Lesson 3 Principles of Flight Cont. Flashcards
What are the four forces of flight during hover?
Lift and thrust vectors are pointed up, while weight and drag are pointed down.
What is coning in helicopter flight?
Coning is the tips of the rotor blades bending slightly upwards and is a normal condition.
What causes pendular action in single rotor helicopters?
Pendular action is caused by over-controlling the aircraft.
What does the Coriolis effect state?
The value of angular momentum of a rotating body does not change unless an external force is applied.
How does gyroscopic precession affect helicopter control?
The effect of a force acted upon a gyroscope is felt 90 degrees later.
What is translating tendency in helicopters?
Translating tendency is when the helicopter drifts in the direction of the tail rotor thrust.
What is ground effect?
Ground effect is the increased efficiency of the rotor disk caused by interference of the airflow when near the ground.
What influences ground effect?
- Type of surface (e.g., flat, sloped, water, grass)
- Recirculation of downwash
What happens when a helicopter is out of ground effect (OGE)?
More power is required to hover OGE than IGE due to increased vortices and drag.
What is translational lift?
Improved rotor efficiency resulting from directional flight, greatly improved with airspeed.
What is the transverse flow effect?
Around 20 knots, induced flow drops in the forward disk area and increases in the aft section.
What is effective translational lift (ETL)?
ETL occurs at about 16-24 knots, where rotor blades become more efficient as they work in undisturbed air.
What causes translational thrust?
Translational thrust occurs when the tail rotor becomes more aerodynamically efficient during the transition to forward flight.
What is dissymmetry of lift?
The variation of lift produced by the advancing and retreating sides of the rotor blades in forward flight.
How does a helicopter compensate for dissymmetry of lift?
The advancing side flaps up to reduce lift, while the retreating side flaps down to increase lift.
What is retreating blade stall?
When the retreating blade reaches an angle and speed that causes it to stall due to exceeding the critical angle of attack.
What is Loss of Tail Rotor Effectiveness (LTE)?
An un-commanded, rapid yaw towards the advancing blade that does not subside of its own accord.
What are some reasons for Loss of Tail Rotor Effectiveness (LTE)?
- Main rotor disc interference
- Tail rotor vortex ring state
- Weather cock stability
- High altitude
What is Vortex Ring State?
A condition in which a helicopter begins an uncontrolled descent into its own downwash
What is the traditional VRS recovery?
Lower collective, apply forward cyclic to increase airspeed and fly out of vortex
What is the Vouchard Recovery Technique?
Apply cyclic and pedal in the direction of tail rotor flow to move laterally out of downwash
What 3 conditions must be met to induce VRS?
Descent rate in excess of 300 feet per minute, airspeed below effective translational lift, power applied (will not occur in autorotation)
