DRAG
Drag is the force that tends to hold an aircraft back.
Drag is caused by the disruption of the airflow about the
wings, fuselage (body), and all protruding objects on
the aircraft. Drag resists motion as it acts parallel and in
the opposite direction in relation to the relative wind.
Figure 3-6 shows the direction in which each of these
forces acts in relation to an aircraft.
Up to this point, you have learned the physical laws
of aerodynamics, airfoils, and the forces affecting
flight. To fully understand flight, you must learn about
the rotational axes of an aircraft.
Q3-7.
What are the four forces that affect flight?
ROTATIONAL AXES
LEARNING
OBJECTIVE:
Identify
the
three axes of rotation and the terms relative to
the aircraft's rotation about these axes.
Any vehicle, such as a ship, a car, or an aircraft, is
capable of making three primary movements (roll,
pitch, and yaw). The vehicle has three rotational axes
that are perpendicular (90 degrees) to each other. These
axes are referred to by their direction—longitudinal,
lateral, and vertical. Perhaps the most descriptive
reference is by what action takes place about a given
axis or pivot point—roll, pitch, and yaw.
LONGITUDINAL AXIS
The longitudinal axis is the pivot point about which
an aircraft rolls. The movement associated with roll is
best described as the movement of the wing tips (one up
and the other down). Figure 3-7 shows this movement.
This axis runs fore and aft through the length (nose to
tail) of the aircraft. This axis is parallel to the primary
direction of the aircraft. The primary direction of a
fixed-wing aircraft is always forward. Figure 3-8 shows
the longitudinal axis.
LATERAL AXIS
The lateral axis is the pivot point about which the
aircraft pitches. Pitch can best be described as the up
and down motion of the nose of the aircraft. Figure 3-7
shows this movement. The pitch axis runs from the left
to the right of the aircraft (wing tip to wing tip). It is
perpendicular to and intersects the roll axis. Figure 3-8
shows the pitch axis and its relationship to the roll axis.
VERTICAL AXIS
The vertical axis runs from the top to the bottom of
an aircraft. It runs perpendicular to both the roll and
pitch axes. The movement associated with this axis is
yaw. Yaw is best described as the change in aircraft
heading to the right or left of the primary direction of an
aircraft. Figure 3-7 shows this movement. Assume you
are walking from your work space to an aircraft located
100 feet away. You are trying to walk there in a straight
line but are unable to do so because there is a strong
wind blowing you off course to your right. This
movement to the right is yaw. The yaw axis is shown in
figure 3-8.
Q3-8.
Any vehicle (ship, car, or aircraft) is capable
of making what three primary movements?
FIXED-WING AND ROTARY-WING
AIRCRAFT
LEARNING OBJECTIVE:
Recognize the
difference in aerodynamic principles that apply
to fixed- and rotary-wing aircraft.
A fixed-wing aircraft depends on forward motion
for lift. A rotary-wing aircraft depends on rotating
airfoils for lift. The airfoil sections of a fixed-wing
aircraft aren't symmetrical. The rotor blades of a
helicopter are symmetrical. These differences are
important to you if you're to understand aerodynamic
principles.
3-4
Figure 3-6.—Forces affecting flight.
