It is demonstrated experimentally and theoretically that through the u
se of a nonlinear feedback controller, one can render a subcritical Ho
pf bifurcation supercritical and thus dramatically modify the nature o
f the flow in a thermal convection loop heated from below and cooled f
rom above. In particular, we show that the controller can replace the
naturally occurring chaotic motion with a stable, periodic limit cycle
. The control strategy consists of sensing the deviation of fluid temp
eratures from desired values at a number of locations inside the loop
and then altering the wall heating to counteract such deviations.