  Here we present an ensemble study of spin-orbit alignment in 51 close double
star systems. We determine spin-orbit angles, obliquities, in 39 of these
systems making use of recently improved apsidal motion rate measurements and
apsidal motion constants. In the remaining 12 systems researchers have
constrained spin-orbit alignment by different combinations of measurements of
apsidal motion rates, projected obliquities and stellar inclinations. Of the 51
systems 48 are consistent with alignment albeit with some measurements having
large uncertainties. A Fisher distribution with mean zero and a concentration
factor $\kappa = 6.7$ represents this ensemble well. Indeed employing a
bootstrapping resampling technique we find our data on these 48 systems is
consistent with perfect alignment. We also confirm significant misalignment in
two systems which travel on eccentric orbits and where misalignments have been
reported on before, namely DI Her and AS Cam. The third misaligned system CV
Vel orbits on a circular orbit. So while there are some glaring exceptions, the
majority of close double star systems for which data are available appear to be
well aligned.
