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Ornithopter is an unmanned aerial vehicle (UAV), which can fly by flapping its wings attached to its body mimicking the bird’s flying motion. For a complete motion, birds use different flight envelopes for achieving different desired capabilities like high-speed forward flight, hovering, backward flight, take-off, long distance soaring without flapping. Similarly the ornithopter has complex motions to decipher the flight of a real bird. Because of its enormous application in various fields like fire fighting, Surveillance, Defence, Metrological survey & many more purposes, most of the re-searchers emphasized their efforts to explore flight characteristics of Ornithopter. Despite evolution of many theories, there are still gaps between experimentation and manufacturing it as a product. Most aerodynamic models used quasi-steady models because it assumes low flapping frequencies due to ignorance of unsteady wake effects. Researches in the field of ornithopter are in its development stage, which can be mimicked using mechanical mechanisms. Aerodynamic forces produced during the flight of birds and insects have different methods for hovering and forward flight. During flight, bird’s wing tip makes a standard path; whereas for insect’s flight, wing tip makes a complex path. Unsteady flight includes various unsteady parameters that can affect the normal course of flight path, which have to be considered for complete force estimations. Flat flapping wings with appropriately chosen constraints including weight limitations can yield required thrust & lift. Angle of attack, flexibility of wings, geometry, incidence angle, flapping frequency & flapping amplitude are some of the design parameters used for analyzing the flight of an ornithopter. The Prandtl lifting-line theory, a mathematical model, predicts lift distribution over a three-dimensional wing, along the span-wise direction. Lift distribution is calculated based on the wing geometry (airfoil, span-wise chord distribution and twist) & the flow conditions. Lifting Line Theory is used here for getting aerodynamic forces (lift & thrust) for flapping motion of wings considering semi-elliptical form. It is observed that the lift force for simple flat wing reduces drastically with low freestream velocity. Hence, in this work a new type of side folding wing is proposed, which can partially overcome the issue of low lift generation. Validation is executed using different aerodynamic variables. In this paper, the plot for variation of lift force and thrust force for the respective foldable wing and normal wing with free stream velocity is studied. All the plots are studied to find optimal parameter values for the efficient flight of the ornithopter.
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