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ATPL POF > Propellers > Flashcards

Propellers Flashcards

1
Q

What 3 parts make up a propeller

A

Blades
Spinner
Hub

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2
Q

What is the chord reference point for a propeller

A

75% of the blade hub> tip

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3
Q

What is the helix angle

A

Angle between the raf and axis of rotation

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4
Q

What is geometric pitch

A

How far the blade would travel if put through a solid material

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5
Q

What is effective pitch

A

Geometric pitch - slip

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6
Q

What does torque do

A

The opposite of what the engine wants

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7
Q

What happens to blade AOA with TAS and RPM

A

TAS up = blade AOA down

Rpm up = blade AOA up

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8
Q

What should you do if engine failure on propeller aircraft

A

Stop propeller from windmilling

Feather

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9
Q

What is the efficiency of a fixed pitch propeller throughout its flight envelope

A

Low efficiency at low speed

Good efficiency at cruise speed

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10
Q

What are high aspect ratio blades good for

A

Efficiency

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11
Q

What are low aspect ratio blades good for

A

Best force

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12
Q

What are short dumpy blades good for

A

Acceleration

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13
Q

What are long blades good for

A

Efficiency

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14
Q

What happens if a blade is noisy

A

Less efficient

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15
Q

What happens if there is too many blades

A

Turbulent air = less efficient

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16
Q

What is blade solidity

A

How much of propeller disk has something solid in it

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17
Q

How does blade solidity affect force

A 
Solidity increase 
=
Torque absorption increase (better able to convert power to thrust)
= 
More force
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18
Q

What’s the max number of blades per hub

A

Around 6 at present

19
Q

What are contra rotating propellers

A

2 sets of blades rotating in opposite directions

20
Q

What is torque reaction

A

Blades rotate to right

Aircraft wants to rotate to left

21
Q

On ground what effect does torque reaction have

A

Wheels on side torque is trying to turn plane have more weight

22
Q

What effect does the slipstream from propellers have on yaw

A

Sideslip on rudder = yaw left (if right hand turning propeller)

23
Q

What is asymmetric blade effect (p-factor)

A

When propeller disk is included (at a higher AOA)

Downgoing blade = fast than upgoing blade = more thrust = thrust line moves to the right = yaw to left

24
Q

What is the pitch difference for asymmetric blade effect (p- factor)

A

Downgoing blade = travels further (greater pitch)

Upgoing blade = travels less = less pitch

25
Q

What is the gyroscopic effect

A

Resulting force 90° to the imput

Nazi symbol

26
Q

When is asymmetric flight at its worst

A

Slow speeds

27
Q

Why is propeller engine failure / asymmetric thrust worse

A

No prob wash from dead engine = less lift on wing

Yaw due to asymmetric thrust = less lift on lost engine wing
+
Drag from prop

28
Q

What is the benefit of the wing down method for asymmetric flight

A

More streamlined

29
Q

What is the drawbacks of the wingdown method for asymmetric flight

A

Subjected to somatogyral illusion

30
Q

Benefits of wings level method

A

All horizons align

31
Q

What happens to Vx for a jet engine with critical engine failure

A

Slower

32
Q

What happens to Vx for a propeller aircraft during critical engine failure

A

Faster

33
Q

What is the critical engine

A

The engine opposite to direction of rotation (for propellers)

Or for jet / counter / contra rotating propellers
Engine on the windward side

34
Q

What is Vmc (A)

A

Velocity minimum control in a given configuration usually take off

When the critical engine fails

35
Q

What is Vmcl

A

Velocity minimum control landing

In landing configuration

When the critical engine fails

36
Q

What is Vmcg

A

Velocity minimum control ground

When on the ground of in (ground effect during take off only)

When critical engine failed

37
Q

How does cg affect vmc speeds

A

Rear cg = higher Vmc speeds

38
Q

How is Vmc (a) determined

A 
Max available take off thrust 
Worst cg position 
Trimmed for take off 
Max sea lever take off mass 
Most critical take off configuration (with gear up)
No more than 5°bank towards live engine 
Out of ground effect 
Propeller windmilling or (if autofreather is fitted)
39
Q

How is Vmcl determined

A 
Go around power 
Worst cg position 
Trimmed for approach 
Heaviest weight 
Critical landing configuration

Also need to roll control = faster speed

40
Q

How is Vmcg determined

A

If critical engine fail you need to maintain control with rudder only without deviating more than 30ft laterally from centre line

Max take off thrust 
Worst cg 
Trimmed for take off
Heaviest mass 
Critical take off config
41
Q

What is the order (fastest to slowest) of the Vmc speeds

A

1) Vmcg
2) Vmcl
3) Vmc (a)

42
Q

How does a temperature affect Vmc speeds

A

Not day = Vmc speeds slower

Because eng produces less thrust = less rudder needed to counter

43
Q

How does altitude affect Vmc speeds

A

Slower = less engine thrust = less rudder needed to counter

ATPL POF (12 decks)

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