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Which force opposes lift in a helicopter?
Which force opposes lift in a helicopter?
What is the purpose of the antitorque rotor in a helicopter?
What is the purpose of the antitorque rotor in a helicopter?
What is the function of the swash plate assembly in a helicopter?
What is the function of the swash plate assembly in a helicopter?
How does a rigid rotor system absorb operating loads?
How does a rigid rotor system absorb operating loads?
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Which force opposes helicopter movement?
Which force opposes helicopter movement?
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What is the major cause of drag at reduced airspeeds?
What is the major cause of drag at reduced airspeeds?
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What is the relationship between thrust and torque in a helicopter?
What is the relationship between thrust and torque in a helicopter?
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What is the purpose of the tail rotor in a helicopter?
What is the purpose of the tail rotor in a helicopter?
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Which axis does a helicopter yaw around?
Which axis does a helicopter yaw around?
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What is the purpose of the anti-torque system in a helicopter?
What is the purpose of the anti-torque system in a helicopter?
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What is autorotation in a helicopter?
What is autorotation in a helicopter?
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What causes the retreating blade stall in a helicopter?
What causes the retreating blade stall in a helicopter?
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Which one of the following statements about the span of a rotor blade is correct?
Which one of the following statements about the span of a rotor blade is correct?
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What does twisting a rotor blade cause?
What does twisting a rotor blade cause?
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What is the pitch angle?
What is the pitch angle?
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What is the angle of attack?
What is the angle of attack?
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Which of the following is true about ground effect in helicopter flight?
Which of the following is true about ground effect in helicopter flight?
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What is the maximum forward speed of a helicopter limited by?
What is the maximum forward speed of a helicopter limited by?
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What is the term for the difference in lift between the advancing and retreating blades of a helicopter rotor system?
What is the term for the difference in lift between the advancing and retreating blades of a helicopter rotor system?
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What is the term for the oscillating tendency of a helicopter's main body when supported by the main rotor system at a single point?
What is the term for the oscillating tendency of a helicopter's main body when supported by the main rotor system at a single point?
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Which component of a helicopter is typically considered its central component?
Which component of a helicopter is typically considered its central component?
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Which type of main rotor system allows the blades to move up and down, back and forth, and around the spanwise axis?
Which type of main rotor system allows the blades to move up and down, back and forth, and around the spanwise axis?
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What is the movement called when the blades of a fully articulated rotor system rotate independently around the vertical hinge?
What is the movement called when the blades of a fully articulated rotor system rotate independently around the vertical hinge?
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What type of rotor system uses two blades rigidly attached to the main rotor hub and allows the blades to flap together?
What type of rotor system uses two blades rigidly attached to the main rotor hub and allows the blades to flap together?
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During autorotation, airflow enters the rotor disc from below as the helicopter ______.
During autorotation, airflow enters the rotor disc from below as the helicopter ______.
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What is the pitch angle of a rotor blade?
What is the pitch angle of a rotor blade?
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A helicopter yaws around the ______ axis, pitches around the lateral axis, and rotates around the longitudinal axis.
A helicopter yaws around the ______ axis, pitches around the lateral axis, and rotates around the longitudinal axis.
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What is the angle of attack of a rotor blade?
What is the angle of attack of a rotor blade?
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Which of the following is NOT a type of anti-torque system used in helicopters?
Which of the following is NOT a type of anti-torque system used in helicopters?
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How is hovering at a constant altitude achieved in a helicopter?
How is hovering at a constant altitude achieved in a helicopter?
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To successfully change the downward flow of air to an upward flow during autorotation, the pitch angle of the main rotor blades must be ______ by lowering the collective pitch.
To successfully change the downward flow of air to an upward flow during autorotation, the pitch angle of the main rotor blades must be ______ by lowering the collective pitch.
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What is disc loading in the context of helicopters?
What is disc loading in the context of helicopters?
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Movement about the ______ axis is referred to as yaw.
Movement about the ______ axis is referred to as yaw.
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In forward flight, moving the cyclic towards the left or right, as desired, tilts the rotor disc ______ and rolls the helicopter about the longitudinal axis.
In forward flight, moving the cyclic towards the left or right, as desired, tilts the rotor disc ______ and rolls the helicopter about the longitudinal axis.
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What is autorotation in the context of helicopters?
What is autorotation in the context of helicopters?
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What is the function of the swash plate assembly in a helicopter?
What is the function of the swash plate assembly in a helicopter?
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Which force opposes lift in a helicopter?
Which force opposes lift in a helicopter?
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What is the purpose of the antitorque system in a helicopter?
What is the purpose of the antitorque system in a helicopter?
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Which of the following is a characteristic of a fully articulated rotor system in a helicopter?
Which of the following is a characteristic of a fully articulated rotor system in a helicopter?
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What is the purpose of dampers in a fully articulated rotor system?
What is the purpose of dampers in a fully articulated rotor system?
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Which of the following is a characteristic of a semirigid rotor system in a helicopter?
Which of the following is a characteristic of a semirigid rotor system in a helicopter?
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Which one of the following statements about the solidity ratio is correct?
Which one of the following statements about the solidity ratio is correct?
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What is the purpose of the tip-path plane in a helicopter?
What is the purpose of the tip-path plane in a helicopter?
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What is the relationship between the angle of attack and lift in a helicopter?
What is the relationship between the angle of attack and lift in a helicopter?
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Which force opposes helicopter movement?
Which force opposes helicopter movement?
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During hovering flight, the variable forces are directed to make the helicopter preform as needed. While hovering, the amount of main rotor thrust is changed to maintain the desired hover altitude. This is done by changing the angle of attack of the main rotor blades and by varying power, as needed. In this case, thrust acts in the same vertical direction as lift. To maintain a hover at a constant altitude, enough lift and thrust must be generated to equal the weight of the helicopter and the drag produced by the rotor blades. The weight that must be supported is the total weight of the helicopter and its occupants. If the amount of thrust is greater than the actual weight, the helicopter gains altitude; if thrust is less than weight; the helicopter loses altitude. The drag of a hovering helicopter is mainly induced drag incurred while the blades are producing lift. There is, however, some parasite drag on the blades as they rotate through the air. Throughout the rest of this discussion, the term “drag” will include both induced and parasite drag.
During hovering flight, the variable forces are directed to make the helicopter preform as needed. While hovering, the amount of main rotor thrust is changed to maintain the desired hover altitude. This is done by changing the angle of attack of the main rotor blades and by varying power, as needed. In this case, thrust acts in the same vertical direction as lift. To maintain a hover at a constant altitude, enough lift and thrust must be generated to equal the weight of the helicopter and the drag produced by the rotor blades. The weight that must be supported is the total weight of the helicopter and its occupants. If the amount of thrust is greater than the actual weight, the helicopter gains altitude; if thrust is less than weight; the helicopter loses altitude. The drag of a hovering helicopter is mainly induced drag incurred while the blades are producing lift. There is, however, some parasite drag on the blades as they rotate through the air. Throughout the rest of this discussion, the term “drag” will include both induced and parasite drag.
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The amount of thrust produced by the tail rotor is varied in relation to the amount of torque produced by the engine. As the engine supplies more power, the tail rotor must produce more thrust. The tail rotor is designed to produce thrust in a direction opposite torque. The thrust produced by the tail rotor is sufficient to move the helicopter laterally. This is normally counteracted in the design of the helicopter by slightly tilting the rotor mast in the opposite direction of tail rotor thrust.
The amount of thrust produced by the tail rotor is varied in relation to the amount of torque produced by the engine. As the engine supplies more power, the tail rotor must produce more thrust. The tail rotor is designed to produce thrust in a direction opposite torque. The thrust produced by the tail rotor is sufficient to move the helicopter laterally. This is normally counteracted in the design of the helicopter by slightly tilting the rotor mast in the opposite direction of tail rotor thrust.
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Which of the following is true about ground effect in helicopter flight?
Which of the following is true about ground effect in helicopter flight?
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What causes the retreating blade stall in a helicopter?
What causes the retreating blade stall in a helicopter?
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What is translational lift in helicopter flight?
What is translational lift in helicopter flight?
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Which of the following is true about the Coriolis effect in helicopter rotor blades?
Which of the following is true about the Coriolis effect in helicopter rotor blades?
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What is the purpose of a freewheeling unit in a helicopter?
What is the purpose of a freewheeling unit in a helicopter?
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What causes the nose of a helicopter to pitch down in forward flight?
What causes the nose of a helicopter to pitch down in forward flight?
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What is the function of the antitorque system in a helicopter?
What is the function of the antitorque system in a helicopter?
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True or false: The cyclic pitch control in a helicopter is primarily responsible for controlling the pitch attitude of the helicopter.
True or false: The cyclic pitch control in a helicopter is primarily responsible for controlling the pitch attitude of the helicopter.
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What is the purpose of the swash plate assembly in a helicopter?
What is the purpose of the swash plate assembly in a helicopter?
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True or false: The retreating blade stall in a helicopter is caused by a high angle of attack and slow relative wind speed.
True or false: The retreating blade stall in a helicopter is caused by a high angle of attack and slow relative wind speed.
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True or false: The combined upward flapping of the advancing blade and downward flapping of the retreating blade equalizes lift in a helicopter.
True or false: The combined upward flapping of the advancing blade and downward flapping of the retreating blade equalizes lift in a helicopter.
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True or false: A freewheeling unit in a helicopter allows the main rotor to continue turning even if the engine is not running.
True or false: A freewheeling unit in a helicopter allows the main rotor to continue turning even if the engine is not running.
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True or false: The Coriolis effect causes the acceleration or deceleration of the rotor blade in a helicopter.
True or false: The Coriolis effect causes the acceleration or deceleration of the rotor blade in a helicopter.
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Study Notes
Helicopter Dynamics and Components
- Lift in a helicopter is opposed by weight and drag.
- The antitorque rotor counteracts the torque produced by the main rotor, maintaining stability.
- The swash plate assembly translates pilot inputs into the pitch angle of the rotor blades, allowing for directional control.
- A rigid rotor system absorbs loads through its structural integrity without independent flapping motion.
- Drag, which opposes helicopter movement, is predominantly induced drag caused by lift generation.
- Major drag at reduced airspeeds is largely due to increased induced drag.
- Thrust in a helicopter is related to torque: as power increases, torque increases, necessitating greater thrust from the tail rotor.
- The tail rotor provides thrust to counteract torque and maintain directional control.
- Yawing occurs around the vertical axis, allowing for left or right turning movements.
- The anti-torque system's purpose is to maintain rotor speed and control yaw by counteracting torque effects.
Flight Mechanisms
- Autorotation is a state of controlled descent allowing the blades to rotate freely without engine power, relying on airflow for lift.
- Retreating blade stall occurs when the relative wind speed decreases too much, leading to loss of lift on one side of the rotor.
- Rotor blade span affects overall lift and performance; longer blades can produce more lift.
- Twisting a rotor blade adjusts its pitch angle along the blade, affecting lift and drag.
- The pitch angle is the angle between the rotor blade and the plane of rotation.
- The angle of attack is the angle between the chord line of the rotor blade and the oncoming airflow.
Performance Factors
- Ground effect enhances lift and reduces drag when a helicopter hovers close to the ground.
- Maximum forward speed is limited by rotor efficiency and the onset of retreating blade stall.
- Lift difference between advancing and retreating blades is known as dissymmetry of lift.
- Oscillations in the helicopter’s body caused by rotor movement are referred to as oscillatory response.
Rotor Systems
- The main rotor is typically the helicopter's central component and vital for flight.
- Fully articulated rotor systems allow for independent movement of rotor blades, providing flexibility and stability.
- The function of dampers in fully articulated systems is to reduce vibrations and oscillations.
- A semi-rigid rotor system allows for limited flapping but maintains a connection between blades.
Operational Controls
- Yawing indicated by movement about the vertical axis; pitching involves tilting around the lateral axis, while rolling concerns the longitudinal axis.
- Maintaining altitude during hovering involves balancing lift, weight, and drag.
- In hovering, variable forces like lift and thrust must equal the helicopter's weight for stable flight.
- The thrust produced by the tail rotor must adjust to match the engine's torque output for stable maneuvers.
Aircraft Stability and Control
- Collective pitch changes the angle of attack across all rotor blades simultaneously, altering lift.
- Translational lift occurs when a helicopter gains increased performance as it transitions from hover to forward flight due to improved airspeed.
- The Coriolis effect changes rotor blade speed depending on the blade's position, influencing flight performance.
Advanced Concepts
- The freewheeling unit allows the rotor to continue spinning when the engine fails, aiding in autorotation.
- A downward pitch condition in forward flight results from the aerodynamic forces acting on the rotor blades.
- The cyclic pitch control primarily adjusts the pitch attitude, enabling altitude changes during flight.
- Observing the relationship between advancing and retreating blade motion is crucial for safe and effective helicopter operation.
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Description
Test your knowledge on rotor blade stalls and the Coriolis effect with this quiz. Learn about the causes and symptoms of retreating blade stall and gyroscopic precession. Discover how the movement of rotor blades affects their center of mass in relation to the axis. Challenge yourself and enhance your understanding of helicopter aerodynamics.
