Evaluation of Bird-Wing-Inspired Features on Biomimetic UAVs

Abstract

Some small UAVs have been designed to resemble birds so that they can blend in with nature when seen from a distance. Wings with various tip configurations were compared to a control wing to observe the variations in aerodynamic performance. Computer simulations were performed to determine expected results and then wings were designed and constructed for wind-tunnel tests to obtain experimental performance data. The wing was built in a standard rectangular configuration and featured an interchangeable plate on the tip to test the effect of the wing slots (feathers that project from the tips) and to see if changing the shape and length of the slots increases the effective aspect ratio (and therefore efficiency). Particle image velocimetry tests in a wind tunnel were performed to observe the vortex created by the wing and how the flow around the wingtips was affected by the changes in the wing slots. Circulation was then calculated and used to find coefficient of lift using the Kutta-Joukowski Theorem. The results were then compared to determine the most effective combination of performance and realistic look to create a bird-mimicking MAV. Nomenclature MAV= Micro Air Vehicle PIV = Particle Image Velocimetry AoA = Angle of Attack α = Alpha (Angle of Attack) V = Velocity V ∞ = Freestream Velocity Re = Reynolds Number Γ = Circulation µ = Dynamic Viscosity ρ = Density ρ ∞ = Freestream Density c = Wing Chord Length b = Wing Span s = Area

A Brief Review on Aerodynamic Performance of Wingtip Slots and Research Prospect

“…The planform and the generated surface mesh as well as the profiles are shown, used in the aerodynamic computation of the yawing moment characteristics; b yawing moment characteristics of the wing with a sweep in slotted tips [24] Fig. 12 a The CAD model: rectangular wing with slotted wingtips; b lift coefficient and c lift-to-drag ratio of the base wing and slotted wing versus angle of attack (base wing: blue line, slotted wing: red line) [25] Mitchell and Jacob [29] investigated the influence of slot length on the aerodynamic properties of wings (Fig. 20).…”

“…Whitcomb's achievement [63], the (A) Whitcomb winglet, marks the first time the wingtip device was formally Fig. 29 Flight test of wing-grid concept [38] Fig. 30 Concept aircraft called "bird of prey", announced by Airbus [39] Fig.…”

“…Wind tunnel test was widely adopted among them, due to the imperfect test conditions and flow field display ability at that time, the outcomes were disturbed. Mitchell et al [29] explained why the lift performance of non-slotted wing obtained by circulation measurement was higher than tip-slotted wing, they proposed that even though wings with tip-slots produced higher circulation values, the strong vortex produced by the wing without tip slots could be more easily measured than the other more dispersed vortices generated by the slotted wing. (ii) A similar situation was encountered in numerical simulation.…”