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order to impress others. This pattern is characteristic
in both men and women.
5. Resignation (“What’s the use?”). These pilots do not
see themselves as being able to make a great deal of
difference in what happens to them. When things go
well, these pilots are apt to think it is due to good luck.
When things go badly, they may feel that someone is
out to get them, or attribute it to bad luck. The pilot
will leave the action to others, for better or worse.
Sometimes, they will even go along with unreasonable
requests just to be a “nice guy.”
1-20
2-1
Introduction
Several factors affect aircraft performance including the
atmosphere, aerodynamics, and aircraft icing. Pilots need an
understanding of these factors for a sound basis for prediction
of aircraft response to control inputs, especially with regard
to instrument approaches, while holding, and when operating
at reduced airspeed in instrument meteorological conditions
(IMC). Although these factors are important to the pilot flying
visual flight rules (VFR), they must be even more thoroughly
understood by the pilot operating under instrument flight
rules (IFR). Instrument pilots rely strictly on instrument
indications to precisely control the aircraft; therefore, they
must have a solid understanding of basic aerodynamic
principles in order to make accurate judgments regarding
aircraft control inputs.
Aerodynamic
Factors
Chapter 2
2-2
Leading Edge
Mean Camber Line
Mean Chord Line Lower Camber
Upper Camber
Trailing Edge
Figure 2-1. The Airfoil.
Figure 2-2. Angle of Attack and Relative Wind.
The Wing
To understand aerodynamic forces, a pilot needs to
understand basic terminology associated with airfoils.
Figure 2-1 illustrates a typical airfoil.
The chord line is the straight line intersecting the leading
and trailing edges of the airfoil, and the term chord refers
to the chord line longitudinal length (length as viewed from
the side).
The mean camber is a line located halfway between the
upper and lower surfaces. Viewing the wing edgewise, the
mean camber connects with the chord line at each end. The
mean camber is important because it assists in determining
aerodynamic qualities of an airfoil. The measurement of
the maximum camber; inclusive of both the displacement
of the mean camber line and its linear measurement from
the end of the chord line, provide properties useful in
evaluating airfoils.
Review of Basic Aerodynamics
The instrument pilot must understand the relationship
and differences between several factors that affect the
performance of an aircraft in flight. Also, it is crucial to
understand how the aircraft reacts to various control and
power changes, because the environment in which instrument
pilots fly has inherent hazards not found in visual flying. The
basis for this understanding is found in the four forces acting
on an aircraft and Newton’s Three Laws of Motion.
Relative Wind is the direction of the airflow with respect to
an airfoil.
Angle of Attack is the acute angle measured between the
relative wind, or flight path and the chord of the airfoil.
[Figure 2-2]
Flight path is the course or track along which the aircraft is
flying or is intended to be flown.
The Four Forces
The four basic forces [Figure 2-3] acting upon an aircraft in
flight are lift, weight, thrust, and drag.
Lift
Lift is a component of the total aerodynamic force on an
airfoil and acts perpendicular to the relative wind. Relative
wind is the direction of the airflow with respect to an airfoil.
This force acts straight up from the average (called mean)
center of pressure (CP), which is called the center of lift. It
should be noted that it is a point along the chord line of an
airfoil through which all aerodynamic forces are considered
to act. The magnitude of lift varies proportionately with
speed, air density, shape and size of the airfoil, and angle
of attack. During straight-and-level flight, lift and weight
are equal.
2-3
Figure 2-3. The Four Forces and Three Axes of Rotation.
Weight
Weight is the force exerted by an aircraft from the pull of
gravity. It acts on an aircraft through its center of gravity
(CG) and is straight down. This should not be confused
with the center of lift, which can be significantly different
from the CG. As an aircraft is descending, weight is greater
than lift.
Thrust
Thrust is a force that drives an aircraft through the air and can
be measured in thrust and/or horsepower. It is a component
　
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