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Aviation History
1909
1909 - 0601.PDF
OCTOBER 2, 1909. HOW TO GLIDE. By WILBUR WRIGHT. IN the following account Wilbur Wright describes some of his early experiments, and points out very clearly the why and wherefore of the many important features of his machine. Why he discarded the tail in favour of the elevator, and how he came to make the important discovery of the retrogression of the centre of pressure on cambered aerofoils at very small angles of incidence, are here set forth with precision and lucidity. As to his style of writing, the frank chattyness of it will come as a surprise to those who have imagined Wilbur Wright as a somewhat dour character; some of his allusions, as for instance to the " gravity motor," are delightfully humorous. Altogether the account of his early experiences forms one of the best guides for the modern, beginner to study that could possibly be published at the present time. The present article is taken from a Paper which Wilbur Wright read before the American Western Society of Engineers, and was originally published in The Automotor Journal of February, 1902. Initial Difficulties. The difficulties in 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 pilot. Men also know how to build engines and propellers of sufficient lightness and power to drive these planes at sustaining speed. As long ago as 1893 a machine (Maxim's) weighing 8,000 lbs. 'demonstrated its power both to lift itself from the ground, and to maintain a speed of from 30 to 40 miles an hour; but it came to grief in an accidental free flight, owing to the inability of the operators to balance and steer it properly. This inability to balance and steer still confronts students of the flying problem, although nearly ten years have past. When this one feature has been worked out, the age of flying machines will have arrived, for all other difficulties are of minor importance. Lessons from Birds and Models. 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. To even mention all the things a bird must constantly keep in mind in order to fly securely through the air would occupy considerable space. If I take a piece of paper and, after placing it parallel with the ground, suddenly let it fall, it will not settle steadily as a staid, sensible piece of paper ought to do, but it insists on contravening every recognised rule of decorum, turning over and darting hither and thither in the most erratic manner, such 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 equilibrum and learned it so thoroughly that its skill is not apparent to our sight. Methods of Learning. Now, there are two ways of learning how 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, retiring to the house, figure out at leisure the best way of overcoming his peculiarities. The latter system is safest; 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. Where Gliding Began. Otto Lilienthal seems to have been the first man who really comprehended that balancing was the first instead of the last of the great problems in connection with human flight. He began where others left off, and thus saved the many thousands of dollars that it had thereto- fore been customary to spend in building and fitting expensive engines to machines which were uncontrollable when tried. He used gravity as his motor, which not only cost him nothing to begin with, but required no expensive fuel while in operation and never had to be sent to the shop for repairs. The gravity engine has this one serious drawback, however, that it always insists on fixing the conditions under which it will work. These are that the man shall first betake himself and his machine to the top of the hill and fly with a downward as well as a forward motion. Although Lilienthal may have thought the conditions rather hard he accepted them until something better should turn up, and in this manner made some 2,000 flights, some of them more than 1,000 ft. in length. Lilienthal, therefore, demonstrated the feasibility of actual practice in the air. He was followed by Pilcher, a young English engineer, and by Chanute, a distinguished member of the American Western Society of Engineers. Theory and Practice. The balancing of a gliding or flying machine is very simple in theory. It- merely consists in causing the centre of pressure to coincide with the centre of gravity, but in actual practice there seems to be an almost bound- less incompatibility of temper which prevents their remaining peaceably together for a single instant, so that the operator, who in this case acts as a peacemaker, often suffers injury to himself while attempting to bring them together. If a wind strikes a vertical plane, the pressure on that part to one side of the centre will exactly balance that on the other side, and the part above the centre will balance that below. This point we call the centre of pressure. But if the plane be slightly inclined, the pressure on the part nearest the wind is increased, so that the centre of pressure is located, not in the centre of surface, but a little towards the side. The Centre of Pressure. If the plane be still further inclined the centre of pressure will move still farther forward ; and if the wind blow a little to one side it will also move over as if to 607
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