Definitions Flashcards
1
Q
Airfoil
A
A structure, piece, or body originally likened to a foil or leaf in being wide and thin and designed to obtain a useful reaction upon itself in its motion through the air. An airfoil may be no more than a flat plate, but usually it has a cross section carefully contoured in accordance with its intended application or function. Airfoils are applied to aircraft, missiles, or other aerial vehicles or projectiles to develop lift (as a wing), for stability (as a fin), for control (as an elevator), and for thrust or propulsion (as a propeller blade). Certain airfoils combine some of these functions.
2
Q
Absolute Altitude
A
The aircraft’s height above the terrain directly beneath the aircraft, measured in feet above ground level (AGL). Absolute altitude is found by subtracting the terrain elevation from the true altitude.
3
Q
Absolute Ceiling
A
The maximum altitude above sea level in a standard atmosphere that an airplane can maintain level flight.
4
Q
Accelerated Spin
A
A spin in which the control stick is not held in the full aft position. An accelerated spin is characterized by steeper pitch attitudes and higher spin rates.
5
Q
Accelerated Stall
A
A stall in which the load factor is greater than one, as in a pullout. Usually more violent and disorienting than a normal stall.
6
Q
Accelerated Stall Line
A
A curved line describing the number of g’s that can be generated at a given indicated airspeed as a function of CLMAX angle of attack for a particular airfoil. Also called line of maximum lift.
7
Q
Acceleration
A
A change in the velocity of a body with respect to magnitude or direction, or both.
8
Q
Accelerometer
A
An instrument that measures one or more components of the acceleration of a vehicle.
9
Q
Adverse Pressure Gradient
A
A pressure gradient of increasing static pressure in the direction of airflow.
10
Q
Adverse Yaw
A
Yaw in the opposite direction of aileron roll input.
11
Q
Aerodynamic Balance
A
The feature of a control surface that reduces the magnitude of the aerodynamic moment around the hingeline. See shielded horn.
12
Q
Aerodynamic Braking
A
A technique for slowing an airplane to a speed suitable for frictional braking. Aerodynamic braking is accomplished by increasing the surface area exposed to the relative wind in order to increase parasite drag, primarily by holding the nose of the airplane in the landing attitude.
13
Q
Aerodynamic Center (AC)
A
The point along the chordline of an airfoil where all changes in aerodynamic force effectively take place. It is normally located at the point of 25% chord.
14
Q
Aerodynamic Force (AF)
A
A force acting on an airfoil that is the result of air pressure and friction distribution over the surface of the airfoil.
15
Q
Aerodynamics
A
The science that studies the motion of gaseous fluid flows, and of their actions against and around bodies, and of the forces acting on bodies within that flow.
16
Q
Aerodynamic Twist
A
Form of wing tailoring that employs a decrease in camber and/or relative thickness from wing root to wingtip. The wing root is more positively cambered and/or thicker (relative to the chord) than the tip, resulting in a root first stall pattern. Also called section variation.
17
Q
Aileron
A
A movable control surface, attached to the wing of an airplane, used to produce a rolling moment around the longitudinal axis by creating unequal lifting forces on opposite sides of an airplane.
18
Q
Aileron Reversal
A
Reversal of the control effect usually produced by an aileron, caused by a moment around the aerodynamic center twisting the wing and changing its angle of attack.
19
Q
Aircraft (A/C)
A
Any device used or intended to be used for flight in the air.
20
Q
Airflow
A
A flow or stream of air. A rate of flow measured by mass per unit time.
21
Q
Airfoil
A
A streamlined shape designed to produce lift as it moves through the air.
22
Q
Airframe
A
The structural components of an airplane including the framework and skin of such parts as the fuselage, wings, empennage, landing gear, and engine mounts.
23
Q
Airplane
A
An engine driven, heavier-than-air, fixed-wing aircraft that is supported by the dynamic reaction of airflow over its wings.
24
Q
Altimeter
A
Any instrument for measuring altitude. An instrument similar to an aneroid barometer that uses the change of atmospheric pressure with altitude to indicate the approximate elevation above a given reference.
25
**Altitude**
The height of a point, measured from a reference plane, such as mean sea level.
26
**Ambient**
Pertaining to the air or air conditions around a flying aircraft but undisturbed or unaffected by it.
27
**Aneroid Barometer**
An instrument for measuring the pressure of the atmosphere which operates on the principle of having changing atmospheric pressure bend a metallic surface which, in turn, moves a pointer across a scale graduated in units of pressure.
28
**Angle of attack (AOA, α)**
The angle formed between the relative wind and the chordline of the airfoil.
29
**Angle of bank (AOB, φ)**
The angle between the horizon and the lateral axis of an aircraft. The angle of lateral displacement (roll) of an aircraft, especially in making a turn.
30
**Angle of climb (AOC, γ)**
The angle between the horizon and the flightpath of a climbing aircraft.
31
**Angle of descent (γ)**
The angle between the horizon and the flightpath of a descending aircraft.
32
**Angle of incidence**
The angle between the airplane’s longitudinal axis and the chordline of its wing. The root chord is commonly chosen to measure the angle of incidence. For rotary wing aircraft, Angle of incidence is the angle between the blade chord line and the plane of rotation of the rotor system. It is a mechanical angle rather than an aerodynamic angle.
33
**Angular acceleration**
Rate of change of angular velocity.
34
**Anhedral angle**
A negative dihedral angle. Also called cathedral angle.
35
**Approach**
A specified flightpath and associated altitudes to be flown in preparation for a landing, especially a published instrument approach.
36
**Artificial feel**
A method of simulating, altering, or otherwise enhancing the feedback or control feel that is transmitted to the cockpit controls by the forces acting on the control surfaces.
37
**Aspect ratio (AR)**
The ratio of the wingspan to the average chord.
38
**Attitude**
The orientation of an aircraft as determined by the relationship between its axes and some reference line or plane. Usually refers to nose attitude or pitch attitude.
39
**Automatic slot**
High lift device that consists of a movable vane attached to the leading edge of the wing that moves away from the body of the wing to allow airflow from below the wing to reach the upper surface and reenergize the boundary layer, delaying boundary layer separation. See slat.
40
**Autorotation**
During powered flight, the rotor drag is overcome with engine power. When the engine fails, or is deliberately disengaged from the rotor system, some other force must be used to sustain rotor RPM so controlled flight can be continued to the ground. This force is generated by adjusting the collective pitch to allow a controlled descent. Airflow during helicopter descent provides the energy to overcome blade drag and turn the rotor. When the helicopter is descending in this manner, it is said to be in a state of autorotation.
41
**Three Regions of Vertical Autorotation:**
The driven region, also called the propeller region, is nearest to the blade tips and normally consists of about 30 percent of the radius. The total aerodynamic force in this region is inclined slightly behind the rotating axis. This results in a drag force which tends to slow the rotation fo the blade.
The driving region or autorotative region, normally lies between about 25 to 70 percent of the blade radius. Total aerodynamic force in this region is inclined slightly forward of the axis of rotation. This inclination supplies thrust which tends to accelerate the rotation of the blade.
The stall region includes the inboard 25 percent of the blade radius. It operates above the stall angle of attack and causes drag which tends to slow the rotation of the blade.
42
**Average ** **C****hord**
The geometric average of every chord from the wing root to the
wingtip. Also called mean geometric chord.
43
**Axis**
A reference line passing through a
body, around which the body rotates.
44
**Axis System**
A set of three mutually perpendicular axes, intersecting at the
center of gravity of an aircraft, around which the motions, moments, and forces
of roll, pitch, and yaw are measured.
45
**Bank**
The position or attitude of an aircraft
when its lateral axis is inclined from the
horizontal.
46
**Bernoulli’s Equation**
In aerodynamics, a law or theorem stating that in a flow of
incompressible fluid, the sum of the static pressure and the dynamic pressure along
a streamline is constant if gravity and frictional effects are disregarded.
47
**Boundary Layer**
The layer of airflow over the surface of an airfoil, which shows
local airflow retardation caused by viscosity. The boundary layer is very thin at the leading edge of an airfoil (about 1
mm) and grows in thickness as it moves over a body. It is composed of laminar flow and turbulent flow.
48
**Boundary Layer Control (BLC)**
The control of the airflow within the boundary layer in
order to prevent its separation at high angles of attack. See also slot and slat.
49
**Buffeting**
The beating, shaking, or
oscillation of an aircraft’s structure or
surfaces by an unsteady flow, gusts,
turbulence, etc.
50
**Cabin**
Compartment of an aircraft in which
passengers, troops, or cargo are loaded.
51
**Calibrated Airspeed (CAS)**
Indicated airspeed corrected for instrument error.
52
**Calibrated Altitude**
Indicated altitude corrected for instrument error.
53
**Camber**
The curvature of the mean line of
an airfoil from leading edge to trailing
edge; the amount of this curvature.
54
**Cantilever**
A beam or object supported only
at or near one end, or one point; without
external bracing.
55
**Cathedral**
See anhedral.
56
**Center of Gravity (CG)**
The point at which
the weight of an object is considered to
be concentrated.
57
**Chord**
A measure of the chordline from the
leading edge to the trailing edge of an
airfoil. The chord may vary in length from
the wingtip to wing root. The root chord,
CR, is the chord at the wing centerline and
the tip chord, CT, is measured at the
wingtip.
58
**Chordline**
An infinitely long, straight line
drawn through the leading and trailing
edges of an airfoil.hordline
59
**Chordwise Flow**
Airflow perpendicular to the
leading edge of an airfoil; airflow along
the chord of an airfoil. Since chordwise
flow is accelerated over a wing, it
produces lift.
60
**Cockpit**
Compartment of an aircraft in which
the flight crew, especially the pilot(s), are
located. The cockpit is where the aircraft
is controlled from.
61
**Coefficient of Aerodynamic Force (CF)**
The dimensionless portion of the aerodynamic
force that is a function of angle of attack,
camber, aspect ratio, compressibility, and
viscosity.
62
**Coefficient of Drag (CD)**
The dimensionless portion of the total drag on an airfoil that
is dependent on the same variables that affect CF.
63
**Coefficient of Friction (μ)**
A dimensionless number whose value depends primarily
on the type of material and condition of
the two surfaces that are in contact.
64
**Coefficient of Lift (CL)**
The dimensionless portion of the total lift on an airfoil that is
dependent on the same variables that affect CF.
65
**Compressibility**
The property of a substance that allows its density to
increase as pressure increases.
66
**Compressible Flow**
Flow at speeds sufficiently high that density changes in the fluid can no longer be neglected.
Compressible flow describes the behavior of fluids that experience significant variations in density.
67
**Constant-Speed Propeller**
A propeller designed to maintain engine speed at a
constant RPM, automatically increasing
or decreasing pitch as engine speed
tends to increase or decrease.
68
**Continuity Equation**
ρ1A1V1 = ρ2A2V2.
Principle of physics that states that for
fluids, the mass flow rate has the same
value at every position along a closed
tube.
69
**Control Feel**
The feel or impression of the
stability and control of an aircraft that a
pilot receives through the cockpit controls,
either from aerodynamic forces acting on
the control surfaces or from devices
simulating these aerodynamic forces.
70
**Control Force**
A force, either aerodynamic
or pilot induced, acting on a control
surface.
71
**Control Horn**
A short lever or rigid post
attached to a control surface, to which a
control cable, wire, line, or rod is attached.
72
**Controllability**
The capability of an aircraft
to respond to control inputs, especially in
direction or attitude.
73
**Control Stick**
A lever for controlling the
movements of an aircraft in flight. On a
fixed-wing airplane, the control stick
operates the elevators by a fore-and-aft
movement and the ailerons by a
side-to-side movement.
74
**Control Surface**
A movable airfoil or surface,
such as an aileron, elevator, rudder, or
spoiler used to control the attitude or
motion of an airplane and to guide it
through the air.
75
**Cosine (cos)**
In a right triangle, the function
of an acute angle that is the ratio of the
length of the adjacent side to the length
of the hypotenuse.
76
**Creep**
The gradual reduction in a material’s
strength over time due to high
temperature and stress. Also known as
plastic deformation.
77
**Critical Altitude**
The maximum altitude at
which, in the standard atmosphere, an
engine produces its sea level rated
horsepower or torque.
78
**Critical Mach Number (MCRIT)**
The free airstream Mach number that produces
the first evidence of local sonic flow.
79
**Crosswind**
A wind blowing across the
flightpath of an airplane.
80
**Density (ρ)**
Mass per unit volume.
81
**Density Altitude (DA)**
Density altitude is pressure altitude corrected for
nonstandard temperature. Density altitude is the pressure altitude on a
standard day that has the same density as the ambient air.
82
**Dihedral Angle**
The angle between the
spanwise inclination of a wing and the
lateral axis. It is the upward slope of the
wings when viewed from head on. A
negative dihedral is called anhedral.
83
**Directional Divergence**
A departure from equilibrium around the vertical axis caused by negative directional static stability. Condition of flight in which the reaction to a small initial sideslip is an increase in sideslip angle. This would result in the airplane yawing broadside to the relative wind.
84
**Directional Moment**
A moment created
around an aircraft’s vertical axis.
85
**DirectionalStability**
The stability of an
aircraft around its vertical axis. The
reaction of an aircraft to a sideslip.
86
**Dive**
A steep descent, usually power on.
87
**Downwash**
Chordwise airflow from the
upper surface of an airfoil passing
downward behind the trailing edge to the
lower surface. Downwash decreases the
amount of lift produced by the wing. Any
downward moving airflow.
88
**Drag (D)**
That component of the
aerodynamic force acting parallel to, and
in the same direction as the relative wind.
It acts as a retarding force.
89
**Dutch Roll**
Dynamic stability that is the result
of strong lateral and weak directional
static stability. An airplane prone to
Dutch roll would appear to describe a
figure eight on the horizon and would tail
wag.
90
**Dynamic pressure (q)**
The pressure of a fluid resulting from its motion, equal to
one half the density times the velocity
squared (q=1/2ρV2).
91
**Dynamic Stability**
The oscillatory motion of
a body, beyond its initial tendency to
move toward or away from equilibrium,
after a disturbance. A measure of
displacement with respect to time.
92
A structure, piece, or body originally likened to a foil or leaf in being wide and thin and designed to obtain a useful reaction upon itself in its motion through the air. An airfoil may be no more than a flat plate, but usually it has a cross section carefully contoured in accordance with its intended application or function. Airfoils are applied to aircraft, missiles, or other aerial vehicles or projectiles to develop lift (as a wing), for stability (as a fin), for control (as an elevator), and for thrust or propulsion (as a propeller blade). Certain airfoils combine some of these functions.
**Airfoil**
93
The aircraft’s height above the terrain directly beneath the aircraft, measured in feet above ground level (AGL). Absolute altitude is found by subtracting the terrain elevation from the true altitude.
**Absolute Altitude**
94
The maximum altitude above sea level in a standard atmosphere that an airplane can maintain level flight.
**Absolute Ceiling**
95
A spin in which the control stick is not held in the full aft position. An accelerated spin is characterized by steeper pitch attitudes and higher spin rates.
**Accelerated Spin**
96
A stall in which the load factor is greater than one, as in a pullout. Usually more violent and disorienting than a normal stall.
**Accelerated Stall**
97
A curved line describing the number of g’s that can be generated at a given indicated airspeed as a function of CLMAX angle of attack for a particular airfoil. Also called line of maximum lift.
**Accelerated Stall Line**
98
A change in the velocity of a body with respect to magnitude or direction, or both.
**Acceleration**
99
An instrument that measures one or more components of the acceleration of a vehicle.
**Accelerometer**
100
A pressure gradient of increasing static pressure in the direction of airflow.
**Adverse Pressure Gradient**
101
Yaw in the opposite direction of aileron roll input.
**Adverse Yaw**
102
The feature of a control surface that reduces the magnitude of the aerodynamic moment around the hingeline. See shielded horn.
**Aerodynamic Balance**
103
A technique for slowing an airplane to a speed suitable for frictional braking. Aerodynamic braking is accomplished by increasing the surface area exposed to the relative wind in order to increase parasite drag, primarily by holding the nose of the airplane in the landing attitude.
**Aerodynamic Braking**
104
The point along the chordline of an airfoil where all changes in aerodynamic force effectively take place. It is normally located at the point of 25% chord.
**Aerodynamic Center (AC)**
105
A force acting on an airfoil that is the result of air pressure and friction distribution over the surface of the airfoil.
**Aerodynamic Force (AF)**
106
The science that studies the motion of gaseous fluid flows, and of their actions against and around bodies, and of the forces acting on bodies within that flow.
**Aerodynamics**
107
Form of wing tailoring that employs a decrease in camber and/or relative thickness from wing root to wingtip. The wing root is more positively cambered and/or thicker (relative to the chord) than the tip, resulting in a root first stall pattern. Also called section variation.
**Aerodynamic Twist**
108
A movable control surface, attached to the wing of an airplane, used to produce a rolling moment around the longitudinal axis by creating unequal lifting forces on opposite sides of an airplane.
**Aileron**
109
Reversal of the control effect usually produced by an aileron, caused by a moment around the aerodynamic center twisting the wing and changing its angle of attack.
**Aileron Reversal**
110
Any device used or intended to be used for flight in the air.
**Aircraft (A/C)**
111
A flow or stream of air. A rate of flow measured by mass per unit time.
**Airflow**
112
A streamlined shape designed to produce lift as it moves through the air.
**Airfoil**
113
The structural components of an airplane including the framework and skin of such parts as the fuselage, wings, empennage, landing gear, and engine mounts.
**Airframe**
114
An engine driven, heavier-than-air, fixed-wing aircraft that is supported by the dynamic reaction of airflow over its wings.
**Airplane**
115
Any instrument for measuring altitude. An instrument similar to an aneroid barometer that uses the change of atmospheric pressure with altitude to indicate the approximate elevation above a given reference.
**Altimeter**
116
The height of a point, measured from a reference plane, such as mean sea level.
**Altitude**
117
Pertaining to the air or air conditions around a flying aircraft but undisturbed or unaffected by it.
**Ambient**
118
An instrument for measuring the pressure of the atmosphere which operates on the principle of having changing atmospheric pressure bend a metallic surface which, in turn, moves a pointer across a scale graduated in units of pressure.
**Aneroid Barometer**
119
The angle formed between the relative wind and the chordline of the airfoil.
**Angle of attack (AOA, α)**
120
The angle between the horizon and the lateral axis of an aircraft. The angle of lateral displacement (roll) of an aircraft, especially in making a turn.
**Angle of bank (AOB, φ)**
121
The angle between the horizon and the flightpath of a climbing aircraft.
**Angle of climb (AOC, γ)**
122
The angle between the horizon and the flightpath of a descending aircraft.
**Angle of descent (γ)**
123
The angle between the airplane’s longitudinal axis and the chordline of its wing. The root chord is commonly chosen to measure the angle of incidence. For rotary wing aircraft, Angle of incidence is the angle between the blade chord line and the plane of rotation of the rotor system. It is a mechanical angle rather than an aerodynamic angle.
**Angle of incidence**
124
Rate of change of angular velocity.
**Angular acceleration**
125
A negative dihedral angle. Also called cathedral angle.
**Anhedral angle**
126
A specified flightpath and associated altitudes to be flown in preparation for a landing, especially a published instrument approach.
**Approach**
127
A method of simulating, altering, or otherwise enhancing the feedback or control feel that is transmitted to the cockpit controls by the forces acting on the control surfaces.
**Artificial feel**
128
The ratio of the wingspan to the average chord.
**Aspect ratio (AR)**
129
The orientation of an aircraft as determined by the relationship between its axes and some reference line or plane. Usually refers to nose attitude or pitch attitude.
**Attitude**
130
High lift device that consists of a movable vane attached to the leading edge of the wing that moves away from the body of the wing to allow airflow from below the wing to reach the upper surface and reenergize the boundary layer, delaying boundary layer separation. See slat.
**Automatic slot**
131
During powered flight, the rotor drag is overcome with engine power. When the engine fails, or is deliberately disengaged from the rotor system, some other force must be used to sustain rotor RPM so controlled flight can be continued to the ground. This force is generated by adjusting the collective pitch to allow a controlled descent. Airflow during helicopter descent provides the energy to overcome blade drag and turn the rotor. When the helicopter is descending in this manner, it is said to be in a state of autorotation.
**Autorotation**
132
The driven region, also called the propeller region, is nearest to the blade tips and normally consists of about 30 percent of the radius. The total aerodynamic force in this region is inclined slightly behind the rotating axis. This results in a drag force which tends to slow the rotation fo the blade.
The driving region or autorotative region, normally lies between about 25 to 70 percent of the blade radius. Total aerodynamic force in this region is inclined slightly forward of the axis of rotation. This inclination supplies thrust which tends to accelerate the rotation of the blade.
The stall region includes the inboard 25 percent of the blade radius. It operates above the stall angle of attack and causes drag which tends to slow the rotation of the blade.
**Three Regions of Vertical Autorotation:**
133
The geometric average of every chord from the wing root to the
wingtip. Also called mean geometric chord.
**Average ** **C****hord**
134
A reference line passing through a
body, around which the body rotates.
**Axis**
135
A set of three mutually perpendicular axes, intersecting at the
center of gravity of an aircraft, around which the motions, moments, and forces
of roll, pitch, and yaw are measured.
**Axis System**
136
The position or attitude of an aircraft
when its lateral axis is inclined from the
horizontal.
**Bank**
137
In aerodynamics, a law or theorem stating that in a flow of
incompressible fluid, the sum of the static pressure and the dynamic pressure along
a streamline is constant if gravity and frictional effects are disregarded.
**Bernoulli’s Equation**
138
The layer of airflow over the surface of an airfoil, which shows
local airflow retardation caused by viscosity. The boundary layer is very thin at the leading edge of an airfoil (about 1
mm) and grows in thickness as it moves over a body. It is composed of laminar flow and turbulent flow.
**Boundary Layer**
139
The control of the airflow within the boundary layer in
order to prevent its separation at high angles of attack. See also slot and slat.
**Boundary Layer Control (BLC)**
140
The beating, shaking, or
oscillation of an aircraft’s structure or
surfaces by an unsteady flow, gusts,
turbulence, etc.
**Buffeting**
141
Compartment of an aircraft in which
passengers, troops, or cargo are loaded.
**Cabin**
142
Indicated airspeed corrected for instrument error.
**Calibrated Airspeed (CAS)**
143
Indicated altitude corrected for instrument error.
**Calibrated Altitude**
144
The curvature of the mean line of
an airfoil from leading edge to trailing
edge; the amount of this curvature.
**Camber**
145
A beam or object supported only
at or near one end, or one point; without
external bracing.
**Cantilever**
146
See anhedral.
**Cathedral**
147
The point at which
the weight of an object is considered to
be concentrated.
**Center of Gravity (CG)**
148
A measure of the chordline from the
leading edge to the trailing edge of an
airfoil. The chord may vary in length from
the wingtip to wing root. The root chord,
CR, is the chord at the wing centerline and
the tip chord, CT, is measured at the
wingtip.
**Chord**
149
An infinitely long, straight line
drawn through the leading and trailing
edges of an airfoil.hordline
**Chordline**
150
Airflow perpendicular to the
leading edge of an airfoil; airflow along
the chord of an airfoil. Since chordwise
flow is accelerated over a wing, it
produces lift.
**Chordwise Flow**
151
Compartment of an aircraft in which
the flight crew, especially the pilot(s), are
located. The cockpit is where the aircraft
is controlled from.
**Cockpit**
152
The dimensionless portion of the aerodynamic
force that is a function of angle of attack,
camber, aspect ratio, compressibility, and
viscosity.
**Coefficient of Aerodynamic Force (CF)**
153
The dimensionless portion of the total drag on an airfoil that
is dependent on the same variables that affect CF.
**Coefficient of Drag (CD)**
154
A dimensionless number whose value depends primarily
on the type of material and condition of
the two surfaces that are in contact.
**Coefficient of Friction (μ)**
155
The dimensionless portion of the total lift on an airfoil that is
dependent on the same variables that affect CF.
**Coefficient of Lift (CL)**
156
The property of a substance that allows its density to
increase as pressure increases.
**Compressibility**
157
Flow at speeds sufficiently high that density changes in the fluid can no longer be neglected.
Compressible flow describes the behavior of fluids that experience significant variations in density.
**Compressible Flow**
158
A propeller designed to maintain engine speed at a
constant RPM, automatically increasing
or decreasing pitch as engine speed
tends to increase or decrease.
**Constant-Speed Propeller**
159
ρ1A1V1 = ρ2A2V2.
Principle of physics that states that for
fluids, the mass flow rate has the same
value at every position along a closed
tube.
**Continuity Equation**
160
The feel or impression of the
stability and control of an aircraft that a
pilot receives through the cockpit controls,
either from aerodynamic forces acting on
the control surfaces or from devices
simulating these aerodynamic forces.
**Control Feel**
161
A force, either aerodynamic
or pilot induced, acting on a control
surface.
**Control Force**
162
A short lever or rigid post
attached to a control surface, to which a
control cable, wire, line, or rod is attached.
**Control Horn**
163
The capability of an aircraft
to respond to control inputs, especially in
direction or attitude.
**Controllability**
164
A lever for controlling the
movements of an aircraft in flight. On a
fixed-wing airplane, the control stick
operates the elevators by a fore-and-aft
movement and the ailerons by a
side-to-side movement.
**Control Stick**
165
A movable airfoil or surface,
such as an aileron, elevator, rudder, or
spoiler used to control the attitude or
motion of an airplane and to guide it
through the air.
**Control Surface**
166
In a right triangle, the function
of an acute angle that is the ratio of the
length of the adjacent side to the length
of the hypotenuse.
**Cosine (cos)**
167
The gradual reduction in a material’s
strength over time due to high
temperature and stress. Also known as
plastic deformation.
**Creep**
168
The maximum altitude at
which, in the standard atmosphere, an
engine produces its sea level rated
horsepower or torque.
**Critical Altitude**
169
The free airstream Mach number that produces
the first evidence of local sonic flow.
**Critical Mach Number (MCRIT)**
170
A wind blowing across the
flightpath of an airplane.
**Crosswind**
171
Mass per unit volume.
**Density (ρ)**
172
Density altitude is pressure altitude corrected for
nonstandard temperature. Density altitude is the pressure altitude on a
standard day that has the same density as the ambient air.
**Density Altitude (DA)**
173
The angle between the
spanwise inclination of a wing and the
lateral axis. It is the upward slope of the
wings when viewed from head on. A
negative dihedral is called anhedral.
**Dihedral Angle**
174
A departure from equilibrium around the vertical axis caused by negative directional static stability. Condition of flight in which the reaction to a small initial sideslip is an increase in sideslip angle. This would result in the airplane yawing broadside to the relative wind.
**Directional Divergence**
175
A moment created
around an aircraft’s vertical axis.
**Directional Moment**
176
The stability of an
aircraft around its vertical axis. The
reaction of an aircraft to a sideslip.
**DirectionalStability**
177
A steep descent, usually power on.
**Dive**
178
Chordwise airflow from the
upper surface of an airfoil passing
downward behind the trailing edge to the
lower surface. Downwash decreases the
amount of lift produced by the wing. Any
downward moving airflow.
**Downwash**
179
That component of the
aerodynamic force acting parallel to, and
in the same direction as the relative wind.
It acts as a retarding force.
**Drag (D)**
180
Dynamic stability that is the result
of strong lateral and weak directional
static stability. An airplane prone to
Dutch roll would appear to describe a
figure eight on the horizon and would tail
wag.
**Dutch Roll**
181
The pressure of a fluid resulting from its motion, equal to
one half the density times the velocity
squared (q=1/2ρV2).
**Dynamic pressure (q)**
182
The oscillatory motion of
a body, beyond its initial tendency to
move toward or away from equilibrium,
after a disturbance. A measure of
displacement with respect to time.
**Dynamic Stability**
