Streamlining
by Adel Salem
In order for a long bird of an average length of 11 to13
inches long (29 to 33 cm as measured from the tip of the chest to the
tail end) to be able to fly smoothly in the air, with speeds of 30 to
60 miles per hour (50-95 km/hr) it must be aerodynamically built. The
distribution of the muscle mass and the feather arrangement on the body
play a major role of thrusting and keeping the ES buoyant in the air for
at least 2 hours during leisure flying and over 6 hours while racing.
General appearance of the flying ES:
Short beak curved downwards, fused directly in a small compacted head
and a conspicuously short neck. The broad erected chest blends in directly
with a long concave back that ends with a long tail. Wings are shorter
than the tail, pressed tightly against a heart-shaped chest and resting
usually above the back. Short powerful legs containing 6% of the ES body
weight helps in jetting the bird rapidly in the air.
Wings and feather arrangement:
Because of a massive length of the wing span reaching over 30 inches (75
cm.), they have to be designed so articulately other wise creating excessive
weight, drag and air turbulence reducing the bird's ability to fly. The
outer vane, which springs from the side of the Rachis (the
shaft or the middle portion of the feather that supports the vane
on each side) should be overlapping the next outer vane with the exception
of the first two primaries (the first nine to ten feathers in the
pigeon's wing) to allow for some air flow to the upper wing. In non-flying
ES the overlapping is minimal.
The primaries act as a propeller by providing forward motion. While the
secondary (the 9 feathers that follow the primaries) give the proper
support of lift in the air.
Slots: The first two primaries don't show the typical vane overlapping
or webbing as the rest, creating gaps or slots. Slots prevent stalling
and increase lift by making airflow fast and evenly over the upper surface,
thus reducing turbulence. Slots also noted between the tips of the outer
most primaries and another between the alula (three stiffened feathers
springing from the outer most edge of the wing) and wing margin. Broad-winged
soaring birds such as eagles and vultures show slots that are very much
larger than any bird. The ES take advantage of this modification by flying
so slowly and effortlessly at times, as they become tired.
Feather characteristics of a weak flying ES:
Stretched wing displays long and narrow primaries bent inwards. Rachis
of weak flyers is brittle, snip easily, and grow slowly and weakly. Weak
Vanes are thin with weak Barbs (plates of hair extending obliquely
from the shaft) showing evidence of stress marks across the wings and
the tail. The general appearance of that bird is of long wings that are
of the same length or even longer than the tail. Wings in weak flyers
are permanently dragging, presenting an overall look of loose feathers.
Not only are these birds’s weak flyers, but also have a lower fertility
rate. The extra length of the primaries reflects entirely on the wing's
lining as Coverts (small feathers covering the upper wing) and
Axilars (under wing feathers lying close to the body) showing also
an excessive length. Loose feathers represent the general appearance of
these birds. Good ES should be compacted with short feathers and streamlined
in order to sail fast and smooth in the air or even look sharp in a show
room. ES that occasionally exhibit wings slightly below the tail are not
considered at fault as long as wings are shorter than the tail with all
the wing feathers tucked together without evidence of fins or sails and
most importantly they have to be pressed tightly against a full chest.
Many of these birds are excellent flyers although hard to pinpoint accurately
even for an experienced eye. The method of choice then is to test them
in the air. I would like to speculate that the droopiness in the flying
birds could be due to the weight exerted on the Triosseum tendon by a
long heavy wing.
Triosseum Tendon:
It is a tendon of 1.2 centimeters (0.48 of an inch) that fastens the lesser
pectoral muscle to the humorous (shoulder bone), thus pulling the
wing upward while the bird in flight. It also helps in keeping the wing
tight to the chest and above the back while the bird is not flying.
As the lesser pectoral muscle contracts, The attached tendon pulls the
humorous lifting the shoulder and the wing up in the air. The greater
pectoral muscle which is attached to the lower humorous then contracts
generating the needed power needed, for the primaries that act as a propeller,
pulling the bird's wing down and moving it forward.
The Tail: the long tail is a modification to help
balancing their large surface area. It contains occasionally more than
12 feathers. The ES make tight circles before landing as compared to a
racing homer that has to make a much wider circle. Ducks and many other
short-tailed birds although fast, their circles are very wide and almost
close to a straight line. This adaptation makes them highly maneuverable
in the air, especially as air predators at high speed chase them.
The muscle mass: The chest or the breast is composed
of two muscles: the great pectoral and the lesser pectoral
muscle. They rest on an oblong sternum one of the most highly specialized
bones of the avian skeleton system. A good flying Egyptian Swift with
a weight of 300 to 320 grams (an average of 10.5 ounces or 0.7 of a pound)
should have up to 32% of its body weight concentrated between the wings
and the chest area. The breast muscle by itself compromises a 20% of the
total body weight or 1:5 ratio of wing muscle to body weight. If the ratio
is increased as the case of utility pigeons or meat pigeons, the bird
becomes too heavy to fly. If decreased the bird becomes so light that
it would not have enough power to push forward in the air. The result
will become evident as the bird Hoover's high in the sky like a kite in
the same spot for hours as noted in many high flying breeds. In the case
of the non-flying ES their air movement will resemble a glider with very
little forward movement.
Flying pigeons that have strong wing-breast muscles is able
to develop a force equal to 10 times the weight of the pigeon or a little
more than 100 ounces. It is for that reason a racing pigeon could be trained
to carry a message or a container of few ounces when properly attached.
This scheme has been used for useful purposes and also abused in cases
of drug smuggling.
The sternum bone or the breast-bone:
Two kinds of sterna exist in the birds: Ratite and Carnite.
The sternum of a ratite bird has the ventral surface flattened, like
the bottom of a raft. Flightless birds like the Ostrich and utility pigeons
posses this kind. It allows for a large build up of chest muscle; however
lacks wing-muscle attachment; witch is essential to a flying bird. The
Carinite sternum has the ventral surfaced keeled, like the bottom of a
sailing boat. Flying pigeons have this kind, because it permits more surfaces
for the attachment of the more vital wing muscles. The prominent heart-shaped
chest in a racing homer is a good example. Some experience is required
to evaluate the muscle attachment o f the ES because of the massive amount
of feathers covering their body.
Streamlining:
Since air has weight and exerts pressure streamlining is an essential
for flight. It allows air to flow smoothly over the wing surface and at
the same time prevents excessive pressure from building up in the front,
reducing pressure on the upper and lower surfaces, and lessens vacuum
and turbulence behind. During flapping flight more pressure of the oncoming
air stream is thus met by the under surface and deflected downward than
is allowed to flow over the upper surface. This gives the required lifting
force because the pressure under the wing is greater, while the pressure
on the upper surface is less. As the wings tilt while in flying the lifting
force increase until a point where air eddies build on the upper wing
interfering with the bird's ability to continue on flying. The effect
of the air turbulence is partially offset by the wing's aspect ratio,
which is the proportion of the length to breadth. In other words, a wing
is long and broad enough to allow for disturbances and yet has sufficient
surface for lifting purposes. Birds with long wings as the ES, don't need
to flap as many times (3.0 times per second) as compared to a racing Pigeon
with shorter wings (more than 3.0 times Per second) or a Herring Gull
of very long wings (2.3 times per second), Pelican (1.2 times per second)
and the Humming bird with wing beat of 60 times a second.
Summary:
excessive length and poor wing design is a hindrance to the ES. On the
other hand long properly constructed wings aided by longer tail could
enhance the ES both in the sky and the show room.
References:
Ornithology by Olin Sewall, - Beebee; The bird and its function -
Roberts; on the normal flight of birds - The pigeon by Levi on chest muscle
E-mail
| FAQ| Home| Links
| News Letter | Sale
| Standards | Swift
Video
|