Propellers

Question 1

Blade Angle

Answer 1

Angle between the plane of rotation and the chord line

Question 2

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

Answer 2

Blade angle decreases towards the tip

Question 3

As speed increases what happens to the blades AOA

Answer 3

Decreased AOA with increase in speed

Question 4

As speed decreases what happens to the AOA of the blade

Answer 4

AOA will increase with reduction in forward speed

Question 5

Component at 90 degree to rotational axis is…

Answer 5

Torque Drag

Question 6

Component parallel to propellers rotational axis is

Answer 6

Thrust

Question 7

Fixed Pitch Propeller produces a….

Answer 7

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

Question 8

RPM increases what happens to the AOA

Answer 8

AOA will increase

Question 9

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

Answer 9

Causes negative AOA and considerable drag for no thrust

Question 10

Blade Twist is

Answer 10

To preserve same AOA along the whole length of the blade

Question 11

Geometric Pitch

Answer 11

The distance travelled in one revolution of the propeller

Question 12

Geometric pitch for a large blade angle

Answer 12

Coarse pitch will have a larger geometric pitch

(Geometric pitch is distance propeller advanced in one revolution)

Question 13

Variable Pitch Propeller purpose and operations

Answer 13

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

Question 14

Blade Pitch - Feathered (90 degrees)

Answer 14

Fully coarse - minimum drag in flight
Used for failed engine

Question 15

Blade Angle - Fully Fine (0 degrees)

Answer 15

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

Question 16

Blade Angle - Reverse - (-18 degrees)

Answer 16

Generates reverse thrust on the ground

Question 17

Centrifugal turning moment

Answer 17

Tries to fine off the propeller

Question 18

Aerodynamic Turning Moment

Answer 18

Tries to coarsen the propeller

Question 19

ATM vs CTM

Answer 19

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

Question 20

Hub Attachment on propeller system is attached to what

Answer 20

Drive shaft or crankshaft directly or via reduction gearbox

Question 21

Purpose of reduction gearbox

Answer 21

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

Question 22

Propeller Construction

Answer 22

Composites/metal alloys

Question 23

Torque drag is

Answer 23

Force opposing rotation

Question 24

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

Answer 24

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

Question 25

Pitch Change Unit role

Answer 25

Moves propeller blades

Question 26

Constant Speed Unit

Answer 26

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

Question 27

Pitch Control Unit

Answer 27

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

Question 28

Advantage of PCU single acting system on a single engine AC

Answer 28

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

Question 29

Single acting PCU on twin A/C

Answer 29

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

Question 30

Double Acting PCU

Answer 30

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

Question 31

Centrifugal Latch

Answer 31

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

Question 32

Propeller RPM falls - CSU response is

Answer 32

Move blades to a finer pitch

Question 33

If propeller RPM rises - CSU will

Answer 33

Move blades to coarser pitch

Question 34

CSU over speed steps

Answer 34

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

Question 35

CSU On speed

Answer 35

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

Question 36

CSU Underspeed

Answer 36

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

Question 37

RPM lever does what

Answer 37

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

Question 38

Forward RPM level will

Answer 38

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

Question 39

Where is the pitch control unit found

Answer 39

Inside the hub

Question 40

Rearward RPM Lever

Answer 40

Feather the propeller

Question 41

Unfeathering

Answer 41

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

Question 42

Alpha Flight Range

Answer 42

Anything from flight idle to coarse Positive angle

Question 43

Beta Range

Answer 43

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

Question 44

Torque Gauges Role

Answer 44

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

Question 45

Power = torque x rpm

Question 46

Beta range is anywhere between

Answer 46

Reverse and flight fine

Question 47

More power

Answer 47

Prop lever first when you need more power to climb

Question 48

Reduce power

Answer 48

Throttle lever first when you need to reduce power in descent