Aerodynamic Characteristics and Flight Testing of a UAV without Control Surfaces Based on Circulation Control

Attitude control of a conventional aircraft usually depends on its rudder surface, which reduces the aircraft’s stealth abilities and makes it heavier. To improve aerodynamic performance and optimize flight attitude control, the authors developed a set of circulation-control actuators (CCAs) based on circulation-control (CC) technology to replace the conventional rudder surface and applied these CCAs to a flight test of a small unmanned aerial vehicle (UAV). The authors measure the main characteristic parameters of the CCAs and the flow-field characteristics, which indicate that the CCAs can suppress separation and delay stall at high angles of attack. An experimental assessment of rudder efficiency shows that the CCAs can produce the rudder efficiency required for conventional flight attitude control. Specifically, the maximum roll rudder efficiency that the CCA generates is equivalent to an aileron deflection of 50°, and the maximum pitch rudder efficiency is equivalent to an elevator deflection of 10° at a speed of $10\mathrm{m}/\mathrm{s}$. Finally, a successful flight test of a rudderless (meaning no control surface) UAV based on CC technology indicates that the CCAs designed in this study could replace conventional ailerons and elevators completely to establish control of aircraft flight attitude.