  We experimentally studied the effect of flexibility on the flow produced by
sinusoidally pitching foil in quiescent fluid. The rigid foil produces a weak,
divergent and meandering jet. On the contrary, the foil with a flexible flap
produces an orderly, narrow, coherent jet. It has been observed that such
orderly jet is produced when the flap has appropriate flexibility. The jet
produced in quiescent fluid by the flexible foil is accompanied by a
corresponding thrust. In that sense, this is simple and different type of
hovering.
