  We study the radiative energy loss of hard partons in a soft medium in the
multiple soft scattering approximation. The soft medium is described by a 3D
hydrodynamical model and we treat the averaging over all possible parton paths
through the medium without approximation. While the nuclear suppression factor
$R_{AA}$ does not reflect the high quality of the medium description (except in
a reduced systematic uncertainty in extracting the quenching power of the
medium), the hydrodynamical model also allows to study different centralities
and in particular the angular variation of $R_{AA}$ with respect to the
reaction plane, allowing for a controlled variation of the in-medium
path-length. We study the angular dependence of $R_{AA}$ for different
centralities, discuss the influence of hydrodynamical expansion and flow and
comment on the comparison with preliminary data.
