Сборник технических текстов для домашнего чтения по английскому языку. Морозова М.А. - 12 стр.

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УлГТУ | Ульяновск

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Yaw Wings
Lift is the aerodynamic force that supports an aircraft in flight, due to the airflow over
the wings or body. Drag is the resistance a vehicle moving through the air
experiences, and pitching
1
moments are a result of aerodynamic forces that make the
nose of an aircraft move either up or down.
The shape of a wing looks like an elongated
2
water drop laying on its side. This shape
is referred to as an airfoil. Usually the top is curved more than the bottom making the
upper surface slightly longer than the bottom. Since air passing over the top and
bottom must reach the rear of the wing at the same time, the air passing over the top
must not only travel faster, but also changes direction and is deflected downward.
This actually results in lift being generated due to a rate of change of vertical momen-
tum and a difference in static pressure between the top and bottom of the wing.
The production of lift is probably the most important topic in the science of
aerodynamics. It is a wing's ability to efficiently produce a force perpendicular to the
air passing over it that makes heavier-than-air flight possible.
In the big picture, all wings produce lift the same way - they push down on the air,
forcing the air downward relative to the wing. It is this force that we call lift.
Many different types of shapes do this, but the shapes built specifically for this
purpose are called "airfoils ."
Various Airfoils
The wing makes its "magic" by forcing the air down. Some people like to compare it
to water skiing, where water skis and speed are used to force the water down and the
skier up. But that analogy tells only part of the story. Most of the time, the top of the
wing does the majority of the "pushing" on the air (actually, in this case, "pulling" the
air down). The top and the bottom of the wing combine to produce a force, and the
part of this force perpendicular to the relative wind is lift. Since the wing not only
pushes the air down but slows it down as well, some drag (induced drag) is caused.
The chord
3
line is an imaginary line drawn from the leading edge to the trailing edge
of an airfoil. Secondly, the relative wind is the airflow which acts on the airfoil and is
paralell to but opposite the direction of flight. The angle between the chord line and
the relative wind is called the angle of attack, which is called "alpha." As the angle of
attack increases, the change of vertical momentum increases. Additionally, as the
angle of attack increases, the coefficient of lift (CL) increases. The result is an
increase in lift. However, there are limits to how much the angle of attack can be
increased. At some higher angle of attack, the lift coefficient begins to decrease. The
angle of attack where the lift coefficient begins to decrease is called the critical angle
of attack. Once the critical angle is exceeded, the wing can no longer produce enough
lift to support the weight of the aircraft and the wing is said to be "stalled." In other
words, the aircraft will stall when the critical angle of attack is exceeded.
1
pitching – продольный момент
2
elongated - обтекаемый
3
chord - хорда

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