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Instrument Flying Handbook
Aerodynamic Factors
Review of Basic Aerodynamics

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Instrument Flying


Table of Contents

Chapter 1. Human Factors
Chapter 2. Aerodynamic Factors
Chapter 3. Flight Instruments
Chapter 4. Section I
Airplane Attitude Instrument
Using Analog Instrumentation
Chapter 4. Section II
Airplane Attitude Instrument
Using an Electronic Flight

Chapter 5. Section I
Airplane Basic
Flight Maneuvers
Using Analog Instrumentation
Chapter 5. Section II
Airplane Basic
Flight Maneuvers
Using an Electronic Flight

Chapter 6. Helicopter
Attitude Instrument Flying

Chapter 7. Navigation Systems
Chapter 8. The National
Airspace System

Chapter 9. The Air Traffic
Control System

Chapter 10. IFR Flight
Chapter 11. Emergency

The Four Forces and Three Axes of Rotation.
Figure 2-3. The Four Forces and Three Axes of Rotation.

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 clown. This should not be confused
with the center of lift, which can be significantly different
from the CO. As an aircraft is descending, weight is greater
than lift.

Thrust is a force that drives an aircraft through the air and can
he measured in thrust and/or horsepower. it is a component
that is parallel to the center of thrust and overcomes drag
providing the aircraft with its forward speed component.

Drag is the net aerodynamic force parallel to the relative
wind and is generally a sum of two components: induced
drag and parasite drag.

Induced drag
Induced drag is caused from the creation of lift and increases
with angle of attack. Therefore, if the wing is not producing
lift, induced drag is zero. Conversely, induced drag decreases
with airspeed.

Parasite drag
Parasite drag is all drag not caused from the production of
lift. Parasite drag is created by displacement of air by the
aircraft, turbulence generated by the airfoil, and the hindrance
of airflow as it passes over the surface of the aircraft or
components. All of these forces create drag not from the
production of lift but the movement of an object through an
sir mass. Parasite drag increases with speed and includes skin
friction drag, interference drag, and form drag.

Skin Friction Drag
Covering the entire "wetted" surface of the aircraft is a thin
layer of air called a boundary layer. The air molecules on the
surface have zero velocity in relation to the surface; however,
the layer just above moves over the stagnant molecules
below because it is pulled along by a third layer close to
the free stream of air. The velocities of the layers increase
as the distance from the surface increases until free stream
velocity is reached, but all are affected by the free stream.
The distance (total) between the skin surface and where free
stream velocity is reached is called the boundary layer. At
subsonic levels the cumulative layers are about the thickness
of a playing card, yet their motion sliding over one another
creates a drag force. This force retards motion due to the
viscosity of the air and is called skin friction drag. Because
skin friction drag is related to a large surface area its affect
on smaller aircraft is small versus large transport aircraft
where skin friction drag may be considerable.

• Interference Drag
Interference drag is generated by the collision of airstreams
creating eddy currents, turbulence, or restrictions to smooth
flow. For instance; the airflow around a fuselage and around
the wing meet at some point, usually near the wing's root..
These airflows interfere with each other causing a greater
drag than the individual values. This is often the case when
external items are placed on an aircraft. That is, the drag of
each item individually, added to that of the aircraft, are less
than that of the two items when allowed to interfere with
one another.