- 1. Single Rotor: Majority of helicopters are designed this way.
Relatively simple way to accomplish everything you need to do.
Limited weight capacity.
Dual Rotor: Chinooks. Counter-rotating. Controls are more
complicated. Rear rotor is yaw and pitch control, and together they
are roll control.
Tilt Rotor: Helicopter vertical capability combined with high speed
flight. (eliminates dissymmetry of lift)
Main rotating wings create lift.
Feathering action:
- Changing the rotor pitch (angle of incidence).
- 2. Rolling the rotor blade side to side. Greater pitch =
greater lift.
3. Will generally have a positive pitch angle, to create
positive lift.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.
Lead/Lag or Hunt: Blades can move in/out
T/T Strap: Tension torsion strap
Common blade is 3, 4 (very common),and 6 (common on larger
helicopters)
Types of Rotors
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 13. Lead/LagForces on the
Rotor
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 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 doesnt 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
