Experimental investigation of an autonomous flap for load alleviation

This paper presents an experimental aeroservoelastic investigation of a novel load alleviation concept using trailing edge flaps. These flaps are autonomous units, which are self-powered and self-actuated, using trailing edge tabs, thereby demonstrating advantages in comparison with conventional flap systems in terms of wiring and structural integration. The flaps are free-floating and mass underbalanced, such that they may flutter at operation velocities unless suppressed by their own control system. This makes the system very responsive for turbulence and control action. In the wind tunnel campaign presented in this paper, the limit cycle behavior of autonomous, free-floating flaps was investigated. It has been shown that limit cycle oscillation can be reached either through structural limiters or by control actions of the trailing edge tabs. In the latter case, the amplitude of the limit cycle oscillation is adjustable to the required energy output. An energy balance of harvested power and power consumption for actuators and sensing system was made showing that the vibration energy of limit cycle oscillations can be used to keep the amplitude of the limit cycle constant, while the electric batteries that power the load alleviation system are being charged.