Answers - Propellers

Flii in th blanks
1. thrust
2. plane, rotation
3. center, hub
4. blade cuff
5. pitch distribution
6. red arc
7. slip
8. constant speed

1. true
2. false
3. false
4. true
5. true

Knowledge Application
1. a. Centrifugal force
b. Thrust bending force
c. Torque bending force
d. Aerodynamic twisting moment
e. Centrifugal twisting moment
f. Vibration

2. a. Threaded
b. Threadless

3. a. Steel hub
b. Compact

4. a. Head
b. Body
c. Base

5. a. Hub, or barrel
b. Dome
c. Distributor valve

6. a. Noise
b. Vibration

7. a. Bend angle
b. Blade station

8. a. Static
b. Dynamic

Multiple Choices
1. b
A typical electric propeller deice system utilizes a set of brush blocks and slip rings to transfer electrical power from the engine to the rotating propeller assembly. The brush blocks are mounted on the engine case just behind the propeller while the slip rings are mounted on the back of the propeller hub assembly.

2. c
A slinger ring is a U-shaped circular channel mounted on the rear of a propeller hub assembly that incorporates a discharge for each propeller blade. When an anti-icing system is on, a pump forces anti-icing fluid into the slinger ring where centrifugal force discharges the fluid from the slinger ring through the discharge tubes and onto the propeller blades.

3. b
A propeller synchronization system provides a means of synchronizing engine rpm by varying the pitch of the propeller blades through a set of propeller governors.

4. b
Propeller fluid anti-icing systems typically use isopropyl alcohol because of its availability and low cost.

5. b
A propeller sycnronization system provides a means of synchronizing engine rpm by varying the pitch of the propeller blades through the propeller governors. Synchronization reduces vibration and eliminates the annoying pulsating produced by unsynchronized propellers.

6. a
Ice formations destroy a propeller's aerodynamic profile which, in turn, reduces thrust. Furthermore, the formation of ice can also cause an unbalanced condition that can induce excessive vibration.

7. b
A typical fluid anti-icing system consists of a tank to hold a supply of anti-icing fluid, a pump, and a control inside the cockpit. The control system typically consists of a rheostat that allows the pilot to control the pump output.

8. a
About the only way to tell if an individual electric deicing boot is operating properly is to turn on the system and feel each boot in sequence while someone else watches the ammeter for proper sequencing.

9. a
Synchrophasing is a form of synchronization that allows the pilot to adjust the phase angle between the propellers to reduce propeller noise and vibration. With this type of system, a pulse generator is keyed to the same blade of each propeller. Each generator produces a signal that is compared to the signal emanating from the opposite generator. If the signals don't match, a signal is sent to the slave governor which establishes the phase angle selected by the pilot.

10. c
Propeller manufacturers are responsible for determining and publishing the oil and grease specifications as well as the proper lubrication procedures for the propellers they produce.

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