  Using time-resolved measurements of the orientation of rigid inertial fibers
in a turbulence-tank, we investigate the autocorrelation of their tumbling
rate. The correlation time ($\tau_d$) is well predicted by Kolmogorov
inertial-range scaling based on the fiber length (L) when the fiber inertia can
be neglected. For inertial fibers, we propose a simple model considering fiber
inertia (measured by a tumbling Stokes number) and a viscous torque which
accurately predicts both the correlation time and the variance of the tumbling
rate.
