There are three main types of helicopter rotors: single rotor, dual rotor, and tilt rotor. Single rotor helicopters are the most common but have limited weight capacity. Dual rotor helicopters like the Chinook have counter-rotating rotors for control and lift. Tilt rotor helicopters can hover like a helicopter and fly fast like an airplane. Rotor blades use different mechanisms for control including feathering, flapping, and lead/lag movement. Forces on the rotor like torque and dissymmetry of lift are counteracted through techniques such as tail rotors and adjusting rotor pitch.

2. Rolling the rotor blade side to side. Greater pitch = greater lift.

4. Blades can feather

5. Blades teeter.

6. Fully Articulated

7. Blades can feather

8. Each blade can flap (individual)

9. Each blade can “hunt” or lead/lag

10. Rigid: Accomplishes a,b,c by making blades flexible. Blade fatigue is very high, so maintenance is very expansive.

11. Feather

12. Flap

14. When slowing blades down, they tend to droop due to less centrifugal force.

15. Static (droop) stop is what limits droop. Prevent blade from dropping and chopping tail boom off.

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. Coning

18. Blade tips “cone” up on takeoff

19. As blades get old and worn, coning gets worse.

20. Torque

21. Helicopter wants to rotate opposite of rotor rotation. Tail rotor counteracts this.

22. Tail rotor also used to control yaw.

23. Foot pedals control pitch and thrust of tail rotor.

24. Counter-Rotating Main rotors.

25. Rotors balance out torque effect. No tail rotor needed. Adjustable trim tabs on rotors.

26. Rotor blade tip powered

27. Power for rotor is powered by ramjets on tip of rotor

28. Eliminates torque effect.

29. Weight on tip of blade is high

30. Fuel consumption high

31. Translating Tendency or Drift

32. Helicopter tends to drift to the right (on American craft) on takeoff

33. Mast may be tilted to compensate for this

34. Gyroscopic Precession

35. Force applied is felt 90 degrees later in direction of rotation.

36. Same works for upward force on blades.

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. Tilt rotor to the left, increase forward blade pitch, decrease rear blade pitch.

39. Ground Effect: Within ½ rotor diameter of the ground, is “in” ground effect

40. Hovering out of ground effect, air is accelerated straight down.

41. Hovering in ground effect, air doesn’t go straight down.

42. Angle of attack is higher. Lift is higher.

43. Flight Forces

44. Forward Flight: At hover, thrust and lift are straight up, weight and drag are straight down.

45. Thrust vector tilted in desired direction = overall loss of upward lift = need more power applied

46. Dissymmetry of lift

47. In forward flight, tip speed of advancing blades is faster than

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. Any relative air motion (wind or flight) = blade going into wind (Advancing Blade) travels faster than Retreating Blade

50. Coriolis Effect

51. As blades flap up, center of mass moves closer to center, advancing blade is speeding up. Opposite on retreating blade.

52. On fully articulated setup, we allow this to happen. It is controlled by a dampener on the hub.

53. On Semi-Rigid setup, uses a delta hinge.

54. Underslung rotor head

55. As center of mass moves in, hub moves out to compensate.

56. Teetering Axis is above Feathering Axis (“Delta Hinge” arrangement) = as teeters it also swings to high side