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| Poul la Cour’s experiments seem to demonstrate that Burnham was in an error, because he proclaimed that there was a great advantage in adopting the old English wind motors types. In other words: more force with a mill of four vanes of the old type was obtained that with a motor of great number of metallic laminae fixed to a wheel . The wind motor is based, for a rational operation, in a different principle that the one applied to the sail boats. An excess of vanes produces some kind of breakage and dispersion of the forces that act on the wheel by the action of the wind, having proven the wise Danish man that it was precise to leave great spaces between the vanes of the motor so that the air can deliver its maximum mechanical energy. As a result of it , the motor constructed scientifically by La Cour for his experimental station had four arms, or vanes, with the picturesque old shape. The four vanes moved by a system of handles and rods very ingeniously studied, so that they varied the aperture of laminae, assembled in blind form, with automatic exactitude and according to the variation of the wind force. The vanes had seven meters in length and 2.30 meters wide, resulting therefore an area of nearly 73 square meters and providing a sufficient force to move the two 12 horsepower dynamos that produced the electricity. The professor La Cour knew whichever precised a man of science, but he needed inventive talent. This knowledge was replaced by another Danish, Sørensen, who before his death introduced to him a new model of wind motor constructed considering the tests and studies of La Cour. This mill had also four vanes, but the peculiar thing of them was that they were curved, thus his author called this apparatus “ conical motor wind ". The professor la Cour compared it with the best German wind mills, and found that, in spite of being the area of the surface exposed to the wind, only one seventh part of the corresponding to the German mills , it developed 50 percent more force! The Sørensen motor could work, with a hardly perceivable airflow; but, naturally, it gave more force when it moved due to a continuous and steady breeze . In Germany and Denmark it was considered more advantageous to construct the wind mills with great vanes and to fit the mechanism so that it moved with slight airflows of a speed of 9.50 to 13 kilometers per hour. This is in fact a very low average march, and in which it was sacrificed a great amount of force in favor of the regularity of the march . This way, a motor of 50 horsepower , used for the lighting system and driving force, could work throughout the year, stopping itself only the equivalent number of hours: to thirty days. The city of Wittke, in Schleswig, Germany , was gotten to be illuminated by a motor of this class of 30 horsepower, working at the minimum speed of the wind of 12.50 kilometers per hour. All the machinery was adjusted for this speed; thus, when the wind was stronger, the vanes were opened partially and allowed to pass the excess of force without using it, closing itself again when the wind force lessened. |
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| Later improvements in the wind mills . If it is precise to make the motor work under an economic operating method , it is very important to regulate the apparatus according to the most frequent speed of the wind in the place of location. Where strong winds blow, a motor regulated for weak breezes would give very little yield, as well as it would make lose the regular force completely to the wind motors for hardly perceivable currents. But in the places where there is only a slight but continuous air movement, the air motor must be constructed so that it gives a small , but specially constant, energy yield. So that this one is greater it is precise to increase the size of the four or six vanes. A square foot of vane surface (0.09 square meter) in a scientifically constructed motor produces an amount of work equivalent to the energy consumed by a horsepower to elevate half a kilogram of weight up to six millimeters of the ground. But to obtain these results the wings must be curved, since they develop double amount of force that the flat ones. It has also been found that if the wings are grooved they have the same capacity to gather and to take advantage of the wind force that if they were curved. As it is much more advisable to use straight and grooved wings, the Denmark Government adopted these last ones for its experimental works. Doubling the size of the curved or grooved vanes doubles the force obtained, and considering these results thousands of dollars had been invested towards 1920 in the construction and mechanisms of enormous wind motors, such as those that were seen in Denmark and the north of Germany. In most of the cases, these expensive wind mills had been established by the State or the Municipalities. |
American mill. Wind mills of fixed blinds, 2.45 meters long , installed in a tower of 9.15 meters, to the right, another one of 6.10 meters, with a tower of 12.20 meters.
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The works done in Denmark had true importance and would have to produce evident beneficial results. Many villages in that country and the north of Germany used these motors, elevating the water for their supplying, producing the necessary electrical power for the public lighting system, and the State dependencies and particular factories obtained from the wind the necessary force to move their machinery. A wind mill installed towards 1928 in Germany costed twice and a half more than a gas motor of the same force; but the wind motor did not burn fuel, and, therefore, it produced a higher yield , which in the mentioned case reached at 12 percent. This extraordinary economic yield impressed the Danish and the Germans, of such a way that in later years there was a progressive installation of those motor in numerous countries, that worked with weak winds and could produce of 30 to 50 horsepower.
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| The competitors the wind mill had to fight to. In an article published in the Elektrotechnische Zeitschrift, his author said that a wind mill, with its electrical machinery, installed to provide energy to the city of Vallikilde (Denmark), had a wheel that measured 14 meters from end to end, being located its axis at 14 meters over the land. Their four vanes, with a surface of about 32 square meters, developed 8.6 horsepower, with a wind speed of 7 meters per second, or 36 kilometers per hour. In order to compare this interesting motor with another one of the American type it is necessary to consider that a motor of this type of 4.87 meters develops 1.08 horsepoerwer on the brake, with a speed in the wind of 25.50 kilometers per hour, and to this regime, the work made in the water elevation is of 0.433 horsepower . La Cour was not successful when devising new economic and practical devices as a means to store the energy to be able to use it in periods in which the wind stopped. In his experimental station he used the storage battery; but this procedure already had been used by Charles F. Brush in America and George Cadbury (1839-1922) in England. The wind motor of La Cour evidently was projected more scientifically, and its mechanical efficiency was greater than those ones devised by the American and English experimenters. But as the Danish inventor did not get to discover the way to store the wind force, it can not be said that he had solved all the important problems related to this type of motors. And of course it is doubtful that he could have arrived at it without the aid of the electrical storage battery, to which, in fact, even needed much time to be perfected.
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A windmill of 12.20 meters with its automatic movable blinds and central gear.
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