3. Flight
Flight is the central avian adaptation
Basic bird flight has many components i.e. taking
off, maneuvering, stabilizing positions, and
landing
Flight requires rapid and constant adjustments of
the wings and tail
The sensory system sends information from
thousands of individual feathers in a bird’s
plumage to the flight control center in the brain
and neural receptors throughout the body
4. Flight is the most economical form of
locomotion
It costs less energy to fly 1 kilometer than to
walk, run, or swim the same distance
A 10-gram bird in flight, for example, expends
less than 1 percent of the total energy
required by a 10-gram mouse to run the same
distance
5. Elementary Aerodynamics
To stay aloft, birds must overcome the forces of gravity and drag by
generating equal and opposite forces, lift and thrust
Lift
Lift is the upward air pressure force that counters the downward force
of gravity, expressed as a bird’s weight
Thrust
• Thrust is a forward force that counteracts the slowing influence of
the forces of turbulence and friction, collectively called drag
• When these four forces weight, lift, drag, and thrust are in dynamic
balance, a bird maintains level flight at a constant speed
• Unlike airplanes, which generate lift with wings and thrust with
engines, birds use their wings to do both
6.
7. The wings of birds produce lift by the passage
of the airstream across their surfaces, usually
by forward movement into the airstream
The upper surfaces of an airfoil are curved
more strongly than the lower surfaces,
producing a curved structure that tapers
posteriorly
8.
9.
10. The orientation, or angle of attack, of the
airfoil with respect to the passing airstream,
called “relative wind” produces the net
upward force called lift
The angle of attack is defined as the angle
between the direction of the airstream and
the straight chord line connecting the leading
and trailing edges of the airfoil
The amount of lift generated must balance a
bird’s weight to sustain level flight
11. Airfoils produce lift by altering the circulation
of air around them
Deflecting some of it downward, and by
increasing the speed of airflow at the upper
surface relative to its speed at the lower
surface of the airfoil
Several components of the alteration of air
circulation by the airfoil contribute to the
production of lift
