Helicopter Aerodynamics

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Which force opposes lift in a helicopter?

Weight

What is the purpose of the antitorque rotor in a helicopter?

To overcome torque

What is the function of the swash plate assembly in a helicopter?

To transmit cyclic pitch control inputs to the rotor head

How does a rigid rotor system absorb operating loads?

In bending

Which force opposes helicopter movement?

Drag

What is the major cause of drag at reduced airspeeds?

Induced drag

What is the relationship between thrust and torque in a helicopter?

Thrust and torque are directly proportional

What is the purpose of the tail rotor in a helicopter?

To counteract torque-induced turning tendency

Which axis does a helicopter yaw around?

Vertical axis

What is the purpose of the anti-torque system in a helicopter?

To control the yawing movement around the vertical axis

What is autorotation in a helicopter?

The state of flight where the main rotor system is being turned by the action of the relative wind passing up through the disc, rather than engine power

What causes the retreating blade stall in a helicopter?

A high angle of attack and slow relative wind speed

Which one of the following statements about the span of a rotor blade is correct?

The span of a rotor blade is the distance from the blade root to the blade tip.

What does twisting a rotor blade cause?

Twisting a rotor blade causes it to produce a more even amount of lift along its span.

What is the pitch angle?

The angle between the blade chord and a reference plane determined by the rotor hub.

What is the angle of attack?

The angle between the blade chord and the relative wind.

Which of the following is true about ground effect in helicopter flight?

Ground effect increases lift and reduces induced drag

What is the maximum forward speed of a helicopter limited by?

Blade flapping and slow relative wind on the retreating blade

What is the term for the difference in lift between the advancing and retreating blades of a helicopter rotor system?

Dissymmetry of lift

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?

Pendular action

Which component of a helicopter is typically considered its central component?

The airframe

Which type of main rotor system allows the blades to move up and down, back and forth, and around the spanwise axis?

Fully articulated

What is the movement called when the blades of a fully articulated rotor system rotate independently around the vertical hinge?

Dragging

What type of rotor system uses two blades rigidly attached to the main rotor hub and allows the blades to flap together?

Semi-rigid

During autorotation, airflow enters the rotor disc from below as the helicopter ______.

descends

What is the pitch angle of a rotor blade?

The angle between the blade chord line and a reference plane

A helicopter yaws around the ______ axis, pitches around the lateral axis, and rotates around the longitudinal axis.

vertical

What is the angle of attack of a rotor blade?

The angle between the rotor's chord and the relative wind

Which of the following is NOT a type of anti-torque system used in helicopters?

Dual-rotor system

How is hovering at a constant altitude achieved in a helicopter?

By generating lift and thrust equal to the weight of the helicopter

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.

reduced

What is disc loading in the context of helicopters?

The ratio of weight to the total main rotor disc area

Movement about the ______ axis is referred to as yaw.

vertical

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.

sideward

What is autorotation in the context of helicopters?

The stage of flight in which the main rotor system is turned by the relative wind

What is the function of the swash plate assembly in a helicopter?

To transmit cyclic pitch control inputs to the rotor head

Which force opposes lift in a helicopter?

Drag

What is the purpose of the antitorque system in a helicopter?

To overcome torque and prevent the helicopter from turning in the opposite direction of main rotor rotation

Which of the following is a characteristic of a fully articulated rotor system in a helicopter?

The blades can move up and down, back and forth, and around the spanwise axis

What is the purpose of dampers in a fully articulated rotor system?

To prevent excessive movement around the drag hinges

Which of the following is a characteristic of a semirigid rotor system in a helicopter?

The blades are rigidly attached to the main rotor hub

Which one of the following statements about the solidity ratio is correct?

The solidity ratio is the ratio of the total rotor blade area to the total rotor disk area.

What is the purpose of the tip-path plane in a helicopter?

The tip-path plane is the imaginary circular plane outlined by the rotor blades tips as they make a cycle of rotation.

What is the relationship between the angle of attack and lift in a helicopter?

Increasing the angle of attack increases lift, up to a point.

Which force opposes helicopter movement?

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.

Weight

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.

Torque

Which of the following is true about ground effect in helicopter flight?

Ground effect occurs when the helicopter is hovering near the ground, causing an increase in lift and a decrease in induced drag.

What causes the retreating blade stall in a helicopter?

The relative wind speed acting on the retreating blade is reduced by the helicopter's forward airspeed.

What is translational lift in helicopter flight?

Translational lift is the additional performance gained from the increase in rotor system efficiency due to accelerated airflow through it.

Which of the following is true about the Coriolis effect in helicopter rotor blades?

The Coriolis effect causes the rotor blade to accelerate when it flaps down

What is the purpose of a freewheeling unit in a helicopter?

To allow the main rotor system to continue turning even if the engine is not running

What causes the nose of a helicopter to pitch down in forward flight?

Applying forward pressure to the cyclic

What is the function of the antitorque system in a helicopter?

To control the yawing movement around the vertical axis

True or false: The cyclic pitch control in a helicopter is primarily responsible for controlling the pitch attitude of the helicopter.

True

What is the purpose of the swash plate assembly in a helicopter?

To tilt the main rotor disc and control the pitch attitude

True or false: The retreating blade stall in a helicopter is caused by a high angle of attack and slow relative wind speed.

True

True or false: The combined upward flapping of the advancing blade and downward flapping of the retreating blade equalizes lift in a helicopter.

True

True or false: A freewheeling unit in a helicopter allows the main rotor to continue turning even if the engine is not running.

True

True or false: The Coriolis effect causes the acceleration or deceleration of the rotor blade in a helicopter.

True

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.

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