WINDMILLS 307 



thrown partially out of gear when the wind velocity is 

 only about 25 miles an hour, many wheels are kept from 

 doing the amount of work which they might be able to 

 do. Any mill should stand a velocity of at least 40 miles 

 an hour. It is understood that as the wind increases, the 

 strain on the working parts decreases. For any given 

 velocity of wind the speed of the wheel should not change, 

 but the load should be so arranged that the work can be 

 done to suit the wind. 



428. The efficiency of a wind wheel is very greatly af- 

 fected by the diameter. This is due to the fact that wind 

 is not the same in any two places on the wheel. The 

 smaller the wheel, the greater efficiency. Experiments 

 were attempted to get the efficiency of a 22-foot wheel, 

 but because the wind did not blow at the same velocity 

 on any two parts of the wheel they were given up. 



429. Gearing. At one time the wind wheel seemed to 

 be the most vital part of a windmill, but from the results 

 of tests and experiments this belief has been obliterated, 

 and now the vital part seems to be the gearing. On all 

 the old standard makes the gearing seems to be as good 

 as ever, even if the mills have run for several years. 

 However, on the new designs, and this is mostly the steel 

 mill, the gears are wearing out. The fault lies with no 

 one but the manufacturers. Competition has been so 

 strong that they have reduced the cost of manufacture at 

 the expense of wearing parts. For this reason the steel 

 wheel, which is far the more powerful, is going out of 

 use in some localities, and the old makes of wooden 

 wheels are coming back. 



In direct-connected mills the main bearings should be 

 long and so placed that they will carry the wheels in 

 good shape, and the guide should be heavy and designed 

 so that it can be lubricated easily. The bumper spring 



