Helicopter Lessons on Rotor Systems and Symmetry of Lift

Introduction

• Instructor: Jacob
• Topic: Compensation for the Symmetry of Lift in Rotor Systems
• Prerequisite: Understanding of the symmetry of lift (recommended prior video)

Symmetry of Lift

• Definition: The difference in lift between the advancing and retreating sides of the rotor disc.
• Problem: Without compensation, the helicopter would constantly roll to the left due to more lift on the advancing side.

Compensation Techniques

1. Blade Flapping

• Mechanism: Allows blades to flap up and down.
• Advancing Side:
  • As the blade moves into the relative wind, it experiences increased air velocity.
  • The blade flaps up, altering lift characteristics by creating a downward flow of air.
  • Resultant relative wind creates a specific lifting area.
• Retreating Side:
  • The blade slows down and flaps downward, increasing lift due to increased angle of attack.
  • Resultant relative wind and upflow of air increase lift on this side.

2. Cyclic Feathering

• Mechanism: Adjusts the pitch of the rotor blades cyclically.
• Process:
  • Forward cyclic input causes a 90-degree phase lag, due to gyroscopic precession.
  • Increases lift on the aft portion of the rotor disc, tilting the disc forward.
  • Alters pitch at the 9 o'clock position, increasing angle of attack and lift on the retreating side, and decreasing it on the advancing side.

Conclusion

• Key Points:
  • Blade flapping increases/decreases lift by changing the angle of attack.
  • Cyclic feathering adjusts the pitch to maintain balance in lift.
• Outcome: These techniques ensure stable forward flight by compensating for lift symmetry.

Additional Information

• Contact: For questions, reach out via the comment section.
• Further Learning: Stay tuned for more videos on helicopter dynamics.