Helicopter Lessons: Transverse Flow Effect

Presenter: Jacob
Series: Helicopter Lessons in 10 Minutes or Less

Introduction

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• Topic of Discussion: Transverse Flow Effect in helicopters.

What is Transverse Flow Effect?

• Definition: The right rolling motion and slight vibrations occurring as a helicopter accelerates into forward flight.
• Flow Transition: Transition of airflow from vertical (stationary hover) to horizontal (forward flight).
• Speed Range: Occurs between 10 to 20 knots of airspeed.

Detailed Explanation

• Airflow Dynamics:
  • Stationary Hover: Airflow is vertical through rotor system.
  • Forward Flight: Airflow becomes horizontal, affecting front and rear parts of rotor disc differently.
  • Front Half: More horizontal airflow, more lift.
  • Aft Half: More vertical airflow, less lift.

Airfoil Analysis

• Aft Half of Rotor System:

  • Components: Chord line, rotational relative wind, induced flow (downwards).
  • Effect: Induced flow reduces angle of attack.
  • Resultant: Combination of rotational wind and induced flow gives resultant relative wind.

• Front Half of Rotor System:

  • Components: Chord line, rotational relative wind, less induced flow.
  • Effect: Larger angle of attack and more lift compared to aft half.

Resulting Motion and Correction

• Lift Distribution: More lift on front half than aft half.
• Gyroscopic Precession: Phenomenon causes effects to manifest 90 degrees later in the rotor disc.
• Compensation: Use of left cyclic to counteract right roll.

Practical Example

• Takeoff Scenario:

  • Helicopter starts takeoff.
  • Experiences right roll pushing it to the right of the lane.
  • Pilot corrects back to center or continues forward.

• Approach Scenario:

  • Between 10 to 20 knots, right roll pushes to side.
  • Correction required to maintain lane.
  • Potential for vibrations due to drag variance.

Conclusion

• Transverse Flow Summary:
  • Right rolling motion between 10-20 knots.
  • Simple to compensate with left cyclic.
• Closing Remarks:
  • Thanks viewers, encourages likes, subscribes, and feedback.
  • Jacob signs off from Helicopter Lessons.