  We use three-dimensional hydrodynamical simulations to study the rapid infall
phase of the common envelope interaction of a red giant branch star of mass
equal to 0.88 \msun and a companion star of mass ranging from 0.9 down to 0.1
\msun. We first compare the results obtained using two different numerical
techniques with different resolutions, and find overall very good agreement. We
then compare the outcomes of those simulations with observed systems thought to
have gone through a common envelope. The simulations fail to reproduce those
systems in the sense that most of the envelope of the donor remains bound at
the end of the simulations and the final orbital separations between the
donor's remnant and the companion, ranging from 26.8 down to 5.9 \rsun, are
larger than the ones observed. We suggest that this discrepancy vouches for
recombination playing an essential role in the ejection of the envelope and/or
significant shrinkage of the orbit happening in the subsequent phase.
