Passively Stable , Untethered Flapping - Hovering Micro - Air Vehicle

I nsects and hummingbirds remain unmatched in their aerodynamic ability to hover in place in addition to other acrobatic feats such as flying backward and sideways by exploiting flapping-wing motion [1]. Although this remarkable ability is key to making small-scale aircraft, flapping-hovering behavior has been difficult to reproduce artificially because of the challenging stability, power, and aeroelastic phenomena involved. Recent interest in small-scale unmanned air vehicles, especially those capable of hovering like insects and hummingbirds, is driven by many potential applications. A number of flapping machines have been developed [2]–[8], but only two are capable of untethered hovering flight [9], [10]. A key challenge is to demonstrate a stable untethered flapping-hovering ability at a weight and power approximating that of insects and birds where flapping-hovering flight is observed in nature. Here we demonstrate, for the first time, a passively stable 24-g machine capable of flapping-hovering flight at a Reynolds number similar to insects (Re ¼ 8 3 10 3). This architecture, particularly the passive stability, may help in the design of insect-sized hovering vehicles as well as shed light on the aeroelastic dynamic principles underlying insect flight. For the past several decades, researchers have been studying the complex flows form that allow insects to perform such incredible aerial feats, and what effect they have on flight at small scales, with the hope of building a fly-sized flapping-hovering machine. Flapping flight, such as that employed by insects, offers several advantages over ornithoptic flapping flight as seen in larger birds or fixed and rotary wing flight, most notably in scalability to small sizes [11]. This is particularly the case for hovering at low air speeds, where it has been shown that the efficiency of flapping wing flight exceeds both the fixed and rotary wing flight [12]. At smaller sizes, such as that of a fruit fly, fixed wing airfoils become less efficient than flapping flight because of the low Reynolds number. Low Reynolds numbers also appear in thin atmospheres such as that found on Mars [13], where conventional airborne exploration would be difficult. Flapping flight also offers the potential for more agile and robust flight systems, as can be observed in the maneuverability and resilience of insects in tangled and confined environments. With these advantages in mind, and the countless applications ranging from surveillance and exploration to artificial pollination and flocks of rapidly reconfigurable three-dimensional (3-D) airborne machines, there has been a …