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Understanding Effective Translational Lift

Aug 30, 2024

Helicopter Lessons in 10 Minutes or Less

Topic: Effective Translational Lift (ETL)

Introduction

  • Instructor: Jacob
  • Series: Helicopter Lessons in 10 Minutes or Less
  • Focus: Effective Translational Lift
  • Pre-requisite videos to understand aerodynamic principles better:
    • Symmetry of Lift
    • Transverse Flow Effect
    • Airflow at a Hover

What is Effective Translational Lift?

  • Definition: The point where the main rotor system of a helicopter outruns the recirculation of old vortices, operating in clean, undisturbed air, thus becoming more efficient.

Progression to Effective Translational Lift

  1. Stationary Hover

    • Airflow enters rotor system vertically.
    • Presence of wingtip vortices.

  2. Transition to Forward Flight

    • Any movement or airspeed initiates translational lift.
    • Airflow starts toward the helicopter.
    • Vortices begin to move back.

  3. Achieving ETL

    • Occurs around 16 to 24 knots.
    • Rotor operates in clean air environment, outrunning vortices.
    • Efficiency increases as vortices are left behind.
    • Factors influencing this range:
      • Blade size
      • Rotor area
      • Rotor RPM

Efficiency in Forward Flight

  • Efficiency improves up to max rate of climb airspeed, where drag is minimized.
  • Upcoming video planned on total drag.

Pilot Observations During ETL

  • Blowback Effect:
    • Nose pitches up due to advancing rotor blades gaining more lift.
    • Requires forward cyclic input to compensate.

ETL vs. Transverse Flow Effect

  • Transverse Flow:

    • Occurs between 10 to 20 knots, during transition to ETL.
    • Difference in airflow from horizontal (front half) to vertical (aft half).

  • ETL:

    • Outrunning of vortices.

Power and Control Adjustments

  • Efficiency Gains:

    • Rotor system requires less power as efficiency increases.
    • Tail rotor becomes more efficient as it outruns its vortices.
    • Vertical fin aids in reducing anti-torque requirements.

  • Pedal Adjustments:

    • Less left pedal required; more right pedal needed to maintain heading.

Landing Considerations

  • Reverse adjustments when landing and slowing down below 16 to 24 knots.
  • Actions Required:
    • Increase main rotor and tail rotor thrust.
    • Adjust collective and pedals to maintain alignment during approach.

Closing Remarks

  • Encouragement to like and comment for feedback.
  • Invitation for viewer input on video improvements.
  • Note: Additional videos will cover related topics like total drag and combined effects of transverse flow and ETL.

Full transcript