Effect of chord-wise flexibility in the lift generation of flapping MAV with membrane wing

Purpose The purpose of this study is to experimentally analyse the effect of flexible and stiffened membrane wings in the lift generation of flapping micro air vehicle (MAV). Design/methodology/approach This is analysed by the rectangle wing made up of polyethylene terephthalate sheets of 100 microns. MAV is tested for the free stream velocity of 2 m/s, 4 m/s, 6 m/s and k* of 0, 0.25, 1, 3, 8. This test is repeated for flapping MAV of the free flapping frequency of 2 Hz, 4 Hz, 6 Hz, 10 Hz and 12 Hz. Findings This study shows that the membrane wing with proper stiffeners can give better lift generation capacity than a flexible wing. Research limitations/implications Only a normal force component is measured, which is perpendicular to the longitudinal axis of the model. Practical implications In MAVs, the wing structures are thin and light, so the effect of fluid-structure interactions is important at low Reynold’s numbers. This data are useful for the MAV developments. Originality/value The effect of chord-wise flexibility in lift generation is the study of the effect of a flexible wing and rigid wing in MAV. It is analysed by the rectangle wing. The coefficient of normal force at different free stream conditions was analysed.

Kinematic Optimization of a Flexible Wing Undergoing Flapping and Pitching

In recent years, there has been widespread interest in the design of microair vehicles (MAVs) for flapping flight with high-aspect ratio wings due to their high efficiency and energy savings. However, the flexibility of a flapping wing causes the aeroelastic effect, which remains a subject of investigation. Generally, existing research simulates active bending and twisting of flexible wings under the assumption of neglecting flapping inertia. In this research, the kinematic optimization of a bionic wing with passive deformation in forward flight while undergoing flapping and pitching is considered. To this end, a computational aeroelasticity framework, which includes the three-dimensional unsteady vortex lattice method (UVLM) and the Newmark-β method, is constructed for flapping flight. Under the assumption of linear elastic deformation, this tool is capable of simulating attached flows over a thin wing and capturing unsteady effects of wakes. A bionic numerical wing with an aspect ratio of 6.5, chord Reynolds number of 1.9 × 105, and reduced frequency less than 0.1 is investigated in kinematic optimization. The computational aeroelasticity framework is combined with a global optimization algorithm to identify the optimal kinematics that maximize the propulsive efficiency under the minimum average lift constraint. Two types of numerical wings, rigid wing and flexible wing, are considered here to compare the influence of deformation on the aerodynamics of the flapping wing. The results show that the aeroelastic effect, which increases the flapping amplitude, yields a significant improvement in terms of propulsive efficiency. In addition, the optimization algorithm maximizes the thrust efficiency while satisfying the required lift. Moreover, the optimal kinematics of both the rigid wing and the flexible wing reach the maximum flapping angle, which indicates that a larger range of motions is needed for optimal kinetics when loosening the boundary conditions.

Functionally Graded Flexural Rigidity Improves Flight Performance in Flapping Wing Insects

Insect wings are highly heterogeneous structures, with flexural rigidity varying one to two orders of magnitude over the wing surface. This heterogeneity influences the deformation the flapping wing experiences under aerodynamic and inertial loads. However, it is not well understood how this flexural rigidity gradient affects wing performance. Here, we develop a reduced-order model of the flapping wing using the assumed mode method and unsteady vortex lattice method to model the structural and fluid dynamics, respectively. We conduct parameter studies to explore how variable flexural rigidity affects mean lift production, power consumption and the forces required to flap the wing. We find that there is an optimal flexural rigidity distribution that maximizes lift production; this distribution generally corresponds to a 3:1 ratio between the wing’s flapping and natural frequencies, though the precise ratio is sensitive to flapping kinematics. For hovering flapping kinematics, the optimized flexible wing produces 20% more lift and requires 15% less power compared to a rigid wing but needs 20% higher forces to flap. Even when flapping kinematics deviate from those observed during hover, the flexible wing outperforms the rigid wing in terms of aerodynamic force generation and power across a wide range of flexural rigidity gradients. Peak force requirements and power consumption are inversely proportional with respect to flexural rigidity gradient, which presents a trade-off between insect muscle size and energy storage requirements. The model developed in this work can be used to efficiently investigate other spatially variant morphological or material wing features moving forward.

Experimental Study of Rigid and Flexible Tandem Wing for Micro Aerial Vehicle

Unmanned aerial vehicle is becoming increasingly popular each year. Now, aeronautical researchers are focusing on size minimization of unmanned aerial vehicle, especially drone and micro aerial vehicle. The lift coefficient of micro aerial vehicle has wing dimension of 12 cm and mass of less than 7 g. In the present study, with the aid of 3D printer, polylactic acid material was used to develop the micro aerial vehicle structure for tandem wing arrangement. The materials for rigid wing skin and flexible wing skin were laminating film and latex membrane, respectively. The present work elaborates the lift coefficient profiles on rigid wing skin and flexible wing skin at wing flapping frequency of 11 Hz, three different Reynolds numbers of 14000, 19000 and 24000, and five different angles of attacks between 0° and 50°. According to the results obtained, the lift coefficient decreased as the Reynolds number increased. The lift coefficient increased up to 9 as the angle of attack increased from 0° to 50° at the Reynolds number of 14000 for flexible wing skin. The results also showed that the lift coefficient of flexible wing skin was higher than that of rigid wing skin at the attack angle of10° and below, except for the Reynolds number of 14000.