17.6 Propeller Maintenance

Question 1

What are the 3 types of balancing?

Answer 1

Static.
Dynamic.
Aerodynamic.

Question 2

What causes static and dynamic imbalance?

Answer 2

Unequal mass distribution.

Question 3

What is aerodynamic balancing for?

Answer 3

To ensure each blade delivers an equal amount of thrust.

Question 4

How is static balance checked?

Answer 4

In the vertical and horizontal plane.

Question 5

What is the purpose of dynamic balancing?

Answer 5

To reduce the moment of imbalance.

Question 6

Are small propellers dynamically balanced?

Answer 6

No as a shift of CG is only small.

Question 7

What is used to check dynamic vibration?
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Answer 7

Electronic equipment.

Question 8

How is dynamic balancing checked?

Answer 8

It is checked by running the engine.

Question 9

What are the 4 steps of dynamically balancing a propeller?

Answer 9

Obtain in flight vibration info.
Ensure vibration is greater than permitted limits.
Calculate the mass and location to reduce vibration to an acceptable level.
Install balance weights and confirm vibration levels are within limits.

Question 10

When is a propeller considered aerodynamically balanced?

Answer 10

When aerodynamic forces acting on the blades result in no periodic vibrations in the mountings.

Question 11

Does vibration increase with increasing engine speed?

Answer 11

No

Question 12

What makes vibration worse?

Answer 12

Pitch and thrust.

Question 13

As thrust and torque can’t be balanced simultaneously, how is thrust and torque correction indicated?

Answer 13

Aerodynamic Correction Factor (ACF) followed by
Thrust = T.
Torque = Q.

Question 14

When is aerodynamic balancing necessary?

Answer 14

Only for high performance propellers.

Question 15

What is blade indexing?

Answer 15

An aerodynamic correction factor.

Manufactured blades are compared individually with a master blade and receive, according to deviation from the zero lift angle, an aerodynamic correction factor in the form of a reference to the blade angle difference necessary to the basic setting.

Question 16

What is a universal blade protractor used for?

Answer 16

To measure the blade angle at a specific blade station to determine is the propeller is properly adjusted.

Question 17

Where is the blade angle referenced from?

Answer 17

The propeller plane of rotation.

Question 18

Where is the master reference station normally?

Answer 18

Either 30, 36 or 42 inch measurement on the blade.

Question 19

What is the master reference station marked in?

Answer 19

Chalk or grease pencil on the blade face.

Question 20

Why is blade tracking held to reasonable limits?

Answer 20

To prevent roughness and vibration.

Question 21

What is done if the blade track is not within limits?

Answer 21

It must be removed and returned to the manufacturer.

Question 22

What are the 2 main methods for checking blade tracking?

Answer 22

Flat bench method.
Block or pointer method.

Question 23

In the flat bench method, what is the maximum blade track deviation?

Answer 23

3 mm.

Question 24

For blade tracking, what is the maximum blade deviation?

Answer 24

1/16 inch.

Question 25

Where does fatigue normally occur?

Answer 25

Within a few inches of the blade tip.

Question 26

Where are airworthy damage limits described?

Answer 26

AMM ATA chapter 61.

Question 27

What can be used for visual inspection

Answer 27

X10 magnifying glass.

Question 28

What is conducted after a visual exam?

Answer 28

A tap test.

Question 29

What must be known during a tap test?

Answer 29

Blades ‘cuff’ has a different tone.

Question 30

What is superior penetrant?

Answer 30

Fluorescent penetrant.

Question 31

What can be said about visible dye penetrant?

Answer 31

It’s not recommended.

Question 32

What is eddy current inspection?

Answer 32

Generate and measure an electric field that deflect flaws at or slightly below surface component been inspected.

Question 33

When is magnetic particle inspection used?

Answer 33

For ferrous parts.

Question 34

What do composite blades have to reduce the effect of erosion?

Answer 34

An erosion strip attached to the blade LE.

Question 35

What are the 3 distinct corrosion types?

Answer 35

Surface, Pitting, Intergranular.

Question 36

Where does Intergranular corrosion occurs?

Answer 36

Grain boundaries.

Question 37

What is a form of Intergranular corrosion?

Answer 37

Exfoliation.

Question 38

What are composite and wood propellers susceptible to?

Answer 38

Delamination from small stone strikes.

Question 39

How must wooden propellers be checked?

Answer 39

Check glue lines for debonding, look for warp and loss of protective coating.

Question 40

What effect can moisture have on existing cracks and delaminations.

Answer 40

Expansion.

Question 41

What are cracks in the paint across the blade a sign off?

Answer 41

Flexural vibrations.

Question 42

How often are inspections carried out on metal propellers?

Answer 42

Every 100 hours or at least every annual check.

Question 43

What can be said about about repairs on the blade root?

Answer 43

Never permitted.

Question 44

Can metal blades with nicks be repaired?

Answer 44

Yes, they can be worked out.

Question 45

What are the limits of metal blade repairs?

Answer 45

X10 depth of repair on the LE. X30 depth of repair elsewhere.

Question 46

What is applied to the hub after cleaning?

Answer 46

A corrosion lubricant spray.

Question 47

What are the 2 groups of composite damages?

Answer 47

Acceptable and Unacceptable.

Question 48

What are the sub-classifications of damage?

Answer 48

Skin perforated damage, Skin not perforated damage.

Question 49

How can static checks be carried out?

Answer 49

Without the engine running.

Question 50

What are static checks carried out with?

Answer 50

Using an electric feathering pump to pressurise the oil in the pitch change mechanism.

Question 51

When is a static check carried out?

Answer 51

Before installations, adjustments and when called for by servicing schedule.

Question 52

What are the static checks?

Answer 52

Flight Fine Pitch Stop (FFPS) Auto-coarsening Manual feather Autofeather Unfeather.

Question 53

How are propeller piston engines classified?

Answer 53

Normally-aspirated engines. Supercharged engines

Question 54

What is related to piston engines?

Answer 54

Manifold Air Pressure (M.A.P)

Question 55

How is reference RPM checked?

Answer 55

Setting the propeller to a fine pitch, Advance throttle, Until manifolds pressure reads zero boost and checking the RPM is the same as that published for that reference RPM.

Question 56

What is a check of the reference RPM called?

Answer 56

Reference power check.

Question 57

What effect does a tail wind have on RPM during an engine run?

Answer 57

Reduces it.

Question 58

When may air inlet icing occur during an engine run?

Answer 58

Below 10 degrees C with visible moisture in the air.

Question 59

What does a piston engine use to determine RPM?

Answer 59

Boost pressure.

Question 60

Why are performance checks done?

Answer 60

To ensure continued safe operation of the propeller/engine combination.

Question 61

What do performance checks check?

Answer 61

Torque RPM Fuel flow EGT.

Question 62

On a turboprop engine, what is SHP determined by?

Answer 62

The amount of torque produced.