BIRD’S AERODYNAMICS

BIRD’SAERODYNAMICS

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

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.

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

BIRD’S AERODYNAMICS