17.6 - Propeller Maintenance

Question 1

What is propeller roughness caused by.

Answer 1

Bent blades.
Imbalance.
Out of track.
Spinner wobble.
Loosely mounted blades.
Blade angles out of tolerance with each other.

Question 2

Static balancing.

Answer 2

Balance is checked in two planes, horizontal or vertical.
Carried out off the aircraft.
Needs to stop in a random position when rotated.

Question 3

Dynamic balancing.

Answer 3

Electronic equipment is used.
Propeller in motion.
Small propellers are not usually dynamically balanced.
Obtain in flight information.
Ensures vibration is outside of limits.
Calculate how to reduce vibration.
Install balance weights.

Question 4

Aerodynamic balancing.

Answer 4

Results from different blade angles.
Balance either the torque reaction or balance thrust.
Aerodynamic correction factor ACF followed by a Q for torque, or a T for thrust.
Done on high performance propellers.
Process is called blase indexing.

Question 5

Universal blade protractor.

Answer 5

Reference station is normally 30 inch, 36 inch or 42 inch.

Question 6

Blade tracking

Answer 6

Prevents roughness
Measurement id from the master reference station.
If not within limits turn to the manufacturer.

Question 7

Flat bench method for blade tracking.

Answer 7

Smooth board just below tip of blade with a piece of paper taped to it.
Lines not separated by more than 3mm

Question 8

Block or pointer tracking method.

Answer 8

Place a solid block next to prop blade.
Rotate the prop to see next blade tracks through same point
+/- 1/16th inch.

Question 9

Blade damage

Answer 9

Fatigue failures are normally within a few inches of the blade tip.
Airworthy damage limits found in AMM chapter 61, not affect flight safety but does affect the props efficiency.

Question 10

Visual inspection

Answer 10

The primary defence against early failures of props.
10x magnifier.

Question 11

Tap test

Answer 11

Blades with a cuff will have a different sound in that area.

Question 12

Penetrant inspection

Answer 12

Fluorescent dye penetrant is far superior than non-fluorescent.
Use of visible dye is not recommended.

Question 13

Ultrasonic inspection.

Answer 13

Uses sound waves to detect flaws on or below the surface.
Can be used on ferrous and non-ferrous materials.

Question 14

Eddy current inspection

Answer 14

Uses an electric field to detect flaws at or slightly below the surface.
Ferrous and non-ferrous.

Question 15

Magnetic particle inspection.

Answer 15

Approved maintenance facilities.
Useful for finding cracks and imperfections.
On or near surface.
Ferrous only.

Question 16

Where are the majority of prop failures found.

Answer 16

At the tip of the blades.

Question 17

Erosion

Answer 17

Loss of material due to small particles like sand and water acting on the leading edge.
Destroys the corrosion protection, can lead to failure.
Composite blades have an erosion strip.

Question 18

Corrosion

Answer 18

Principal cause of loss of airworthiness.
Surface corrosion
Intergranular
Pitting.

Question 19

Surface corrosion.

Answer 19

Loss of material due to chemical action.
Visible oxidation.

Question 20

Pitting

Answer 20

Pits extending inwards.

Question 21

Intergranular corosion.

Answer 21

Exfoliation corrosion is a type.

Question 22

Composite or wood prop delamination.

Answer 22

In wooden props check the glue lines for debonding.
Intrusion of moisture will promote expansion of cracks.
Check drain holes, if present, aren’t clogged.

Question 23

Repairs to wooden props.

Answer 23

Cracks in paint are signs of fleuras vibrations.
Loose rivets are a sign that wood is damaged.

Question 24

Are repairs permitted in the root of prop blades

Answer 24

No.

Question 25

What radius do nicks on leading and trailing edges need to be worked out at

Answer 25

10x the depth of the damage.

Question 26

What radius do nicks I the face and back of the blade need to be worked out at

Answer 26

30x

Question 27

Who is allowed to repair prop blades

Answer 27

Approved repair facilities.

Question 28

What is a unique quality of steel blades

Answer 28

They are brittle. So any damage is critical. Meaning all repairs are major repairs.

Question 29

Inspection of the hub

Answer 29

Inspection for leaks and cracks

Question 30

Inspection and repair of composite props.

Answer 30

2 classification of damage: acceptable and unacceptable. Unacceptable damge usually starts as acceptable damage. Meaning minor damage has to be monitored and rectified as early as possible. Sub divided into skin perforated damage and non-skin perforated.

Question 31

What is the causes of skin perforated damge of composite props

Answer 31

Lightning strikes Holes.

Question 32

Can major repairs be undergone while the propeller is attached in composite propellers

Answer 32

No

Question 33

Is a lightning strike acceptable in a composite blade

Answer 33

No, unacceptable.

Question 34

Static checks

Answer 34

Engine not running. Auto feather Manual feather Flight fine pitch stop. Unfeather. Carried out with electric pump to do pitch change checks.

Question 35

Engine ground run Piston engine.

Answer 35

Piston engines use manifold air pressure MAP. Reference power check - checks engines produce a specific RPM for a set manifold pressure. Face into wind Use anti icing if temp is less than +10 degrees with visible moisture in the air.

Question 36

Turboprop engine ground running.

Answer 36

Uses shaft horsepower. Wind below 25 knots EPR and fuel flow are monitored and referenced against torque and RPM to check engine performance. Allows relationship between prop and engine are correct.

Question 37

What is used to check turbine engine performance is correct

Answer 37

EPR and fuel flow are compared to prop RPM and torque.