Helicopter Lessons: Auto Rotations Expansion

Introduction

• Presenter: Jacob
• Focus: Address common questions from previous auto rotations video and expand on auto rotation considerations.
• Prerequisite: View the original auto rotations video first.

Why Doesn't the Rotor Reverse in Auto Rotation?

• Powered Flight:
  • Rotor works against drag with engine power overcoming it to create lift.
  • Use of a basic airfoil diagram to illustrate forces:
    • Lift (above)
    • Thrust (front)
    • Weight (below)
    • Drag (behind)
• Unpowered Flight:
  • Thrust stops if the engine stops or powers down.
  • Without reducing pitch, drag slows down rotor RPM.
• Solution:
  • Lower collective to flatten pitch, allowing air flow to continue turning the rotor.
  • Neutral pitch maintains rotor RPM.
  • Positive pitch slows or reverses rotor RPM.
  • Negative pitch (if possible) accelerates rotor RPM.
• Key Point: Proper auto rotation execution prevents rotor reversal.

Effects of Turning in Auto Rotation

• General Rule: Anything that makes you fall faster increases rotor RPM.
• Factors Influencing Rotor RPM:
  • Weight: Heavier helicopter falls faster, increasing rotor RPM.
  • Density Altitude: Thin air (e.g., high altitudes) reduces air friction, increasing fall speed and rotor RPM.
  • Trim: Out of trim leads to less aerodynamic efficiency, increasing fall speed and rotor RPM.
• Turns:
  • Turning shifts lift/glide vector, affecting fall speed.
  • Left turn increases rotor RPM slightly.
  • Right turn increases rotor RPM rapidly.
  • Based on rotor efficiencies from transient torque spikes.
• Cyclic Adjustments:
  • Forward cyclic slows rotor, increases descent rate.
  • Aft cyclic increases rotor RPM, decreases descent rate.

Auto Rotate with Rotor Within Limits vs. High Rotor RPM

• Autorotative Regions:
  • Stall Region: Not much activity.
  • Driving Region: Harnesses airflow to maintain rotor RPM.
  • Driven Region: Affects glide.
• High Rotor RPM:
  • Expands driving region, contracts driven region.
  • Leads to higher descent rates.
• Impact:
  • Higher rotor RPM means higher descent rates, more energy to dissipate in flare.
  • Important for judging touchdown point.
  • Survivability: 50% chance of surviving a 30-knot impact.
  • Descent rate conversion: Feet per minute x 100 = knots of descent.

Tail Rotor in Auto Rotation

• Linkage: Tail rotor mechanically linked to main rotor.
• Impact:
  • If main rotor RPM is high/low, tail rotor follows suit.
  • No change in tail rotor authority as long as rotor RPM is managed.

Conclusion

• Encouragement to leave comments and questions.
• Potential for a third video based on feedback.
• Closing by Jacob, promoting safe flying.