How Does a Bird Fly??The Flying Mechanism of Birds & The Physics Beyond it

"Bird is a Biological Flying machine created by Nature"***

 Like other flying machines such as Aeroplanes, the requirements for heavier-than-air flying machines is a structure that combines strength with light weight. Birds have many physical features, besides wings, that work together to enable them to fly. They need lightweight, streamlined, rigid structures for flight. 

The four forces of flight – i)Weight ii)  Lift iii) Drag and iv)  Thrust – affect the flight of birds.

Forces Involved in Flight

Flying birds have:

i) lightweight, smooth feathers – this reduces the forces of weight and drag

ii) a beak, instead of heavy, bony jaws and teeth (reduces the weight)

iii) an enlarged breastbone called a sternum for flight muscle attachment (helps with the force of thrust)

iv) light bones (Pneumatic bones) – A bird’s bones are basically hollow with air sacs and thin, tiny cross pieces to make bones stronger – this reduces the force of weight

v) a rigid skeleton to provide firm attachments for powerful flight muscles – this helps with the force of thrust

vi) a streamlined body – this helps reduce the force of drag

vii)wings – these enable the force of lift. The shape of a bird’s wing is important for producing lift. The air is moving more quickly over the top surface of the wing, reducing air pressure on the top of the wing and creating lift. Also, the angle of the wing (tilt) deflects air downwards, causing a reaction force in the opposite direction and creating lift. Larger wings produce greater lift than smaller wings. So smaller-winged birds (and planes or any such flying objects) need to fly faster to maintain the same lift as those with larger wings.

The key Physics :

A bird's wing acts as an airfoil, a curved surface evolved to provide lift and reduce drag (turbulance and friction). Air pushed into the airfoil by the bird's forward motion pushes more forcefully on the curved underside of the somewhat upward-tilted wing. This forces air downward and causes and equal and opposite reaction causing the bird to rise. At the same time air is moving more quickly over the upperside of the airfoil (wing) than the stream below the wing. As the air moves faster over the top of the wing, pressure is diminished relative to that of the underside and the bird gains lift (rises). This follows Bernoulli's principle.

Bernouli's Principle (Depiction)

Basic Flight Types:

1.Gliding: When a bird is gliding, it doesn’t have to do any work. The wings are held out to the side of the body and do not flap. As the wings move through the air, they are held at a slight angle  (Tilt) , which deflects the air downwards and causes a reaction in the opposite direction, which is lift. But there is also drag (air resistance) on the bird’s body, so every now and then, the bird has to tilt forward and go into a slight dive so that it can maintain forward speed.

2. Soaring: Soaring flight is a special kind of glide in which the bird flies in a rising air current (called a thermal). Because the air is rising, the bird can maintain its height relative to the ground. 

3. Flapping: Birds’ wings flap with an up-and-down motion. This propels them forward. The entire wingspan has to be at the right angle of attack, which means the wings have to twist (and do so naturally) with each downward stroke to keep aligned with the direction of travel.

Obtaining thrust : Birds obtain thrust by using their strong muscles and flapping their wings. Some birds may use gravity (for example, jumping from a tree) to give them forward thrust for flight. Others may use a running take-off from the ground. A bird’s wing produces lift and thrust during the downstroke. The air is deflected downwards and also to the rear. The bird reduces its angle of attack and partially folds its wings on the upward stroke so that it passes through the air with the least possible resistance. The inner part of the wing has very little movement and can provide lift in a similar way to gliding.

Downstroke: Provided by the Muscle Pectoralis major. The pectoralis major (think outer breast meat), a bird's largest muscle, provides power ,which in birds is the engine of forward movement.

Upstroke: Provided by the  Supracoracoideus Muscle, Beneath the pectoralis major lies the supracoracoideus, the breast muscle that powers the upstroke. It is the muscle immediately over the breast bone. The tendon of this muscle passes through the Triossial canal, an opening between the coracoid, humerus and furcula and inserts into the humerus. When the supracoracoideus contracts, the tendon pulls the humerus and consequently the rest of the wing) upward. The peculiar arrangement of this muscle helping to stabilize flight. During the upstroke, wings are partially folded to reduce drag. 

Muscles Involved (Anatomy)

The rudder: The tail is used as a rudder to aid turning in flight or staying level while in shifting air currents.

Braking/slowing Down: When a bird needs to slow down, it positions its tails and wings in a more vertical orientation causing it to stall.

Aerial View of a Flock Of Birds in Flight

***(The Heading)~ A quote By Sahdul Islam (The Writer of the article)

                         (Written/Authored and Presented By: Sahidul Islam)

                                           Dated: Nov 12, 2020  (vetuniverse.blogspot.com)