It is a great story, this of the Wright Brothers, and one worth all the detail that can be spared it. It begins on the 16th April, 1867, when Wilbur Wright was born within eight miles of Newcastle, Indiana. Before Orville’s birth on the 19th August, 1871, the Wright family had moved to Dayton, Ohio, and settled on what is known as the ‘West Side’ of the town. Here the brothers grew up, and, when Orville was still a boy in his teens, he started a printing business, which, as146 Griffith Brewer remarks, was only limited by the smallness of his machine and small quantity of type at his disposal. This machine was in such a state that pieces of string and wood were incorporated in it by way of repair, but on it Orville managed to print a boys’ paper which gained considerable popularity in Dayton ‘West Side.’ Later, at the age of seventeen, he obtained a more efficient outfit8, with which he launched a weekly newspaper, four pages in size, entitled The West Side News. After three months’ running the paper was increased in size and Wilbur came into the enterprise as editor, Orville remaining publisher. In 1894 the two brothers began the publication of a weekly magazine, Snap-Shots, to which Wilbur contributed a series of articles on local affairs that gave evidence of the incisive9 and often sarcastic10 manner in which he was able to express himself throughout his life. Dr Griffith Brewer describes him as a fearless critic, who wrote on matters of local interest in a kindly11 but vigorous manner, which did much to maintain the healthy public municipal life of Dayton.
Editorial and publishing enterprise was succeeded by the formation, just across the road from the printing works, of the Wright Cycle Company, where the two brothers launched out as cycle manufacturers with the ‘Van Cleve’ bicycle, a machine of great local repute for excellence12 of construction, and one which won for itself a reputation that lasted long after it had ceased to be manufactured. The name of the machine was that of an ancestor of the brothers, Catherine Van Cleve, who was one of the first settlers at Dayton, landing there from the River Miami on April 1st, 1796, when the country was virgin13 forest.
147 It was not until 1896 that the mechanical genius which characterised the two brothers was turned to the consideration of aeronautics14. In that year they took up the problem thoroughly15, studying all the aeronautical information then in print. Lilienthal’s writings formed one basis for their studies, and the work of Langley assisted in establishing in them a confidence in the possibility of a solution to the problems of mechanical flight. In 1909, at the banquet given by the Royal Aero Club to the Wright Brothers on their return to America, after the series of demonstration16 flights carried out by Wilbur Wright on the Continent, Wilbur paid tribute to the great pioneer work of Stringfellow, whose studies and achievements influenced his own and Orville’s early work. He pointed17 out how Stringfellow devised an aeroplane having two propellers18 and vertical20 and horizontal steering21, and gave due place to this early pioneer of mechanical flight.
Neither of the brothers was content with mere23 study of the work of others. They collected all the theory available in the books published up to that time, and then built man-carrying gliders26 with which to test the data of Lilienthal and such other authorities as they had consulted. For two years they conducted outdoor experiments in order to test the truth or otherwise of what were enunciated27 as the principles of flight; after this they turned to laboratory experiments, constructing a wind tunnel in which they made thousands of tests with models of various forms of curved planes. From their experiments they tabulated28 thousands of readings, which Griffith Brewer remarks as giving results equally efficient with those of the elaborate tables prepared by learned institutions.
148 Wilbur Wright has set down the beginnings of the practical experiments made by the two brothers very clearly. ‘The difficulties,’ he says, ‘which obstruct29 the pathway to success in flying machine construction are of three general classes: (1) Those which relate to the construction of the sustaining wings; (2) those which relate to the generation and application of the power required to drive the machine through the air; (3) those relating to the balancing and steering of the machine after it is actually in flight. Of these difficulties two are already to a certain extent solved. Men already know how to construct wings, or aeroplanes, which, when driven through the air at sufficient speed, will not only sustain the weight of the wings themselves, but also that of the engine and the engineer as well. Men also know how to build engines and screws of sufficient lightness and power to drive these planes at sustaining speed. Inability to balance and steer22 still confronts students of the flying problem, although nearly ten years have passed (since Lilienthal’s success). When this one feature has been worked out, the age of flying machines will have arrived, for all other difficulties are of minor30 importance.
‘The person who merely watches the flight of a bird gathers the impression that the bird has nothing to think of but the flapping of its wings. As a matter of fact, this is a very small part of its mental labour. Even to mention all the things the bird must constantly keep in mind in order to fly securely through the air would take a considerable time. If I take a piece of paper and, after placing it parallel with the ground, quickly let it fall, it will not settle steadily31 down as a staid, sensible piece of paper ought to do, but it insists149 on contravening32 every recognised rule of decorum, turning over and darting33 hither and thither34 in the most erratic35 manner, much after the style of an untrained horse. Yet this is the style of steed that men must learn to manage before flying can become an everyday sport. The bird has learned this art of equilibrium36, and learned it so thoroughly that its skill is not apparent to our sight. We only learn to appreciate it when we can imitate it.
‘Now, there are only two ways of learning to ride a fractious horse: one is to get on him and learn by actual practice how each motion and trick may be best 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 of overcoming his jumps and kicks. The latter system is the safer, but the former, on the whole, turns out the larger proportion of good riders. 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 a fence and watch the birds, but if you really wish to learn you must mount a machine and become acquainted with its tricks by actual trial. The balancing of a gliding37 or flying machine is very simple in theory. It merely consists in causing the centre of pressure to coincide with the centre of gravity.’
Wilbur Wright.
These comments are taken from a lecture delivered by Wilbur Wright before the Western Society of Engineers in September of 1901, under the presidency38 of Octave Chanute. In that lecture Wilbur detailed39 the way in which he and his brother came to interest themselves in aeronautical problems and constructed their first glider25. He speaks of his own notice of the death of Lilienthal in 1896, and of the way in which150 this fatality40 roused him to an active interest in aeronautical problems, which was stimulated41 by reading Professor Marey’s Animal Mechanism42, not for the first time. ‘From this I was led to read more modern works, and as my brother soon became equally interested with myself, we soon passed from the reading to the thinking, and finally to the working stage. It seemed to us that the main reason why the problem had remained so long unsolved was that no one had been able to obtain any adequate practice. We figured that Lilienthal in five years of time had spent only about five hours in actual gliding through the air. The wonder was not that he had done so little, but that he had accomplished so much. It would not be considered at all safe for a bicycle rider to attempt to ride through a crowded city street after only five hours’ practice, spread out in bits of ten seconds each over a period of five years; yet Lilienthal with this brief practice was remarkably43 successful in meeting the fluctuations44 and eddies45 of wind-gusts. We thought that if some method could be found by which it would be possible to practise by the hour instead of by the second there would be hope of advancing the solution of a very difficult problem. It seemed feasible to do this by building a machine which would be sustained at a speed of eighteen miles per hour, and then finding a locality where winds of this velocity46 were common. With these conditions a rope attached to the machine to keep it from floating backward would answer very nearly the same purpose as a propeller19 driven by a motor, and it would be possible to practise by the hour, and without any serious danger, as it would not be necessary to rise far from the ground, and the machine would not have any forward motion151 at all. We found, according to the accepted tables of air pressure on curved surfaces, that a machine spreading 200 square feet of wing surface would be sufficient for our purpose, and that places would easily be found along the Atlantic coast where winds of sixteen to twenty-five miles were not at all uncommon48. When the winds were low it was our plan to glide24 from the tops of sandhills, and when they were sufficiently49 strong to use a rope for our motor and fly over one spot. Our next work was to draw up the plans for a suitable machine. After much study we finally concluded that tails were a source of trouble rather than of assistance, and therefore we decided50 to dispense51 with them altogether. It seemed reasonable that if the body of the operator could be placed in a horizontal position instead of the upright, as in the machines of Lilienthal, Pilcher, and Chanute, the wind resistance could be very materially reduced, since only one square foot instead of five would be exposed. As a full half horse-power would be saved by this change, we arranged to try at least the horizontal position. Then the method of control used by Lilienthal, which consisted in shifting the body, did not seem quite as quick or effective as the case required; so, after long study, we contrived52 a system consisting of two large surfaces on the Chanute double-deck plan, and a smaller surface placed a short distance in front of the main surfaces in such a position that the action of the wind upon it would counterbalance the effect of the travel of the centre of pressure on the main surfaces. Thus changes in the direction and velocity of the wind would have little disturbing effect, and the operator would be required to attend only to the steering of the machine, which was to be effected152 by curving the forward surface up or down. The lateral53 equilibrium and the steering to right or left was to be attained55 by a peculiar56 torsion of the main surfaces, which was equivalent to presenting one end of the wings at a greater angle than the other. In the main frame a few changes were also made in the details of construction and trussing employed by Mr Chanute. The most important of these were: (1) The moving of the forward main crosspiece of the frame to the extreme front edge; (2) the encasing in the cloth of all crosspieces and ribs57 of the surfaces; (3) a rearrangement of the wires used in trussing the two surfaces together, which rendered it possible to tighten58 all the wires by simply shortening two of them.’
The brothers intended originally to get 200 square feet of supporting surface for their glider, but the impossibility of obtaining suitable material compelled them to reduce the area to 165 square feet, which, by the Lilienthal tables, admitted of support in a wind of about twenty-one miles an hour at an angle of three degrees. With this glider they went in the summer of 1900 to the little settlement of Kitty Hawk59, North Carolina, situated60 on the strip of land dividing Albemarle Sound from the Atlantic. Here they reckoned on obtaining steady wind, and here, on the day that they completed the machine, they took it out for trial as a kite with the wind blowing at between twenty-five and thirty miles an hour. They found that in order to support a man on it the glider required an angle nearer twenty degrees than three, and even with the wind at thirty miles an hour they could not get down to the planned angle of three degrees. Later, when the wind was too light to support the machine with a man on it,153 they tested it as a kite, working the rudders by cords. Although they obtained satisfactory results in this way they realised fully61 that actual gliding experience was necessary before the tests could be considered practical.
A series of actual measurements of lift and drift of the machine gave astonishing results. ‘It appeared that the total horizontal pull of the machine, while sustaining a weight of 52 lbs., was only 8.5 lbs., which was less than had been previously62 estimated for head resistance of the framing alone. Making allowance for the weight carried, it appeared that the head resistance of the framing was but little more than fifty per cent of the amount which Mr Chanute had estimated as the head resistance of the framing of his machine. On the other hand, it appeared sadly deficient63 in lifting power as compared with the calculated lift of curved surfaces of its size ... we decided to arrange our machine for the following year so that the depth of curvature of its surfaces could be varied64 at will, and its covering air-proofed.’
After these experiments the brothers decided to turn to practical gliding, for which they moved four miles to the south, to the Kill Devil sandhills, the principal of which is slightly over a hundred feet in height, with an inclination65 of nearly ten degrees on its main north-western slope. On the day after their arrival they made about a dozen glides66, in which, although the landings were made at a speed of more than twenty miles an hour, no injury was sustained either by the machine or by the operator.
‘The slope of the hill was 9.5 degrees, or a drop of one foot in six. We found that after attaining67 a speed of about twenty-five to thirty miles with reference to154 the wind, or ten to fifteen miles over the ground, the machine not only glided68 parallel to the slope of the hill, but greatly increased its speed, thus indicating its ability to glide on a somewhat less angle than 9.5 degrees, when we should feel it safe to rise higher from the surface. The control of the machine proved even better than we had dared to expect, responding quickly to the slightest motion of the rudder. With these glides our experiments for the year 1900 closed. Although the hours and hours of practice we had hoped to obtain finally dwindled69 down to about two minutes, we were very much pleased with the general results of the trip, for, setting out as we did with almost revolutionary theories on many points and an entirely70 untried form of machine, we considered it quite a point to be able to return without having our pet theories completely knocked on the head by the hard logic71 of experience, and our own brains dashed out in the bargain. Everything seemed to us to confirm the correctness of our original opinions: (1) That practice is the key to the secret of flying; (2) that it is practicable to assume the horizontal position; (3) that a smaller surface set at a negative angle in front of the main bearing surfaces, or wings, will largely counteract72 the effect of the fore6 and aft travel of the centre of pressure; (4) that steering up and down can be attained with a rudder without moving the position of the operator’s body; (5) that twisting the wings so as to present their ends to the wind at different angles is a more prompt and efficient way of maintaining lateral equilibrium than shifting the body of the operator.’
Wilbur Wright in a high glide, 1903.
Orville Wright making the world’s record in gliding flight, 10 minutes 1 second, stationary73 against a wind of 25 miles per hour, east of Kill Devil Hill.
For the gliding experiments of 1901 it was decided to retain the form of the 1900 glider, but to increase155 the area to 308 square feet, which, the brothers calculated, would support itself and its operator in a wind of seventeen miles an hour with an angle of incidence of three degrees. Camp was formed at Kitty Hawk in the middle of July, and on July 27th the machine was completed and tried for the first time in a wind of about fourteen miles an hour. The first attempt resulted in landing after a glide of only a few yards, indicating that the centre of gravity was too far in front of the centre of pressure. By shifting his position farther and farther back the operator finally achieved an undulating flight of a little over 300 feet, but to obtain this success he had to use full power of the rudder to prevent both stalling and nose-diving. With the 1900 machine one-fourth of the rudder action had been necessary for far better control.
Practically all glides gave the same result, and in one the machine rose higher and higher until it lost all headway. ‘This was the position from which Lilienthal had always found difficulty in extricating74 himself, as his machine then, in spite of his greatest exertions75, manifested a tendency to dive downward almost vertically77 and strike the ground head on with frightful78 velocity. In this case a warning cry from the ground caused the operator to turn the rudder to its full extent and also to move his body slightly forward. The machine then settled slowly to the ground, maintaining its horizontal position almost perfectly79, and landed without any injury at all. This was very encouraging, as it showed that one of the very greatest dangers in machines with horizontal tails had been overcome by the use of the front rudder. Several glides later the same experience was repeated with the same result. In the latter case156 the machine had even commenced to move backward, but was nevertheless brought safely to the ground in a horizontal position. On the whole this day’s experiments were encouraging, for while the action of the rudder did not seem at all like that of our 1900 machine, yet we had escaped without difficulty from positions which had proved very dangerous to preceding experimenters, and after less than one minute’s actual practice had made a glide of more than 300 feet, at an angle of descent of ten degrees, and with a machine nearly twice as large as had previously been considered safe. The trouble with its control, which has been mentioned, we believed could be corrected when we should have located its cause.’
It was finally ascertained80 that the defect could be remedied by trussing down the ribs of the whole machine so as to reduce the depth of curvature. When this had been done gliding was resumed, and after a few trials glides of 366 and 389 feet were made with prompt response on the part of the machine, even to small movements of the rudder. The rest of the story of the gliding experiments of 1901 cannot be better told than in Wilbur Wright’s own words, as uttered by him in the lecture from which the foregoing excerpts81 have been made.
‘The machine, with its new curvature, never failed to respond promptly82 to even small movements of the rudder. The operator could cause it to almost skim the ground, following the undulations of its surface, or he could cause it to sail out almost on a level with the starting point, and, passing high above the foot of the hill, gradually settle down to the ground. The wind on this day was blowing eleven to fourteen miles157 per hour. The next day, the conditions being favourable83, the machine was again taken out for trial. This time the velocity of the wind was eighteen to twenty-two miles per hour. At first we felt some doubt as to the safety of attempting free flight in so strong a wind, with a machine of over 300 square feet and a practice of less than five minutes spent in actual flight. But after several preliminary experiments we decided to try a glide. The control of the machine seemed so good that we then felt no apprehension84 in sailing boldly forth85. And thereafter we made glide after glide, sometimes following the ground closely and sometimes sailing high in the air. Mr Chanute had his camera with him and took pictures of some of these glides, several of which are among those shown.
‘We made glides on subsequent days, whenever the conditions were favourable. The highest wind thus experimented in was a little over twelve metres per second—nearly twenty-seven miles per hour.
‘It had been our intention when building the machine to do the larger part of the experimenting in the following manner:—When the wind blew seventeen miles an hour, or more, we would attach a rope to the machine and let it rise as a kite with the operator upon it. When it should reach a proper height the operator would cast off the rope and glide down to the ground just as from the top of a hill. In this way we would be saved the trouble of carrying the machine uphill after each glide, and could make at least ten glides in the time required for one in the other way. But when we came to try it, we found that a wind of seventeen miles, as measured by Richards’ anemometer, instead of sustaining the machine with its operator, a total weight of 240 lbs.,158 at an angle of incidence of three degrees, in reality 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 porosity86 of the cloth, we constructed two small experimental surfaces of equal size, one of which was air-proofed and the other left in its natural state; but we could detect no difference in their lifting powers. For a time we were led to suspect that the lift of curved surfaces very little exceeded that of planes of the same size, but further investigation87 and experiment led to the opinion that (1) the anemometer used by us over-recorded the true velocity of the wind by nearly 15 per cent; (2) that the well-known Smeaton coefficient of .005 V2 for the wind pressure at 90 degrees is probably too great by at least 20 per cent; (3) that Lilienthal’s estimate that the pressure on a curved surface having an angle of incidence of 3 degrees equals .545 of the pressure at 90 degrees is too large, being nearly 50 per cent greater than very recent experiments of our own with a pressure testing-machine indicate; (4) that the superposition of the surfaces somewhat reduced the lift per square foot, as compared with a single surface of equal area.
‘In gliding experiments, however, the amount of lift is of less relative importance than the ratio of lift to drift, as this alone decides the angle of gliding descent. In a plane the pressure is always perpendicular88 to the surface, and the ratio of lift to drift is therefore the same as that of the cosine to the sine of the angle of incidence. But in curved surfaces a very remarkable89 situation is found. The pressure, instead of being uniformly normal to the chord of the arc, is usually159 inclined considerably90 in front of the perpendicular. The result is that the lift is greater and the drift less than if the pressure were normal. 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 investigators91 not only as to the accuracy of his figures, but even as to the existence of any tangential92 force at all. Our experiments confirm the existence of this force, though our measurements differ considerably from those of Lilienthal. While at Kitty Hawk we spent much time in measuring the horizontal pressure on our unloaded machine at various angles of incidence. We found that at 13 degrees the horizontal pressure was about 23 lbs. This included not only the drift proper, or horizontal component93 of the pressure on the side of the surface, but also the head resistance of the framing as well. The weight of the machine at the time of this test was about 108 lbs. Now, if the pressure had been normal to the 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 × 108) / .97 = 24 + lbs.; but this slightly exceeds the total pull of 23 pounds on our scales. Therefore it is evident that the average pressure on the surface, instead of being normal to the chord, was so far inclined toward the front that all the head resistance of framing and wires used in the construction was more than overcome. In a wind of fourteen miles per hour resistance is by no means a negligible factor, so that tangential is evidently a force of considerable value. In a higher wind, which sustained the machine at an angle of160 10 degrees the pull on the scales was 18 lbs. With the pressure normal to the chord the drift proper would have been (17 × 98) / ·98. The travel of the centre of pressure made it necessary to put sand on the front rudder to bring the centres of gravity and pressure into coincidence, consequently the weight of the machine varied from 98 lbs. to 108 lbs. in the different tests) = 17 lbs., so that, although the higher wind velocity must have caused an increase in the head resistance, the tangential force still came within 1 lb. of overcoming it. After our return from Kitty Hawk we began a series of experiments to accurately94 determine the amount and direction of the pressure produced on curved surfaces when acted upon by winds at the various angles from zero to 90 degrees. These experiments are not yet concluded, but in general they support Lilienthal in the claim that the curves give pressures more favourable in amount and direction than planes; but we find marked differences in the exact values, especially at angles below 10 degrees. We were unable to obtain direct measurements of the horizontal pressures of the machine with the operator on board, but by comparing the distance travelled with the vertical fall, it was easily calculated that at a speed of 24 miles per hour the total horizontal resistances of our machine, when bearing the operator, amounted to 40 lbs, which is equivalent to about 2? horse-power. It must not be supposed, however, that a motor developing this power would be sufficient to drive a man-bearing machine. The extra weight of the motor would require either a larger machine, higher speed, or a greater angle of incidence in order to support it, and therefore more power. It is probable, however, that an engine of 6 horse-power,161 weighing 100 lbs. 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 hour reduced the total horizontal pressure from 40 to about 35 lbs. This was quite an advantage in gliding, as it made it possible to sail about 15 per cent farther with a given drop. However, it would be of little or no advantage in reducing the size of the motor in a power-driven machine, because the lessened95 thrust would be counterbalanced by the increased speed per minute. Some years ago Professor Langley called attention to the great economy of thrust which might be obtained by using very high speeds, and from this many were led to suppose that high speed was essential to success in a motor-driven machine. But the economy to which Professor Langley called attention was in foot pounds per mile of travel, not in foot pounds per minute. It is the foot pounds per minute that fixes the size of the motor. The probability is that the first flying machines will have a relatively96 low speed, perhaps not much exceeding 20 miles per hour, but the problem of increasing the speed will be much simpler in some respects than that of increasing the speed of a steamboat; for, whereas in the latter case the size of the engine must increase as the cube of the speed, in the flying machine, until extremely high speeds are reached, the capacity of the motor increases in less than simple ratio; and there is even a decrease in the fuel per mile of travel. In other words, to double the speed of a steamship97 (and the same is true of the balloon type of airship) eight times the engine and boiler98 capacity162 would be required, and four times the fuel consumption per mile of travel; while a flying machine would require engines of less than double the size, and there would be an actual decrease in the fuel consumption per mile of travel. But looking at the matter conversely, the great disadvantage of the flying machine is apparent; for in the latter no flight at all is possible unless the proportion of horse-power to flying capacity is very high; but on the other hand a steamship is a mechanical success if its ratio of horse-power to tonnage is insignificant99. A flying machine that would fly at a speed of 50 miles per hour with engines of 1,000 horse-power would not be upheld by its wings at all at a speed of less than 25 miles an hour, and nothing less than 500 horse-power could drive it at this speed. But a boat which could make 40 miles an hour with engines of 1,000 horse-power would still move 4 miles an hour even if the engines were reduced to 1 horse-power. The problems of land and water travel were solved in the nineteenth century, because it was possible to begin with small achievements, and gradually work up to our present success. The flying problem was left over to the twentieth century, because in this case the art must be highly developed before any flight of any considerable duration at all can be obtained.
‘However, there is another way of flying which requires no artificial motor, and many workers believe that success will come first by this road. I refer to the soaring flight, by which the machine is permanently100 sustained in the air by the same means that are employed by soaring birds. They spread their wings to the wind, and sail by the hour, with no perceptible exertion76 beyond that required to balance and steer themselves.163 What sustains them is not definitely known, though it is almost certain that it is a rising current of air. But whether it be a rising current or something else, it is as well able to support a flying machine as a bird, if man once learns the art of utilising it. In gliding experiments it has long been known that the rate of vertical descent is very much retarded101, and the duration of the flight greatly prolonged, if a strong wind blows up the face of the hill parallel to its surface. Our machine, when gliding in still air, has a rate of vertical descent of nearly 6 feet per second, while in a wind blowing 26 miles per hour up a steep hill we made glides in which the rate of descent was less than 2 feet per second. And during the larger part of this time, while the machine remained exactly in the rising current, there was no descent at all, but even a slight rise. If the operator had had sufficient skill to keep himself from passing beyond the rising current he would have been sustained indefinitely at a higher point than that from which he started. The illustration shows one of these very slow glides at a time when the machine was practically at a standstill. The failure to advance more rapidly caused the photographer some trouble in aiming, as you will perceive. In looking at this picture you will readily understand that the excitement of gliding experiments does not entirely cease with the breaking up of camp. In the photographic dark-room at home we pass moments of as thrilling interest as any in the field, when the image begins to appear on the plate and it is yet an open question whether we have a picture of a flying machine or merely a patch of open sky. These slow glides in rising current probably hold out greater hope of extensive practice than any other method164 within man’s reach, but they have the disadvantage of requiring rather strong winds or very large supporting surfaces. However, when gliding operators have attained greater skill, they can with comparative safety maintain themselves in the air for hours at a time in this way, and thus by constant practice so increase their knowledge and skill that they can rise into the higher air and search out the currents which enable the soaring birds to transport themselves to any desired point by first rising in a circle and then sailing off at a descending102 angle. This illustration shows the machine, alone, flying in a wind of 35 miles per hour on the face of a steep hill, 100 feet high. It will be seen that the machine not only pulls upward, but also pulls forward in the direction from which the wind blows, thus overcoming both gravity and the speed of the wind. We tried the same experiment with a man on it, but found danger that the forward pull would become so strong, that the men holding the ropes would be dragged from their insecure foothold on the slope of the hill. So this form of experimenting was discontinued after four or five minutes’ trial.
‘In looking over our experiments of the past two years, with models and full-size machines, the following points stand out with clearness:—
‘1. That the lifting power of a large machine, held stationary in a wind at a small distance from the earth, is much less than the Lilienthal table and our own laboratory experiments would lead us to expect. When the machine is moved through the air, as in gliding, the discrepancy103 seems much less marked.
‘2. That the ratio of drift to lift in well-shaped165 surfaces is less at angles of incidence of 5 degrees to 12 degrees than at an angle of 3 degrees.
‘3. That in arched surfaces the centre of pressure at 90 degrees is near the centre of the surface, but moves slowly forward as the angle becomes less, till a critical angle varying with the shape and depth of the curve is reached, after which it moves rapidly toward the rear till the angle of no lift is found.
‘4. That with similar conditions large surfaces may be controlled with not much greater difficulty than small ones, if the control is effected by manipulation of the surfaces themselves, rather than by a movement of the body of the operator.
‘5. That the head resistances of the framing can be brought to a point much below that usually estimated as necessary.
‘6. That tails, both vertical and horizontal, may with safety be eliminated in gliding and other flying experiments.
‘7. That a horizontal position of the operator’s body may be assumed without excessive danger, and thus the head resistance reduced to about one-fifth that of the upright position.
‘8. That a pair of superposed, or tandem104 surfaces, has less lift in proportion to drift than either surface separately, even after making allowance for weight and head resistance of the connections.’
The Wrights’ first power-driven machine, 1903.
Thus, to the end of the 1901 experiments, Wilbur Wright provided a fairly full account of what was accomplished; the record shows an amount of patient and painstaking105 work almost beyond belief—it was no question of making a plane and launching it, but a business of trial and error, investigation and tabulation166 of detail, and the rejection106 time after time of previously accepted theories, till the brothers must have felt that the solid earth was no longer secure, at times. Though it was Wilbur who set down this and other records of the work done, yet the actual work was so much Orville’s as his brother’s that no analysis could separate any set of experiments and say that Orville did this and Wilbur did that—the two were inseparable. On this point Griffith Brewer remarked that ‘in the arguments, if one brother took one view, the other brother took the opposite view as a matter of course, and the subject was thrashed to pieces until a mutually acceptable result remained. I have often been asked since these pioneer days, “Tell me, Brewer, who was really the originator of those two?” In reply, I used first to say, “I think it was mostly Wilbur,” and later, when I came to know Orville better, I said, “The thing could not have been done without Orville.” Now, when asked, I find I have to say, “I don’t know,” and I feel the more I think of it that it was only the wonderful combination of these two brothers, who devoted107 their lives together for this common object, that made the discovery of the art of flying possible.’
Beyond the 1901 experiments in gliding, the record grows more scrappy, less detailed. It appears that once power-driven flight had been achieved, the brothers were not so willing to talk as before; considering the amount of work that they put in, there could have been little time for verbal description of that work—as already remarked, their tables still stand for the designer and experimenter. The end of the 1901 experiments left both brothers somewhat discouraged, though they had accomplished more than any others. ‘Having set out167 with absolute faith in the existing scientific data, we were driven to doubt one thing after another, till finally, after two years of experiment, we cast it all aside, and decided to rely entirely on our own investigations108. Truth and error were everywhere so intimately mixed as to be indistinguishable.... We had taken up aeronautics as a sport. We reluctantly entered upon the scientific side of it.’
Yet, driven thus to the more serious aspect of the work, they found in the step its own reward, for the work of itself drew them on and on, to the construction of measuring machines for the avoidance of error, and, to the making of series after series of measurements, concerning which Wilbur wrote in 1908 (in the Century Magazine) that ‘after making preliminary measurements on a great number of different shaped surfaces, to secure a general understanding of the subject, we began systematic110 measurements of standard surfaces, so varied in design as to bring out the underlying111 causes of differences noted112 in their pressures. Measurements were tabulated on nearly fifty of these at all angles from zero to 45 degrees, at intervals113 of 2? degrees. Measurements were also secured showing the effects on each other when surfaces are superposed, or when they follow one another.
‘Some strange results were obtained. One surface, with a heavy roll at the front edge, showed the same lift for all angles from 7? to 45 degrees. This seemed so anomalous114 that we were almost ready to doubt our own measurements, when a simple test was suggested. A weather vane, with two planes attached to the pointer at an angle of 80 degrees with each other, was made. According to our table, such a vane would be in unstable168 equilibrium when pointing directly into the wind; for if by chance the wind should happen to strike one plane at 39 degrees and the other at 41 degrees, the plane with the smaller angle would have the greater pressure, and the pointer would be turned still farther out of the course of the wind until the two vanes again secured equal pressures, which would be at approximately 30 and 50 degrees. But the vane performed in this very manner. Further corroboration115 of the tables was obtained in experiments with the new glider at Kill Devil Hill the next season.
‘In September and October, 1902, nearly 1,000 gliding flights were made, several of which covered distances of over 600 feet. Some, made against a wind of 36 miles an hour, gave proof of the effectiveness of the devices for control. With this machine, in the autumn of 1903, we made a number of flights in which we remained in the air for over a minute, often soaring for a considerable time in one spot, without any descent at all. Little wonder that our unscientific assistant should think the only thing needed to keep it indefinitely in the air would be a coat of feathers to make it light!’
It was at the conclusion of these experiments of 1903 that the brothers concluded they had obtained sufficient data from their thousands of glides and multitude of calculations to permit of their constructing and making trial of a power-driven machine. The first designs got out provided for a total weight of 600 lbs., which was to include the weight of the motor and the pilot; but on completion it was found that there was a surplus of power from the motor, and thus they had 150 lbs. weight to allow for strengthening wings and other parts.
169 They came up against the problem to which Riach has since devoted so much attention, that of propeller design. ‘We had thought of getting the theory of the screw-propeller from the marine116 engineers, and then, by applying our table of air-pressures to their formul?, of designing air-propellers suitable for our uses. But, so far as we could learn, the marine engineers possessed117 only empirical formul?, and the exact action of the screw propeller, after a century of use, was still very obscure. As we were not in a position to undertake a long series of practical experiments to discover a propeller suitable for our machine, it seemed necessary to obtain such a thorough understanding of the theory of its reactions as would enable us to design them from calculation alone. What at first seemed a simple problem became more complex the longer we studied it. With the machine moving forward, the air flying backward, the propellers turning sidewise, and nothing standing109 still, it seemed impossible to find a starting point from which to trace the various simultaneous reactions. Contemplation of it was confusing. After long arguments we often found ourselves in the ludicrous position of each having been converted to the other’s side, with no more agreement than when the discussion began.
‘It was not till several months had passed, and every phase of the problem had been thrashed over and over, that the various reactions began to untangle themselves. When once a clear understanding had been obtained there was no difficulty in designing a suitable propeller, with proper diameter, pitch, and area of blade, to meet the requirements of the flier. High efficiency in a screw-propeller is not dependent upon any particular or peculiar shape, and there is no such170 thing as a “best” screw. A propeller giving a high dynamic efficiency when used upon one machine may be almost worthless when used upon another. The propeller should in every case be designed to meet the particular conditions of the machine to which it is to be applied118. Our first propellers, built entirely from calculation, gave in useful work 66 per cent of the power expended119. This was about one-third more than had been secured by Maxim120 or Langley.’
Langley had made his last attempt with the ‘aerodrome,’ and his splendid failure but a few days before the brothers made their first attempt at power-driven aeroplane flight. On December 17th, 1903, the machine was taken out; in addition to Wilbur and Orville Wright, there were present five spectators: Mr A. D. Etheridge, of the Kill Devil life-saving station; Mr W. S. Dough121, Mr W. C. Brinkley, of Manteo; Mr John Ward47, of Naghead, and Mr John T. Daniels.3 A general invitation had been given to practically all the residents in the vicinity, but the Kill Devil district is a cold area in December, and history had recorded so many experiments in which machines had failed to leave the ground that between temperature and scepticism only these five risked a waste of their time.
First flight of first power-driven machine, 17th December, 1903, near Kill Devil Hill, Kitty Hawk, N.C. Starting rail on left. Orville Wright piloting machine.
And these five were in at the greatest conquest man had made since James Watt122 evolved the steam engine—perhaps even a greater conquest than that of Watt. Four flights in all were made; the first lasted only twelve seconds, ‘the first in the history of the world in which a machine carrying a man had raised itself into the air by its own power in free flight, had sailed forward on a level course without reduction of speed,171 and had finally landed without being wrecked,’ said Wilbur Wright concerning the achievement.4 The next two flights were slightly longer, and the fourth and last of the day was one second short of the complete minute; it was made into the teeth of a 20 mile an hour wind, and the distance travelled was 852 feet.
This bald statement of the day’s doings is as Wilbur Wright himself has given it, and there is in truth nothing more to say; no amount of statement could add to the importance of the achievement, and no more than the bare record is necessary. The faith that had inspired the long roll of pioneers, from da Vinci onward123, was justified124 at last.
Having made their conquest, the brothers took the machine back to camp, and, as they thought, placed it in safety. Talking with the little group of spectators about the flights, they forgot about the machine, and then a sudden gust7 of wind struck it. Seeing that it was being overturned, all made a rush toward it to save it, and Mr Daniels, a man of large proportions, was in some way lifted off his feet, falling between the planes. The machine overturned fully, and Daniels was shaken like a die in a cup as the wind rolled the machine over and over—he came out at the end of his experience with a series of bad bruises125, and no more, but the damage done to the machine by the accident was sufficient to render it useless for further experiment that season.
A new machine, stronger and heavier, was constructed by the brothers, and in the spring of 1904 they began experiments again at Simms Station, eight miles to the east of Dayton, their home town. Press172 representatives were invited for the first trial, and about a dozen came—the whole gathering126 did not number more than fifty people. ‘When preparations had been concluded,’ Wilbur Wright wrote of this trial, ‘a wind of only three or four miles an hour was blowing—insufficient for starting on so short a track—but since many had come a long way to see the machine in action, an attempt was made. To add to the other difficulty, the engine refused to work properly. The machine, after running the length of the track, slid off the end without rising into the air at all. Several of the newspaper men returned next day but were again disappointed. The engine performed badly, and after a glide of only sixty feet the machine again came to the ground. Further trial was postponed127 till the motor could be put in better running condition. The reporters had now, no doubt, lost confidence in the machine, though their reports, in kindness, concealed128 it. Later, when they heard that we were making flights of several minutes’ duration, knowing that longer flights had been made with airships, and not knowing any essential difference between airships and flying machines, they were but little interested.
‘We had not been flying long in 1904 before we found that the problem of equilibrium had not as yet been entirely solved. Sometimes, in making a circle, the machine would turn over sidewise despite anything the operator could do, although, under the same conditions in ordinary straight flight it could have been righted in an instant. In one flight, in 1905, while circling round a honey locust-tree at a height of about 50 feet, the machine suddenly began to turn up on one wing, and took a course toward the tree. The operator,173 not relishing129 the idea of landing 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 ground and carried away several branches; but the flight, which had already covered a distance of six miles, was continued to the starting point.
‘The causes of these troubles—too technical for explanation here—were not entirely overcome till the end of September, 1905. The flights then rapidly increased in length, till experiments were discontinued after October 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 sides by much-travelled thoroughfares, with electric cars passing every hour, and seen by all the people living in the neighbourhood for miles around, and by several hundred others, yet these flights have been made by some newspapers the subject of a great “mystery.”’
Viewing their work from the financial side, the two brothers incurred130 but little expense in the earlier gliding experiments, and, indeed, viewed these only as recreation, limiting their expenditure131 to that which two men might spend on any hobby. When they had once achieved successful power-driven flight, they saw the possibilities of their work, and abandoned such other business as had engaged their energies, sinking all their capital in the development of a practical flying machine. Having, in 1905, improved their designs to such an extent that they could consider their machine a practical aeroplane, they devoted the years 1906 and 1907 to business negotiations132 and to the construction of new machines, resuming flying experiments in May of 1908 in order to test the ability of their machine to174 meet the requirements of a contract they had made with the United States Government, which required an aeroplane capable of carrying two men, together with sufficient fuel supplies for a flight of 125 miles at 40 miles per hour. Practically similar to the machine used in the experiments of 1905, the contract aeroplane was fitted with a larger motor, and provision was made for seating a passenger and also for allowing of the operator assuming a sitting position, instead of lying prone133.
Before leaving the work of the brothers to consider contemporary events, it may be noted that they claimed—with justice—that they were first to construct wings adjustable134 to different angles of incidence on the right and left side in order to control the balance of an aeroplane; the first to attain54 lateral balance by adjusting wing-tips to respectively different angles of incidence on the right and left sides, and the first to use a vertical vane in combination with wing-tips, adjustable to respectively different angles of incidence, in balancing and steering an aeroplane. They were first, too, to use a movable vertical tail, in combination with wings adjustable to different angles of incidence, in controlling the balance and direction of an aeroplane.5
A certain Henry M. Weaver135, who went to see the work of the brothers, writing in a letter which was subsequently read before the Aero Club de France, records that he had a talk in 1905 with the farmer who rented the field in which the Wrights made their flights. ‘On October 5th (1905) he was cutting corn in the next field east, which is higher ground. When he noticed the aeroplane had started on its flight he remarked175 to his helper: “Well, the boys are at it again,” and kept on cutting corn, at the same time keeping an eye on the great white form rushing about its course. “I just kept on shocking corn,” he continued, “until I got down to the fence, and the durned thing was still going round. I thought it would never stop.”’
He was right. The brothers started it, and it will never stop.
Mr Weaver also notes briefly136 the construction of the 1905 Wright flier. ‘The frame was made of larch137 wood—from tip to tip of the wings the dimension was 40 feet. The gasoline motor—a special construction made by them—much the same, though, as the motor on the Pope-Toledo automobile—was of from 12 to 15 horse-power. The motor weighed 240 lbs. The frame was covered with ordinary muslin of good quality. No attempt was made to lighten the machine; they simply built it strong enough to stand the shocks. The structure stood on skids138 or runners, like a sleigh. These held the frame high enough from the ground in alighting to protect the blades of the propeller. Complete with motor, the machine weighed 925 lbs.’
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1
derived
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| vi.起源；由来；衍生；导出v.得到( derive的过去式和过去分词 )；（从…中）得到获得；源于；（从…中）提取 | |
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brewer
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| n. 啤酒制造者 | |
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3
aeronautical
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| adj.航空（学）的 | |
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accomplished
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| adj.有才艺的；有造诣的；达到了的 | |
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apparently
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| adv.显然地；表面上，似乎 | |
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fore
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| adv.在前面；adj.先前的；在前部的；n.前部 | |
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gust
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| n.阵风，突然一阵（雨、烟等），（感情的）迸发 | |
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outfit
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| n.（为特殊用途的）全套装备，全套服装 | |
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incisive
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| adj.敏锐的，机敏的，锋利的，切入的 | |
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sarcastic
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| adj.讥讽的，讽刺的，嘲弄的 | |
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kindly
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| adj.和蔼的，温和的，爽快的；adv.温和地，亲切地 | |
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excellence
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| n.优秀，杰出，(pl.)优点，美德 | |
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virgin
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| n.处女，未婚女子；adj.未经使用的；未经开发的 | |
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aeronautics
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| n.航空术，航空学 | |
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thoroughly
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| adv.完全地，彻底地，十足地 | |
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demonstration
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| n.表明，示范，论证，示威 | |
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pointed
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| adj.尖的，直截了当的 | |
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propellers
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| n.螺旋桨，推进器( propeller的名词复数 ) | |
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propeller
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| n.螺旋桨，推进器 | |
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vertical
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| adj.垂直的，顶点的，纵向的；n.垂直物，垂直的位置 | |
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steering
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| n.操舵装置 | |
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steer
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| vt.驾驶，为…操舵；引导；vi.驾驶 | |
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mere
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| adj.纯粹的；仅仅，只不过 | |
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glide
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| n./v.溜，滑行；(时间)消逝 | |
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glider
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| n.滑翔机；滑翔导弹 | |
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gliders
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| n.滑翔机( glider的名词复数 ) | |
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enunciated
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| v.（清晰地）发音( enunciate的过去式和过去分词 )；确切地说明 | |
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tabulated
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| 把（数字、事实）列成表( tabulate的过去式和过去分词 ) | |
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obstruct
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| v.阻隔，阻塞(道路、通道等)；n.阻碍物，障碍物 | |
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minor
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| adj.较小(少)的，较次要的；n.辅修学科；vi.辅修 | |
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steadily
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| adv.稳定地；不变地；持续地 | |
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contravening
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| v.取消，违反( contravene的现在分词 ) | |
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darting
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| v.投掷，投射( dart的现在分词 )；向前冲，飞奔 | |
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thither
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| adv.向那里；adj.在那边的，对岸的 | |
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erratic
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| adj.古怪的，反复无常的，不稳定的 | |
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equilibrium
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| n.平衡，均衡，相称，均势，平静 | |
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gliding
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| v. 滑翔 adj. 滑动的 | |
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presidency
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| n.总统(校长，总经理)的职位(任期) | |
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detailed
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| adj.详细的，详尽的，极注意细节的，完全的 | |
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fatality
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| n.不幸，灾祸，天命 | |
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stimulated
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| a.刺激的 | |
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mechanism
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| n.机械装置；机构，结构 | |
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remarkably
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| ad.不同寻常地，相当地 | |
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44
fluctuations
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| 波动，涨落，起伏( fluctuation的名词复数 ) | |
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45
eddies
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| （水、烟等的）漩涡，涡流( eddy的名词复数 ) | |
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46
velocity
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| n.速度，速率 | |
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ward
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| n.守卫，监护，病房，行政区，由监护人或法院保护的人（尤指儿童）；vt.守护，躲开 | |
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48
uncommon
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| adj.罕见的，非凡的，不平常的 | |
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49
sufficiently
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| adv.足够地，充分地 | |
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50
decided
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| adj.决定了的，坚决的；明显的，明确的 | |
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51
dispense
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| vt.分配，分发；配(药)，发(药)；实施 | |
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52
contrived
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| adj.不自然的，做作的；虚构的 | |
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53
lateral
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| adj.侧面的，旁边的 | |
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54
attain
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| vt.达到，获得，完成 | |
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attained
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| （通常经过努力）实现( attain的过去式和过去分词 )； 达到； 获得； 达到（某年龄、水平、状况） | |
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56
peculiar
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| adj.古怪的，异常的；特殊的，特有的 | |
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57
ribs
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| n.肋骨( rib的名词复数 )；（船或屋顶等的）肋拱；肋骨状的东西；（织物的）凸条花纹 | |
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58
tighten
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| v.(使)变紧；(使)绷紧 | |
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59
hawk
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| n.鹰，骗子；鹰派成员 | |
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60
situated
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| adj.坐落在...的，处于某种境地的 | |
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61
fully
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| adv.完全地，全部地，彻底地；充分地 | |
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previously
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| adv.以前，先前（地） | |
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deficient
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| adj.不足的，不充份的，有缺陷的 | |
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64
varied
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| adj.多样的，多变化的 | |
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65
inclination
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| n.倾斜；点头；弯腰；斜坡；倾度；倾向；爱好 | |
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66
glides
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| n.滑行( glide的名词复数 )；滑音；音渡；过渡音v.滑动( glide的第三人称单数 )；掠过；（鸟或飞机 ） 滑翔 | |
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67
attaining
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| （通常经过努力）实现( attain的现在分词 )； 达到； 获得； 达到（某年龄、水平、状况） | |
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68
glided
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| v.滑动( glide的过去式和过去分词 )；掠过；（鸟或飞机 ） 滑翔 | |
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69
dwindled
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| v.逐渐变少或变小( dwindle的过去式和过去分词 ) | |
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70
entirely
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| ad.全部地，完整地；完全地，彻底地 | |
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71
logic
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| n.逻辑(学)；逻辑性 | |
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72
counteract
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| vt.对…起反作用，对抗，抵消 | |
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73
stationary
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| adj.固定的，静止不动的 | |
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74
extricating
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| v.使摆脱困难，脱身( extricate的现在分词 ) | |
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75
exertions
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| n.努力( exertion的名词复数 )；费力；（能力、权力等的）运用；行使 | |
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76
exertion
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| n.尽力，努力 | |
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77
vertically
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| adv.垂直地 | |
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78
frightful
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| adj.可怕的；讨厌的 | |
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perfectly
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| adv.完美地，无可非议地，彻底地 | |
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ascertained
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| v.弄清，确定，查明( ascertain的过去式和过去分词 ) | |
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excerpts
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| n.摘录，摘要( excerpt的名词复数 )；节选（音乐，电影）片段 | |
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promptly
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| adv.及时地，敏捷地 | |
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favourable
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| adj.赞成的，称赞的，有利的，良好的，顺利的 | |
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apprehension
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| n.理解，领悟；逮捕，拘捕；忧虑 | |
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forth
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| adv.向前；向外，往外 | |
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86
porosity
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| n.多孔性，有孔性 | |
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87
investigation
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| n.调查，调查研究 | |
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88
perpendicular
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| adj.垂直的，直立的；n.垂直线，垂直的位置 | |
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remarkable
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| adj.显著的，异常的，非凡的，值得注意的 | |
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considerably
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| adv.极大地；相当大地；在很大程度上 | |
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investigators
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| n.调查者，审查者( investigator的名词复数 ) | |
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tangential
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| adj.离题的，切线的 | |
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component
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| n.组成部分，成分，元件；adj.组成的，合成的 | |
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accurately
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| adv.准确地，精确地 | |
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lessened
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| 减少的，减弱的 | |
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relatively
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| adv.比较...地，相对地 | |
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steamship
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| n.汽船，轮船 | |
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boiler
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| n.锅炉；煮器(壶，锅等) | |
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insignificant
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| adj.无关紧要的，可忽略的，无意义的 | |
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permanently
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| adv.永恒地，永久地，固定不变地 | |
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retarded
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| a.智力迟钝的，智力发育迟缓的 | |
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102
descending
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| n. 下行 adj. 下降的 | |
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103
discrepancy
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| n.不同；不符；差异；矛盾 | |
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104
tandem
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| n.同时发生；配合；adv.一个跟着一个地；纵排地；adj.（两匹马）前后纵列的 | |
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painstaking
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| adj.苦干的；艰苦的，费力的，刻苦的 | |
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rejection
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| n.拒绝，被拒，抛弃，被弃 | |
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devoted
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| adj.忠诚的，忠实的，热心的，献身于...的 | |
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108
investigations
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| （正式的）调查( investigation的名词复数 )； 侦查； 科学研究； 学术研究 | |
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109
standing
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| n.持续，地位；adj.永久的，不动的，直立的，不流动的 | |
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systematic
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| adj.有系统的，有计划的，有方法的 | |
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111
underlying
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| adj.在下面的，含蓄的，潜在的 | |
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noted
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| adj.著名的，知名的 | |
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113
intervals
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| n.[军事]间隔( interval的名词复数 )；间隔时间；[数学]区间；（戏剧、电影或音乐会的）幕间休息 | |
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114
anomalous
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| adj.反常的；不规则的 | |
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115
corroboration
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| n.进一步的证实，进一步的证据 | |
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116
marine
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| adj.海的；海生的；航海的；海事的；n.水兵 | |
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117
possessed
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| adj.疯狂的；拥有的，占有的 | |
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118
applied
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| adj.应用的；v.应用，适用 | |
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119
expended
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| v.花费( expend的过去式和过去分词 )；使用（钱等）做某事；用光；耗尽 | |
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maxim
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| n.格言，箴言 | |
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121
dough
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| n.生面团；钱，现款 | |
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122
watt
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| n.瓦，瓦特 | |
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onward
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| adj.向前的，前进的；adv.向前，前进，在先 | |
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justified
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| a.正当的，有理的 | |
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125
bruises
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| n.瘀伤，伤痕，擦伤( bruise的名词复数 ) | |
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126
gathering
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| n.集会，聚会，聚集 | |
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127
postponed
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| vt.& vi.延期，缓办，（使）延迟vt.把…放在次要地位；[语]把…放在后面（或句尾）vi.（疟疾等）延缓发作（或复发） | |
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128
concealed
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| a.隐藏的，隐蔽的 | |
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129
relishing
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| v.欣赏( relish的现在分词 )；从…获得乐趣；渴望 | |
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130
incurred
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| [医]招致的，遭受的； incur的过去式 | |
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131
expenditure
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| n.(时间、劳力、金钱等)支出；使用，消耗 | |
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132
negotiations
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| 协商( negotiation的名词复数 )； 谈判； 完成（难事）； 通过 | |
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133
prone
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| adj.(to)易于…的，很可能…的；俯卧的 | |
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134
adjustable
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| adj.可调整的，可校准的 | |
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135
weaver
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| n.织布工；编织者 | |
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136
briefly
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| adv.简单地，简短地 | |
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137
larch
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| n.落叶松 | |
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138
skids
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| n.滑向一侧( skid的名词复数 )；滑道；滚道；制轮器v.（通常指车辆） 侧滑( skid的第三人称单数 )；打滑；滑行；（住在）贫民区 | |
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