BERNOULLI'S PRINCIPLE
Bernoulli's principle (fig. 3-2) states that when a
fluid flowing through a tube reaches a constriction or
narrowing of the tube, the speed of the fluid passing
through the constriction is increased and its pressure is
decreased.
Q3-1.
The willingness of an object to stay at rest
because of inertia is described by which of
Newton's laws of motion?
Q3-2.
A heavy object will accelerate more slowly
than a light object when an equal amount of
force is applied. Which of Newton's laws
describes this statement?
Q3-3.
If you blow up a balloon and then release it, it
will move in what direction?
Q3-4.
When fluid reaches a narrow part of a tube, its
speed increase and its pressure is decreased.
What law does this statement describe?
THE AIRFOIL
LEARNING OBJECTIVE: Recognize the
terms used to describe the various parts of an
airfoil section and the terms used in explaining
the airflow lift generation.
An airfoil is defined as that part of an aircraft that
produces lift or any other desirable aerodynamic effect
as it passes through the air. The wings and the propeller
blades of a fixed-wing aircraft and the rotor blades of a
helicopter are examples of airfoils.
AIRFOIL TERMINOLOGY
The shape of an airfoil and its relationship to the
airstream are important. The following are common
terms that you should understand before you learn
about airfoils.
Leading edge
The front edge or surface of the
airfoil (fig. 3-3).
Trailing edge
The rear edge or surface of the
airfoil (fig. 3-3).
Chord line
An imaginary straight line from
the leading edge to the trailing
edge of an airfoil (fig. 3-3).
Camber
The curve or departure from a
straight line (chord line) from the
leading to the trailing edge of the
airfoil (fig. 3-3).
Relative wind
The direction of the airstream in
relation to the airfoil (fig. 3-4).
Angle of attack
The angle between the chord line
and the relative wind (fig. 3-4).
AIRFLOW AROUND AN AIRFOIL
The generation of lift by an airfoil depends on the
airfoil's being able to create a special airflow in the
airstream. This airflow develops the lifting pressure
over the airfoil surface. The effect is shown in figure
3-5, which shows the relationship between lift and
Bernoulli's principle. As the relative wind strikes the
leading edge of the airfoil, the flow of air is split. A
portion of the relative wind is deflected upward and aft,
and the rest is deflected downward and aft. Since the
3-2
Figure 3-2.—Bernoulli's principle.
Figure 3-3.—Airfoil terminology.
