Effect of Flexural Stiffness on the Aerodynamic Forces of Flapping MAVs

Abstract

*† ‡ § Analog to the natural flyers, the application of flexible polymer films and carbon fibers as the wing stuff is employed in the flapping micro aerial vehicles (MAVs) and proves to be successful. One of the major characteristics is that the oscillating flexible wings can automatically adjust their deformation levels according to the air pressure loading applied on the wing frame to generate aerodynamic forces. The appropriate design in wing configuration can not only provide necessary strength to support the structure of airframe but also generate enough lift and thrust forces for vehicle flight in sky. To develop a flapping MAV with successful flying record, present study aims to investigate the influences of wing configuration and wing foil stiffness (or thickness) on the aerodynamic forces of a 20 cm wing-span flapping MAVs via wind tunnel testing. These wings with the same wing skeleton are made with polyethylene (PE), polyethyleneterephthalate (PET), or parylene (polyxylylene). The thickness of foil ranges from 17 μm to 43 μ μ μ μm corresponding to the variant stiffness of membrane. From the force measurement data, it is found that the lift coefficient of the thicker parylene wing obviously surpasses the other thinner ones, while the (net) thrust coefficient has minor relevance with the wing foil thickness of several tens of micrometers. Inspection on the relations between power consumption and the flexural stiffness of tested flapping wings reveals that the larger lift force is associated with the 35 and 43 μm thick of parylene wings which also consumed more power. Among test cases, present study demonstrated the flying test of a MAV with an optimal wing foil of 24 μ μ μ μm thick PET and created the longest endurance of 367 s. The instantaneous angle of attack of its quasi-steady forward flight is verified as 15 ° by a high speed CCD.