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Aerodynamics > Propeller Dynamics > Flashcards

Propeller Dynamics Flashcards

1
Q

What is the plane of rotation?

A

Perpendicular to the propeller shaft.

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2
Q

Why is the propeller blade twisted?

A

To keep the relative airflow constant along the length of the blade as the speed of prop at the tip is greater at the top.

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3
Q

What is the propeller blade angle?

A

The blade angle is the angle between the chord line of the propeller blade and the plane of rotation.

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4
Q

How far along the blade is the measurement of blade angle?

A

75%

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5
Q

What is the helix angle?

A

Angle between the plane of rotation and the relative airflow.

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6
Q

What happens to the helix angle with increasing forward speed?

A

Helix angle decreases

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7
Q

What is the blade AOA?

A
  • Angle between the blade chord line and the relative airflow.
  • Blade angle minus the helix angle.
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8
Q

What occurs to the angle of attack as forward speed increases?

A

Angle of attack will decrease

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9
Q

What is the propeller pitch?

A
  • The distance the propeller would move forward in one revolution if the helix angle were equal to the blade angle.
  • Angle between the chord and the plane of rotation
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10
Q

What is prop feathering?

A

When the blade angle is set to a zero lift angle, minimizing drag and stopping prop rotation.

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11
Q

What is reverse thrust?

A

When the blade is rotated in a reverse angle such that the prop produces reverse thrust.

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12
Q

What are some design methods to absorb greater engine power?

A

1) Increase the blade AOA
2) increase the blade length
3) Increase propeller RPM
4) Increase the camber of the prop blades

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13
Q

What is the preferred form of power absorption?

A
  • Propeller solidity.

- the ratio of the blade frontal area to the area of the propeller circumference

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14
Q

What can be done to increase the blade solidity?

A
  • Increase the chord of the propeller

- Increase the number of blades

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15
Q

What is the helical path?

A

The spiral path of the prop during flight.

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16
Q

What is the geometric pitch ?

A
  • The theoretical distance the prop would move forward in one relocation if the AOA is zero degrees.
17
Q

What is the effective pitch?

A

The actual distance the blade travels in one revolution due to its angle of attack.

18
Q

What is the difference between the geometric and effective pitch?

A

The propeller slip

19
Q

Why are the main forces that act on the propeller? Draw a diagram

A
  • Total Aerodynamic force
  • Drag
  • Thrust
  • Engine torque
20
Q

What is the thrust bending force?

A

Lift force being greater further from the hub which results in a prop bending force.

21
Q

How far along the chord is the thrust a maximum?

A

60-80%

22
Q

What are the two main twisting forces on the propeller?

A

1) Aerodynamic twisting moment

2) Centrifugal twisting moment

23
Q

What causes the aerodynamic twisting moment?

A
  • The centre of pressure being in front of the pitch change axis, causing the total reaction to produce a moment.
  • tends to increase pitch.
24
Q

What is the centrifugal twisting moment?

A

Moment cause by centrifugal force that tends to fin the blade pitch angle.

25
Q

What occurs under normalcy operating conditions with the ATM and the CTM?

A

ATM partially offsets the CDM

26
Q

What does the prop efficienxy depend on?

A

The angle of attack of the blade

27
Q

What are the two types of variable pitch propellers?

A

1) Controllable pitch

2) Constant Speed propeller

28
Q

What occurs with a windmilling prop?

A

Prop is rotated by air flowing over the blades.

Large increase in drag.

29
Q

What are the four left turning tendencies on an A/C?

A
  • Torque reaction
  • Gyroscopic effect
  • Prop slipstream
  • P factor
30
Q

What two types of left turning tendencies are prominent for tail dragger aircraft?

A

Gyro and p factor

Aerodynamics (13 decks)

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