Helicopters (11 30 09)
4
1. Vibrations a. Large number of moving and rotating parts = susceptible to vibrations b. Vibrations = abnormal wear, premature part failure, and uncomfortable ride for people c. Must minimize this 2. Types a. Low Frequency b. Feel as “beat” in structure and may be able to almost count the beats. c. Comes from main rotor d. Two types i. Vertical Vibration 1. Out of Track ii. Lateral vibration 1. Out of balance Out of Track: Track = path blade tips follow during rotation In-Track = all tips follow same path (or cone the same amount or fly in the same plane) and = minimal vertical vibrations. All M/Rs need to be checked and adjusted, and sometimes T/R’s Out of Balance: Normally caused by an out of balance main rotor. e. Medium Frequency f. High Frequency i. Tail rotor (generally) ii. Could also be caused by accessories iii. “Buzz” iv. Pilot complains of his feet going to sleep while flying 3. Measurement of Vibrations a. Feel b. Electronic i. Control box with strobe light that keys into vibrations of whatever you’re measuring. 4. Correction of Vibrations a. If OUT OF BALANCE condition: i. May require static or dynamic procedures (or both, depending on the helicopter) ii. Some require static balancing after assembly
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Transcript of Helicopters (11 30 09)
- 1.
- Vibrations
- 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 13. Out of
balanceOut of Track:
Track = path blade tips follow during rotation
In-Track = all tips follow same path (or cone the same amount or
fly in the same plane) and = minimal vertical vibrations.
All M/Rs need to be checked and adjusted, and sometimes T/Rs
Out of Balance:
Normally caused by an out of balance main rotor.
- Medium Frequency
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 youre measuring. 23. Correction of
Vibrations 24. IfOUT 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/Rs dont need dynamic after static but
all T/Rs 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 dont 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 wont 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
