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propellers > Handout > Flashcards

Handout Flashcards

1
Q

What is the purpose of a propeller

A

Convert engine power to thrust

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2
Q

How does a propeller produce thrust

A

Bernoullis principle (Blade aerofoil)

Newtons 3rd law (cold jet principle)

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3
Q

What is thrust in the context of propellers

A

Acts along the longitudinal axis of the aircraft

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4
Q

What is torque (propellers)

A

Acts at right angles to the propeller longitudinal axis

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5
Q

What forces are acting on a blade

A 
centrifugal force 
thrust bending force
torque bending force
aerodynamic twisting moment 
centrifugal twisting moment
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6
Q

What is centrifugal force trying to do

A

Pull the blades out of the hub as it spins

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7
Q

What is thrust bending force

A

Similar to helicopter coning angle

The tips of the blade bend forward in the direction of travel

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8
Q

What is torque bending force

A

Similar to lead and lag (helicopter)

Resistance to the air bending the blade in the opposite direction of rotation

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9
Q

What is aerodynamic twisting moment

A

The aerodynamic twisting moment tries to increase the blade angle

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10
Q

What is centrifugal twisting moment

A

The centrifugal twisting moment tries to decrease the blade angle

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11
Q

Where is blade back and face

A

Blade face scoops the air, blade back is the side facing away from the pilots

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12
Q

How is a prop connected to the hub

A

The shoulders on blade shank connect to the blade hub grooves

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13
Q

What are blade stations

A

Used to specify points along the blade from their centre of rotation (the hub)

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14
Q

What is the difference between angle of attack and pitch or blade angle

A

AOA Is the angle between the aerofoils chord line and the relative airflow.

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15
Q

Blades are twisted, why?

A

The outside of the blade travels faster than the inside, blades have a twist to keep generate equal thrust along the entirety of the blade

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16
Q

What is geometric pitch

A

How far the aircraft should travel forward due to the thrust produced by one full rotation of the propeller in theory

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17
Q

What is effective pitch

A

How far the aircraft actually travels forward due to the thrust produced by one full rotation of the propeller in reality

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18
Q

What is slip

A

The difference between geometric and effective pitch

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19
Q

What is torque reaction

A

A twisting force exerted on aircraft due to the torque generated by the propeller spinning cause the aircraft to slowly roll

Similar to the torque produces by the main rotors on a helicopter

20
Q

What is on speed

A

The most efficient desired rpm for the propellers

21
Q

What is windmilling

A

Spinning freely in the wind

22
Q

What is feathering

A

Making the blades straight on for the least air resistance

23
Q

What is reversing the blades

A

Reversing the pitch to slow the A/C

24
Q

What is a negative torque system

A

prevents the torque from turning the engine, used in descent

25
Q

What is a de coupling

A

Disconnects prop from engine

Similar to a free wheeling unit

26
Q

What is auto feathering

A

Auto feather the blade to take the load off the pilot during takeoff

27
Q

What is a pitch lock

A

Safety feature that lock the propeller to provide thrust

28
Q

What is a propeller brake

A

Similar to a rotor brake

29
Q

What is the front spinner

A

Aerodynamic fairing

30
Q

What are the 3 purposes of a barrel ASSY

A

Hold blades in place
Secure prop to shaft
Transfer torque from engine to thrust

31
Q

What is inside the dome ASSY

A

The mechanism for changing blade angles

32
Q

Describe the components in a propeller assy

A

Front spinner (fairing)

Dome (Stationary and rotating cam, piston ASSY)

Barrell ASSY (retaining nut, front + rear cone)

Rear spinner

Afterbody (upper and lower)

Control ASSY (upper and lower)

Upper is the brains (Valve housing)
Lower is the muscle (pump housing)

33
Q

What components make up the barrel assy

A

Front and rear barrel halves

Front and rear cones (Cones expand against shaft and hold everything in place)

retention nut and snap ring

34
Q

What is the purpose of blade cuffs

A

Improve airflow around the blade shanks

Increase the flow of cooling air to the engine nacelle

35
Q

What is a fixed pitch prop

A

Prop can’t change

36
Q

What is variable pitch blade

A

The blades have adjustable pitch

Achieve best performance by adjusting the blade angle

Hubs have clamp rings or bolts

37
Q

What are the three types of fixed pitch propellers

A

Climb (Slow)

Cruise (faster)

Constant speed (works best at high speed)

38
Q

What is a governor

A

device which automatically adjusts the angle of the aircraft propeller blade as necessary to maintain a constant engine speed under varying flight conditions.

(send fluid to the dome to move the pitch change mechanism)

39
Q

What are the three purposes of a governor

A

Boost pressure of engine oil

Control amount of oil that flows to the propellor

Senses rotational speed of the engine

40
Q

What are the three main components in a governor

A

Fly weights

Pilot valve

Pump

41
Q

What are the two types of anti/de ice on props

A

Fluid and electrical heating elements

Anti is used on the low speed area and around the engine nacelle

42
Q

How are props balanced

A

Vertically or horizontally.

If its vertically balanced it will remain vertical regardless of what blade is facing up

weights are added to balance

43
Q

What are protractors used for

A

Used to measure blade angle

Calibrated off dome then held against blade to check it

44
Q

What are 3 lethal warnings

A

Keep clear of the propeller arc when the GTC or APU is operating or when an external air starter is connected

Remove power IAW the relevant MM

Open (pull) circuit breakers IAW relevant MM

45
Q

What are 4 safety precautions

A

Never walk through a Propeller Arc

Use warning signs in the cockpit

Isolate engine starter system

Isolate propeller feathering system

propellers (1 decks)

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