Helicopter Lessons - Transient Torque Spikes

Introduction

• Presenter: Jacob
• Topic: Transient torque spikes in helicopters
• Request: Audience feedback and topic suggestions are encouraged

Definition

• Transient Torque Spikes: Aerodynamic phenomena occurring with lateral cyclic inputs (left or right)
  • Different from manual-labeled torque transients which limit time at certain torque values

Causes

• Occur due to aerodynamic forces on the rotor disc
• Result from engine control units maintaining constant rotor RPM
  • ECUs like FADAC, fuel governing systems, etc.

Mechanism

• Left Turn (Lateral Cyclic): Increase in torque

  • More lift on right side of rotor disc
  • Gyroscopic precession: Input 90 degrees prior
  • Increase in lift and drag on the aft half of the rotor disc
  • ECU senses decrease in rotor RPM and surges fuel to maintain constant RPM

• Right Turn (Lateral Cyclic): Decrease in torque

  • More lift on left side of rotor disc
  • Decrease in pitch over tail, less induced flow
  • Increase in pitch over front half

Analogy

• Compared to a runner maintaining speed with added or removed weight
  • Left turn (adding load): Increase heart rate and torque
  • Right turn (reducing load): Decrease heart rate and torque

Factors Influencing Torque Spikes

1. Rate of Movement: Faster cyclic inputs lead to higher fluctuations
2. Magnitude of Movement: Greater displacement leads to bigger spikes
3. Power Applied: Higher initial power setting increases spike magnitude
4. Airspeed: Faster speeds increase induced flow and torque fluctuations
5. Weight: Heavier load causes more pronounced rotor coning

Mitigation

• String Theory: A conceptual tool
  • Imagine a string between collective and cyclic
  • Keep string tight by adjusting collective with cyclic inputs

Conclusion

• Transient torque spikes arise from lateral cyclic inputs
• Important to consider for avoiding over-torque in aggressive maneuvers
• Reminder: Like and subscribe for more content

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The lecture concludes by emphasizing the importance of managing transient torque spikes to avoid mechanical issues during helicopter maneuvers.