Helicopter Lessons: Forces Acting on an Airfoil

Introduction

• Presenter: Jakob
• Format: Short video
• Objective: Label and explain the forces acting on an airfoil

Airfoil Basics

• Shapes: Symmetric and asymmetric shapes, each with different benefits
• Chord Line:
  • Defined from leading edge to trailing edge of the airfoil
  • Baseline for measuring forces related to the blade

Forces on Airfoil

• Rotational Relative Wind:
  • Created by rotor turning around the mast
  • Perpendicular to axis of rotation when aircraft is level
  • Also known as the "tip path plane"
• Induced Flow/Downwash:
  • Caused by increases in pitch angle
  • Results in downward air flow through the rotor system

Resultant Relative Wind

• Resultant Relative Wind:
  • Combination of rotational relative wind and induced flow
  • Basis for finding angle of attack

Angles Involved

• Angle of Attack (AoA):
  • Between chord line and resultant relative wind
  • Determines lift produced
  • Not directly controlled but influenced by other factors
• Pitch Angle:
  • Angle between chord line and rotational relative wind
• Angle of Incidence:
  • Mechanical angle controlled with collective and cyclic inputs
  • Adjusts pitch angle
  • Often confused with angle of attack

Aerodynamic Forces

• Lift:
  • Acts perpendicular to resultant relative wind
• Drag:
  • Opposite to resultant wind
• Total Aerodynamic Force:
  • Combination of lift and drag vectors
  • Also known as the resultant force
  • Generally directed up and aft of the airfoil

Practical Implications

• Changes in induced flow without changing angle of incidence affect angle of attack:
  • Increased induced flow without angle of incidence change reduces AoA, reducing lift
  • Critical in maneuvers like transitioning to hover
• Importance of understanding diagrams for better piloting:
  • Helps understand changes in lift during various flight maneuvers
  • Differences in airflow in ground effect and out of ground effect

Conclusion

• Understanding the forces and angles lays the groundwork for effective helicopter flight

• Additional Resources: Refer to Jakob’s other videos for insights on ETL and hover dynamics.
• Call to Action: Like, subscribe, and comment on the video.

Note: This video covers the foundational concepts of airfoil dynamics in a helicopter, useful for pilots to understand the physics behind lift generation and control during flight.