Jeffcott

Jeffcott is a surname. In engineering, the name is associated with the Jeffcott rotor, a classical idealized model in rotor dynamics used to study unbalance and vibration of a rotating shaft carrying a single disk. The model is named after a British engineer who introduced the concept and is widely used in textbooks and teaching laboratories.

The Jeffcott rotor consists of a massless, flexible shaft supporting a single rigid disk. The system is analyzed in lateral motion in two orthogonal planes; the unbalance of the disk creates forcing terms that drive steady vibration as the shaft spins. In the classical formulation, damping is included and the natural frequency is set by the shaft stiffness and disk mass. The model yields characteristic whirl behavior and critical speeds, providing a simple framework for understanding how unbalance, stiffness, and damping influence resonant response.

It is widely used as an instructional baseline in rotor dynamics courses and in the early stages of machine design to estimate unbalance response and critical speeds. Although simplified, Jeffcott analysis helps motivate more advanced models that include shaft elasticity, gyroscopic effects, and multi-disk configurations.

Limitations include a single disk on a massless shaft, linear behavior, no gravity effect, and negligible gyroscopic coupling; real rotors require more detailed modeling for accurate predictions.