L2 Redfern - Evolution of Avian Flight Flashcards
What 2 factors was he development of modern powered flight dependent on?
- Aerodynamic shape, structure of the body
- Physiology to provide energy
These adaptions opened up a new niche and allowed the tremendous diversification of birds
Describe the arboreal theory of how flight developed
Perhaps flight developed from parachuting and gliding from high perches.
Even though it would take the Archaeopteryx energy to climb the tree, it would conserve energy during the gliding phase
Similar to sugar gliders and flying squirrels today
Describe the cursorial theory of how flight developed
Perhaps elongated forelimbs gave better leaping ability and control to a small theropod dinosaur, that ran and jumped to catch insects. A proto-wing increased arboreal habitats, gliding is the next thing.
BUT to achieve lift off the Archaeopteryx would have to run 3 times faster than modern birds to achieve lift off due to its weight
Also when flight is achieved, the air drag would cause the velocity to instantly decrease resulting in short ineffective flight`
Give the other theory to flight that isn’t the arboreal and cursorial
NEW THEORY:
Forelimb modifications allowed down force to allow birds to run up extremely steep slopes to escape.
Birds need down force to give their feet increasing grip and enhanced limb trajectory
Transition of the proto-wing to powered flight is limited by relative size and muscle power of the wings
What are the 4 elements of flight?
- Aerodynamics
- Feathers
- Mechanics
- Respiration
What are the 4 parts of a bird that are important for aerodynamics?
- streamlined shape - bread end and narrow rear
- maintaining laminar flow
- turbulence of air
- drag on wing
What are the 4 basic forces acting on a flying object?
- Lift - acting upwards to keep the animal in the air
- Thrust - to move the animal forwards in the air
- Drag - opposes forwards thrust
- Gravity - pull the bird back to ground
What 2 factors produce the high lift force birds need?
- high air flow
- increased effective curvature of the wing - e.g. angle of attack
What is the downfall of increased angle of attack?
As AOA increases, laminar flow tends to break up towards the back of the wing - leading to stalling of the aerofoil and reduced lift.
Define stalling
Stalling is when air flow breaks up and is no longer laminar
Describe the shape of a wing
Cross section - aerofoil shape
Convex upper surface, concave lower surface
- the underside air therefore has to travel a shorter distance than the air passing over the top
- this means it moves at a slower speed, and creates lift
- the angle of attack - same amount of lift at slower speeds with increased AOA
What 2 things are critical for the maintenance of lift?
- smooth flow over wing surfaces
- laminar flow
What does increasing the AOA cause
Increased AOA means greater lift and greater drag - speed slows but increased lift keeps the bird aloft
What is the stalling angle?
A stall is a reduction in the lift coefficient generated by a foil as angle of attack increases.This occurs when the critical angle of attack of the foil is exceeded.
The critical angle of attack is typically about 15 degrees
What are the 2 main sources of drag on a flying bird?
- Profile drag - air dragged along by moving body - increases with speed
- Induced drag - resistance to laminar flow around the wing - decrease with increased speed
