<ul><li>Vibrations
Large number of moving and rotating parts = susceptible to vibrations
Vibrations = abnormal wear, premature part failure, and uncomfortable ride for people
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Helicopters (11 30 09)

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Helicopters (11 30 09)

  1. 1. <ul><li>Vibrations
  2. 2. Large number of moving and rotating parts = susceptible to vibrations
  3. 3. Vibrations = abnormal wear, premature part failure, and uncomfortable ride for people
  4. 4. Must minimize this
  5. 5. Types
  6. 6. Low Frequency
  7. 7. Feel as “beat” in structure and may be able to almost count the beats.
  8. 8. Comes from main rotor
  9. 9. Two types
  10. 10. Vertical Vibration
  11. 11. Out of Track
  12. 12. Lateral vibration
  13. 13. Out of balance</li></ul>Out of Track:<br />Track = path blade tips follow during rotation<br />In-Track = all tips follow same path (or cone the same amount or fly in the same plane) and = minimal vertical vibrations.<br />All M/Rs need to be checked and adjusted, and sometimes T/R’s<br />Out of Balance:<br />Normally caused by an out of balance main rotor.<br /><ul><li>Medium Frequency
  14. 14. High Frequency
  15. 15. Tail rotor (generally)
  16. 16. Could also be caused by accessories
  17. 17. “Buzz”
  18. 18. Pilot complains of his feet going to sleep while flying
  19. 19. Measurement of Vibrations
  20. 20. Feel
  21. 21. Electronic
  22. 22. Control box with strobe light that keys into vibrations of whatever you’re measuring.
  23. 23. Correction of Vibrations
  24. 24. If OUT OF BALANCE condition:
  25. 25. May require static or dynamic procedures (or both, depending on the helicopter)
  26. 26. Some require static balancing after assembly
  27. 27. Put on balance stand and adjust until no movement when released
  28. 28. T/R done like propeller (knife-edge stand)
  29. 29. M/R done on special stand with bulls-eye level
  30. 30. M/R may also require Blade Sweep to be adjusted (for chordwise balance)
  31. 31. = Stretch string until string between blades and adjust until blades are exactly 180 degrees forward or aft, as necessary.
  32. 32. Dynamic balancing done during operations on ground and in air
  33. 33. Some M/R’s don’t’ need dynamic after static but all T/R’s do.
  34. 34. If OUT OF TRACK condition
  35. 35. Use marking stick
  36. 36. Flag tracking
  37. 37. Adjust by changing the length of the Pitch (change) links
  38. 38. For ground and hover adjustment, user pitch links
  39. 39. For in flight adjustment, most blades have trailing edge trim tabs to allow limited bending.
  40. 40. Ground & Flight
  41. 41. Use spotlight or strobe
  42. 42. Spotlight uses colored reflectors attached to blade
  43. 43. Light shows colored streaks and can see “altitude” difference between them
  44. 44. Strobe is keyed by pickup on swashplate
  45. 45. Flashes once for each blade
  46. 46. Has reflectors on each blade with different angled “Target” line
  47. 47. Flashes ‘stop’ targets at one location and can easily see difference and which blade to adjust
  48. 48. Power Systems and Other Components
  49. 49. Reciprocationg
  50. 50. See all types: Radials and horizontal and vertical mount opposed.
  51. 51. Verticals and radials are usually dry-sump with M/R transmission (gearbox) mounted on top and using same oil supply.
  52. 52. Horizontally opposed usually use some form of belt drive
  53. 53. Cooling Fan
  54. 54. Usually hard to start (due to no fly wheel)
  55. 55. Engine and Rotor Tach and manifold Pressure
  56. 56. Collective basically controls manifold pressure
  57. 57. Powerplants
  58. 58. Turbines (turboshafts)
  59. 59. Direct shaft type
  60. 60. Free Turbine Type
  61. 61. Turbine Instruments
  62. 62. Measure power output with Tachometers, Torquemeters, and turbine temperature gauges.
  63. 63. Turbine inlet temp gauge is important on start of engine, to monitor for hot starts.
  64. 64. Transmissions
  65. 65. For speed and/or directional change of rotating shaft(s)
  66. 66. May be Rack & Pinion or Planetary Gear systems
  67. 67. Uses engine oil or has own supply
  68. 68. Clutch
  69. 69. USED TO RELIEVE THE ENGINE LOAD DURING STARTING
  70. 70. May be manual, electrical, or centrifugal
  71. 71. Free turbine turboshafts don’t need them.
  72. 72. Manual and Electrical pull Idler Pulley against Belt(s) to tighten them and connect engine with Transmission
  73. 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. 74. Freewheeling Unit
  75. 75. FOR AUTOROTATION PURPOSES
  76. 76. Disconnects M/R from engine if engine turns slower than M/R
  77. 77. Usually either Roller or Sprag style</li></ul>For 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”<br />

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