FARM MOTORS 341 



required tends to reduce the efficiency. Especially large 

 windmills have been attempted, but they have not been 

 successful. 



Construction. The most important points involved in the 

 construction of a windmill are the strength and the rigidity 

 of the wind wheel and the durability of the bearings and gears. 

 The wheel must necessarily be light, yet it must be carefully 

 constructed or it will not be able to withstand the strenuous 

 service imposed upon it. The bearings should be large, of 

 material that resists wear, and be easily replaceable. The 

 gearing should also be of liberal dimensions. 



Lubrication. One of the most important features of the 

 windmill is provision for adequate lubrication by means of 

 magazine oilers or lubricators, one filling of which will supply 

 sufficient lubrication to last for a month or more. Many 

 mills are destroyed by failure to give them attention in this 

 respect. Some makers have tried to provide roller bearings 

 which will not be seriously damaged when adequate lubrica- 

 tion is not provided. 



Regulation. All windmills must have some means of reg- 

 ulating the speed. One common method is to have a small 

 side vane that turns the wind wheel edgewise to the wind as 

 the velocity of the wind becomes high. Another plan is to set 

 the wheel to one side of the center of the mast on which it is 

 mounted, when the unequal pressure tends to turn the wheel 

 away from the wind. Again, windmills have a tendency to 

 turn around on the mast as the rotating speed increases, and 

 this tendency is made use of in regulating speed. In some 

 wheels the sections are hinged and are connected with a 

 centrifugal governor which allows them to be turned par- 

 tially out of gear as the wind velocity increases. 



Power of Windmills. One authority concludes that the 

 power of a windmill increases as the cube of the wind velocity 



