1913] on Gyrostats and Gyrostatic Action 637 



direction as the wheels. As the bicycle turns a corner it is con- 

 strained to precess, and a couple is needed to produce this precession 

 of the rotating parts quite apart from that required to turn the rest 

 of the machine. This the rider applies by leaning over to the inside 

 of the turn, and leans over more than he would have to if the fly- 

 wheel were not there or were not rotating. 



Good examples of gyrostatic action are given by paddle and tur- 

 bine steamers. K paddle steamer is steadier in a cross-sea than a 

 screw steamer of the same size. This is due in part to the gyrostatic 

 action of the paddle-wheels, which, but for their comparatively slow 

 speed of rotation, would form a compound gyrostat of considerable 

 power. For this gyrostat the spin-momentum may be conveniently 

 represented l)y a line drawn from the steamer towards the port-side. 

 A couple tending to tilt the steamer over to starboard is represented 

 by a line drawn towards the bow, and a couple tending to tilt the 

 steamer to port by a line drawn towards the stern. Hence, if the 

 steamer heels over to starboard, her bow, in consequence of gyrostatic 

 action, precesses to starboard, but the starboard wheel, becoming 

 somewhat more deeply immersed, uses more power and exerts a turn- 

 ing influence to port. Thus the steersman has less difficulty in 

 keeping the vessel on a straight course. But if the vessel be turned 

 by the rudder, say to port, the vessel will by gyrostatic action be 

 slightly heeled over to starboard, and the starboard wheel, being more 

 deeply immersed, will assist the turning-action of the rudder. When, 

 however, the steamer falls off her course, to port or starboard, the 

 gyrostatic action causes the correcting action applied by the rudder 

 to be resisted. Though the gyrostatic action of the wheels is not 

 very great, calculation shows that it is enough to produce an appreci- 

 able variation in the immersion of the wheels. 



The gyrostatic action of the fly-wheel in a motor-car is of some 

 practical interest. The fly-wheel is placed with its plane athwart the 

 car — that is, with the axis, so to speak, fore and aft. It rotates in 

 the clockwise direction as viewed by an observer behind the car. 

 The eff'ect of turning a corner to the left gives a gyrostatic couple 

 throwing the weight of the car more on the back wheels ; turning 

 to the right throws the weight more on the front wheels. The forces 

 applied by the ground to the front wheels are diminished in the 

 former case and increased in the latter. There is danger, therefore, 

 of the steering power of the car being interfered with, if the corner 

 is taken at too great a speed. 



As a final example, we take an aeroplane. Here the rotor of the 

 engine and the propeller together form a compound gyrostat of con- 

 sideralde power. As the bearings are fore and aft, the action is simi- 

 lar to that of the fly-wheel of the motor-car. Turning horizontally 

 in one direction gives rise to the gyrostatic couple tending to make 

 the aeroplane dive turning the opposite way sets up a couple which 



