  We report on a study of the phonon-mediated frictional drag between
two-dimensional electron layers at the Landau level filling factor $\nu=1/2$
predicted by Chern-Simons composite-fermion theory. Frictional drag between
widely spaced layers is dominated by the phonon-mediated interaction and is
altered from its zero-field form because of the large composite-fermion
effective mass and, less strongly, by magnetic local-field effects. We find
that the reduced drag resistance $\rho(T)/T^2$ peaks at a larger temperature
and has a different density dependence than at zero field. We compare these
results with recent experimental findings.
