304 Mr. W. Duddell on a 



alternator. Practically, the whole of the difference between 

 the power required to drive the motor and one wheel and 

 that required to drive the motor alone, was expended in over- 

 coming air-friction on the wheel, as the increase of the 

 bearing friction due to the extra weight of the wheel cannot 

 be large, the armature being many times heavier than the 

 wheel ; and the extra C 2 R loss due to the extra armature 

 current is only 22 watts at a speed of 1200 revolutions 

 per minute. 



The air-friction on this single bicycle-wheel running at 

 1200 revolutions per minute, or at a rim-velocity of about 

 85 \ miles per hour, required an expenditure of energy at the 

 rate of about 200 watts ; so that for a cyclist to attain this 

 speed he would have to develop over J H.P. to overcome the 

 air-friction on his two wheels alone. 



The motor and bicycle- wheels were therefore replaced by 

 two phosphor-bronze disks driven from an 8 K.W. motor 

 by means of |-inch gut bands. This arrangement is illus- 

 trated by the photograph PL VI. fig. 4, and a working 

 drawing of one of the disks is given in PL V. fig. 5. 



In the figure-of-8 drive with only one wheel acting as 

 driver, the spindle cannot be relieved of all pressure due to 

 the belt, if the tension-wheel takes any considerable power 

 to drive it. Both disks were therefore made drivers, each 

 being separately belted to the motor. 



Before taking these disks into use, each one was tested 

 by twice running it up to about 6500 revolutions per minute 

 for a few minutes to see if there was any risk of its bursting. 

 From this test it was concluded that, as far as safety was con- 

 cerned, any speed up to 5000 revolutions per minute, or a rim- 

 velocity of 327 feet per second, might be employed ; but 

 owing to the excessive vibration, due to the disks not being 

 perfectly balanced, 4000 revolutions per minute, or a rim- 

 velocity of 262 feet per second, was the highest speed at which 

 they could be continually run. 



This rim- velocity, which is practically the same as the 

 linear belt-velocity, being so much higher than that attained 

 with the bicycle-wheels, the 10 mm. steel pulleys on the 

 alternator spindle were removed and replaced by larger ones 

 of red fibre, as it was thought that this change would reduce 

 the tension in the belt necessary to drive the alternator. It 

 had, however, quite the opposite effect, owing to the inertia 

 forces lifting the belt out of contact with the pulleys at the 

 higher belt speeds necessary to obtain the same speed of the 

 alternator-spindle. The extra tension required to make the 

 belt wrap round and drive the pulleys was much larger than 



