Module 17 Propeller 100 Important Sentences for Revision

 1. Propeller Fundamentals

1. A propeller converts engine power into thrust.
2. It acts as a rotating wing producing aerodynamic lift in the forward direction.
3. Each propeller blade is an airfoil section.
4. Thrust is produced by the pressure difference between the blade surfaces.
5. The propeller efficiency is the ratio of thrust power to engine power.
6. Maximum efficiency is around 85%.
7. Efficiency decreases at very low or very high airspeeds.
8. The propeller provides both thrust and engine load.
9. Propeller blades work under tension, bending, and torsional stresses.
10. Propeller performance depends on blade shape, pitch, and speed.

2. Types of Propellers

11. Fixed-pitch propellers have a constant blade angle.
12. Ground-adjustable propellers can be adjusted on the ground only.
13. Variable-pitch propellers can change blade angle in flight.
14. Constant-speed propellers automatically maintain selected RPM.
15. Feathering propellers reduce drag by aligning blades with airflow.
16. Reversible propellers allow thrust direction reversal.
17. Controllable-pitch propellers are manually controlled by the pilot.
18. Constant-speed units use governors to adjust pitch automatically.
19. Feathering is used in twin-engine aircraft to reduce drag after engine failure.
20. Reversing is used for braking during landing roll.

3. Propeller Geometry

21. Blade angle is measured between the chord line and the plane of rotation.
22. Pitch is the theoretical distance the propeller moves forward in one revolution.
23. Geometric pitch is the designed pitch angle.
24. Effective pitch is the actual distance moved through the air.
25. Slip is the difference between geometric and effective pitch.
26. Blade twist maintains a uniform angle of attack along the blade.
27. The root has a higher angle than the tip.
28. Blade chord is the width of the blade.
29. The hub connects the blades to the crankshaft or reduction gear.
30. The propeller disc area affects thrust production.

4. Aerodynamic Forces

31. Propeller blades experience lift and drag.
32. Centrifugal force acts outward on rotating blades.
33. Thrust bending force acts forward on the blade.
34. Torque bending force acts opposite to rotation.
35. Aerodynamic twisting moment tends to increase pitch.
36. Centrifugal twisting moment tends to reduce pitch.
37. Vibrations can occur due to aerodynamic or mechanical imbalance.
38. As speed increases, the angle of attack decreases.
39. High RPM can cause compressibility effects near the tip.
40. Blade stress increases with rotational speed.

5. Fixed and Variable Pitch Operation

41. Fixed-pitch propellers are simple and reliable.
42. They are efficient only at one combination of speed and power.
43. Variable-pitch propellers optimize efficiency across flight conditions.
44. Constant-speed propellers use oil pressure to adjust pitch.
45. The governor maintains selected RPM by changing blade angle.
46. When engine load increases, blade angle decreases automatically.
47. When engine load decreases, blade angle increases.
48. The pilot selects desired RPM using the propeller control lever.
49. Oil pressure is supplied from the engine or a separate pump.
50. Spring and counterweights assist in pitch change operation.

6. Propeller Control and Governors

51. The propeller governor senses engine RPM.
52. It adjusts oil pressure to change blade pitch.
53. A flyweight assembly controls the pilot valve.
54. Flyweights move outwards when RPM increases.
55. This movement ports oil to increase pitch and reduce RPM.
56. When RPM decreases, oil pressure decreases and pitch is reduced.
57. The governor maintains equilibrium between flyweight and speeder spring forces.
58. A speeder spring is adjusted by the cockpit propeller lever.
59. Overspeed condition occurs when RPM exceeds the selected limit.
60. Under speed condition occurs when RPM falls below the set limit.

7. Feathering and Reverse Operation

61. Feathering aligns blades parallel to airflow.
62. It minimizes drag in case of engine failure.
63. Feathering is achieved by increasing blade pitch to maximum.
64. Feathering systems use oil pressure and spring or counterweights.
65. Automatic feathering may be fitted to some aircraft.
66. Unfeathering uses oil pressure to return blades to normal pitch.
67. Reverse pitch changes blade angle beyond low pitch.
68. Reverse thrust helps slow the aircraft on landing.
69. Beta range includes all blade angles between fine and reverse.
70. Reverse operation is common on turboprops.

8. Propeller Synchronization

71. Multi-engine aircraft use synchronization systems.
72. They reduce noise and vibration caused by RPM differences.
73. The master engine speed is sensed electronically.
74. The slave engine propeller speed is adjusted automatically.
75. Synchrophasing adjusts blade positions for smoother operation.
76. Proper synchronization improves passenger comfort.
77. Synchronizing systems prevent propeller beat frequency.
78. Manual synchronization may be done by monitoring engine sound.
79. Electronic systems use sensors and actuators.
80. Correct adjustment prevents asymmetric thrust.

9. Propeller Maintenance

81. Propeller blades must be inspected for nicks and cracks.
82. Corrosion is common near the hub and leading edge.
83. Blade tracking ensures all tips follow the same path.
84. Blade balance prevents vibration.
85. Static balancing checks propeller balance at rest.
86. Dynamic balancing checks balance during rotation.
87. Grease and oil leakage may indicate seal failure.
88. Pitch change mechanism must be clean and lubricated.
89. Over-speeding may damage the propeller hub.
90. Regular overhaul ensures safe and efficient operation.

10. Propeller Materials and Construction

91. Wooden propellers are used on light aircraft.
92. Wooden blades are laminated for strength.
93. Metal propellers are usually made from aluminum alloy.
94. Metal blades are forged and machined.
95. Composite propellers use carbon fiber or fiberglass.
96. Composite blades are lightweight and corrosion resistant.
97. Metal hubs provide attachment and load transmission.
98. De-icing boots may be installed on the leading edge.
99. Some propellers use electric or fluid de-icing systems.
100. Proper material choice ensures strength, efficiency, and safety.

 

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