Helicopter Lessons: Airflow at Hover

Introduction

• Focus: Airflow at a hover in helicopters.
• Conditions: Stationary hover with no wind.
• Future: Will combine effects in flight examples later.

Types of Airflow at Hover

• In Ground Effect (IGE): Increase in lift when the helicopter is within one rotor diameter of the surface.
• Out of Ground Effect (OGE): Helicopter is above one rotor diameter from the surface.

Ground Effect

• Definition: Increase in lift due to proximity to the ground.
• Example: Rotor diameter = 50 feet. In IGE: hover within 50 feet.

In Ground Effect (IGE)

• Airflow Characteristics:
  • Airflow comes vertically through the rotor disc.
  • As it nears the ground, it's pushed outwards.
  • Wingtip vortices form but are pushed out by ground effect.
  • Induced flow is interrupted by ground, reducing lift interference.

Out of Ground Effect (OGE)

• Airflow Characteristics:
  • Airflow comes straight down through the rotor disc uninterrupted.
  • Larger wingtip vortices due to lack of ground interference.
  • Higher velocity of induced flow reduces lift.

Lift Characteristics

• In Ground Effect:

  • Induced flow is less due to ground interference.
  • Angle of attack is maintained with less pitch.

• Out of Ground Effect:

  • Greater induced flow, requiring increased blade pitch to maintain lift.
  • Angle of attack decreases unless pitch is adjusted.

Angle of Incidence vs. Angle of Attack

• Angle of Incidence: Controlled by the collective, relates to blade pitch.
• Angle of Attack: Combination of blade pitch and induced flow.

Additional Factors

• Ground Obstacles: Can affect airflow and lift distribution.
• Surface Type: Grass, water, etc., can alter airflow characteristics.

Conclusion

• Summary of IGE and OGE effects on hover performance.
• Invitation to comment and ask questions.

[Applause] [Music]