Propellers

Question 1

Why do some aircraft engines have a critical range of operation?

Answer 1

The engine and propeller combination have a resonant frequency problem in which excessive vibration can occur in a certain range of RPM. The tachometer for an aircraft with this limitation is marked with a red arc. When it is necessary to pass through this range it must be done as quickly as practical.

Question 2

Does the centrifugal twisting moment on a propeller blade tend to move the blades toward high pitch or toward low pitch?

Answer 2

Toward low pitch.

Question 3

Do the counterweights on a propeller tend to move the blades toward high pitch or toward low pitch?

Answer 3

Toward high pitch.

Question 4

What is the function of the accumulator used with some McCauley feathering prpellers?

Answer 4

The accumulator stores oil under pressure when the engine is operating normally. This oil is used to help the propeller blades move toward low pitch when the propeller is being unfeathered.

Question 5

What is meant by the alpha range of operation of a turboprop propeller?

Answer 5

This is the in-flight mode of operation from takeoff to landing.

Question 6

Should an adjustable-pitch propeller be in high pitch or in low pitch for takeoff?

Answer 6

In low pitch.

Question 7

What can be done to prevent the front cone from bottoming when installing a propeller on a splined shaft?

Answer 7

Install a spacer behind the rear cone to move the propeller forward on the shaft.

Question 8

Why is a propeller indexed to the engine crankshaft?

Answer 8

The relationship between the propeller and the engine crankshaft is chosen to produce the minimum vibration.

Question 9

What is the function of the snap ring inside the hub of a propeller that is mounted on a tapered or splined shaft?

Answer 9

The snap ring allows the propeller to be pulled off of the shaft when the retaining nut is backed off.

Question 10

What are the basic types of propellers?

Answer 10

-Fixed pitch
-Ground adjustable
-Constant-speed non-feathering
-Constant-speed feathering

Question 11

What materials are propeller blades made from?

Answer 11

-Wood
-Aluminum
-Composit construction

Question 12

What is adjusted inside the governor for a constant-speed propeller to change the speed at which the propeller is operating?

Answer 12

The compression of the speeder spring.

Question 13

What is done to cause a McCauley propeller to feather?

Answer 13

Oil is allowed to drain out of the propeller.

Question 14

What keeps a McCauley feathering propeller from feathering when the engine is shut down on the ground?

Answer 14

A spring-loaded latch mechanism prevents the blades moving into the feather position when the engine is shut down on the ground. In the air, aerodynamic forces keep the propeller rotating fast enough that centrifugal force holds the blades unlatched so they can move to the feather position when oil pressure is taken out of the propeller.

Question 15

What is done to cause a hydromatic propeller to feather?

Answer 15

high-pressure engine oil is directed into the propeller through the governor.

Question 16

What does the pilot do to change the RPM of an engine equipped with a constant-speed propeller when it is operating within the constant-speed range?

Answer 16

The pilot moves the propeller pitch control. This changes the compression on the speeder spring inside the governor which moves the pilot valve. The pilot valve directs oil into or out of the propeller to change the pitch of the blades. The change in pitch changes the air load on the propeller which changes the RPM.

Question 17

What is the difference between a controllable propeller and a constant-speed propeller?

Answer 17

Basically, it is the control system. A controllable-pitch propeller uses a manually operated oil valve to control the pitch, and a constant-speed propeller uses a governor to control the valve.

Question 18

When making a magneto check on an engine equipped with a constant-speed propeller, should the propeller control be in the low-pitch or the high-pitch?

Answer 18

It should be in the low-pitch, high RPM position.

Question 19

What is meant by the beta range of operation of a turboprop propeller?

Answer 19

This is the mode of ground operation, and it includes starting, taxiing, and ground reverse operation.

Question 20

what controls the blade angle of a propeller when operating in the beta range?

Answer 20

When operating in the beta range, blade angle is controlled by the position of the power lever.

Question 21

Where do you find a list of the lubricants that are approved for use in a constant-speed propeller?

Answer 21

In the maintenance manual for the propeller.

Question 22

What is the extent of the repairs a mechanic with a powerplant rating can make to a propeller?

Answer 22

Only minor repair or minor alterations.

Question 23

Where can examples of acceptable repairs to aluminum allow propeller blades be found?

Answer 23

In AC 43.13-1B, Chapter 8, Section 4, and in the propeller manufacturer’s service manual.

Question 24

Is it permissible to cold straighten a damaged aluminum allow propeller blade to facilitate shipping it to a repair station?

Answer 24

No, this could cause hidden damage that may render the blade nonrepairable.

Question 25

What would the classification of maintenance for shortening a propeller blade?

Answer 25

Major repair.

Question 26

Mayu transverse cracks in a metal propeller blade be repaired?

Answer 26

No, a transverse crack or any size is reason for rejecting the blade.

Question 27

What damage to an aluminum alloy propeller blade can be repaired by a mechanic holding a powerplant rating?

Answer 27

-Small roughness
-Nicks
-Scratches in the leading edge of the blades.

Question 28

How are small nicks removed from the leading edge of a propeller blade?

Answer 28

File them out with a fine file or stone, leaving a smooth contour.

Question 29

How can you determine that a surface scratch in an aluminum alloy propeller blade is not actually a crack?

Answer 29

Clean the damage of to a saucer-shaped depression and spay the area with a dye-penetrant liquid. Allow it time to seep into a crack if one is present, then wipe all of the liquid off the surface. Spray the area with a developer. If the damage is actually a crack, the developer will pull the penetrant out and it will form a visible line.

Question 30

Who, or what facility is authorized to perform major repairs to a propeller?

Answer 30

An FAA-approved propeller repair station that is authorized for the specific propeller.

Question 31

What checks and maintenance is a mechanic with a powerplant rating allowed to make on a propeller?

Answer 31

-Check the track of the propeller bladed
-Remove small nicks and scratches from the blades
-Check the dynamic balance of a propeller
-Lubricate the propeller

Question 32

What adjustment can a mechanic with a powerplant rating make to a propeller governor?

Answer 32

Adjust the maximum RPM stop.

Question 33

What instrument is used to measure the blade angle of a propeller?

Answer 33

A universal propeller protractor.

Question 34

Where is the propeller protractor placed to measure the propeller blade angle?

Answer 34

At a distance from the center of the propeller hub. this distance is specified in the propeller maintenance manual in terms of propeller blade stations.

Question 35

What are the basic steps for removing a typical propeller?

Answer 35

1. Remove the spinner and remove safety wire from the mounting bolts.
   2 Support the propeller with a sling mark the alignment between the propeller hub and the engine flange with a felt-tipped pen.
2. Unscrew the mounting nuts and protect the threads of the mounting studs or bolts as the propeller is removed.
3. Place the propeller on a cart for transport.

Question 36

What alignment method is used to align a propeller to the engine in a position that reduces operating vibrations?

Answer 36

Special studs of dowel pins align the propeller to the engine in the proper orientation.

Question 37

Who is allowed to reduce the diameter of a type certificated propeller?

Answer 37

An FAA-certificated propeller repair station with approval for the particular propeller.

Question 38

Which TCDS specifies that a propeller can be installed on the aircraft in question?

Answer 38

The aircraft TCDS specifies which propellers are approved for installation.

Question 39

What is meant by a slave engine with regard to propeller synchronization?

Answer 39

This is the engine in a multi-engine airplane whose RPMs follow those set on the master engine.

Question 40

How are propellers on a twin-engine airplane synchronized?

Answer 40

the propeller governor of the master engine is set to the desired RPM. A signal from the master engine governor is sent to the control box which send a signal to a stepping motor. This motor adjusts the propeller governor and fuel control of the slave engine causing it to maintain exactly the same RPM as the master engine.

Question 41

How is ice prevented from forming on propeller blades?

Answer 41

A chemical anti-icing system is sued. A mixture of isopropyl alcohol and ethylene glycol is pumped into a slinger ring on the back of the propeller hub. From there centrifugal force slings it out along the blades. Ice cannot form on the resulting slick surface.

Question 42

How is ice removed from propeller blades?

Answer 42

An electrothermal deicing system is used. Electrical heating elements are embedded in rubber boots that are bonded to the leading edges of the blades. Low-voltage DC flows from the propeller deicer control through brushes and slip rings to the heating elements. The timer sends current to one propeller for about 90 seconds and then the other for the next 90 seconds. This allows the ice to form and the break loose and blow away.

Question 43

How can you determine that the electrically heated deicer boots on the propeller blades are working as they should?

Answer 43

Observe the loadmeter or ammeter to see if the proper current is flowing, and follow the sequence of boot heating by feeling with your hands to see which one is heating. The boots should all have a similar heat rise in the same length of time.