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PROPELLER SYSTEM

PROPELLER SYSTEM. 1 st - Look at how lift is generated. Then see how it applies to propellers. How lift is generated. PROPELLER SYSTEM. In this direction. Pressure Decreases here. Pressure Remains Constant here. In this example. The result is LIFT. How lift is generated.

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PROPELLER SYSTEM

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  1. PROPELLER SYSTEM 1st - Look at how lift is generated Then see how it applies to propellers

  2. How lift is generated PROPELLER SYSTEM

  3. In this direction Pressure Decreases here Pressure Remains Constant here In this example The result is LIFT How lift is generated PROPELLER SYSTEM

  4. The result is MORE LIFT Greater Pressure Decrease here Small Pressure Increase here How lift is increased PROPELLER SYSTEM

  5. Direction of travel Aerofoil incline The difference in direction of travel and aerofoil incline is called:- The ANGLE of ATTACK How lift is increased PROPELLER SYSTEM

  6. How does lift apply to PROPELLORS? On Propellers, LIFT is called THRUST And propeller Blades work the same way as aircraft wings When a propeller spins and the aircraft moves forward, the tips of the propeller blades move in a ‘corkscrew’ path This path is called a HELIX PROPELLER SYSTEM

  7. How the HELIX ANGLE is generated

  8. How the blade tip travel produces the HELIX ANGLE PROPELLER SYSTEM

  9. How the blade tip travel produces the HELIX ANGLE PROPELLER SYSTEM

  10. How the blade tip travel produces the HELIX ANGLE PROPELLER SYSTEM

  11. How the blade tip travel produces the HELIX ANGLE PROPELLER SYSTEM

  12. How the blade tip travel produces the HELIX ANGLE PROPELLER SYSTEM

  13. How the blade tip travel produces the HELIX ANGLE PROPELLER SYSTEM

  14. How the blade tip travel produces the HELIX ANGLE PROPELLER SYSTEM

  15. How the blade tip travel produces the HELIX ANGLE PROPELLER SYSTEM

  16. How the blade tip travel produces the HELIX ANGLE PROPELLER SYSTEM

  17. How the blade tip travel produces the HELIX ANGLE PROPELLER SYSTEM

  18. How the blade tip travel produces the HELIX ANGLE PROPELLER SYSTEM

  19. How the blade tip travel produces the HELIX ANGLE PROPELLER SYSTEM

  20. How the blade tip travel produces the HELIX ANGLE PROPELLER SYSTEM

  21. How the blade tip travel produces the HELIX ANGLE PROPELLER SYSTEM

  22. How the blade tip travel produces the HELIX ANGLE PROPELLER SYSTEM

  23. How the blade tip travel produces the HELIX ANGLE PROPELLER SYSTEM

  24. How the blade tip travel produces the HELIX ANGLE PROPELLER SYSTEM

  25. How the blade tip travel produces the HELIX ANGLE PROPELLER SYSTEM

  26. How the blade tip travel produces the HELIX ANGLE PROPELLER SYSTEM

  27. How the blade tip travel produces the HELIX ANGLE PROPELLER SYSTEM

  28. Rotation - Number of Rotations per Minute Forward Speed - Distance Travelled over One Minute How the blade tip travel produces the HELIX ANGLE PROPELLER SYSTEM

  29. RPM Forward Speed How the blade tip travel produces the HELIX ANGLE PROPELLER SYSTEM

  30. RPM Forward Speed How the blade tip travel produces the HELIX ANGLE PROPELLER SYSTEM

  31. RPM Forward Speed How the blade tip travel produces the HELIX ANGLE PROPELLER SYSTEM

  32. RPM Forward Speed How the blade tip travel produces the HELIX ANGLE PROPELLER SYSTEM

  33. RPM Forward Speed How the blade tip travel produces the HELIX ANGLE PROPELLER SYSTEM

  34. RPM Forward Speed How the blade tip travel produces the HELIX ANGLE PROPELLER SYSTEM

  35. RPM Forward Speed How the blade tip travel produces the HELIX ANGLE PROPELLER SYSTEM

  36. How the HELIX ANGLE is changed by engine rpm and forward speed

  37. RPM Faster RPM Forward Speed Changes in FORWARD SPEED and RPM will change the Helix Angle How an increase in RPM changes the Helix Angle How the blade tip travel produces the HELIX ANGLE PROPELLER SYSTEM

  38. RPM RPM Forward Speed Faster Forward Speed Changes in FORWARD SPEED and RPM will change the Helix Angle How an increase in FORWARD SPEED changes the HELIX ANGLE PROPELLER SYSTEM

  39. This is the Helix Angle This is the Angle of Attack Direction of rotation Direction of blade through the air with forward speed Let’s take a closer look at the blade aerofoil and the Helix Angle and thrust (lift) generation If the Helix Angle changes, then we need to change the blade angle. Remember (from the comparison with the aircraft wing), the optimum Angle of Attack is required to maintain most efficient thrust generation. PROPELLER SYSTEM

  40. Mechanical STOPS and blade angles

  41. Sliding Piston Actuating Lever Propeller Blade Direction of Rotation Direction of Flight Actuating Link Hard Stops Fine Pitch Coarse Pitch All propeller blades are actuated by the same mechanical linkage PROPELLER SYSTEM

  42. Coarse pitch Or ‘Feathered’ Fine pitch Direction Of Rotation Maximum resistance to forward speed Minimum resistance to forward speed Maximum resistance to rotation Minimum resistance to rotation Pistontravels between ‘hard’ stops At this hard stop the blade is in this position At this hard stop the blade is in this position The blade angle changes through 90deg with piston travel Note: - blade angle is relative to piston travel PROPELLER SYSTEM

  43. Fine pitch Maximum resistance to forward speed In-flight engine failure – loss of control and Minimum resistance to rotation engine disintegration Zero pitch – or Ground Fine Pitch Good for:- Easier Starting of engine Running engine with no/minimal thrust Direction of Rotation High drag – braking effect on ground Bad for:- In-flight – loss of control Direction of travel Importance of set blade angle PROPELLER SYSTEM

  44. Maximum resistance to rotation Maximum pitch – or Feathered Minimum resistance to forward speed Bad for:- Starting of engine Could cause engine burn-out if running Direction of Rotation Low drag – NO braking effect on ground Good for:- In-flight – loss of control In-flight engine failure – control maintained and engine stops rotating minimizing damage Direction of travel Importance of set blade angle PROPELLER SYSTEM

  45. Reverse Pitch Used for:- High drag – high braking effect on ground Air pushed forward giving reverse thrust Direction of Rotation Usually for military aircraft only Minimal resistance to rotation Bad for:- In-flight – loss of forward speed, aircraft stalls In-flight engine failure – loss of control and reverse rotation increasing engine disintegration Direction of travel Importance of set blade angle PROPELLER SYSTEM

  46. Flight Fine pitch Used for:- Low drag on final approach Used for:- Cruise pitch In-flight descent – faster forward speed than final approach Flight Fine and Cruise Pitch Direction of Rotation Both give minimal drag at low power settings Direction of travel Importance of set blade angle PROPELLER SYSTEM

  47. Blade Twist

  48. MID-SPAN ROOT TIP COARSE ANGLE MEDIUM ANGLE FINE ANGLE Typical Blade Typical 3 Blade Prop BLADE ANGLE RELATIVE TO DISTANCE (AND THEREFORE SPEED) TRAVELLED BY ROOT, MID-SPAN AND TIP DISTANCE TRAVELLED BY ROOT, MID-SPAN AND TIP THICK FOR STRENGTH THINNER FOR STRENGTH AND THRUST THIN FOR THRUST Blade Twist PROPELLER SYSTEM

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