BIRD’S AERODYNAMICS

ABSTRACT Man has always dreamed of being able to fly. Our long years of experiment and research have resulted in machine with advanced technologies. However our techniques are really primitive as compared to nature’s flying machine.

IMPORTANT TERMS Essential for understanding their flight mechanism Lift Drag Angle of attack Stalling Covert eddy flaps Flapping Take off and Landing Camber

LIFT Due to difference in pressures in upper and lower surface of wing Upper surface of air deflects the air downwards Airflow follows the tilted wing,sticks to surface, called COANDA EFFECT

Lift increases with increase in angle of attack Difference in pressures creates lift Air above the wing moves faster ,creating low pressure above ,hence creating lift Lift increases with increase in angle of attack

ANGLE OF ATTACK Angle between reference line of lifting boy and incoming air flow Also called as angle of incidence Coefficient of lift increases with increase in angle of attack upto critical angle of attack After critical angle of attack,STALLING occurs

STALL After critical angle of incidence is attained,flow separates of the wing,causing less lift. Stalling occurs generally during beginning of flight or at slow speeds Slower moving air may not move smoothly over the wing Airflow above the wing becomes turbulent

ALULA Thumb shaped,also called as ‘COVERTS’. Eddy developed starts from trailing edge to leading edge ‘COVERT EDDY FLAPS’ prevent eddy to reach to leading edge Help maintain lift at low speeds,prevent STALL.

FLAPPING Flapping in such a way so as to create both THRUST and LIFT. THRUST counteracts DRAG, LIFT counteracts WEIGHT. Flapping involves two stages: downstroke and upstroke Downstroke causes majority of lift and thrust

Upstroke also causes some lift, depending upon shape of wing During upstroke wing is folded slightly inwards to reduce friction Angle of attack increases during downstroke,while decreases during upstroke

DRAG Three major drag forces Frictional drag(caused by friction of air and body surfaces). Form drag Lift -induced drag

FORM DRAG Arises because of form of object. Larger apparent cross-section area will have larger drag than thinner bodies. Sleek design or design that are streamlined are critical for achieving minimum drag. Form drag increases with increase in air speed. e

LIFT INDUCED DRAG Occurs whenever a moving object redirects the airflow coming at it. Induced drag increases with increase in angle of attack. Induced drag decreases with increase in air speed.

TAKE-OFF Most energetically demanding aspects of flight. Large birds like albatrosses need to run up in order to generate airflow to take off Small birds can do so by taking a jump PECTORA muscle provides about 95% of strength required for flight.

LANDING Problem for large birds with high wing loadings Landing on water is simpler,using their feet as skids Certain birds aim at intended landing area and pull up before hand Large birds like geese involve in rapid alternating series of sideslips called WHIFFLING

CAMBER Symmetry between top and bottom curves of an airfoil Symmetric airfoils( with zero camber) generate no lift at zero angle of attack. Generally upper camber of an airfoil is greater than lower camber. Supersonic flights use supercritical airfoil;one with negative camber

When camber is increased beyond a limit,STALLING occurs Even if angle of attack is zero,airflow above the upper surface can be separated due to excessive cambering Idea of cambering helps designing aircraft wings

TYPES OF WINGS ELLIPTICAL WINGS-(short,rounded,for rapid take-offs) HIGH ASPECT RATIO WINGS-(far longer than they are wide,for gliding )

HIGH SPEED WINGS-(short,pointed,for high speeds) SOARING WINGS WITH DEEP SLOTS-(shorter size of wings helps in take-off,slots at tips of wings prevent induced drag)

HOVERING Done by birds with high aspect ratio wings Humming birds are exception as they create lift in both upstroke and downstroke Generally small birds hover, but some larger birds do so by flying in headwind