Brainscape's Knowledge GenomeTM

Browse over 1 million classes created by top students, professors, publishers, and experts.


See full index

Mod 17: Propellers > 17.1 - Fundamentals - 6q > Flashcards

17.1 - Fundamentals - 6q Flashcards

1
Q

Explan Blade Angle

A

Blade Angle is the angle between the chord of the blade and the plane of rotation. (measured in degrees)

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
2
Q

Explain Angle of Attack

A

The Angle of Attack is the angle between the airfoil chord line and the relative wind.

Note: The relative wind is the resultant vector of the airspeed and RPM vectors.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
3
Q

Explain Reverse Angle

A
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
4
Q

Explain Rotational Speed

A

Rotational Speed is the speed of the propeller expressed in RPM

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
5
Q

Explain Geometric Pitch

A

Geometric pitch is the theoretical forward distance in inches that a propeller will travel in one revolution. (Based on the blade angle at the 75% station)

Geometric pitch = Propeller pitch

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
6
Q

Explain Effective Pitch

A

Effective pitch is the actual disance that the prop travels. The range is from 0% to 85% of Geometric Pitch

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
7
Q

Explain Propeller Slip

A

Propeller slip is the difference between the geometric pitch of the propeller and its effective pitch.

Geometric pitch - effective pitch = Propeller Slip (Slippage)

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
8
Q

How efficient is a propeller with a low rate of slip?

A

Very Efficient

as Rate of slip is the difference between geometric pitch and effective pitch

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
9
Q

Explain the following force acting on a prop:(what does it try to do?)

Aerodynamic Twisting Moment (ATM)

A

Aerodynamic Twisting Moment (ATM ) tries to twist a blade to a higher blade angle by aerodynamic action.

ATM is more apparent at higher blade angles of attack and is used in some designs to aid feathering the propeller.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
10
Q

Explain the following force acting on a prop:

Centrifugal Twisting Moment (CTM)

(what does it try to do?)

A

Centrifugal Twisting Moment (CTM) tends to decrease blade angle and oppose aerodynamic twisting moment.

Caused by all parts of a rotating propeller trying to move in the same plane of rotation as the blade centreline.

CTM > ATM

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
11
Q

Explain the following force acting on a prop:

(What does it try to do?)

Thrust Bending

A

Bends the blades forward at the tips due to high thrust and thin blade cross section

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
12
Q

Explain the following force acting on a prop:

Torque Bending Force

A

Torque Bending Force tends to bend the blade back against the direction of rotation

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
13
Q

Explain the following force acting on a prop:

Centrifugal Force?

A

Centrifugal force tends to pull the blades from the hub

Causes the greatest stress and the greater the rpm, the greater the stress

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
14
Q

What is the angle of attack on a blade with no forward velocity?

A

20 degrees AOA

With no forward velocity, resultant vector (relative wind) is the rotational vector

=> Blade angle = AOA

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
15
Q

What happens to the angle of attack on a blade as forward velocity increases?

A

It decreases (verified by Kevin)

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
16
Q

What is pitch distribution?

A

Pitch distribution is the gradual twist in the blade (decrease in blade angle) moving outboard from the hub to the tip

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
17
Q

Where is most stress on a propeller blade?

A

Blade Shank

(This is where must be extemely strong as centrifugal force tries to pull apart)

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
18
Q

What does a propeller convert (one type of energy to another)?

A

Props convert Rotary motion from an engine into a swirling slipstream to push or pull an aircraft

19
Q

The geometric pitch of a prop is what?

A

Geometric pitch is the theoretical forward distance in inches that a propeller will travel in one revolution. (Based on the blade angle at the 75% station).

Geometric pitch = propeller pitch

20
Q
A
21
Q

A fixed pitch propeller is usually at what angle for Take Off?

A

A low blade angle (fine pitch) is used for take off (and landing)

Angle?

22
Q

If a blade angle is increased, does that mean it becomes finer or coarser?

A

Coarser

23
Q

What is the chord line of a propeller?

A

The chord line is an imaginary line drawn through the blade from its leading edge to its trailing edge.

24
Q

Define propeller blade angle?

A

Blade angle, usually measured in degrees, is the angle between the chord of the blade and the plane of rotation.

25
Q

In which areas are blade reparis not permitted?

A

Blade shank

26
Q

The centrifugal twisting moment (CTM) tends to turn the blade in what direction?

A

CTM tends to decrease the blade angle.

All parts of the rotating propeller trying to move in the same plane of rotation as the blade centreline.

Opposite to CTM and CTM > ATM

27
Q

Where is the greatest load felt on a propeller?

A

At the blade shank due to the strongest force being the centrifugal force

28
Q

Define a constant speed propeller?

A

Constant speed propeller is found on modern, medium and high performance aircraft.

The RPM of the propeller is selected by the pilot and maintained by a governing device.

It tries to keep a constant propeller speed through all phases of flight.

29
Q

What is the greatest force acting on a propeller

A

Centrifugal Force

Causes thr greatest stress, tends to pull the blades from the hub

The greater the RPM, the greater the stress

30
Q

What force tries to bend a propeller blade forward?

A

Thrust bending force bends the blades forward at the tips due to high thrust and thin blade cross section

31
Q

The actual distance a propeller advances in one revolution is called what?

A

Effective pitch

(ranges from 0% to 85% of Geometric pitch)

32
Q

What is the optimum angle for a fixed pitch prop?

A

Between 2 and 4 degrees

33
Q

What force on a propeller blade turns the propeller blade to a fine pitch?

A

Fine pitch = low blade angle

CTM (Centrifugal Twisting Moment) tends to decrease blade angle.

34
Q

The blade angle at the root, is it the same, larger or smaller than the angle at the tip?

A

Larger (more coarse)

35
Q

What is the purpose of a blade cuff?

A
  1. Reduces aerodynamic losses
  2. induces cooling airflow to the engine nacelle

Goes at base of blade, almost around shank

36
Q

The thrust developed by a propeller is in accordance with which of newton’s laws?

A
  • 2nd law; F=Ma, thrust is equal to the mass of the air times the acceleration of the air
  • 3rd law: For every action, there is an equal and opposite reaction. If mass of air is accelerated in one direction by the propeller, then an equal force tries to move the propeller in the opposite direction.
37
Q

When the blades are set to a low angle, what will happen to the load on the engine?

A

When the blades are set to a low blade angle, it will reduce the load on the engine which will cause the RPM of the engine to increase.

38
Q

What is the main purpose of a reverse angle on a propeller?

A

Reverse angle a propeller is seleccted principally as an aerodynamic brake to reduce ground roll on landing

(also reduces brake wear)

39
Q

Define geometric pitch

A

This is the theoretical forward distance in inches that a propeller will travel in one revolution. (Based on the blade angle at the 75% station)

Same as propeller pitch

40
Q

Define ATM (Aerodynamic Twisting Moment)

A

Aerodynamic Twisting Moment is the tendency to increase blade pitch through aerodynamic pressure.

It is opposite to CTM but CTM > ATM

'’Tries to twist a blade to a higher angle by aerodynamic action’’

41
Q

What is the purpose of blade twist?

A

Propeller designers twist the blade to obtain the blade angle that will give the most efficient angle of attack for the designed velocity of each blade station.

(Pitch distribution)

42
Q

Where are blade stations measured from?

A

Measured from centre hub outboard towards tip and in inches

43
Q

The resultant airflow over a prop blade depends on what?

A
  1. Forward velocity
  2. RPM (rotational speed)
44
Q

Reverse thrust occurs when propeller blades do what?

A

When the blades are rotated below their positive angle until a negative blade angle is obtained which will produce a thrust force acting in the opposite direction to the forward thrust normally produced by the propeller.

Mod 17: Propellers (10 decks)

Brainscape helps you reach your goals faster, through stronger study habits.
© 2024 Bold Learning Solutions. Terms and Conditions