For the flexible wing with [f.sup.*] = 1.00, the peak negative angle takes place at a phase angle of 0.86[pi], while for flapping angle [theta], the peak negative angle happens at a phase angle of 1.01[pi]; moreover, the passive pitching angle [beta] of the flexible wing with [f.sup.*] = 1.00 also has a larger amplitude than the flapping angle [theta].
Caption: Figure 9: Time variation of passive pitching angle of flexible wings with [f.sup.*] = 1.00 and 1.50 and flapping angle [theta].
where [[theta].sub.i] is the flapping angle of the ith hydrofoil, [A.sub.i] is the crest value of [[theta].sub.i], [[phi].sub.i] is the original phase angle, and [[theta].sup.0.sub.i] is the central angle of the flapping hydrofoil.
The biorobotic UUV can complete the motion of change depth through changing the central flapping angles of the two frontal flapping hydrofoils.
The flapping angle is measured by the use of a sliped rheostat, and all signals are acquired by the use of DSP board.
The relationship between aerodynamic force and instantaneous flapping angle was shown fig5.
Figure 7 shows the closed-loop responses of the linear velocities of the helicopter (i.e., [[phi].sub.A] : roll angle; [[theta].sub.A]: pitch angle; and [[psi].sub.A] angle) states, longitudinal linear velocity (i.e., u) state, and collective blade flapping angle
(i.e., [[beta].sub.0]) state for the 1st closed-loop system (solid black line), 2nd closed-loop system (solid red line), and 3rd closed-loop system (solid blue line).