Active Rigidity Smart Joint for a Bat-Wing Micro Air Vehicle

In order to maximize lift for use in turning and landing maneuvers, bats make use of continuous camber change along their fifth metacarpal more effectively than all modern-day aircraft flaps. This biological shape change produces lower drag than modern aircraft, allowing for greater flight efficiency and lower noise signatures. A mechanism to replicate this demands a seamless actuator to avoid gaps and discontinuities, and requires the use of morphing structures. However, a recurring problem in morphing aircraft design is inefficiency of both space and power consumption. Problems often stem from the replacement of rigid structural elements with actuator elements that must be powered in order to carry static loads. To resolve this issue, a ‘smart joint’ concept is proposed which allows rigidity in its passive state, and becomes compliant while serving as an actuator by way of a composite of smart materials. Using a network of shape memory alloy and shape memory polymer, the joint is capable of rotations on the order of 5 percent camber over an arbitrary length when placed along a skeletal element of a bat-like wing structure. An analytical model is used to predict the behavior of the joint as a function of resistive heating and external loading, and is used to examine the layer thicknesses and locations (i.e. bimorph vs. unimorph) and placement of rigid elastic members in order to maximize deflection under a given load. Validation of the joint using is conducted via finite element modeling, and expected airfoil data for a generic shape maneuver to be accomplished by this joint is shown.