Wing designs for Flapping Wing Micro Air Vehicles (FWMAVs) might use a properly tuned elastic hinge at the wing root to obtain the required passive pitching motion to achieve enough lift production to stay aloft. Practical use of this type of FWMAVs requires some form of control which can be achieved by actively adjusting the elastic hinge stiffness and, thus, the pitching motion and lift production of the wing. This paper studies an elastic hinge design consisting of stacked layers which can be sticked together using electrostatics. This sticking changes the bending stiffness of the hinge. The voltage-dependent behavior of this elastic hinge during the large pitching motion are described in detail. The passive pitching motion is governed by the equation of motion which is a function of the elastic hinge stiffness and the applied control voltage. The lift generated by the passive pitching wings is predicted by a quasi-steady aerodynamic model. Numerical simulations show significant changes of the passive pitching motion and, consequently, of the lift production, if slipping stacked layers stick together. Experiments are conducted to study the practical applicability of this method on FWMAVs. The experiments show similar trends as the numerical simulations in modifying the pitching motion although the effect is less significant which is mainly due to manufacturing difficulties. This approach is, in conclusion, promising to control FWMAV flight. ... Read more

Lightweight vibrating structures (such as flapping wing micro air vehicle (FWMAV) designs) often require some form of control. To achieve controllability, local structural property changes (e.g., damping and stiffness changes) might be induced in an active manner. The stroke-averaged lift force production of a FWMAV wing can be modified by changing the structural properties of that wing at carefully selected places (e.g., changing the properties of the elastic hinge at the wing root as studied in this work). To actively change the structural properties, we investigate three different methods which are based on: (1) piezoelectric polymers, (2) electrorheological fluids, and (3) electrostatic softening. This work aims to gain simple yet insightful ways to determine the potential of these methods without focusing on the precise modeling. Analytical models of FWMAV wing designs that include control approaches based on these three methods are used to calculate the achievable lift force modifications after activating these methods. The lift force production as a result of a wing flapping motion is determined using a quasi-steady aerodynamic model. Both piezoelectric polymers and electrostatic softening are found to be promising in changing the structural properties and, hence, the lift force production of FWMAV wings. For the control of lightweight FWMAV designs, numerical simulations reveal a promising roll maneuverability due to the induced lift force difference between a pair of opposite wings. Although applied to a specific FWMAV design, this work is relevant for control of small, lightweight, possible compliant, vibrating structures in general. ... Read more