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Rotorcraft (11 16 09)


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Rotorcraft (11 16 09)

  1. 1. Single Rotor: Majority of helicopters are designed this way. Relatively simple way to accomplish everything you need to do. Limited weight capacity.<br />Dual Rotor: Chinooks. Counter-rotating. Controls are more complicated. Rear rotor is yaw and pitch control, and together they are roll control.<br />Tilt Rotor: Helicopter vertical capability combined with high speed flight. (eliminates dissymmetry of lift)<br />Main rotating wings create lift.<br />Feathering action: <br /><ul><li>Changing the rotor pitch (angle of incidence).
  2. 2. Rolling the rotor blade side to side. Greater pitch = greater lift.
  3. 3. Will generally have a positive pitch angle, to create positive lift.</li></ul>Flap or Teeter: Blades going up and down. Some have each blade moving independently, others the entire rotor system teeters on center point. Used to counteract DISSYMMETRY OF LIFT.<br />Lead/Lag or Hunt: Blades can move in/out<br />T/T Strap: Tension torsion strap<br />Common blade is 3, 4 (very common), and 6 (common on larger helicopters)<br />Types of Rotors<br /><ul><li>Semi-Rigid:
  4. 4. Blades can feather
  5. 5. Blades teeter.
  6. 6. Fully Articulated
  7. 7. Blades can feather
  8. 8. Each blade can flap (individual)
  9. 9. Each blade can “hunt” or lead/lag
  10. 10. Rigid: Accomplishes a,b,c by making blades flexible. Blade fatigue is very high, so maintenance is very expansive.
  11. 11. Feather
  12. 12. Flap
  13. 13. Lead/Lag</li></ul>Forces on the Rotor<br /><ul><li>Static (blade droop)
  14. 14. When slowing blades down, they tend to droop due to less centrifugal force.
  15. 15. Static (droop) stop is what limits droop. Prevent blade from dropping and chopping tail boom off.
  16. 16. Hinged weight with spring. At high rpm, weight is pulled down by centrifugal force, and stop is out of the way. At low rpm, weight is up, stop is in place, and spring keeps blades from drooping too far.
  17. 17. Coning
  18. 18. Blade tips “cone” up on takeoff
  19. 19. As blades get old and worn, coning gets worse.
  20. 20. Torque
  21. 21. Helicopter wants to rotate opposite of rotor rotation. Tail rotor counteracts this.
  22. 22. Tail rotor also used to control yaw.
  23. 23. Foot pedals control pitch and thrust of tail rotor.
  24. 24. Counter-Rotating Main rotors.
  25. 25. Rotors balance out torque effect. No tail rotor needed. Adjustable trim tabs on rotors.
  26. 26. Rotor blade tip powered
  27. 27. Power for rotor is powered by ramjets on tip of rotor
  28. 28. Eliminates torque effect.
  29. 29. Weight on tip of blade is high
  30. 30. Fuel consumption high
  31. 31. Translating Tendency or Drift
  32. 32. Helicopter tends to drift to the right (on American craft) on takeoff
  33. 33. Mast may be tilted to compensate for this
  34. 34. Gyroscopic Precession
  35. 35. Force applied is felt 90 degrees later in direction of rotation.
  36. 36. Same works for upward force on blades.
  37. 37. To move aircraft to the left, you need lift on right. To get lift on right ,you need upward force on forward edge.
  38. 38. Tilt rotor to the left, increase forward blade pitch, decrease rear blade pitch.
  39. 39. Ground Effect: Within ½ rotor diameter of the ground, is “in” ground effect
  40. 40. Hovering out of ground effect, air is accelerated straight down.
  41. 41. Hovering in ground effect, air doesn’t go straight down.
  42. 42. Angle of attack is higher. Lift is higher.
  43. 43. Flight Forces
  44. 44. Forward Flight: At hover, thrust and lift are straight up, weight and drag are straight down.
  45. 45. Thrust vector tilted in desired direction = overall loss of upward lift = need more power applied
  46. 46. Dissymmetry of lift
  47. 47. In forward flight, tip speed of advancing blades is faster than
  48. 48. At a hover with no wind the rotor blades are all traveling at the same speed in relation to the air around them
  49. 49. Any relative air motion (wind or flight) = blade going into wind (Advancing Blade) travels faster than Retreating Blade
  50. 50. Coriolis Effect
  51. 51. As blades flap up, center of mass moves closer to center, advancing blade is speeding up. Opposite on retreating blade.
  52. 52. On fully articulated setup, we allow this to happen. It is controlled by a dampener on the hub.
  53. 53. On Semi-Rigid setup, uses a delta hinge.
  54. 54. Underslung rotor head
  55. 55. As center of mass moves in, hub moves out to compensate.
  56. 56. Teetering Axis is above Feathering Axis (“Delta Hinge” arrangement) = as teeters it also swings to high side