BIRD’S AERODYNAMICS

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.

ABSTRACT

IMPORTANT TERMSEssential forunderstanding their flight

mechanismLiftDragAngle of attackStallingCovert eddy flapsFlappingTake off and LandingCamber

LIFTDue 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 ATTACKAngle 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

STALLAfter 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

ALULAThumb 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.

FLAPPINGFlapping 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

DRAGThree major drag

forces Frictional

drag(caused by friction of air and body surfaces).

Form drag

Lift -induced drag

FORM DRAGArises 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 DRAGOccurs 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-OFFMost 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.

LANDINGProblem for large birds

with high wing loadingsLanding 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

CAMBERSymmetry 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 WINGSELLIPTICAL 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)

HOVERINGDone 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