  We study viscous effects on heavy quark radiative energy loss in a
dynamically screened medium with boost-invariant longitudinal expansion. We
calculate, to first order in opacity, the energy loss by incorporating viscous
corrections in the single-particle phase-space distribution function within
relativistic dissipative hydrodynamics. We consider the Grad's 14-moment and
the Chapman-Enskog-like methods for the nonequilibrium distribution functions.
Our numerical results for the charm quark radiative energy loss show that, as
compared to static fluid, an expanding ideal (nonviscous) fluid causes a much
smaller energy loss. Viscosity in the evolution lead to somewhat enhanced
energy loss which is insensitive to the underlying viscous hydrodynamic models
used. Further inclusion of viscous correction induces larger energy loss, the
magnitude and pattern of this enhancement crucially depend on the form of
viscous corrections used.
