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EGK Engines > Propellers > Flashcards

Propellers Flashcards

1
Q

Blade Angle

A

Angle between the plane of rotation and the chord line

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2
Q

What happens to the blade angle from the root to the tip

A

Blade angle decreases towards the tip

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3
Q

As speed increases what happens to the blades AOA

A

Decreased AOA with increase in speed

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4
Q

As speed decreases what happens to the AOA of the blade

A

AOA will increase with reduction in forward speed

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5
Q

Component at 90 degree to rotational axis is…

A

Torque Drag

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6
Q

Component parallel to propellers rotational axis is

A

Thrust

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7
Q

Fixed Pitch Propeller produces a….

A

Produces it optimum AOA at a pre determined speed and operates and less efficiently at any other speed

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8
Q

RPM increases what happens to the AOA

A

AOA will increase

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9
Q

What happens when RPM is reduced but TAS stays the same on propeller

A

Causes negative AOA and considerable drag for no thrust

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10
Q

Blade Twist is

A

To preserve same AOA along the whole length of the blade

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11
Q

Geometric Pitch

A

The distance travelled in one revolution of the propeller

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12
Q

Geometric pitch for a large blade angle

A

Coarse pitch will have a larger geometric pitch

(Geometric pitch is distance propeller advanced in one revolution)

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13
Q

Variable Pitch Propeller purpose and operations

A

Designed to maintain optimum blade angle
Can be made to be fine pitches or fully coarse

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14
Q

Blade Pitch - Feathered (90 degrees)

A

Fully coarse - minimum drag in flight
Used for failed engine

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15
Q

Blade Angle - Fully Fine (0 degrees)

A

Minimum drag for engine start or max drag for braking on the ground

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16
Q

Blade Angle - Reverse - (-18 degrees)

A

Generates reverse thrust on the ground

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17
Q

Centrifugal turning moment

A

Tries to fine off the propeller

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18
Q

Aerodynamic Turning Moment

A

Tries to coarsen the propeller

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19
Q

ATM vs CTM

A

CTM (Centrifugal turning moment) is more dominant than aerodynamic turning moment

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20
Q

Hub Attachment on propeller system is attached to what

A

Drive shaft or crankshaft directly or via reduction gearbox

21
Q

Purpose of reduction gearbox

A

Translate large amounts of power into torque
Reduce propeller rpm to optimum

22
Q

Propeller Construction

A

Composites/metal alloys

23
Q

Torque drag is

A

Force opposing rotation

24
Q

How does a variable pitch system work/What happens when TAS increases

A

Propeller coarsens to absorb power

RPM will be constant
Blade angle coarser
Thrust and torque will be higher
AOA will be back to an efficient value

25
Q

Pitch Change Unit role

A

Moves propeller blades

26
Q

Constant Speed Unit

A

CSU moves propeller blade angle to maintain RPM (picture computer doing work)
Matches torque drag to engine torque
Uses oil to pitch change unit to coarsen blade pitch angle and increase torque drag

27
Q

Pitch Control Unit

A

Mechanism that changes the blade angle

Single acting - pressured oil to one side to coarsen pitch and when oil pressure reduces returns to fine pitch via CTM moment

28
Q

Advantage of PCU single acting system on a single engine AC

A

Engine output drops so therefore oil pressure in PCU so blade will fine off to reduce torque drag

29
Q

Single acting PCU on twin A/C

A

Has fly weights to coarsen off the propeller to feather position
Creates a couple under centrifugal force to overcome CTM force and twist towards feathered position

30
Q

Double Acting PCU

A

Has oil pressure supplied to both sides of piston to adjust propeller pitch towards coarse or fine

Used on larger propellers where greater centrifugal force would not be able to cope with just fly weights

31
Q

Centrifugal Latch

A

Prevent twin engine from feathering on ground at shutdown
Spring pressure overcomes centrifugal force

32
Q

Propeller RPM falls - CSU response is

A

Move blades to a finer pitch

33
Q

If propeller RPM rises - CSU will

A

Move blades to coarser pitch

34
Q

CSU over speed steps

A

RPM increases
Governors flyweights thrown outwards
Valve lifts against spring
Pressurised oil directed to coarse side of PCU
Propeller torque drag increases and rpm reduces

35
Q

CSU On speed

A

Propeller torque and engine output match
Governor flyweight moves inwards to shut off oil supply
Hydraulic lock which holds propeller at pitch angle

Counterweights is exactly counterbalanced by pressure on regulating spring

36
Q

CSU Underspeed

A

Governor flyweights experience less centrifugal force so move inwards
Lowering landed valve
Direct oil to fine pitch side of PCU and allows oil to drain from coarse pitch back to pump.
Moves to finer pitch
Torque drag reduces below engine torque allow propeller to accelerate

37
Q

RPM lever does what

A

Acts on the governor spring to change compression force on the CSU unit

38
Q

Forward RPM level will

A

Finer pitch adjustment
RPM will increase
Prop will accelerate until prop drag matches torque output

39
Q

Where is the pitch control unit found

A

Inside the hub

40
Q

Rearward RPM Lever

A

Feather the propeller

41
Q

Unfeathering

A

Moving from coarse to finer pitch using a accumulator with high pressure oil to move blade

42
Q

Alpha Flight Range

A

Anything from flight idle to coarse
Positive angle

43
Q

Beta Range

A

Range below flight idle - negative angle
Negative pitch creates large amount of torque drag which increases further into beta range
Turboprop engines usually only have enough power to drive to true beta range

44
Q

Torque Gauges Role

A

Measure engine torque which is the turning force exerted by engine on propeller shaft

45
Q

Power = torque x rpm

A
46
Q

Beta range is anywhere between

A

Reverse and flight fine

47
Q

More power

A

Prop lever first when you need more power to climb

48
Q

Reduce power

A

Throttle lever first when you need to reduce power in descent

EGK Engines (22 decks)

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