Flight Conditions<br />Translational Lift<br /><ul><li> 16-24 knots forward speed.
At low forward speed, air is re-circulated.
Wingtip vortices are created at forward edge.
Starts to climb on its own.</li></ul>Transverse Flow Effect<br /><ul><li>Low power conditions
Felt most at hover
Air is being accelerated in a more downward angle, epically towards the rear of the rotor system.
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Flight Conditions

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Flight Conditions

  1. 1. Flight Conditions<br />Translational Lift<br /><ul><li> 16-24 knots forward speed.
  2. 2. At low forward speed, air is re-circulated.
  3. 3. Wingtip vortices are created at forward edge.
  4. 4. Starts to climb on its own.</li></ul>Transverse Flow Effect<br /><ul><li>Low power conditions
  5. 5. Felt most at hover
  6. 6. Air is being accelerated in a more downward angle, epically towards the rear of the rotor system.
  7. 7. Angle of attack decreases in rear (reaction is 90 degrees to the right) causes helicopter to pull to the right.</li></ul>Auto-rotations: Emergency capability in case of engine failure<br /><ul><li>In normal flight, air is pulled down through rotors
  8. 8. Engine failure:
  9. 9. Push collective all the way down
  10. 10. Establish a certain forward airspeed (varies among aircraft)
  11. 11. As aircraft falls, air is pushed UP through rotors
  12. 12. Maintains rotor rpm at full rpm
  13. 13. At about 50 ft. of altitude, pull the nose up
  14. 14. Slows airspeed, and increases volume of air blowing through rotors eg: more energy available.
  15. 15. Add full right peddle (to keep fuselage from spinning)
  16. 16. Around 10 ft. pull up on the collective to slow as much as possible before touchdown. (uses up built up airspeed in rotor system)</li></ul>Altitude is important in autorotation<br />” Dead mans curve”<br />Retreating Blade Stall: Extreme dissymmetry of lift, at very high forward air speeds.<br /><ul><li>Excessive angle of attack on retreating blade side.
  17. 17. Feel a slight vibration
  18. 18. Either slow down or lower the collective</li></ul>Vortex Ring State (Settling with power): During steep approaches. Slow your decent. Coming down fast, you get into your downwash. Increase in power will increase the effect eg: speed your decent more.<br /><ul><li>If descending at 300 fpm or more
  19. 19. + less than 10 mph forward airspeed
  20. 20. + 20 to 100% power applied
  21. 21. = can descend inside rotor downwash</li></ul>Ground Resonance<br />Controls<br />Axes of Flight<br /><ul><li>Lateral Axis = Pitch,
  22. 22. Vertical Axis = Yaw
  23. 23. Longitudinal Axis = Roll</li></ul>Three basic controls: Cyclic (stick between your legs), Collective, Pedals<br />To go forward, you need rotor to drop in front and raise rotors in rear. To raise rotors in rear, you need force on left.<br />Cyclic<br /><ul><li>Pitch
  24. 24. Roll</li></ul>The cyclic controls the swash plate.<br />This swash plate is setup for a two blade helicopter (note there is only 2 pitch links)<br />Collective: Changes amount of pitch to main rotor system (all blades affected the same)<br />Pull up on collective, more lift. As you pull up on collective, more throttle is requred.<br />The end of the collective is the engine throttle.<br />Starter button is commonly on the end of the collective.<br />Pedals: Yaw left and right.<br />On takeoff when adding more collective, need to add left peddle to fight drift.<br />Tail Rotors: Most of the noise you hear from a helicoptor is the tail rotor.<br />Types:<br /><ul><li>Semi-Rigid
  25. 25. Most common until recently
  26. 26. Usually 2-bladed
  27. 27. Has same Dissymmetry of Lift problems as M/R so will teeter usually (some let blades flap)
  28. 28. Most use Offset Hinges so pitch is physically changed as rotor teeters = minimal actual teetering action
  29. 29. Fenestron
  30. 30. French design
  31. 31. Enclosed multi-bladed variable-pitch fan
  32. 32. Safer and quieter
  33. 33. NOTAR
  34. 34. No tail rotor
  35. 35. Uses fan inside tail boom with exhaust out side of boom through variable vent connected to pedals
  36. 36. Also uses Coanda Effect from rotor downwash
  37. 37. Air flowing over the curved surface “sticks” to that surface and creates lift sideways
  38. 38. “A variable pitch fan is enclosed in the aft fuselage section immediately forward of the tail boom and driven by the main rotor transmission. This fan forces low pressure air through two slots on the right side of the tail boom, causing the downwash from the main rotor to hug the tail boom, producing lift, and thus a measure of directional control. This is augmented by a direct jet thruster and vertical stabilizers.” –Wikipedia</li></ul>Stabilizer Surfaces <br />Fixed Horizontal<br />Creates download on tail to keep fuselage more level during high speed flight<br />Synchronized Elevator<br />Connected to Cyclic<br />Changes pitch to change tail down load for various flight speeds<br />Fixed Vertical<br /><ul><li>For directional stability</li></ul>Hydraulics<br />For larger or heavier M/R systems<br />Mostly use Irreversible type systems to overcome flight loads and dampen vibrations in sticks<br />Stabilizer Controls<br />Are inherently unstable<br />As rotor lift/thrust vector tilts away from vertical = creates vector to pull away from center<br />= negative stability<br />Compensations<br />Bell Stabilizer Bar<br />Bar below M/R @ 90o to blade span<br />Acts like gyroscope and uses Rigidity in Space characteristic to try and keep rotor and aircraft in one attitude<br />Worked too well so needs hydraulic damper to limit it’s effectiveness and allow reasonable maneuverability <br />Offset Flapping Hinge<br />On fully-articulated rotor heads and on some tail rotors<br />Hinge moved a distance from rotor’s rotation axis = acts like lever to provide restoring force<br />Stabilization Augmentation System (SAS)<br />Like simple autopilot<br />One- or two-axis<br />Only to aid stability, not true autopilot<br />

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