5. The lift and drag coefficients were measured for wings of varying aspect ratio, compliancy, and prestrain values. In addition, the static and dynamic deformations of compliant membrane wings were measured using stereo photogrammetry. A theoretical model for membrane camber due to aerodynamic loading is presented, indicating that the appropriate nondimensional parameter describing the problem is a Weber number that compares the aerodynamic load to the membrane elasticity. Excellent agreement between the theory and experiments is found. Measurements of aerodynamic performance show that, in comparison with rigid wings, compliant wings have a higher lift slope, maximum lift coefficients, and a delayed stall to higher angles of attack. In addition, they exhibit a strong hysteresis botharoundazeroangleofattackaswellasaroundthestallangle.Unsteadymembranemotionswerealsomeasured, anditisobservedthatthe membranevibrateswithaspatialstructure thatisclosely relatedto thefreeeigenmodesof themembraneundertensionandthattheStrouhalnumberatwhichthemembranevibratesriseswiththefreestream velocity, coinciding with increasing multiples of the natural frequency of the membrane.

Aeromechanics of Membrane Wings with Implications for Animal Flight ArnoldSong, ∗ XiaodongTian, † EmilyIsraeli, ‡ RicardoGalvao, § KristinBishop, ¶ SharonSwartz, ∗∗

This is an ideal book for graduate students and researchers interested in the aerodynamics, structural dynamics and flight dynamics of small birds, bats and insects, as well as of micro air vehicles (MAVs), which present some of the richest problems intersecting science and engineering. The agility and spectacular flight performance of natural flyers, thanks to their flexible, deformable wing structures, as well as to outstanding wing, tail and body coordination, is particularly significant. To design and build MAVs with performance comparable to natural flyers, it is essential that natural flyers' combined flexible structural dynamics and aerodynamics are adequately understood. The primary focus of this book is to address the recent developments in flapping wing aerodynamics. This book extends the work presented in Aerodynamics of Low Reynolds Number Flyers (Shyy et al. 2008).

/pdf/an-introduction-to-flapping-wing-aerodynamics-j5o8vy2ryx.pdf

An Introduction to Flapping Wing Aerodynamics

Bats and other flying mammals are distinguished by thin, compliant membrane wings. In an effort to understand the dependence of aerodynamic performance on membrane compliancy, wind-tunnel tests of low-aspect-ratio, compliant wings were conducted for Reynolds numbers in the range of 0.7-2.0 x 10 5 . The lift and drag coefficients were measured for wings of varying aspect ratio, compliancy, and prestrain values. In addition, the static and dynamic deformations of compliant membrane wings were measured using stereo photogrammetry. A theoretical model for membrane camber due to aerodynamic loading is presented, indicating that the appropriate nondimensional parameter describing the problem is a Weber number that compares the aerodynamic load to the membrane elasticity. Excellent agreement between the theory and experiments is found. Measurements of aerodynamic performance show that, in comparison with rigid wings, compliant wings have a higher lift slope, maximum lift coefficients, and a delayed stall to higher angles of attack. In addition, they exhibit a strong hysteresis both around a zero angle of attack as well as around the stall angle. Unsteady membrane motions were also measured, and it is observed that the membrane vibrates with a spatial structure that is closely related to the free eigenmodes of the membrane under tension and that the Strouhal number at which the membrane vibrates rises with the freestream velocity, coinciding with increasing multiples of the natural frequency of the membrane.

Aeromechanics of Membrane Wings with Implications for Animal Flight

Fixed membrane wings for micro air vehicles: Experimental characterization, numerical modeling, and tailoring

Micro air vehicles (MAV’s) have the potential to revolutionize our sensing and information gathering capabilities in environmental monitoring and homeland security areas. Due to the MAV’s’ small size, flight regime, and modes of operation, significant scientific advancement will be needed to create this revolutionary capability. Aerodynamics, structural dynamics, and flight dynamics of natural flyers intersects with some of the richest problems in MAV’s, including massively unsteady three-dimensional separation, transition in boundary layers and shear layers, vortical flows and bluff body flows, unsteady flight environment, aeroelasticity, and nonlinear and adaptive control are just a few examples. A challenge is that the scaling of both fluid dynamics and structural dynamics between smaller natural flyer and practical flying hardware/lab experiment (larger dimension) is fundamentally difficult. In this paper, we offer an overview of the challenges and issues, along with sample results illustrating some of the efforts made from a computational modeling angle.

/pdf/computational-aerodynamics-of-low-reynolds-number-plunging-4p4r90qtcm.pdf

Computational aerodynamics of low Reynolds number plunging, pitching and flexible wings for MAV applications

A low-aspect-ratio, low-Reynolds-number membrane wing has been identified as a viable platform for micro air vehicle applications. Desirable flying qualities include high lift and larger stability margins. Several challenges are associated with the numerical modeling of such a wing, including highly three-dimensional flows, separation bubbles, and nonlinear membrane behavior. A thorough model validation and system identification effort is therefore required. A novel experimental setup integrates a wind tunnel with a visual image correlation system for simultaneous measurement of wing displacements, strains, and aerodynamic loads. These three metrics are used for a direct comparison of numerical and experimental data for both pre- and poststall angles of attack. Suitable correspondence is demonstrated for moderate angles of attack; methods for increasing the model fidelity can be made for angles with poor predictive capability. Computed flow structures reveal further information concerning the aeroelastic behavior of membrane wings.

/pdf/static-aeroelastic-model-validation-of-membrane-micro-air-2nhtwoxj8y.pdf

Static Aeroelastic Model Validation of Membrane Micro Air Vehicle Wings

CD = drag coefficient CL = lift coefficient CLmax = maximum lift coefficient Cm = pitching moment coefficient C p = pressure coefficient D = drag Dtool = tool diameter hscallop = scallop height L = lift Re = Reynolds number U = displacement in the X direction V = displacement in the Y direction W = displacement in the Z direction xstepover = stepover distance xx = normal strain in x direction xy = Shearing strain

Michael J. Sytsma

Papers

Static Aeroelastic Model Validation of Membrane Micro Air Vehicle Wings

5 Flexible-Wing Micro Air Vehicles