M17.6 Maintenance

Question 1

What are the three types of balancing on propellers?

Answer 1

. Static
. Dynamic
. Aerodynamic

Question 2

What are static and dynamic imbalances caused by? Compared to aerodynamic?

Answer 2

Unequal mass distribution while aerodynamic is to ensure each blade delivers equal amount of thrust

Question 3

When is dynamic balancing only necessary?

Answer 3

On large props or fast running props

Question 4

Where is static balancing carried out?

Answer 4

Off the aircraft, either at the manufacturer, overhauled or in an approved propeller repair facility

Question 5

On fixed pitch wood propellers how can horizontal imbalance be corrected?

Answer 5

By applying small amounts of varnish or paint to the light blade.
Or if larger amounts required, then solder can be applied to the metal tipping

Question 6

How can vertical imbalance be corrected?

Answer 6

By adding weights to the hub

Question 7

For fixed pitch metal props how can you correct static balancing?

Answer 7

By removing some metal from the heavy side and then refinishing to prop using no anodic protective coating (alodine)

Question 8

For propellers of aircraft up tot 5700kg what is the general permissible tolerance??

Answer 8

2 gm
(However specifications of manufacture are binding)

Question 9

How are minor adjustments for a metal or composite variable pitch prop done?

Answer 9

To balance it you correct it by placing lead wool into the balancing tube located within the hollow root of the blade

Question 10

When must dynamic balancing be carried out??

Answer 10

When the engine is running

Question 11

Why must dynamic balancing only done when engines are running?

Answer 11

Because might be smooth running on ground but vibrations in flight

Question 12

Wha5 is one method for a vibration pick up on the engine?

Answer 12

A defined weight is attached to each blade, then a result of a polar diagram is drawn, the balancing weight is then attached at the position of the greatest imbalance. Then a ground run

Question 13

What differs small props and large props IAW dynamic balancing?

Answer 13

Small props are not normally dynamically balanced as any shift of the centre of gravity is only small

Question 14

What balancing systems are used on modern electronically controlled turbo props?

Answer 14

Propeller balance monitoring system (PBMS)

Question 15

Props can be affected by vibration because of what?

Answer 15

Differing aerodynamic loads of the blades resulting from different blade angles

Question 16

If total thrust is off centre what does this cause?

Answer 16

Rotates with the propeller leading to vibrations

Question 17

What type of aircraft is aerodynamic balancing needed on?

Answer 17

Only props with high performance

Question 18

What is usually marked on the blade root?

Answer 18

The correction factor

Question 19

What’s aerodynamic corrective balancing also know as?

Answer 19

Blade indexing

Question 20

What is the universal blade protractor used for?

Answer 20

To measure the prop blade angle at a specific station to determine if the prop is promptly adjusted

Question 21

There is a movable ring in the frame of the protractor, what is it used for?

Answer 21

To set the zero reference angle for blade angle measurements

Question 22

What is the ring engraved with??

Answer 22

Index marks which allow readings as small as one tenth of a degree

Question 23

For blade tracking, the small pencil lines should be separated by no more than?

Answer 23

3mm

Question 24

Differences more than 3mm indicate what?

Answer 24

Bent blades

Question 25

What are the two types of propeller damages?

Answer 25

. Airworthy
, unairworthy

Question 26

On wooden props what must the surface protection coat condition be?

Answer 26

100% intact so that no moisture can penetrate

Question 27

On the trailing edge or blade if there is less significant damage what can you do for wooden props?

Answer 27

Fill it with plastic

Question 28

After the installation of a new fixed pitch wood prop, what must you do??

Answer 28

The attachment bolts must be re tightened after 25 hours with the torque prescribed. After this, the torque must be checked every 50 hours as humidity will cause wood to shrink and expand

Question 29

What are metal props partially subject too?

Answer 29

Metal fatigue

Question 30

Can you repair the blade root?

Answer 30

No. No repair is permissible at the blade root

Question 31

How must you work out a nick??

Answer 31

Must be worked out with a large radius (10 x depth of nick for the leading edge and 30x the depth)

Question 32

After material of a prop have been removed what must you do?

Answer 32

A ground run to see if unbalanced

Question 33

In the case of a two blade prop, the removal of how much material is noticeable?

Answer 33

2-3gm is noticeable as vibration

Question 34

What must you do if damage on steel props?

Answer 34

Damage must be located and corrected asap

Question 35

All repairs to steel props and blades are classified as what?

Answer 35

Major repairs and must be perfomered at an approved repair facility

Question 36

What are oil leaks a sign off??

Answer 36

A sign of damaged seals in the pitch change cycle see or damage to blade attachments (oil smeared blade bearings)

Question 37

When the propeller is still attached what repairs are possible?

Answer 37

Only minor repairs such as re coating of polyurethane finish