Download Flight in Nature

FlightinNature:Bird&InsectFlight–EVERYTHINGYOUNEEDTOKNOW!!!!
Feathers and flight
A bird is designed for flight. The combination of light weight, strength and
shape, as well as precision control, is largely responsible for giving birds
their special ability for sustained flight. Every part gives maximum power
with a minimum of weight. The heavier the animal, the bigger its wings
need to be. The bigger the wings, the more muscle is needed to move
them.
Birds’ feathers are essential for flight.
Birds’ feathers are light, strong and flexible
Birds’ feathers are designed to be light but very strong, flexible but very
tough. Although it looks like feathers grow all over a bird, they actually
grow in specific areas called feather tracks. In between the feather tracks
are down feathers. This keeps the body weight down. Feathers are made
of a tough and flexible material called keratin. The spine down the middle,
called the shaft, is hollow. The vanes are on the two halves of the feather.
They are made of thousands of branches called barbs. Because there are
many spaces between these barbs, a feather has as much air as matter.
Contour feathers
The contour feathers of a bird are the outside feathers – the ones that you
can see. They provide the colour and the shape of the bird. The contour
feathers tend to overlap each other, much like tiles on a roof. The feathers
tend to shed rain, keeping the body dry and well insulated. Each contour
feather can be controlled by a set of specialised muscles, which controls
the position of the feathers, allowing the bird to keep the feathers in a
smooth and neat condition. The smooth and streamlined surface is
achieved because the feathers’ barbs are joined together with barbules
(branches on the barbs). The barbules have hooks that lock the barbs
together. If the barbules are disrupted, the bird passes its bill though the
feather to link them again. The contour feathers used for flight are known
as remiges (wing feathers) and rectrices (tail feathers).
Remiges (wing flight feathers)
These feathers are strong and stiff, supporting the bird during flight. They
can be divided into three groups:
• Primary feathers: These are the largest of the flight feathers and propel
the bird through the air. They are the farthest away from the body,
attached to the skin of the wing on the ‘hand’ of the bird. In most bird
species, there are 10 primary feathers on each wing. If these flight
feathers are damaged or lost, a bird cannot fly.
• Secondary feathers: These run along the ‘arm’ of the wing and sustain
the bird in the air, giving it lift. The number of secondary feathers
varies with different species. Experiments have shown that, if half of
the secondaries are removed, a bird will still be able to fly, but some
control will be lost.
• Tertiary feathers: These are on the ‘upper arm’ of the bird. They are the
short, innermost flight feathers on the rear edge of a wing, close to
the body of the bird. They are not as important for flight as the
primary and secondary feathers.
Rectrices (tail flight feathers)
The rectrices or tail flight feathers are mainly concerned with stability and
control. They are used as a rudder, helping to steer and balance the bird
and allow the bird to twist and turn in flight. These feathers also act as a
brake for landing.
Coverts
Bordering and overlaying the edges of the remiges and the rectrices are
rows of feathers called coverts. These help streamline the shape of the
wings and tail (minimising drag) while providing the bird with insulation.
Angle of Attack:
An important aspect of lift is the angle of attack (defined as the angle the wing is
to the oncoming air force). At a certain angle of attack the bird will stall and fall.
This happens with planes if they try to fly up to fast- they stall. What is the critical
angle of attack anyhow? This is a tricky questions because it depends a lot on
airspeed. It also depends on the type of wing a bird has. For instance, certain
birds that fly at low speeds, like vultures, have different types of wings with slits in
them that allow them to break up turbulence and gain lift. (Birds also have an
alula, or a mid wing slot that allows them to fly at different speeds - similar to the
flaps on an airplane wing).
THRUST:
While lift is always an issue for birds, we have yet to talk about thrust, or the act
of moving the bird forward. Just flapping a wing up and down isn't going to move
it forward, just up. For birds, their solution comes from the unique rotation of their
wings. As the wings beat, the primary flight feathers actually twist to provide
thrust. This twist is partly a result of asymmetrical veining of the feathers.
Types of Wings
•
•
•
•
High Aspect Ratio Wing:
a. Much longer than it is wide. Has lot of vertical lifting area. Not much slotting.
b. Not fast flying birds but more soaring birds
c. Albatross, or Frigate bird.
• Elliptical Wing:
• a. Tends to be even pressure over most of the surface.
• b. Usually found in birds that live in forests. … facilitates a subtle change in the
angle of the wing.
• c. Sparrows.
. Falcons, Plovers
• High speed Wing: a
• b. Wings that are narrow and come out to a sharp tip. These wings reduce
drag. More of the wing-beat is producing forward thrust.
• High lift Wing
• a. Extreme slotting in the wing-tips
• b. Vultures, Eagles, etc.
How Hummingbirds Fly:
The key to a hummingbird's flight is in its wing patterns.
Generally, birds flap their wings up and down. This is not the case
with the hummingbird, however. The hummingbird flies by
oscillating its wings forward and backward in a figure eight pattern
very rapidly. Seventy-five percent of the bird's lift is produced
during the downstroke of this wing pattern. The figure eight
pattern can be likened to a swimmer doing figure eights in the
water to remain afloat.
Bat flight vs. bird flight – which one is most efficient?!
Unlike insects and birds, which have relatively rigid wings that can
move in only a few directions, a bat’s wing contains more than two
dozen joints that are overlaid by a thin elastic membrane that can
stretch to catch air and generate lift in many different ways [video].
This gives bats an extraordinary amount of control over the threedimensional shape their wings take during flight, Swartz explained.
“Insects can move the joint at the insect equivalent of a shoulder,
but that’s the only place where they can exert force and control
movement,” she said. Birds have many more joints in their wings,
but it’s nothing compared to bats.
“Bats are operating with the same skeleton that we have. Every
joint in the human hand is there in the bat’s wing and actually a
couple more,” Swartz told LiveScience. “Think about the degree of
control that we have over the shape of our hands—bats are able to
extend that to make fine scale adjustments during flight.”
It was once thought that despite having so many wing joints, it was
more efficient for bats to stabilize their wings and wave them up
and down like relatively rigid paddles the way birds do.
“What we see when we look more closely is that in fact, it’s not
what they’re doing,” Swartz said in a telephone interview. “It
suggests that they’re able to take advantage of this highly jointed
system to make subtle adjustments to the wing shape during
flight.”
The other key to a bat’s efficient flight lies in its highly elastic
wing. Videos from the wind tunnel tests show that a bat’s wing is
mostly extended for the down stroke during straightforward flight.
But because the membrane can curve and stretch much more than a
bird’s wing can, bats can generate greater lift for less energy.
By blowing non-toxic smoke over the bats [video] as they were
flying, the researchers were also able to create a video that
revealed how air flows around the creatures as they flap their
wings. The data showed that during the down stroke, the air
vortex—which generates much of the lift in flapping-wing flight—
closely tracks the animals’ wingtips. But in the upstroke, the vortex
appears to come from another location entirely, perhaps the wrist
joint.
The researchers think this unusual pattern helps to make bat flight
more efficient and credit it to the tremendous flexibility and
articulation of the wing.
Insect Flight Basics
Insect wings are driven up and down by flight muscles located
in the animal's thorax. There are two types of insect flight
mechanisms, based on how the flight muscles transmit force
to the wings. They are called direct and indirect flight
mechanisms. In the direct flight mechanism, at least one power
muscle connects to the wing…DIRECTLY! For example, a wing
depressor muscle might attach to a special part of the wing
near the wing base, and directly pulls the wing down when the
muscle contracts. The direct flight mechanism is more
primitive than the indirect mechanism, and so we find it on
older insects (evolutionarily speaking), such as dragonflies and
mayflies. Make no mistake, however – insects with the direct
flight mechanism are not inherently worse flyers than those
with the more advanced indirect mechanism. In fact,
dragonflies are some of the most impressive fliers out there,
due in part because their direct flight mechanism allows them
to independently control each of their 4 wings.
In the indirect flight mechanism, on the other hand, the flight
muscles invest their energy into deforming the insect’s thorax,
which in turn causes the wings to move up and down. This
mechanism in particular involves a pretty complicated hinge
system at the wing base, which scientists are still trying to
understand. The majority of flying insects have indirect flight
muscles, including butterflies and moths, beetles,
grasshoppers and crickets, flies and bees. The big benefit of
the indirect flight mechanism is that the thorax is able to store
substantial elastic energy from each half-stroke (like a spring),
and return it to help propel the subsequent half-stroke, in a
process that involves mechanical resonance. Such a system
makes flapping flight more energy-efficient.
Wing Movement
In most insects, the forewings and hindwings work together.
During flight, the front and rear wings remain locked
together, and both move up and down at the same time. In
some insect orders, most notably the Odonata, the wings
move independently during flight. As the forewing lifts, the
hindwing lowers. Insect flight requires more than a simple
up and down motion of the wings. The wings also move
forward and back, and rotate so the leading or trailing edge
of the wing is pitched up or down. These complex
movements help the insect achieve lift, reduce drag, and
perform acrobatic maneuvers.
How Insects Fly
When a bee zips across your garden, it blurs by at jet speed and turns on a dime
like no airplane in the world. And when a fly zooms through your kitchen and
sniffs a possible snack, it can stop short in midair and hover like a helicopter to
check it out. If disappointed, the fly can twirl in an aerial loop-the-loop and land
upside down on the ceiling. Then it takes off backward, and flies sideways out
the open window. "Insects don't just stay in the air," says entomologist (scientist
who studies insects) Michael Dickinson at the University of California at Berkeley.
"They perform aerial maneuvers, fly up, down, and sideways, and respond to
changes in wind speed and direction."
For many bugs, flying is the only way to travel, providing access to food that
other creatures can't reach, and a swift escape from predators. More than 99.9
percent of the 900,000 species of insects on Earth are classified as Pterygota, or
winged insects. Entomologists say these invertebrates (backboneless animals)
were the first creatures to fly, dating from the Carboniferous period about 360
million years ago.
But for centuries, scientists have puzzled over exactly how insects perform their
amazing acrobatic aeronautics. Though they haven't deciphered every secret,
researchers have made new discoveries-and are now applying the principles of
insect flight to the designing of sophisticated new planes.
Winging It
The real secret to how insects fly lies in the wings, both in their design and in
how they're used. Most insects rely on two pairs of wings, which join or overlap
so they work together as a single pair. Insect wings are one of nature's lightest
structures, lacking bone and muscle; they're made of chitin, an extremely tough
material that also composes an insect's hard outer skin. Chitin is a
polysaccharide, a chemical compound that forms fibrous molecules (in which
hydrogen atoms bond to produce extra strength). A network of veins also lends
insect wings extra support.
Wings on insects, bats, birds, and airplanes share a similar shape, called an
airfoil: they're curved on top and flat on the bottom. Air rushing over the wing has
to travel farther because of the curvature, so this air moves faster than air below
the wing. Since fast-moving air exerts less pressure than slow-moving air, the
difference creates suction, called lift. Lift is what pulls a wing-and a plane or
critter-skyward. Each downward wing flap creates more lift, propelling the
creature up and forward.
Flying Flap
But the researchers found that insect flight is far more complex than previously
thought. Large-bodied insects lift off by flapping their wings very rapidly: for bees
and flies, about 200 times per second. Some midges and wasps flap their wings
up to 1,000 times per second! What powers such energy? Strong muscles in the
midsection, or thorax. For their size, they're the most powerful muscles known in
nature.
Michael Dickinson has also discovered that insect wings don't just flap up and
down. On the upstroke, insect wings move differently from those of most other
flying creatures-in a kind of figureeight motion. As the insect wing nears the end
of a forward stroke, the wing rotates backward, twisting upside down, parallel to
the ground. This rotation accelerates (speeds up) the flow of air over the wing.
This means that insect wings generate a burst of lift and speed from the upstroke
as well as the downstroke-unlike the wings of birds or bats, which derive most of
their flying power only from the downstroke. "Such elaborate wing movements
create miniature tornadoes that send bugs soaring by sucking the wings upward.”
Buggy Helicopters
Ellington's team documented wing movements of hawkmoths and the air currents
they whip up. The scientists tethered a hawkmoth to the end of a wind tunnel,
then blasted it with smoke. Using a strobe light to freeze motion, they snapped 3D pictures of the moth flapping wildly in the gale.
But insects are also nature's helicopters, with their wings acting as helicopter
blades. To fly forward, bugs tilt their bodies forward, pulling air from in front and
pushing it out behind as they flap wings back and forth. To hover, they tilt their
bodies upward and fan wings horizontal to the ground, blowing air straight down
so they can hang in midair. But, says Dickinson, there's still a lot of mystery
surrounding insect flight. "We don't know what the animal does to initiate and
control such forces, and it's going to take a lot more work by scientists with
different specialties to find out."