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Module 17 > 17.1 > Flashcards

17.1 Flashcards

1
Q

What is the purpose of the design of turboprop engines?

A

To push air rearwards to aeorfoil blades that push the air rearwards to create lift to move the aicraft forwards

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2
Q

What is the propellor?

A

A device consisting of a rotating hub with two or more rotating blades

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3
Q

What is the hub?

A

The central portion of the propellor that carries the blades

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4
Q

What is the purpose of the blades?

A

An aerofoil section that is attached to the hub

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5
Q

What is the blade butt?

A

The base of the propeller where the root ends

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6
Q

What is the blade root/shank?

A

The thickest part of the blade closest to the hub

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7
Q

What is a blade station?

A

A distance measured from the centre of rotation (inches or cm)

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8
Q

What is a master reference section?

A

A distance measured from the centre if rotation where all measurements are taken from

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9
Q

What is the master reference station on a fixed pitch propellor?
Variable pitch propellor?

A

75%
50%-75%

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10
Q

What is the blade face?

A

The flat side that produces thrust

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11
Q

What is the blade back?

A

The curved side of the propellor blade facing the direction of flight

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12
Q

Where does the blade chord line run?

A

Through the face and back surfaces

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13
Q

What is the plane of rotation?

A

The line at which the propellor turns. 90 degrees to the engines centreline

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14
Q

What is the blade angle?

A

The angle between the blade chord line and the plane of rotation

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15
Q

What is the pitch?

A

The distance advanced in one complete revolution

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16
Q

What is ‘Fine Pitch’?

A

Vertical blade angles. ‘Low pitch’

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17
Q

What is ‘Coarse Pitch’?

A

Horizontal blades angles. ‘High pitch’

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18
Q

How do you achieve reverse pitch?

A

Turning the propellor blades to negative angles to use for braking/reverse thrust

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19
Q

What does the dome assembly encase?

A

The pitch change mechanism

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20
Q

What is the spinner?

A

An aerodynamic fairing that overs the centre of the propellor

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21
Q

What is a tractor propellor?

A

A propellor mounted in front of the wing’s leading edge, also on the nose of the aircraft

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22
Q

What is a pusher propellor?

A

A propellor mounted behind the wing’s trailing edge, towards thew rear of the aircraft

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23
Q

Which of Newtons Law do propellors work off of and why?

A

Third law because the rotation of the propellors are converted to forward thrust.

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24
Q

What does the hub attach the blades to?

A

Piston engine, reduction gearbox and electric motor shaft

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25
Q

How does a propellor distribute air?

A

Large amounts of air slowly rearwards

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26
Q

What is the slipstream?

A

The backward moving air

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27
Q

What are the two losses involved in the slipstream?

A

Kinetic energy and friction between the air and the propellor blades

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28
Q

How do you work out propellor efficiency?

A

The ratio between the power developed by the propellor (Less due to friction), and the power obtained from the engines power plant

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29
Q

Who created the ‘Momentum Theory’?

A

W.J.M. Rankine and R.E. Froude

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30
Q

The moment energy describes what two factors that impart air?

A

Kinetic and momentum

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31
Q

What is the momentum theory?

A

This theory is an assumed disc to be producing uniform thrust due to a constant pressure difference

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32
Q

What does the moment theory assume about the characteristics of the air?

A

Incompressible and without viscosity. Also streamlined and continuous in velocity

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33
Q

What does the element theory deal with that momentum doesn’t?

A

The effect of aerodynamic forces on the propellor blade

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34
Q

What does the element theory involve?

A

Breaking a blade down into many sections and determining thrust and torque along the different sections.

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35
Q

Using the element theory how can you tell the overall different forces and motions produced over the whole propellor?

A

The different sections are integrated along the entire blade over one revolution

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36
Q

What is slip?

A

The difference between geometric pitch and effective pitch (50%-90%)

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37
Q

What are fixed-pitch and ground adjustable propellors designed for?

A

best efficiency at one rotation and forward speed

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38
Q

What is geometric pitch?

A

The theoretical distance a propellor should advance in one revolution based on blade angle

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39
Q

What is effective pitch?

A

The distance it actually travels

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40
Q

In regards to slip when Is your engine most efficient?

A

With minimal slip

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41
Q

What is propellor efficiency?

A

It is used to define how well a propellor transmits rotational force or energy into thrust

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42
Q

What is greater, the energy it takes for the propellor to be driven, or the thrust from the propellor?

A

The amount of energy is takes for the propellor to be driven. So propellor efficiency is the minimising of this

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43
Q

What is the amount of thrust generated by a propellor reliant on?

A

The angle at which the blades attack the air

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44
Q

What determines the efficiency of the propellor more than the speed at which it turns?

A

The design an the shape of the propellor

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45
Q

The larger or smaller the prop diameter, means it is more efficient?

A

Larger

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46
Q

What limit the large size of the propellor?

A

The speed of the propellor tip

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47
Q

In a jet engine, what is the efficiency of the engine measured as a fraction of?

A

The potential heat energy of the fuel as it is converted into thrust

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48
Q

What about piston engines?

A

Brake power

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49
Q

What measures turboprop?

A

Shaft power (Horsepower)

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50
Q

What is the double drag coefficient that takes a toll on propellor efficiency?

A

The propellor fights its way through the air ahead of the aircraft
The propellor must fight its way through the air infant of each propeller blade as it makes each revolution

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51
Q
A

Friction and drag

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52
Q

What is the usual symbol for propellor efficiency?

A

ETA

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53
Q

What are the ranges of propellor efficiency?

A

0.8 to 0.9 (80%-90%)

54
Q

What is the highest static load felt on the propellor?

A

Centrifugal force

55
Q

What does the centrifugal force try to do?

A

Pull the blades out of the hub

56
Q

What is Thrust bending force an example of?

A

Static Loads

57
Q

What is Thrust Bending Force?

A

It attempts to bend the propeller blade tips forward due to the lift flexing the thin blade section

58
Q

What is torque bending force also known as?

A

Braking moment

59
Q

What is Torque bending force?

A

It tends to try to bend the blade angle against the direction of the propellor rotation

60
Q

What does torque bending force create?

A

A resistance to the torque being produced by the engine

61
Q

What is Aerodynamic and Centrifugal Twisting force an example of?

A

Static loads

62
Q

What is Aerodynamic Twisting moment?

A

The centre of pressure being forward of the blades centre of rotation, will try to turn the blade to a higher (Coarser) blade angle

63
Q

In reverse pitch, what will the ATM turn the blade to?

A

A coarser Negative Blade Angle

64
Q

What is Centrifugal Twisting moment?

A

The mass of the blade is thrown out from the blades centre of rotation trying to turn the blade to a lower (finer) blade angle

65
Q

What wins the opposition, CTM or ATM?

A

CTMS

66
Q

Where are Aerodynamic, Centrifugal and thrust loads felt at?

A

The root so the most stresses will occur in this area and at the hub

67
Q

During windmilling, what occurs between the ATM’s and CTM’s?

A

The ATM acts with the CTM to fine off the blades

68
Q

Where is no damage or repair work permitted?

A

On the blade root

69
Q

When will the maximum dynamic loading on a propellor blade occur?

A

Within its natural frequency range

70
Q

What are the vibrations the result of on piston engines and propellors?

A

Operating strokes of a piston engine
Propeller reduction gearbox

71
Q

What are the dynamic loads induced by?

A

Aerodynamic and mechanical forces

72
Q

Where do aerodynamic forces have a greater vibration effect?

A

On the tip where the effects of the transonic speeds cause buffering and vibration

73
Q

How can you decrease vibrations?

A

By using the correct aerofoil shape and tip design

74
Q

What does the basic frequency ranges range from?

A

20 Hz to 6Hz

75
Q

What is the Outer Nodal Point?

A

The highest vibrational loads are felt about 80% of the blades length making it susceptible to failure

76
Q

What does the natural frequency of a propellor blade depend on?

A

Length, shape blade root and material

77
Q

How can you decrease vibration?

A

Using correct aerofoil shape and tip design

78
Q

How can you increase the power of the engine?

A

Increasing the amount of blades

79
Q

What must the propellor absorb?

A

The power produced by the engine and transmit that power to the air flow passing through propellor disc.

80
Q

What must the propellor be tailored to?

A

The specific needs of the engine it is fitted to

81
Q

Increasing the Blade angles to help absorb power increases what?

A

The AOA allowing the propellors to impart more energy to airflow

82
Q

What is a disadvantage of increasing the blade angle?

A

Optimises Aerodynamic efficiency

83
Q

How does increasing the blade length allow the propellors to optimise more energy?

A

It makes the blades longer so can transfer more energy by affecting a larger volume of air

84
Q

What is a drawback of making the blades longer by expanding the diameter of the propeller disc?

A

Tip blade speed

85
Q

How does increasing the RPM of the propeller ensure the propellers can absorb more air?

A

The same amount of energy is transferred to the air but in a shorter time

86
Q

What is bad about increasing the rpm of the propellor?

A

Blade tip speed

87
Q

How does increasing the camber ensure the propellers can absorb more air?

A

It creates a greater thrust

88
Q

What is bad about increasing the camber?

A

Blade structural problems
Optimum aerodynamic efficiency

89
Q

What does increasing there chord of the propeller blades and the number increase?

A

The solidity (The outer aerodynamic circle when blades spin) meaning the propeller can transfer more power to the air.

90
Q

Why is increasing the blade chord (increasing thickness) less efficient?

A

The aspect ratio is decreased so less aerodynamic efficiency

91
Q

What is the most attractive option?

A

Increases the number of blades

92
Q

Because they ran out of room on the propeller hub, what did they adopt to compensate for this?

A

Twin propellers on the same engine rotating in opposite directions (Contra-rotating propellers)

93
Q

What is the propeller tip to fuselage?

A

1 inch

94
Q

Propeller to nose wheel?

A

1/2 inches

95
Q

What is the propeller tip to the ground (Nose wheel)?

A

7 inches

96
Q

Propeller tip to ground (Tail wheel in flight attitude) (When the tail wheel has come off the ground due to the take off configuration)?

A

9 inches

97
Q

Propeller Tip to Water (Float-Plane)?

A

18 Inches

98
Q

What is torque reacting?

A

More lift is created on one wing so is being pulled downward

99
Q

How do you correct torque reaction?

A

An offset in the engine (modern)
More lift in the downward wing (old)

100
Q

What are the compensating factors permanently set for what phase of flight?

A

Cruise because this is where the aircraft is mostly

101
Q

What do aileron trim tabs do?

A

Permit further adjustments for other speeds

102
Q

When the wheels are on the ground during take off rolls and taxing, what occurs?

A

Yaw (A turning moment around the vertical axis) induced by a torque reaction

103
Q

If the left side of the aircraft is being forced down, where is more weight placed?

A

On the left main landing gear

104
Q

What does putting more weight on the left landing gear increase?

A

Ground friction or drag on the right tyre causing a further movement to the left

105
Q

How do you correct yawing moment on the take off roll?

A

Rudder or Rudder trim

106
Q

What is the twist effect?

A

The high speed of rotation got a propeller gives a spiralling rotation to the slipstream (exerts a sidewards force on vertical tail)

107
Q

How can you correct the twist effect?

A

Move the vertical stabiliser 1 to 2 degrees along longitudinal axis
Pilot input on rudder

108
Q

What is moving the vertical stabiliser 1 to 2 degrees along the longitudinal axis only good for?

A

Cruise

109
Q

What does the corkscrew flow of the slipstream causes what?

A

A rolling moment on longitudinal axis in the opposite direction to the one caused by torque reaction.

110
Q

What is gyroscopic effect?

A

When you put an input in, there is a resultant force at 90 degrees trying to oppose it

111
Q

What does precession occur?

A

When a force is applied to any point on the rim of the propellors plane of rotation

111
Q

When is the gyroscopic effect more likely?

A

During take-off role when the tail is being raised In tail wheel aircraft

112
Q

What does gyroscopic effects rely on?

A

Rigidity and precession (More of interest)

113
Q

What is precession?

A

The resultant action or deflection of a spinning rotor when a deflecting force is applied to its rim

114
Q

How do you fix the gyroscopic effect?

A

Elevators and Rudder to prevent undesired yawing and pitching

115
Q

When is Asymmetric loading (P-factor) a problem?

A

During climbing

116
Q

What does Asymmetric loading (P-factor cause)

A

Yaw

117
Q

The angle of the blade going down does what?

A

Creates more lift (bigger angle of attack)

118
Q

The angle of the upgoing blade creates more or less lift ?

A

Creates less lift (smaller angle of attack)

119
Q

What does the difference in lift cause?

A

A yaw towards the side giving less thrust (more thrust takes over)

120
Q

What is the critical engine?

A

The engine that if it fails will create the highest yaw

121
Q

What is relative airflow?

A

The speed (velocity) and direction of airflow moving past an airfoil

122
Q

What two things have an effect on the relative airflow?

A

Rotational speed and forward speed

123
Q

In normal flight, what is the state of the angle of attack and the blade angle?

A

Positive

124
Q

What is windmilling?

A

A change in airspeed or rotational velocity resulting in a change of airflow over the blade leading to a negative angle of attack

125
Q

If you have a fixed pitch propellor how do you prevent windmilling?

A

By choosing a blade angle that
need to be good for;

Good climbing performance
High cruising speed
Towing

126
Q

What is Propeller Brake Moment?

A

The effort which is required to be able to spin the propeller

127
Q

What happens to the brake moment if you have a higher angle of attack?

A

Higher blade angle is more brake moment

128
Q

What is the brake moment on windmilling?

A

If you go into a negative angle of attack, meaning the air pushes the propeller to turn and then the propeller drives the engine. The rake moment works in the direction of rotation and begins to drive the propellor

129
Q

How does the angle of attack change in regards to air speed?

A

If airspeed increases, angle of attack decrease and the other way round

130
Q

How does the angle of attack change in regards to RPM?

A

If RPM increases, the angle of attack increases and the other way around

131
Q
A

Module 17 (1 decks)

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