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PPL Principles of Flight > 4 Primary Forces > Flashcards

4 Primary Forces Flashcards

1
Q

During unaccelerated flight, the four main forces are said to be

A

in a state of equilibrium

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2
Q

The product of mass and gravitational force is called

A

Weight

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3
Q

What is the centre of gravity?

A

The point through which the weight of a body acts

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4
Q

Wing loading is calculated how?

A

Weight of aircraft / Wing area

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5
Q

Wing loading is simply the

A

Weight supported per unit area of wing

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6
Q

The Bernoulli Principle

A

High flow gives low pressure

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7
Q

What term is given to layer of air closest to an aerofoil’s surface?

A

Boundary layer

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8
Q

What term is given to the point at which air within the boundary layer becomes turbulent and thickens significantly?

A

Transition point

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9
Q

When an airflow no longer follows a streamlined flow pattern, it has become..?

A

Turbulent

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10
Q

What term is given to the point at which the boundary layer separates from the aerofoil and becomes turbulent?

A

Separation point

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11
Q

The separation point is where what leaves the aerofoil?

A

Boundary layer

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12
Q

Describe the venturi effect in terms of pressure?

A

Pressure energy decreases, kinetic energy increases

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13
Q

Dynamic pressure equation

A

1/2 x rho x V-squared

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14
Q

Bernoulli’s principle states that increased velocity means

A

Decreased static pressure

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15
Q

The angle-of-attack is simply the,..

A

The angle at which the aerofoil is presented to the airflow

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16
Q

Camber is a term for what?

A

Curvature

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17
Q

Increasing the camber does what to airflow?

A

Airflow accelerates and generates greater lift

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18
Q

What causes the air to accelerate as it flows over an aerofoil?

A

An upwash is created and the air flows through a more constricted area

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19
Q

What term is given to the straight line between the ends of the camber line?

A

Chord line

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20
Q

The chord line connects the ends of what?

A

Mean camber line

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21
Q

What is the name of the measurement of a chord line’s length?

A

Chord

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22
Q

The distance between the mean camber line and chord lines called the?

A

Camber

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23
Q

The camber is the distance between what?

A

Mean camber line and chord line

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24
Q

What is the camber of a symmetrical aerofoil?

A

Zero

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25
Q

Lift’s equivalent of CoG is called what?

A

Centre of Pressure

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26
Q

The centre of pressure is…

A

The point at which the total reaction of the aerodynamic forces of an aerofoil act through

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27
Q

Total reaction has which two components?

A

Lift and drag

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28
Q

Lift and drag combine to form what force that acts through the centre of pressure?

A

Total reaction

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29
Q

Lift acts at what relation to the relative airflow?

A

Perpendicular

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30
Q

Drag acts at what relation to the relative airflow?

A

Parallel

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31
Q

What angle of the wing is AoA measured from?

A

Chord line

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32
Q

What is the angle of incidence?

A

Angle at which the wing is fixed to the airframe relative to longitudinal axis

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33
Q

What is the term given to the angle at which the wing is fixed to the airframe relative to longitudinal axis?

A

Angle of incidence

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34
Q

What term is given to the point at which the airflow comes to rest relative to the wing?

A

Stagnation point

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35
Q

If the Centre of Pressure moves forward, what is occurring?

A

AoA is increasing

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36
Q

AoA increasing has what effect on the Centre of Pressure’s position?

A

It moves forward

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37
Q

Air density is given what Greek letter?

A

Rho

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38
Q

The coefficient of lift is considered what?

A

Lifting ability of a wing at a given AoA

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39
Q

Equation of lift

A

Coefficient of Lift x 1/2 x Rho x V-Squared x Wing Surface Area

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40
Q

As wing shape is fixed, any change in Coefficient of Lift only occurs when what changes?

A

AoA

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41
Q

When is the Centre of Pressure at its furthest point forward?

A

Stalling AoA

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42
Q

The lift curve for a symmetrical aerofoil will give a Coefficient of Lift of 0 at what AoA?

A

0 degrees Angle of Attack

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43
Q

For a symmetrical aerofoil, 0 degrees AoA equattes to what Coefficient of Lift?

A

0

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44
Q

A laminar flow wing has what properties?

A

Low curvature that allows air to retain laminar flow over more of its surface than a cambered aerofoil

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45
Q

Laminar essentially means what in terms of airflow?

A

Streamlined

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46
Q

Laminar flow wing’s advantages over cambered aerofoil?

A

Same lift produced for less drag at cruise speed

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47
Q

The higher stalling speed of a laminar flow wing can be explained how?

A

The Maximum Coefficient of Lift is a lower value than the C-Lift Max for a well-cambered aerofoil

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48
Q

Longitudinal axis of the aircraft is important for what angle?

A

Angle of incidence

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49
Q

Air resistance is commonly known as what?

A

Drag

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50
Q

Types of drag can be split into what two categories?

A

Induced drag
Parasite drag

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51
Q

Induced drag is…

A

Drag associated with production of lift

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52
Q

Drag associated with production of lift is known as..?

A

Induced drag

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53
Q

Parasite drag consists of what 3 sub-categories?

A

Skin friction
Form
Inteference

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54
Q

For skin friction drag, what occurs within an increase in airspeed?

A

Increase of skin friction drag

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55
Q

For skin friction drag, what occurs within an increase in AoA?

A

Increase of skin friction drag

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56
Q

Form drag is created how?

A

Airflow separates from the surface
Eddies are formed
Streamline flow distrubed and thus increases drag

57
Q

Skin friction drag is essentially the…

A

Friction forces between an object and air

58
Q

How do designers reduce form drag?

A

Delay separation of the boundary layer from the surface

59
Q

How does form drag result in stalling on a wing at high AoAs?

A

Pressure gradient on upper surface is too severe
Boundary layer no longer adheres to the surface
Separation occurs well forward near the leading edge

60
Q

If you streamline a surface and decrease its curvature, what effect is had on the boundary layer?

A

Delaying separation of the boundary layer and reducing eddying

61
Q

Interference drag can be thought of as drag occuring from..

A

Combined parts of an aircraft as a whole

62
Q

Parasite drag’s relationship with airspeed

A

An increase in airspeed will increase parasite drag

63
Q

Parasite drag increases in what manner with increased airspeed

A

As a square rule (V-squared)

64
Q

Spanwise flow of induced drag on lower surface of wing?

A

Outwards from fuselage

65
Q

Spanwise flow of induced drag on upper surface of wing?

A

Inwards towards fuselage

66
Q

Why are wingtip vortices greatest at high values of C-Lift?

A

The pressure difference between upper and lower wing surfaces are greatest

67
Q

Aspect ratio equation (span, chord)

A

Span / Chord

68
Q

Aspect ratio equation (wing arrea, chord)

A

Area / Chord-squared

69
Q

Why do tapered wings have weaker wingtip vortices?

A

Relatively, there is less wingtip so the induced drag is less

70
Q

A wing whose AoA differs at the wingtip and wing root possesses what?

A

Washout

71
Q

How does inbuilt washout reduce induced drag?

A

Wingtip AoA is lower than wing root AoA

72
Q

Inbuilt washout means lift is produced where on a wing?

A

Predominantly by the inner part of the wing

73
Q

WInglets or wing fences can reduced induced drag how?

A

Spanwise flow is reduced so induced drag is less

74
Q

Why is induced drag greater at lower airspeeds?

A

AoA must increase to maintain given lift
Slower passage of air rearwards forms greater vortices and greater downwash
Greater downwash inclines local airflow downwards further
Lift force tilted further back
Stronger component of lift force is in the drag direction

75
Q

Relationship between lift and induced drag

A

The greater the lift produced, the greater the induced drag

76
Q

What occurs in a total drag graph

A

As airspeed increases:
Induced drag reduces
Parasite drag increases
Total drag initially decreases then increases

77
Q

What drag predominates at low speeds?

A

Induced drag

78
Q

What drag predominates at high speeds?

A

Parasite drag

79
Q

Total drag is least when what is equal?

A

Parasite and induced drag

80
Q

Minimum drag speed is where on a total drag graph?

A

Where the parasite drag and induced drag lines intersect

81
Q

The point at which parasite drag and induced drag intersect on a total drag graph (and equal zero) is known as what?

A

Minimum drag speed

82
Q

Minimum drag speed is considered the speed at which…

A

The wings produce lift to balance weighht but with minimum amount of drag possible

83
Q

Drag equation

A

Coefficient of Drag x 1/2 x rho x V-Squared x S

84
Q

The only difference between the equations for drag and lift are the presence of?

A

The respective coefficients (of lift or drag)

85
Q

Lift/Drag Ratio is calculated how?

A

C-Lift / C-Drag

86
Q

The AoA at the highest point of a Lift/Drag ratio curve can be described as

A

The most efficient angle of attack

87
Q

With decreasing weight and flying at the same IAS, what happens to the AoA?

A

It decreases

88
Q

With decreasing weight and flying at the same AoA, what happens to the airspeed?

A

It decreases

89
Q

Using the AoA and C-lift equation, explain how IAS remains constant but TAS changes at different airspeeds?

A

Rho is less at higher altitudes, so V (in V-squared) must increase to maintain IAS

90
Q

What type of airspeed is most important for AoA and lift considerations?

A

IAS

91
Q

Why is IAS the most significant airspeed for AoA and lift considerations?

A

IAS is related to dynamic pressure, thus impacting aerodynamics

92
Q

What does S denote in drag calculations?

A

Wing area

93
Q

Wing area is denoted by what term in drag equations?

A

S

94
Q

The axis upon which a propeller rotates is called the…?

A

Plane of rotation

95
Q

Static pressure situation surrounding a propeller blade?

A

The static pressure ahead of the blade is less than that behind

96
Q

Name of angle between chord line of a propeller and the plane of rotation?

A

Blade angle

97
Q

The blade angle is the angle between what?

A

Propeller chord line and plane of rotation

98
Q

Name of cambered side of propeller blade?

A

Blade back

99
Q

Name of flat side of propeller bade?

A

Blade face

100
Q

Name of angle between the resultant veolicty of the propeller blade and the plane of rotation?

A

Helix angle

101
Q

The Helix angle is the angle between what?

A

Resultant velocity of the propeller blade and the plane of rotation

102
Q

What two angles combine to form the blade angle of a propeller?

A

AoA + Helix angle

103
Q

The AoA + Helix angle forms what angle for a propeller?

A

Blade angle

104
Q

How does blade angle change from the hub of a propeller to its tip?

A

It decreases

105
Q

Why does blade change decrease from the hub to tip of a propeller?

A

Greater velocity meeans less AoA needed

106
Q

Approximately where on the propeller blade is thrust produced effectively?

A

Between 60% and 90% of the tip radius

107
Q

Why is the direction of the relative airflow on a propeller and the direction of flight not parallel?

A

Rotational velocity offsets the forward motion of the aircraft

108
Q

In theory, it is assumed that the direction of flight is what relation to the plane of propeller rotation?

A

Perpendicular

109
Q

In theory, it is assumed that the direction of flight is perpendicular to what?

A

Plane of propeller rotation

110
Q

Propeller torque is…?

A

Resistance to motion in the plane of rotation

111
Q

For propellers, total reaction is divided into what two components?

A

Propeller torque force
Thrust

112
Q

For the components of propeller torque force and thrust, which is related to the plane of rotation?

A

Propeller torque force

113
Q

For the components of propeller torque force and thrust, which is related to the direction of flight?

A

Thurst

114
Q

What is the angle between propeller torque force and thrust?

A

Perpendicular

115
Q

Lift/drag comparative forces for propellers?

A

Lift is enngine torque and drag is propelller torque

116
Q

Why does RPM increase in a dive with constant throttle position?

A

Relative airflow is changed
Forward speed increases
Propeller torque is reduced

117
Q

Why does a propeller blade’s AoA decrease as speed increases at constant RPM?

A

Forward motion component is greater so the relative airflow hits the blade at a shallower angle

118
Q

Why does a propeller blade’s AoA increase as speed decreases at constant RPM?

A

Forward motion component is less so the relative airflow hits the blade at a higher angle

119
Q

At constant speed, why does a propeller blade’s AoA increase as the RPM increases?

A

Rotational motion component is greater so the relative airflow hits the blade at a higher angle

120
Q

At constant speed, why does a propeller blade’s AoA decrease as the RPM decreases?

A

Rotational motion component is less so the relative airflow hits the blade at a shallower angle

121
Q

For variable-pitch propellers, what pitch is optimum for lower airspeeds?

A

Fine pitch

122
Q

For variable-pitch propellers, what pitch is optimum for higher airspeeds?

A

Coarse pitch

123
Q

Fine pitch means what kind of pitch for a propeller?

A

Low pitch

124
Q

Coarse pitch means what kind of pitch for a propeller?

A

High pitch

125
Q

What happens to the AoA as RPM remains constant in a variable-pitch propeller?

A

It remain constant

126
Q

Variable-pitch propellers are also known by what other name?

A

Constant-speed propellers

127
Q

What kind of speed is referred to in the term ‘constant-speed’ for variable-pitch propellers?

A

RPM

128
Q

Feathering a propeller does what?

A

Aligns the blades with the airflow

129
Q

Slipstream effect causes an AoA to be created where?

A

Between the tailfin and slipstream airflow

130
Q

Name of effect that occurs with propellers under high power conditions?

A

Slipstream effect

131
Q

A clockwise-rotating propeller will possess effects that will yaw an aircraft in what direction?

A

Left

132
Q

When discussing fine and coarse pitch, these terms are described relative to what?

A

Plane of rotation

133
Q

For a propeller diagram, what is represented by the x-axis?

A

Forward motion of a propeller blade

134
Q

For a propeller diagram, what is represented by the y-axis?

A

Rotational motion of a propeller blade

135
Q

For a propeller diagram, a higher airspeed does what to the ‘triangle’?

A

Lengthens its base
Hypotenuse strikes blade at reduced angle

136
Q

For a propeller diagram, a higher RPM does what to the ‘triangle’?

A

Lengthens its height
Hoptenuse strikes blade at greater angle

137
Q

For a propeller diagram, what two ‘triangle’ transformations will increase the AoA?

A

Reducing the base (reducing the forward speed)
Increasing the height (increasing the RPM)

138
Q

For a propeller diagram, what is the hypotenuse?

A

Resultant velocity of propeller blade through the air

PPL Principles of Flight (6 decks)

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