2. Large number of moving and rotating parts = susceptible to vibrations

3. Vibrations = abnormal wear, premature part failure, and uncomfortable ride for people

4. Must minimize this

5. Types

6. Low Frequency

7. Feel as “beat” in structure and may be able to almost count the beats.

8. Comes from main rotor

9. Two types

10. Vertical Vibration

11. Out of Track

12. Lateral vibration

14. High Frequency

15. Tail rotor (generally)

16. Could also be caused by accessories

17. “Buzz”

18. Pilot complains of his feet going to sleep while flying

19. Measurement of Vibrations

20. Feel

21. Electronic

22. Control box with strobe light that keys into vibrations of whatever you’re measuring.

23. Correction of Vibrations

24. If OUT OF BALANCE condition:

25. May require static or dynamic procedures (or both, depending on the helicopter)

26. Some require static balancing after assembly

27. Put on balance stand and adjust until no movement when released

28. T/R done like propeller (knife-edge stand)

29. M/R done on special stand with bulls-eye level

30. M/R may also require Blade Sweep to be adjusted (for chordwise balance)

31. = Stretch string until string between blades and adjust until blades are exactly 180 degrees forward or aft, as necessary.

32. Dynamic balancing done during operations on ground and in air

33. Some M/R’s don’t’ need dynamic after static but all T/R’s do.

34. If OUT OF TRACK condition

35. Use marking stick

36. Flag tracking

37. Adjust by changing the length of the Pitch (change) links

38. For ground and hover adjustment, user pitch links

39. For in flight adjustment, most blades have trailing edge trim tabs to allow limited bending.

40. Ground & Flight

41. Use spotlight or strobe

42. Spotlight uses colored reflectors attached to blade

43. Light shows colored streaks and can see “altitude” difference between them

44. Strobe is keyed by pickup on swashplate

45. Flashes once for each blade

46. Has reflectors on each blade with different angled “Target” line

47. Flashes ‘stop’ targets at one location and can easily see difference and which blade to adjust

48. Power Systems and Other Components

49. Reciprocationg

50. See all types: Radials and horizontal and vertical mount opposed.

51. Verticals and radials are usually dry-sump with M/R transmission (gearbox) mounted on top and using same oil supply.

52. Horizontally opposed usually use some form of belt drive

53. Cooling Fan

54. Usually hard to start (due to no fly wheel)

55. Engine and Rotor Tach and manifold Pressure

56. Collective basically controls manifold pressure

57. Powerplants

58. Turbines (turboshafts)

59. Direct shaft type

60. Free Turbine Type

61. Turbine Instruments

62. Measure power output with Tachometers, Torquemeters, and turbine temperature gauges.

63. Turbine inlet temp gauge is important on start of engine, to monitor for hot starts.

64. Transmissions

65. For speed and/or directional change of rotating shaft(s)

66. May be Rack & Pinion or Planetary Gear systems

67. Uses engine oil or has own supply

68. Clutch

69. USED TO RELIEVE THE ENGINE LOAD DURING STARTING

70. May be manual, electrical, or centrifugal

71. Free turbine turboshafts don’t need them.

72. Manual and Electrical pull Idler Pulley against Belt(s) to tighten them and connect engine with Transmission

73. With a fully articulated head, if clutch is engaged too fast, the rotor will turn but the blade won’t turn, and the blade will lag out of position.

74. Freewheeling Unit

75. FOR AUTOROTATION PURPOSES

76. Disconnects M/R from engine if engine turns slower than M/R

77. Usually either Roller or Sprag styleFor FAA and LCC test purposes: Clutch is used to relieve engine stress during starting, Freewheeling unit is used for autorotation. Not always so in real world. Freewheeling unit sometimes called “freewheeling clutch”