Experimental investigation of span-wise folding motion flapping wings

Flapping wing micro air vehicles (FMAVs) for practical application are most inspired by birds' flight. FMAVs ' flight efficiency to some extent depends on the bionic degree. Single degree flapping motion is no more satisfy the high efficiency of flight. A unique span-wise folding mechanism for flapping wing is developed to carry out the multiple degrees of freedom flapping. The aerodynamic characteristics of flapping wing applied with span-wise folding are tested in a small wind-tunnel special for MAVs. The instantaneous analysis shows that the distinction between folding wing and normal wing happens in the up-stroke process. The folding motion can notably increase the lift generated by the flapping, and reduce the power consumption in some conditions. The experiments indicate that folding up the small area of wing tip is good for maximum lift generation, appropriate restrict the folding area and folding angle can reduce the thrust and power lose. The maximum lift increment of the folding wing is 26 % , with less than 4 % thrust lose.