the main reason why the problem had remainedso long unsolved was that no one had been able to obtain any adequatepractice. We figured that Lilienthal in five years of time had spentonly about five hours in actual gliding through the air. The wonder wasnot that he had done so little, but that he had accomplished so much. Itwould not be considered at all safe for a bicycle rider to attempt toride through a crowded city street after only five hours' practice, spread out in bits of ten seconds each over a period of five years; yetLilienthal with this brief practice was remarkably successful in meetingthe fluctuations and eddies of wind gusts. We thought that if somemethod could be found by which it would be possible to practice by thehour instead of by the second there would be hope of advancing thesolution of a very difficult problem. It seemed feasible to do this bybuilding a machine which would be sustained at a speed of 18 miles perhour, and then finding a locality where winds of this velocity werecommon. With these conditions a rope attached to the machine to keep itfrom floating backward would answer very nearly the same purpose as apropeller driven by a motor, and it would be possible to practice by thehour, and without any serious danger, as it would not be necessary torise far from the ground, and the machine would not have any forwardmotion at all. We found, according to the accepted tables of airpressures on curved surfaces, that a machine spreading 200 square feetof wing surface would be sufficient for our purpose, and that placescould easily be found along the Atlantic coast where winds of 16 to 25miles were not at all uncommon. When the winds were low it was our planto glide from the tops of sand hills, and when they were sufficientlystrong to use a rope for our motor and fly over one spot. Our next workwas to draw up the plan for a suitable machine. After much study wefinally concluded that tails were a source of trouble rather than ofassistance, and therefore we decided to dispense with them altogether. It seemed reasonable that if the body of the operator could be placed ina horizontal position instead of the upright, as in the machines ofLilienthal, Pilcher and Chanute, the wind resistance could be verymaterially reduced, since only one square foot instead of five would beexposed. As a full half-horse-power could be saved by this change, wearranged to try at least the horizontal position. Then the method ofcontrol used by Lilienthal, which consisted in shifting the body, didnot seem quite as quick or effective as the case required; so, afterlong study, we contrived a system consisting of two large surfaces onthe Chanute double-deck plan, and a smaller surface placed a shortdistance in front of the main surfaces in such a position that theaction of the wind upon it would counterbalance the effect of the travelof the center of pressure on the main surfaces. Thus changes in thedirection and velocity of the wind would have little disturbing effect, and the operator would be required to attend only to the steering of themachine, which was to be effected by curving the forward surface up ordown. The lateral equilibrium and the steering to right or left was tobe attained by a peculiar torsion of the main surfaces, which wasequivalent to presenting one end of the wings at a greater angle thanthe other. In the main frame a few changes were also made in the detailsof construction and trussing employed by Mr. Chanute. The most importantof these were: (1) The moving of the forward main cross-piece of theframe to the extreme front edge; (2) the encasing in the cloth of allcross-pieces and ribs of the surfaces; (3) a rearrangement of the wiresused in trussing the two surfaces together, which rendered it possibleto tighten all the wires by simply shortening two of them. 

[Illustration]

With these plans we proceeded in the summer of 1900 to Kitty Hawk, North Carolina, a little settlement located on the strip of landthat separates Albemarle Sound from the Atlantic Ocean. Owing to theimpossibility of obtaining suitable material for a 200-square-footmachine, we were compelled to make it only 165 square feet in area, which, according to the Lilienthal tables, would be supported at anangle of three degrees in a wind of about 21 miles per hour. On the veryday that the machine was completed the wind blew from 25 to 30 miles perhour, and we took it out for a trial as a kite. We found that while itwas supported with a man on it in a wind of about 25 miles, its anglewas much nearer 20 degrees than three degrees. Even in gusts of 30 milesthe angle of incidence did not get as low as three degrees, although thewind at this speed has more than twice the lifting power of a 21-milewind. As winds of 30 miles per hour are not plentiful on clear days, itwas at once evident that our plan of practicing by the hour, day afterday, would have to be postponed. Our system of twisting the surfacesto regulate the lateral balance was tried and found to be much moreeffective than shifting the operator's body. On subsequent days, whenthe wind was too light to support the machine with a man on it, wetested it as a kite, working the rudders by cords reaching to theground. The results were very satisfactory, yet we were well aware thatthis method of testing is never wholly convincing until the results areconfirmed by actual gliding experience. 

We then turned our attention to making a series of actual measurementsof the lift and drift of the machine under various loads. So far as wewere aware, this had never previously been done with any full-sizemachine. The results obtained were most astonishing, for it appearedthat the total horizontal pull of the machine, while sustaining a weightof 52 lbs. , was only 8. 5 lbs. , which was less than had previously beenestimated for head resistance of the framing alone. Making allowance forthe weight carried, it appeared that the head resistance of the framingwas but little more than 50 per cent. Of the amount which Mr. Chanutehad estimated as the head resistance of the framing of his machine. Onthe other hand, it appeared sadly deficient in lifting power as comparedwith the calculated lift of curved surfaces of its size. This deficiencywe supposed might be due to one or more of the following causes:--(1)That the depth of the curvature of our surfaces was insufficient, beingonly about one in 22, instead of one in 12. (2) That the cloth used inour wings was not sufficiently air-tight. (3) That the Lilienthal tablesmight themselves be somewhat in error. We decided to arrange our machinefor the following year so that the depth of the curvature of itssurfaces could be varied at will and its covering air-proofed. 

Our attention was next turned to gliding, but no hill suitable for thepurpose could be found near our camp at Kitty Hawk. This compelled us totake the machine to a point four miles south, where the Kill Devil sandhill rises from the flat sand to a height of more than 100 feet. Itsmain slope is toward the northeast, and has an inclination of 10degrees. On the day of our arrival the wind blew about 25 miles an hour, and as we had had no experience at all in gliding, we deemed it unsafeto attempt to leave the ground. But on the day following, the windhaving subsided to 14 miles per hour, we made about a dozen glides. Ithad been the original intention that the operator should run with themachine to obtain initial velocity, and assume the horizontal positiononly after the machine was in free flight. When it came time to land hewas to resume the upright position and alight on his feet, after thestyle of previous gliding experiments. But in actual trial we found itmuch better to employ the help of two assistants in starting, which thepeculiar form of our machine enabled us readily to do; and in landing wefound that it was entirely practicable to land while still reclining ina horizontal position upon the machine. Although the landings were madewhile moving at speeds of more than 20 miles an hour, neither machinenor operator suffered any injury. The slope of the hill was 9. 5 deg. , ora drop of one foot in six. We found that after attaining a speed ofabout 25 to 30 miles with reference to the wind, or 10 to 15 miles overthe ground, the machine not only glided parallel to the slope of thehill, but greatly increased its speed, thus indicating its ability toglide on a somewhat less angle than 9. 5 deg. , when we should feel itsafe to rise higher from the surface. The control of the machine provedeven better than we had dared to expect, responding quickly to theslightest motion of the rudder. With these glides our experiments forthe year 1900 closed. Although the hours and hours of practice we hadhoped to obtain finally dwindled down to about two minutes, we were verymuch pleased with the general results of the trip, for, setting out aswe did with almost revolutionary theories on many points and an entirelyuntried form of machine, we considered it quite a point to be able toreturn without having our pet theories completely knocked on the headby the hard logic of experience, and our own brains dashed out in thebargain. Everything seemed to us to confirm the correctness of ouroriginal opinions--(1) that practice is the key to the secret offlying; (2) that it is practicable to assume the horizontal position;(3) that a smaller surface set at a negative angle in front of themain bearing surfaces, or wings, will largely counteract the effectof the fore-and-aft travel of the center of pressure; (4) thatsteering up and down can be attained with a rudder without movingthe position of the operator's body; (5) that twisting the wings soas to present their ends to the wind at different angles is a moreprompt and efficient way of maintaining lateral equilibrium than thatemployed in shifting the body of the operator of the machine. 

When the time came to design our new machine for 1901 we decided to makeit exactly like the previous machine in theory and method of operation. But as the former machine was not able to support the weight of theoperator when flown as a kite, except in very high winds and at verylarge angles of incidence, we decided to increase its lifting power. Accordingly, the curvature of the surfaces was increased to one in 12, to conform to the shape on which Lilienthal's table was based, and to beon the safe side we decided also to increase the area of the machinefrom 165 square feet to 308 square feet, although so large a machine hadnever before been deemed controllable. The Lilienthal machine had anarea of 151 square feet; that of Pilcher, 165 square feet; and theChanute double-decker, 134 square feet. As our system of controlconsisted in a manipulation of the surfaces themselves instead ofshifting the operator's body, we hoped that the new machine would becontrollable, notwithstanding its great size. According to calculations, it would obtain support in a wind of 17 miles per hour with an angle ofincidence of only three degrees. 

[Illustration]

Our experience of the previous year having shown the necessity of asuitable building for housing the machine, we erected a cheap framebuilding, 16 feet wide, 25 feet long, and 7 feet high at the eaves. Asour machine was 22 feet wide, 14 feet long (including the rudder), andabout 6 feet high, it was not necessary to take the machine apart in anyway in order to house it. Both ends of the building, except the gableparts, were made into doors which hinged above, so that when opened theyformed an awning at each end and left an entrance the full width of thebuilding. We went into camp about the middle of July, and were soonjoined by Mr. E. C. Huffaker, of Tennessee, an experienced aeronauticalinvestigator in the employ of Mr. Chanute, by whom his services werekindly loaned, and by Dr. A. G. Spratt, of Pennsylvania, a young man whohas made some valuable investigations of the properties of variouslycurved surfaces and the travel of the center of pressure thereon. Earlyin August Mr. Chanute came down from Chicago to witness our experiments, and spent a week in camp with us. These gentlemen, with my brother andmyself, formed our camping party, but in addition we had in many of ourexperiments the valuable assistance of Mr. W. J. Tate and Mr. Dan Tate, of Kitty Hawk. 

 * * * * *

It had been our intention when building the machine to do most of theexperimenting in the following manner:--When the wind blew 17 miles anhour, or more, we would attach a rope to the machine and let it rise asa kite with the operator upon it. When it should reach a proper heightthe operator would cast off the rope and glide down to the ground justas from the top of a hill. In this way we would be saved the trouble ofcarrying the machine uphill after each glide, and could make at least 10glides in the time required for one in the other way. But when we cameto try it we found that a wind of 17 miles, as measured by Richards'anemometer, instead of sustaining the machine with its operator, a totalweight of 240 lbs. , at an angle of incidence of three degrees, inreality would not sustain the machine alone--100 lbs. --at this angle. Its lifting capacity seemed scarcely one-third of the calculated amount. In order to make sure that this was not due to the porosity of thecloth, we constructed two small experimental surfaces of equal size, oneof which was air-proofed and the other left in its natural state; but wecould detect no difference in their lifting powers. For a time we wereled to suspect that the lift of curved surfaces little exceeded that ofplanes of the same size, but further investigation and experiment led tothe opinion that (1) the anemometer used by us over-recorded the truevelocity of the wind by nearly 15 per cent. ; (2) that the well-knownSmeaton coefficient of . 005 V^2 for the wind pressure at 90 degrees isprobably too great by at least 20 per cent. ; (3) that Lilienthal'sestimate that the pressure on a curved surface having an angle ofincidence of three degrees equals . 545 of the pressure at 90 degrees istoo large, being nearly 50 per cent. Greater than very recentexperiments of our own with a special pressure testing machine indicate;(4) that the superposition of the surfaces somewhat reduced the lift persquare foot, as compared with a single surface of equal area. 

[Illustration]

In gliding experiments, however, the amount of lift is of less relativeimportance than the ratio of lift to drift, as this alone decides theangle of gliding descent. In a plane the pressure is alwaysperpendicular to the surface, and the ratio of lift to drift istherefore the same as that of the cosine to the sine of the angle ofincidence. But in curved surfaces a very remarkable situation is found. The pressure, instead of being uniformly normal to the chord of the arc, is usually inclined considerably in front of the perpendicular. Theresult is that the lift is greater and the drift less than if thepressure were normal. While our measurements differ considerably fromthose of Lilienthal, Lilienthal was the first to discover thisexceedingly important fact, which is fully set forth in his book, "BirdFlight the Basis of the Flying Art, " but owing to some errors in themethods he used in making measurements, question was raised by otherinvestigators not only as to the accuracy of his figures, but even as tothe existence of any tangential force at all. Our experiments confirmthe existence of this force. At Kitty Hawk we spent much time inmeasuring the horizontal pressure on our unloaded machine at variousangles of incidence. We found that at 13 degrees the horizontal pressurewas about 23 lbs. This included not only the drift proper, or horizontalcomponent of the pressure on the side of the surface, but also the headresistance of the framing as well. The weight of the machine at the timeof this test was about 108 lbs. Now, if the pressure had been normal tothe chord of the surface, the drift proper would have been to the lift(108 lbs. ) as the sine of 13 degrees is to the cosine of 13 degrees, or(. 22 x 108) / . 97 = 24+ lbs. ; but this slightly exceeds the total pullof 23 lbs. On our scales. Therefore, it is evident that the averagepressure on the surface, instead of being normal to the chord, was sofar inclined toward the front that all the head resistance of framingand wires used in the construction was more than overcome. In a wind of14 miles per hour resistance is by no means a negligible factor, so thattangential is evidently a force of considerable value. In a higher wind, which sustained the machine at an angle of 10 degrees, the pull on thescales was 18 lbs. With the pressure normal to the chord the driftproper would have been (. 17 x 98) / . 98 = 17 lbs. , so that, although thehigher wind velocity must have caused an increase in the headresistance, the tangential force still came within one pound ofovercoming it. After our return from Kitty Hawk we began a series ofexperiments to accurately determine the amount and direction of thepressure produced on curved surfaces when acted upon by winds at thevarious angles from zero to 90 degrees. These experiments are not yetconcluded, but in general they support Lilienthal in the claim that thecurves give pressures more favorable in amount and direction thanplanes; but we find marked differences in the exact values, especiallyat angles below 10 degrees. We were unable to obtain direct measurementsof the horizontal pressures of the machine with the operator on board, but by comparing the distance traveled in gliding with the verticalfall, it was easily calculated that at a speed of 24 miles per hour thetotal horizontal resistance of our machine when bearing the operator, amounted to 40 lbs. , which is equivalent to about 2-1/3 horse-power. Itmust not be supposed, however, that a motor developing this power wouldbe sufficient to drive a man-bearing machine. The extra weight of themotor would require either a larger machine, higher speed, or a greaterangle of incidence in order to support it, and therefore more power. Itis probable, however, that an engine of six horse-power, weighing 100lbs. , would answer the purpose. Such an engine is entirely practicable. Indeed, working motors of one-half this weight per horse-power (9 lbs. Per horse-power) have been constructed by several different builders. Increasing the speed of our machine from 24 to 33 miles per hourreduced the total horizontal pressure from 40 to about 35 lbs. This wasquite an advantage in gliding, as it made it possible to sail about 15per cent. Further with a given drop. However, it would be of little orno advantage in reducing the size of the motor in a power-drivenmachine, because the lessened thrust would be counterbalanced by theincreased speed per minute. Some years ago Professor Langley calledattention to the great economy of thrust which might be obtained byusing very high speeds, and from this many were led to suppose that highspeed was essential to success in a motor-driven machine. But theeconomy to which Professor Langley called attention was in foot-poundsper mile of travel, not in foot-pounds per minute. It is the foot-poundsper minute that fixes the size of the motor. The probability is that thefirst flying machines will have a relatively low speed, perhaps not muchexceeding 20 miles per hour, but the problem of increasing the speedwill be much simpler in some respects than that of increasing the speedof a steamboat; for, whereas in the latter case the size of the enginemust increase as the cube of the speed, in the flying machine, untilextremely high speeds are reached, the capacity of the motor increasesin less than simple ratio; and there is even a decrease in the fuelconsumption per mile of travel. In other words, to double the speed of asteamship (and the same is true of the balloon type of airship) eighttimes the engine and boiler capacity would be required, and four timesthe fuel consumption per mile of travel; while a flying machine wouldrequire engines of less than double the size, and there would be anactual decrease in the fuel consumption per mile of travel. But lookingat the matter conversely, the great disadvantage of the flying machineis apparent; for in the latter no flight at all is possible unless theproportion of horse-power to flying capacity is very high; but on theother hand a steamship is a mechanical success if its ratio ofhorse-power to tonnage is insignificant. A flying machine that would flyat a speed of 50 miles an hour with engines of 1, 000 horse-power wouldnot be upheld by its wings at all at a speed of less than 25 miles anhour, and nothing less than 500 horse-power could drive it at thisspeed. But a boat which could make 40 miles per hour with engines of1, 000 horse-power would still move four miles an hour even if theengines were reduced to one horse-power. The problems of land and watertravel were solved in the nineteenth century, because it was possible tobegin with small achievements and gradually work up to our presentsuccess. The flying problem was left over to the twentieth century, because in this case the art must be highly developed before any flightof any considerable duration at all can be obtained. 

[Illustration]

However, there is another way of flying which requires no artificialmotor, and many workers believe that success will first come by thisroad. I refer to the soaring flight, by which the machine is permanentlysustained in the air by the same means that are employed by soaringbirds. They spread their wings to the wind, and sail by the hour, withno perceptible exertion beyond that required to balance and steerthemselves. What sustains them is not definitely known, though it isalmost certain that it is a rising current of air. But whether it be arising current or something else, it is as well able to support a flyingmachine as a bird, if man once learns the art of utilizing it. Ingliding experiments it has long been known that the rate of verticaldescent is very much retarded, and the duration of the flight greatlyprolonged, if a strong wind blows up the face of the hill parallel toits surface. Our machine, when gliding in still air, has a rate ofvertical descent of nearly six feet per second, while in a wind blowing26 miles per hour up a steep hill we made glides in which the rate ofdescent was less than two feet per second. And during the larger part ofthis time, while the machine remained exactly in the rising current, there was no descent at all, but even a slight rise. If the operator hadhad sufficient skill to keep himself from passing beyond the risingcurrent he would have been sustained indefinitely at a higher point thanthat from which he started. 

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[Illustration]

In looking over our experiments of the past two years, with models andfull-size machines, the following points stand out with clearness:--

1. That the lifting power of a large machine, held stationary in a windat a small distance from the earth, is much less than the Lilienthaltable and our own laboratory experiments would lead us to expect. Whenthe machine is moved through the air, as in gliding, the discrepancyseems much less marked. 

2. That the ratio of drift to lift in well-balanced surfaces is less atangles of incidence of five degrees to 12 degrees than at an angle ofthree degrees. 

3. That in arched surfaces the center of pressure at 90 degrees is nearthe center of the surface, but moves slowly forward as the anglebecomes less, till a critical angle varying with the shape and depth ofthe curve is reached, after which it moves rapidly toward the rear tillthe angle of no lift is found. 

4. That with similar conditions large surfaces may be controlled withnot much greater difficulty than small ones, if the control is effectedby manipulation of the surfaces themselves, rather than by a movement ofthe body of the operator. 

5. That the head resistances of the framing can be brought to a pointmuch below that usually estimated as necessary. 

6. That tails, both vertical and horizontal, may with safety beeliminated in gliding and other flying experiments. 

7. That a horizontal position of the operator's body may be assumedwithout excessive danger, and thus the head resistance reduced to aboutone-fifth that of the upright position. 

8. That a pair of superposed, or tandem, surfaces has less lift inproportion to drift than either surface separately, even after makingallowance for weight and head resistance of the connections. 

[Illustration]

 +------------------------------------------------------------------+ |Transcriber's Note: | | | | | |On page 15: | | | |Wilbur, who was at one end, seized it in front, Mr. Daniels and I, | |who were behind, tried to stop it behind, tried to stop it by | |holding to the rear uprights. | | | |has been changed to | | | |Wilbur, who was at one end, seized it in front, Mr. Daniels and I, | |who were behind, tried to stop it by holding to the rear uprights. | | | | | |On page 21: | | | |Lilienthal was the first to discover this exceedingly though our | |measurements differ considerably from those of Lilienthal. While | |important fact, which is fully set forth in his book, "Bird | |Flight the Basis of the Flying Art, " but owing to some errors in | |the methods he used in making measurements, question was raised | |by other investigators not only as to the accuracy of his | |figures, but even as to the existence of any tangential force at | |all. Our experiments confirm the existence of this force, at Kitty| |Hawk we spent much time in measuring the horizontal pressure on | |our unloaded machine at various angles of incidence. | | | |has been changed to | | | |While our measurements differ considerably from those of | |Lilienthal, Lilienthal was the first to discover this exceedingly | |important fact, which is fully set forth in his book, "Bird | |Flight the Basis of the Flying Art, " but owing to some errors in | |the methods he used in making measurements, question was raised | |by other investigators not only as to the accuracy of his | |figures, but even as to the existence of any tangential force at | |all. Our experiments confirm the existence of this force. At | |Kitty Hawk we spent much time in measuring the horizontal | |pressure on our unloaded machine at various angles of incidence. | +------------------------------------------------------------------+