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Questions and Answers
In forward flight, what is the relationship between the airflow and the helicopter's flight path?
The velocity of airflow decreases from the right side to the left side of the helicopter during forward flight.
True
What happens to the lift of the advancing blade as its relative wind speed increases?
The advancing blade gains lift and begins to flap up.
The ________ occurs at the 3 o'clock position where airspeed is maximized.
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Match the following components with their respective effects on airflow:
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What causes the dissymmetry of lift in a helicopter?
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The retreating blade of a helicopter experiences an increase in relative wind speed as the helicopter moves forward.
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What is the approximate blade tip speed of the helicopter mentioned?
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In a single main rotor helicopter, the lateral movement during hovering flight is known as __________.
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Match the following helicopter terms with their definitions:
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Study Notes
Airflow in Forward Flight
- Airflow in forward flight is different than in hover
- Airflow in forward flight flows opposite the aircraft's flight path
- The velocity of the airflow is equal to the helicopter's forward speed
- The velocity across the blade depends on its position in the plane of rotation, rotational velocity, and airspeed
Advancing Blade
- Advancing blade has higher relative wind speed
- Advancing blade gains lift and flaps up
- The upflap creates a downward flow of air
- Downward air flow has the same effect as increasing the induced flow velocity
- Increased induced flow velocity decreases the angle of attack
Retreating Blade
- Retreating blade has lower relative wind speed
- Retreating blade loses lift and flaps down
- The downflap creates an upward flow of air
- The upward flow has the same effect as decreasing induced flow velocity
- Decreased induced flow velocity increases the angle of attack
Dissymmetry of Lift
- Caused by the differential (unequal) lift between advancing and retreating blades
- Results from different wind flow velocity across each half of the rotor disk
- Could cause the helicopter to be uncontrollable if not for other factors
- Blade tip speed is approximately 400 knots
- A helicopter traveling at 100 knots will have a relative speed of 500 knots at the advancing side and 300 knots at the retreating side
Translating Tendency
- Refers to the tendency of a helicopter to move laterally in the direction of tail rotor thrust
- Also known as Drift
Pendular Action
- Refers to the swinging motion of the fuselage (side to side or back and forth)
- Caused by changes in lift or thrust
Coning
- The rotation of the rotor disk creates centrifugal force
- Centrifugal force pulls the blades outward from the hub
- Faster rotation creates greater centrifugal force
- Slower rotation creates smaller centrifugal force
Coriolis Effect
- Also known as the law of conservation of angular momentum
- States that angular momentum remains constant unless an external force is applied
- Essentially, a rotating body will continue rotating at the same speed unless a force changes it's speed
Gyroscopic Precession
- Spinning main rotor of a helicopter acts like a gyroscope
- Precession is the resultant action or deflection of a spinning object when a force is applied
- Precession occurs approximately 90° in the direction of rotation from the point of force
Autorotation
- When the main rotor disk is turned by the action of air moving up through the rotor, not engine power
- A freewheeling unit allows the main rotor to continue turning even if the engine is not running
- Allows for a safe landing in the event of an engine failure
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Description
Test your understanding of airflow dynamics in helicopter flight. This quiz covers key concepts such as the differences between advancing and retreating blades, as well as the phenomenon of dissymmetry of lift. Explore how these factors affect helicopter performance during forward flight.
