CHARTS AND TABLES 

 RADII OF GYRATION FOR ROTATING BODIES 



17 



KC-1 



l-c-1 



ri 



l^c-M 



y 



Solid 

 cylinder 

 about its 

 own axis 



Hollow 

 cylinder 

 about its 

 own axis 



Rectan- 

 gular 

 prism 

 about 

 axis 



through 

 center 



Rectan- 

 gular 

 prism 

 about 

 axis at 



one end 



Rectan- 

 gular 

 prism 

 about 



outside 



«2 = 



ii2 = 



7-2i -j- r'^. 



R^ = 



12 



fl2 = 



4b^ + c' 

 12 



R' = 



462 -I- c2 -f 12bd + 12d- 



12 



APPROXIMATIONS FOR CALCULATING MOMENTS OF INERTIA 

 Name of Part Moment of Inertia 



Flywheels (not applicable to belt pulleys) Moment of inertia equal to 1.08 to 1.15 times that of 



rim alone 



Flywheel (based on total weight and out- Moment of inertia equal to two-thirds of that of total 

 side diameter) weight concentrated at the outer circumference 



Spur or helical gears (teeth alone) 



Spur or helical gears (rim alone) 



Moment of inertia of teeth equal to 40 per cent of that 

 of a hollow cylinder of the limiting dimensions 



Figured as a hollow cylinder of same limiting dimensions 



Spur or helical gears (total moment of Equal to 1.25 times the sum of that of teeth plus rim 

 inertia) 



Spur or helical gears (with only weight and Moment of inertia considered equal to 0.60 times the 



pitch diameter known) 



Motor armature 



(based on total weight and outside diam- 

 eter) 



moment of inertia of the total weight concentrated 

 at the pitch circle 



Multiply outer radius of armature by following factors 

 to obtain radius of gyration: 



Large slow-speed motor . 75-0 . 85 



Medium speed d-c or induction motor . 70-0 . 80 



Mill-type motor 0. 60-0. 65 



