18 - Flywheels

18-1 Flywheel Usage
18-2 Sizing the Flywheel
18-3 Stress
18-4 Flywheels for Energy Storage
18-5 Strength and Safety

The energy-storage capacity of a flywheel is determined from its polar moment of inertia J and its maximum safe running speed. The necessary inertia depends on the cyclic torque variation and the allowable speed variation or, in the case of energy-storage flywheels, the maximum energy requirements. The safe running speed depends on the geometry and material of the flywheel.

18-1 Flywheel Usage

Flywheel store energy. Indeed, flywheels are used as energy reservoirs. In machine design, it is used to smooth the variations in shaft speed that are caused by loads or power sources that vary in a cyclic fashion. By using its stored kinetic energy 0.5Jw^2 to absorb the variation in torque during a machine cycle, a flywheel smooths the fluctuating speed of a machine and reduces undersirable transient loads. The effect of a flywheel is therefore fundamentally
different from the regulator.

The flywheel has other features which have to be considered in design. Its size, speed, and windage effect can all be used to advantage in providing a secondary function as part of a clutch, gear, belt pulley, cooling fan, pump, gyroscope, or torsonal damper.

18-2 Sizing the Flywheel