Proportions of Windmill Sails.-The following rules enable area, speed, and power of windmills to be calculated : To find the horse-power developed by a windmill: V = velocity of wind in feet per second; Effective horse-power = A X V3 1,080,000* Area of Sails. We next come to the calculation of the proper area of sail to represent a given power. or This area in square feet equals Horse-power X 1,080,000 The velocity of the wind in feet per second, cubed, Horse-power X 1,080,000 Proportions of Sails.-The usual practice in proportioning the standard windmill sails was to adopt a length of whip or arm, which was usually 30 feet, and then proportion the whip and sails as follows: Width of sail at axis, say of length of whip. Distance of the sail from axis, say of length. Axis Line. The axis or centre line of the shaft of the sails should be tipped on level ground 8 degrees from the horizontal. In high, exposed positions, 15 degrees from the horizontal. The modern windmills have an essential improvement over the old sail-mill, their vanes or sails being made of wood, and designed in such a form that when the wind pressure exceeds an amount of 14 or 18 miles per hour, they commence automatically to "feather," or assume a more acute angle to the direction of the wind, this process continuing with any further increase, until the sails present only an edge to the force of a high storm-which then blows through the structure with a minimum of obstruction. By this ingenious arrangement, which may be varied at will by hand-gear, windmills become practically self-regulating, and the chief difficulty of their management is quite overcome. Some designs are made with arrangements to bring the entire wheel edgeways to a storm. These are not to be commended. The "Halladay" wheel is very ingenious and successful. The vanes, or slats, are arranged so as to present their points or lower edges only, in a storm, to the wind.. The wheel is a skeleton frame-work, into which a series of wooden sections are centred, which vary in number according to the size of the windmill. The sections are connected with the counter-balance weights, which balance them to such a nicety that when the wind presses too heavily on them, as for instance in a storm, the wheel opens, and assumes a tubular form, allowing the wind to pass freely through it, which stops the windmill. As the pressure decreases the sails tilt back again into their old position, when the windmill recommences work. Steering. Small mills are usually steered by a vane or flat plate of wood attached to the rear of the wheel-framing. A better arrangement is a steering paddle wheel, which is proportioned so as to prevent the swaying or "creeping" of the sail face in a wind. Speed of Windmill Wheels.-To find the velocity of the tips of the vanes, the rule is 2.6 X the velocity of the wind in feet per second = velocity of the tips of the vanes in feet. Modern wheels run as follows: Diameter in feet..... ΙΟ 12 13 14 16 18 20 22 25 28 30 Revolutions per minute.. 50 48 46 43 40 37 34 32 30 28 26 Practical Uses.-As now constructed the windmill may be purchased in many commercial sizes, and has been applied to such a number of practical installations as to afford reliable data upon which to rely in deciding on the use of such a motor. Some of these are detailed as follows: 10-foot wheel, pumping from a well 63 feet deep into a reservoir. 10-foot wheel, pumping from a well 80 feet deep to a distance of 300 yards. 14-foot wheel, pumping from a well 100 feet deep into a reservoir. 16-foot wheel, on a roof 70 feet high, driving a lathe and drilling machine and also pumping from basement to roof. 16-foot wheel, on steel tower 24 feet high, pumping from well 100 feet deep. 18-foot wheel, pumping water 180 foot lift and to 1,000 yards distance. 20-foot wheel, on steel tower 24 feet high, lifting water by a scoop-wheel from 200 acres of marsh land, at 1,000 to 2,000 gallons per minute. 30-foot wheel, 100 feet from ground level, driving two pairs of 4-foot millstones and a friction hoist for sacks. In a day this mill, with one pair of stones, grinds 15 sacks of wheat. 30-foot wheel, driving a pair of 48-inch burr stones, a crushing mill, and a circular saw. 30-foot wheel, on a tower 76 feet high, supplying local waterworks by a set of three-throw 6-inch pumps, lifting the water 150 feet high through mile of mains to reservoir. 30-foot wheel, on top of building of 7 floors, pumping 11,000 gallons per hour to top of building with two 6 inch double-acting pumps, also working grain elevators. From the above facts it will be sufficiently evident that 'these machines are applicable to a variety of work, notwithstanding the irregularities of the wind. In arranging for pumping purposes a reservoir should be provided giving at least two days' reserve, or more if conveniently possible. Electric Work. For electric lighting purposes, a set of accumulators should be provided, answering the same purpose of a reserve of power, which can be utilized for lighting or for driving a motor. Such a plant was in successful operation for some time in London until stopped by action taken against the use of the wheel as infringing the law with reference to sky signs. A description of this will be of interest as a successful record: The wheel was erected on the roof of the building on substantial timber supports, and was set to drive a dynamo capable of developing a current of about 30 ampères with 70 volts pressure. The windmill drove this at a rate which, taken with the use of the governor and "cut-out" employed, was sufficiently uniform to charge a battery of 28 accumulators. From this battery sufficient electricity was obtained for two and sometimes three 1,500 candle-power arc-lamps and 27 incandescent lamps. The windmill consisted of a sectional wheel with a vane at the back, the whole arrangement being mounted on a turntable. The vane acted as a rudder and kept the wheel always facing the wind. The wheel, which was 30 feet in diameter, consisted of a skeleton framework, into which a series of wooden sections were centred, and these were connected with counterbalance weights which acted as governors, and caused the sections to open and shut, according to the strength of the wind blowing, thus obtaining a comparatively uniform speed. By means of a sliding contact, worked by a governor on the dynamo shaft, the charging circuit of the electrical apparatus was switched on when the speed was high enough, and switched off when it dropped too low, and there was also an automatic switch which reduced the existing current when the speed was too high, and thus prevented too much current being forced into the cells at any time. In addition to this there was a resistance in the main circuit, which aided the automatic excess-switch in its action. The governor controlled a lever which short-circuited and opened up resistances which were arranged in the shunt of the machine, and so regulated the electro-motive force according to speed. In Chapter XXXV., devoted to electricity and its storage, will be found full particulars and costs of dynamos and accumulators, with their outputs of current and correspond |