Answers - Propellers (Part 1) | Aircraft Systems

Answers - Propellers (Part 1)

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.

11. a
The reduction of frictional resistance refers to a lubricant's anti-friction characteristics, while the ease at which a lubricant is molded under pressure refers to a lubricant's plasticity characteristics.

12. a
When a propeller is placed in a vertical position on a balancing stand and it rotates to a horizontal position, it is said to be vertically imbalanced.

13. a
The basic components of a typical propeller static balance stand include the bushing, arbor, knife edges, and balancing stand. The bushings are placed in a propeller's engine shaft hole while the arbor is inserted through the bushings. The arbor is designed to support and permit free rotation of the propeller on the knife edges which rest on the balancing stand.


14. c
All of the blades on a conventional propeller assembly must be precisely the same length, profile, and weight to prevent severe vibration. Therefore, if the shape or length of one blade is changed, the opposite blade must also be changed.

15. c
Minor horizontal propeller imbalances on a wood propeller may be corrected by applying an additional protective coating to the light blade.

16. c
Centrifugal force increases as an object's rotational speed increases. As a result, vibration emanating from an unbalanced propeller increases with an increase in propeller rpm.

17. c
To correct a horizontal imbalance on a wooden propeller, a small amount of solder is melted onto the face side of the metal tip cap of the light blade and filed smooth. Brass screws should not be attached to wood propellers unless recommended by the propeller manufacturer.

18. a
Aerodynamic thrust imbalance results when one propeller blade produces more thrust then the other blade. This type of unbalance can largely be eliminated by making sure all propeller blades are contoured properly and that they all have the same blade angle setting.

19. a
On aircraft that utilize a constant-speed propeller, the pitch of the propeller blades is controlled by a governor consisting of an oil pump, pilot valve, speeder spring, and flyweights. When the propeller is in an on-speed condition, the centrifugal force exerted on the rotating flyweights is exactly balanced by the force exerted by the speeder spring and the propeller blade angle remains constant. If the speeder spring force is reduced through the use of the propeller control, the flyweights tilt outward into an over-speed position and the pilot valve allows oil to drain out of the propeller hub. This results in an increased blade angle, a reduction in rpm, and an increase in manifold pressure.

20. a
The pulley stop screw limits the amount of tension put on the governor speeder spring which, in turn, limits the maximum engine speed with full power applied.

21. c
When an engine operates at speeds lower than those the governor can govern in the INCREASE RPM position, the propeller will remain in the full LOW PITCH position. This occurs because, at low engine speeds the governor senses an under-speed condition and directs oil to position the propeller blades in the low pitch position in an effort to reduce engine load and increase rpm.

22. c
When engine power is increased, the propeller governor senses an over-speed condition. In an over-speed condition, centrifugal force causes the governor flyweights to tip outward causing the pilot valve to allow oil to drain from the propeller hub. As the oil drains, the propeller blade angle increases so the selected rpm can be maintained.

23. a
The propeller governor controls the flow of oil into and out of the pitch change mechanism in the propeller hub assembly.

24. c
On aircraft that utilize a constant-speed propeller, the pitch of the propeller blades is controlled by a governor consisting of an oil pump, pilot valve, speeder spring, and flyweights. When the propeller is in an on-speed condition, the centrifugal force exerted on the rotating flyweights is exactly balanced by the force exerted by the speeder spring and the propeller blade angle remains constant.

25. b
The governor flyweights actuate the pilot valve in a constant-speed propeller governor. When the governor flyweights tilt outward, the pilot valve is raised and oil flows in to the propeller hub assembly. On the other hand, when the flyweights tilt inward, the pilot valve is lowered, and oil flows out of the propeller.


26. a
The propeller control in the cockpit allows a pilot to change the propeller blade angle by adjusting the tension on the governor speeder spring. When spring tension is increased, the propeller blade angle decreases and when spring tension is decreased the blade angle increases.

27. c
When the propeller control in the cockpit is moved forward, governor speeder spring tension increases and causes the governor flyweights to tilt inward. This causes the pilot valve to lower and port oil in the direction necessary to decrease the propeller blade angle and increase rpm.

28. c
To change the rotational speed of a constant-speed propeller in flight, the pilot adjusts the prop lever which varies the spring tension on the governor speeder spring. Moving the prop control forward increases spring tension which tilts the governor flyweights inward and lowers the pilot valve. On the other hand, moving the prop control aft decreases spring tension which allows the flyweights to tilt outward and raise the pilot valve.

29. c
An over-speed condition exists when an engine turns at a faster rpm than that selected. When this occurs, centrifugal force causes the governor flyweights to overcome the speeder spring tension and raise the pilot valve. This ports oil to the propeller dome which increases a propeller's blade angle.

30. b
The greatest stress on a propeller is the centrifugal force created by the propeller's rotation. Depending on a blade's weight and rpm, centrifugal force can be greater than 25 tons.

31. b
A propeller blade is an airfoil and is subject to the same aerodynamic forces as any other airfoil. On all propeller blades, the center of lift, or center of pressure, is forward of the blade's center of rotation. Therefore, when a propeller blade is producing lift (thrust), the blade tends to rotate to a higher angle. This is called aerodynamic twisting force.

32. c
On turboprop engines, the fuel control unit and propeller governor are interconnected. Therefore, in flight, when a pilot moves the power lever, the fuel control and governor establish the correct combination of rpm, fuel flow, and propeller blade angle to provide the desired power output.

33. a
A propeller blade is an airfoil and is subject to the same aerodynamic forces as any other airfoil. On all propeller blades, the center of lift, or center of pressure, is forward of the blade's center of rotation. Therefore, when a propeller blade is producing lift (thrust), the blade tends to rotate to a higher angle. This is called aerodynamic twisting force.

34. a
When a propeller control is in a high rpm position, there is a relatively low pitch on the propeller blades. When a propeller moves to reverse pitch, the blades rotate through the low blade angle and into a negative blade angle. Therefore, if a propeller blade is in a low pitch position when reverse pitch is selected, the blades will move directly to the reverse pitch position.

35. b
If a propeller has been exposed to salt water, it should be flushed with fresh water until all traces of salt have been removed. This should be accomplished as soon as possible after the salt water has been splashed on a propeller. After flushing, all parts should be dried thoroughly.

36. b
Of the choices given, magnetic particle inspection is the preferred method for inspecting a steel propeller hub for cracks.

37. a
When measuring a propeller's blade angle, a reference blade angle measuring station is always specified by the propeller manufacturer. Therefore, you must be familiar with and use a propeller blade station to measure a propeller's blade angle.

38. a
The propeller blade angle is the acute angle between the airfoil section chord line at the proper reference station and the propeller's rotational plane. The reference station is typically at a point approximately 75 percent of the distance from the hub to the tip.

39. c
To obtain the maximum amount of engine power during takeoff and climb a low propeller blade angle is used. However, during high-speed, high-altitude cruising flight, less engine power is needed and, therefore, the propeller blade angle is typically greater.

40. a
Effective pitch is the actual distance a propeller moves through the air in one revolution.

41. a
The same oil that is used to change the pitch of a propeller blade is also used to lubricate the pitch-changing mechanism on a hydromatic propeller. No greases or other lubrication are required for the pitch-change mechanism.

42. a
When the throttle is opened on an engine which has a constant-speed propeller operating in the constant-speed range, the propeller governor increases the blade angle to absorb the additional engine power and maintain the desired rpm.

43. b
Propeller blade stations are measured from the hub centerline. Each blade has its own set of stations starting from station zero at the hub centerline and increasing out to the blade tip.

44. b
A propeller is a rotating airfoil and creates thrust the same way an airplane's wing creates lift. When the propeller rotates, an area of decreased pressure forms in front of the propeller blade, while an area of constant or higher pressure forms in back of the propeller. The pressure differential between the front and back of the propeller is the source of thrust.

45. a
Some constant-speed counterweight propellers use an exposed actuating piston to change the pitch of the propeller blade. Therefore, when shutting down an engine equipped with this type of propeller, the propeller should be placed in the full HIGH PITCH position so that the actuating piston is covered and somewhat protected from corrosion causing moisture by the propeller hub.

46. a
The low pitch stop on a constant-speed propeller is set so that the engine can develop its rated power at sea level at the rpm specified by the propeller manufacturer. If the low pitch stop is improperly set, the engine could fail to attain rated power.

47. c
Propeller angle of attack is the acute angle between the blade chord and the relative wind.

48. b
When an object rotates, its center of mass tends to align with its center of rotation. A propeller's center of mass is typically ahead of its center of rotation. Therefore, when a propeller rotates, centrifugal force tries to pull the propeller's center of mass in line with its center of rotation thereby decreasing the propeller's pitch angle.

49. a
The curved, or cambered side of a propeller blade is called the blade back and the flat side is called the blade face.

50. b
When a propeller is set in the LOW RPM position, the blade pitch is high. Therefore, when feathering is begun, the propeller blades move directly from high pitch into the feather position.

51. c
The holding coil on a feathering propeller keeps the feathering button in the depressed position and provides current to the propeller feathering pump motor.

52. b
Metal tipping is applied to the leading edge and tip of wood propeller blades to prevent damage from small stones or debris which might strike the prop during ground operations. This tipping is attached to the blade with countersunk screws in the thick blade sections and with copper rivets in the thin sections.

53. b
Blade angle is the acute angle formed by a line perpendicular to the crankshaft centerline and the chord of the blade at a specified reference station.

54. a
Propeller blade stations are measured from the hub centerline. Each blade has its own set of stations starting from station zero at the hub centerline and increasing out to the blade tip.

55. b
A propeller blade is an airfoil and is subject to the same aerodynamic forces as any other airfoil. On all propeller blades, the center of lift, or center of pressure, is forward of the blade's center of rotation. Therefore, when a propeller blade is producing lift (thrust), the blade tends to rotate to a higher angle. This is called aerodynamic twisting force.

56. b
With counterweight-type propellers, centrifugal force acting on a set of counterweights tends to rotate the blades to a high pitch angle.

57. c
Some models of McCauley propellers use dyed oil to aid in the detection of cracks. The propeller hub is permanently sealed and partially filled with red-dyed oil. If red dye appears on the hub or blades, some component in the hub has failed and the propeller should be removed and serviced.

58. c
When a propeller is set in the HlGH RPM position, the blade pitch is low. Therefore, when the feathering action begins, the blades must rotate from low pitch through high pitch and then to the feather position.

59. b
A propeller's blade angle decreases from the hub to the tip. This is necessary because the further a blade station is from the hub, the faster the airfoil moves through the air. Therefore, in order to maintain a relatively equal amount of thrust along the entire blade length, the blade angle must decrease from the hub to the tip.

60. a
When the feather button is pushed in a normally functioning full-feathering hydromatic propeller system, a holding coil keeps the button in the depressed position until the feather cycle is completed. Furthermore, when unfeathering, the feathering button must be held manually until the propeller blades unfeather and reach low pitch.