Aerodynamic (multiple choice) + drawings Flashcards by Nicolai Thomsen

Cyclic stick movement:

☐ Alters the tip path plane attitude.

☐ Alters the amount of total rotor thrust.

☐ Changes the coning angle.

☐ Causes an equal blade pitch change on all blades together.

☐ Alters the tip path plane attitude.

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The rotor thrust is always:

☐ Parallel with the main rotor shaft.

☐ Perpendicular to the plane which contains the swash plate.

☐ Perpendicular to the hub plane.

☐ Perpendicular to the tip path plane.

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In level flight, as forward speed is increased, induced airflow velocity:

☐ Decreases and the component of the horizontal airflow through the disc decreases.

☐ Increases and the component of the horizontal airflow through the disc decreases.

☐ Increases and the component of the horizontal airflow through the disc increases.

☐ Decreases and the component of the horizontal airflow through the disc increases.

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What can be noticed during transition from hover to forward flight (anti-clockwise rotor)?

☐ Sudden yawing motion.

☐ Rolling motion to the retreating blade.

☐ Nose-down attitude.

☐ Significant climb without raising the collective pitch lever.

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Translational lift becomes useful:

☐ As soon as the helicopter moves from a stationary hovering.

☐ Only when the helicopter is operating in-ground-effect.

☐ Only at high all up weights.

☐ As airspeed reaches a value of approximately 20 kts.

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The coning angle is the angle:

☐ Between the plane of rotation in forward flight and the rotation in the flare.

☐ Between the longitudinal axis of the blade and the horizon.

☐ Between maximum flapping up and maximum flapping down of the blade in autorotation.

☐ Between the longitudinal axis of the blade and the tip path plane.

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Transition to forward flight:

☐ Causes a rolling motion only if the blades are rotating below normal rotor RPM speed.

☐ Causes a roll towards the advancing side.

☐ Causes a roll towards the advancing side only if the blades are rotating anti-clockwise.

☐ Causes a roll towards the retreating side.

☐ Causes a roll towards the advancing side.

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When the cyclic stick is pushed forward, a main rotor blade will reach its maximum blade pitch angle:

☐ On the retreating side.

☐ In the rearmost position.

☐ On the advancing side.

☐ In the foremost position.

☐ On the retreating side.

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If the collective pitch lever is raised during straight and level flight, the helicopter will roll to the (1) because (2):

☐ (1) Advancing blade (2) the coning angle decreases.

☐ (1) Advancing blade (2) of the dissymmetry of lift.

☐ (1) Advancing blade (2) the coning angle increases.

☐ (1) Retreating blade (2) of the dissymmetry of lift.

☐ (1) Advancing blade (2) the coning angle increases.

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A “transition” in a helicopter is:

☐ The force acting on the rotor head in forward flight.

☐ Tilting the disc as a result of cyclic control movement.

☐ A change in the flight condition from or to hovering flight.

☐ The take-off.

☐ A change in the flight condition from or to hovering flight.

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A helicopter is most likely to encounter vortex ring state under conditions of:

☐ cruising airspeed with power, rate of descent 500ft/min.

☐ a vertical or low airspeed autorotation.

☐ zero airspeed with power; rate of descent less than 200ft/min.

☐ low airspeed with power; rate of descent greater than 300 ft/min.

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In a free air hover how does Vi vary along the blade?

☐ It is less at the tip because of tip vortices.

☐ It is less at the tip because of recirculation.

☐ It is greater at the tip because of tip vortices.

☐ It is greater at the root because of the demarcation vortex.

☐ It is greater at the tip because of tip vortices.

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In a hovering helicopter, recirculated air at the main rotor blade tips will cause:

☐ Increased lift.

☐ Increase in ground effect.

☐ No effect on lift.

☐ A reduction of lift.

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The effects of recirculation are at their worst:

☐ While making a transition to forward flight.

☐ Over level ground.

☐ Over water.

☐ Close to building-type obstructions.

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In a constant speed vertical climb outside ground effect, if the effects of parasite drag on the helicopter fuselage are ignored:

☐ Blade pitch angle will be decreased.

☐ Angle of attack must be greater than the blade pitch angle.

☐ Total rotor thrust will need to be greater than aircraft weight.

☐ Total rotor thrust will equal aircraft weight.

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The “vortex ring state” which may develop under conditions of a power-on descent at low forward airspeed is:

☐ A stable condition which reduces the rate of descent.

☐ An unstable condition which may result in an uncontrolled rate of descent.

☐ A desirable condition since it causes the helicopter to flare automatically on landing.

☐ Normally controlled by increasing the collective blade pitch angle on the main rotor blades.

☐ An unstable condition which may result in an uncontrolled rate of descent.

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What is the aerodynamic result when a vertical climb is initiated by raising the collective pitch? Explain by means of the blade element theory:

☐ ↑ AoA ↑ cL ↑ FT ↓ FV ↑ Σ FV ↓ FT ↑ FW → uniform motion

☐ ↓ AoA ↓ cL ↓ FV ↑ FT ↓ FW → uniform motion

☐ ↓ AoA ↓ cL ↑ FT ↓ FV ↓ FT ↓ FT < FW → accelerated motion

☐ ↑ AoA ↑ cL↑ FL ↑ FV ↑ Σ FV ↑ FT ↑ FT > FW → accelerated motion

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The in-ground-effect on a hovering helicopter is greatest on:

☐ Sloping ground with an upslope wind.

☐ Level ground with no wind.

☐ Sloping ground with no wind.

☐ Level ground with a strong wind.

☐ Level ground with no wind.

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The in-ground-effect is caused by:

☐ Air flowing through the disc creating a divergent (spread out) duct with higher pressure beneath the rotor.

☐ Increasing the mass airflow through the rotor.

☐ High pressure beneath the rotor creating a convergent duct from the downwash.

☐ Recirculation of air through the rotor disc causing air to flow outwards at ground level.

☐ Air flowing through the disc creating a divergent (spread out) duct with higher pressure beneath the rotor.

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Rotor blade sections are designed so that the center of pressure:

☐ Is normally positioned close to the feathering axis to reduce control system loads.

☐ Can move forward rapidly to aid forward CG and reduce stress related problems at high speeds.

☐ Has a large degree of movement for stability at high and low speeds to reduce stress-related problems.

☐ Move outwards and inwards according to the rotor speed to reduce stress related problems.

☐ Is normally positioned close to the feathering axis to reduce control system loads.

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The term “washout” means:

☐ That blade pitch angle varies over the span of the blade.

☐ That the used airfoil varies in design (e.g., thickness, camber) from blade root towards blade tip.

☐ The airmass which is accelerated down through the main rotor.

☐ That the blade’s airfoil is constant over the whole length of the blade.

☐ That the used airfoil varies in design (e.g., thickness, camber) from blade root towards blade tip.

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An increase in angle of attack of a rotor blade would cause an increase in:

☐ Lift only.

☐ Induced drag and a decrease in parasite drag but no change in lift unless rotor speed is increased.

☐ Drag and lift forces.

☐ Induced drag and parasite drag but a reduction in lift.

☐ Drag and lift forces.

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On a symmetrical blade element with a positive angle of attack lift is produced by:

☐ An increase in flow velocity giving an increase in pressure on the lower surface.

☐ Airflow velocity increasing over upper surface giving decreased pressure and velocity decreasing over lower surface giving increased pressure.

☐ Airflow velocity increasing downward having been deflected by the blade pitch angle and creating an upward pressure on the blade.

☐ An increase in flow velocity on the lower surface and decrease on the upper surface.

☐ Airflow velocity increasing over upper surface giving decreased pressure and velocity decreasing over lower surface giving increased pressure.

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Rotor blades profile drag is:

☐ A force acting behind the total reaction and at right angles to the relative airflow.

☐ A component of total reaction acting at right angles perpendicular to the relative airflow.

☐ A force proportional to the size of the blade.

☐ A component of total reaction to the aerodynamic forces, acting parallel to the plane of rotation and backward at 90 degrees to total rotor thrust.

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The amount of lift produced by a given helicopter rotor blade element is dependent upon: ☐ The angle of attack of the blade, the square of the forward speed of the helicopter and the air density. ☐ Angle of attack of the blade, the square of the air velocity relative to the blade element and the air density. ☐ Pitch angle, the square of the forward speed of the helicopter and the square root of the air density. ☐ Angle of attack of the blade, the square root of the relative air velocity to the blade element and the air density.

☐ Angle of attack of the blade, the square of the air velocity relative to the blade element and the air density.

The technical term "geometric twist" can be described as: ☐ A reduction in blade angle towards the tip to reduce the chances of Retreating Blade Stall (RBS). ☐ An increase in blade angle towards the tip to delay the onset of compressibility. ☐ A reduction in blade angle towards the tip to delay the onset of compressibility. ☐ A reduction in blade angle towards the tip to give a more equal distribution of lift along the span.

☐ A reduction in blade angle towards the tip to give a more equal distribution of lift along the span.

A current requirement for the main rotor blade section is that: ☐ Pitch changes produce large changes in the position of the center of pressure to minimise control forces. ☐ The center of pressure moves rapidly forward as the angle of attack is increased to ensure correct blade flapping. ☐ Changes in angle of attack produce minimum center of pressure movement. ☐ Its induced drag characteristics are insignificant compared with profile drag.

☐ Changes in angle of attack produce minimum center of pressure movement.

The total rotor thrust is: ☐ A force acting parallel to the plane of rotation. ☐ A component of total reaction acting at right angles of the aerodynamic forces on the blades, and perpendicular to the plane of rotation. ☐ A force opposite to weight. ☐ A force acting at right angles perpendicular to the relative air flow.

☐ A component of total reaction acting at right angles of the aerodynamic forces on the blades, and perpendicular to the plane of rotation.

The resultant force from pressure envelopes around an aerofoil can be described as: ☐ Lift ☐ Rotor thrust ☐ The total reaction ☐ The vertical component of rotor thrust

☐ The total reaction

State the drag formula! ☐ FD = cD * 2 * ρ * v² * S ☐ FD = cD * ρ * v² * S ☐ FD = cD * ½ * ρ² * v * S ☐ FD = cD * ½ * ρ * v² * S

☐ FD = cD * ½ * ρ * v² * S

cL varies with: ☐ Angle of attack. ☐ Pressure. ☐ Density. ☐ Velocity.

☐ Angle of attack.

What is the advantage of a symmetrical aerofoil section as related to helicopter blade design? ☐ The centre of pressure moves little in the normal angle of attack range. ☐ It produces no lift at zero degrees angle of attack. ☐ It has good stalling characteristics. ☐ For a given angle of attack, it has a greater cL than other aerofoil sections.

☐ The centre of pressure moves little in the normal angle of attack range.

What is the load factor? ☐ Factor which refers to the extent of thrust that must be decreased to hold altitude while turning. ☐ Factor which refers to the extent of thrust that must be increased to hold altitude while turning. ☐ Factor which refers to the extent of the bank angle that must be decreased to hold while turning. ☐ Ratio of the horizontal part of thrust and the centrifugal force.

☐ Factor which refers to the extent of thrust that must be increased to hold altitude while turning.

You are in a trimmed left turn. What happens if you pull collective? (clockwise turning rotor) ☐ Turning radius increases, load-factor decreases. ☐ Turning radius increases, load-factor increases. ☐ Turning radius decreases, load-factor decreases. ☐ Turning radius decreases, load-factor increases.

☐ Turning radius decreases, load-factor increases.

The purpose of the swept back tip region in some modern rotor blade designs is to: ☐ Reduce blade tip vortices. ☐ Improve high speed performance. ☐ Reduce blade tip stresses. ☐ Reduce the amount of flapping up.

☐ Improve high speed performance.

What happens to the coning angle if rotor RPM decreases and collective pitch is constant? ☐ Nothing. ☐ It increases. ☐ It decreases. ☐ It is balanced by an increase in centrifugal force.

☐ It increases.

How does rotor downwash affect a helicopter with horizontal stabilizers (mounted at the tailboom) in a free air hover? ☐ It will pitch nose down. ☐ It will descend. ☐ It will pitch nose up. ☐ The downwash will not affect the stabiliser.

☐ It will pitch nose up.

Compared to a straight and level flight, to perform a coordinated turn (same altitude and speed) the collective blade pitch angle (1) and power (2) must be: ☐ (1) Increased (2) increased. ☐ (1) Decreased (2) increased. ☐ (1) Decreased (2) decreased. ☐ (1) Increased (2) decreased.

☐ (1) Increased (2) increased.

Which factors have an influence on the bank angle in turning flights? ☐ Weight, velocity, curve radius ☐ Velocity, curve radius, gravity ☐ Mass, velocity, curve radius ☐ Weight, velocity, gravity

☐ Velocity, curve radius, gravity

Reverse airflow is associated with: ☐ Very high forward speed only and leads to the formation of shock waves. ☐ Flight at high forward speed and originates at the root of the retreating blade. ☐ The “vortex ring state” and originates at the tip of the advancing blade. ☐ Autorotation and originates at the root of the advancing blade if rotor RPM is allowed to fall.

☐ Flight at high forward speed and originates at the root of the retreating blade.

If the collective pitch lever is lowered during straight and level flight, the helicopter will pitch (1) because (2): ☐ (1) Down (2) the coning angle decreases ☐ (1) Up (2) of the dissymmetry of lift ☐ (1) Up (2) of reverse flow at the root of the retreating blade ☐ (1) Down (2) of the dissymmetry of lift

☐ (1) Down (2) of the dissymmetry of lift

If the collective pitch lever is raised during straight and level flight, the helicopter will roll to the (1) because (2): ☐ (1) Advancing blade (2) the coning angle decreases ☐ (1) Advancing blade (2) of the dissymmetry of lift ☐ (1) Advancing blade (2) the coning angle increases ☐ (1) Retreating blade (2) of the dissymmetry of lift

☐ (1) Advancing blade (2) the coning angle increases

When the cyclic stick is pushed forward, a main rotor blade will reach its maximum blade pitch angle: ☐ On the retreating side. ☐ In the rearmost position. ☐ On the advancing side. ☐ In the foremost position.

☐ On the retreating side.

Retreating blade stall is most likely to occur at: ☐ Vortex ring. ☐ High forward speed, at high gross weight, high altitude and temperature. ☐ Low forward speed with high gross weight. ☐ High gross weight.

☐ High forward speed, at high gross weight, high altitude and temperature.

The tip path plane is: ☐ The path described by the blade tips during rotation and perpendicular to the plane of rotation. ☐ The path plane described by the blade tips during rotation and perpendicular to the axis of rotation. ☐ The plane perpendicular to the shaft axis of the main rotor. ☐ The path plane described by the disc in forward flight.

☐ The path plane described by the blade tips during rotation and perpendicular to the axis of rotation.

For a rotor which turns in an anti-clockwise direction seen from above, a sideways hover to the left with zero wind, the pilot will have the advancing blade: ☐ In front of him. ☐ On his left. ☐ On his right. ☐ Behind him.

☐ In front of him.

For a rotor which turns in a clockwise direction seen from above, in a sideways hover to the right, with zero wind, the pilot will see the retreating blade: ☐ Behind him. ☐ On his right. ☐ On his left. ☐ In front of him.

☐ Behind him.

For a rotor which turns in a clockwise direction seen from above, in a backward hover, with zero wind, the pilot will see the retreating blade: ☐ Behind him. ☐ On his right. ☐ On his left. ☐ In front of him.

☐ On his left.

How does an airfoil generate lift? ☐ Air flows across a lower surface of the airfoil because of the low pressure region lift is the action force. ☐ Air flows across a curved upper surface and is accelerated → a low pressure region is formed; ⊥ to the relative wind → lift is the reaction. ☐ Air particles are separated at the stagnation point and must meet again at the rear stagnation point → the upper particles must be faster → lift is produced. ☐ Air flows across a lower surface of an airfoil and is accelerated lift is produced because of the increased dynamic pressure.

☐ Air flows across a curved upper surface and is accelerated → a low pressure region is formed; ⊥ to the relative wind → lift is the reaction.

The angle of attack of a helicopter rotor blade is defined as the angle between the: ☐ Blade's chord line and the airflow upstream of the helicopter. ☐ Blade's chord line and the relative airflow. ☐ Bottom surface of the blade and the tip path plane. ☐ Blade's chord line and the plane of rotation.

☐ Blade's chord line and the relative airflow.

State the lift formula! ☐ FL = cL * ρ * v^2 * S ☐ FL = cL * 2 * ρ * v^2 * S ☐ FL = cL * ½ * ρ^2 * v * S ☐ FL = cL * ½ * ρ * v^2 * S

☐ FL = cL * ½ * ρ * v^2 * S

The lift coefficient of an airfoil section: ☐ Is at its maximum value at that angle of attack giving the maximum lift to drag ratio. ☐ Increases with an increase in angle of attack up to the stall. ☐ Changes with density. ☐ Changes with the velocity of the airflow, squared.

☐ Increases with an increase in angle of attack up to the stall.

What is the Magnus effect? ☐ Superposition of translational and rotational velocities of a rotating body (e.g., drum) with the result of pressure differences which cause a lift force. ☐ A vortex is created at the leading edge of an airfoil → "lifting vortex" (known as circulation) is produced which causes wake turbulences. ☐ A vortex is created at the trailing edge of an airfoil → "lifting vortex" (known as circulation) is produced because vortices always occur in pairs. ☐ Superposition of translational and rotational velocities of a helicopter rotor which gives an explanation of the generated drag.

☐ Superposition of translational and rotational velocities of a rotating body (e.g., drum) with the result of pressure differences which cause a lift force.

Which factors determine the magnitude and direction of the relative airflow in a still air hover? ☐ Induced airflow velocity and rotational velocity of the blade element. ☐ Total rotor thrust and rotor drag. ☐ Lift and rotor drag. ☐ Lift and total aerodynamic forces.

☐ Induced airflow velocity and rotational velocity of the blade element.

The blade pitch angle of a rotor blade element is: ☐ The angle between the chord line and the tip path plane. ☐ The angle between the tip path plane and the relative airflow. ☐ The angular difference between the root and tip of the blade section. ☐ The angle at which the induced flow passes over the blade section.

☐ The angle between the chord line and the tip path plane.

The chord line of an airfoil section is the line: ☐ Of points equidistant from upper and lower surfaces. ☐ Drawn between the leading and the trailing edges. ☐ Relative to the upstream airflow. ☐ The tangent at the leading edge of the camber line.

☐ Drawn between the leading and the trailing edges.

The center of pressure of an airfoil element: ☐ Depends on the height of the airfoil element. ☐ Is located in a fixed point in an asymmetric airfoil. ☐ Is the point where the total aerodynamic force is acting. ☐ Depends only on the boundary layer.

☐ Is the point where the total aerodynamic force is acting.

The centre of pressure of a symmetrical airfoil section is behind the leading edge approximately at the following % of the section chord: ☐ 0.15 ☐ 0.35 ☐ 0.1 ☐ 0.25

☐ 0.25

The force which acts at right angles to the relative airflow is: ☐ Lift ☐ Drag ☐ Total reaction ☐ Thrust

☐ Lift

The Centre of Pressure of an aerofoil section is: ☐ Where the largest component of lift is said to be produced. ☐ The point on the chord line through which the resultant of all aerodynamic forces acts. ☐ Where the resultant of all the centrifugal forces acts relative to the shape of the aerofoil. ☐ The point about which the airflow is deflected around the aerofoil.

☐ The point on the chord line through which the resultant of all aerodynamic forces acts.

The chord line of a blade section is: ☐ A line tangential to the wing surface on the leading edge. ☐ A line equidistant from the upper and lower surface of the blade. ☐ A straight line from leading to trailing edge. ☐ The line of the chord used to determine balance on some smaller helicopters.

☐ A straight line from leading to trailing edge.

The camber line of a symmetrical airfoil section is: ☐ Curved towards the upper surface. ☐ Common with the chord line. ☐ Curved towards the lower surface. ☐ A circular arc.

☐ Common with the chord line.

In the case of a symmetrical aerofoil: ☐ There is no downwash at any angle of attack. ☐ Its characteristics make it totally unsuitable for main rotor applications although it is frequently used for tail rotors. ☐ Induced drag will not be generated at any angle of attack due to the symmetrical pressure distribution. ☐ Pitching moment variations due to centre of pressure movement are small.

☐ Pitching moment variations due to centre of pressure movement are small.

Thickness/chord ratio of an aerofoil section is expressed in percentage of: ☐ Chord ☐ Wingspan ☐ Blade surface ☐ Thickness

☐ Chord

That point where airflow leaves the surface of an aerofoil is known as: ☐ The separation point ☐ The critical point ☐ The stagnation point ☐ The transition point

☐ The separation point

What sources of energy are available in case of a double engine failure? ☐ Energy of the electrical generation system. ☐ Energy of the momentum due to the rotor RPM. ☐ Potential energy because of the height, kinetic energy because of airspeed and rotor RPM. ☐ Only potential energy because of the height.

☐ Potential energy because of the height, kinetic energy because of airspeed and rotor RPM.

In a normal forward autorotation descent, if the collective lever is raised by a small amount, the rotor RPM will (1) and the rate of descent will (2): ☐ (1) Decrease (2) decrease. ☐ (1) Decrease (2) increase. ☐ (1) Increase (2) decrease. ☐ (1) Increase (2) increase.

☐ (1) Decrease (2) decrease.

What is the effect of an increasing airspeed on the region of driving blade elements during autorotation? ☐ Shifting of the driving blade elements to the advancing blade. ☐ Shifting of the driving blade elements to the retreating blade. ☐ Shifting of the driving blade elements to the front blade. ☐ Shifting of the driving blade elements to the rear blade.

☐ Shifting of the driving blade elements to the retreating blade.

During an autorotation descent the maximum gliding distance will be obtained at: ☐ The speed associated with the minimum rate of descent. ☐ A speed slightly less than that associated with the minimum rate of descent. ☐ Speed greater than that associated with the minimum rate of descent. ☐ The minimum speed that will sustain rotor RPM.

☐ Speed greater than that associated with the minimum rate of descent.

The "avoid" areas in a height/velocity diagram (deadman’s curve) define the height/velocity combinations: ☐ From which it is not possible to make a safe autorotation landing. ☐ In which it is not possible to hover out of ground effect. ☐ In which it is only possible to make a transition into forward flight. ☐ From which it is not possible to operate because of engine power limitations.

☐ From which it is not possible to make a safe autorotation landing.

A tail rotor is fitted to most helicopters to compensate for: ☐ Main rotor torque reaction only. ☐ Main rotor torque reaction when entering an autorotation. ☐ Main rotor torque reaction and give directional control (yaw control). ☐ Lateral drift when in hovering flight.

☐ Main rotor torque reaction and give directional control (yaw control).

Yawing in a helicopter is the term used to define a rotation: ☐ About the vertical axis. ☐ Which is always about the horizontal axis. ☐ About the lateral axis. ☐ About the longitudinal axis.

☐ About the vertical axis.

A helicopter having an anti-clockwise rotating main rotor (when seen from above), with power on, will have a natural tendency to drift: ☐ To the right. ☐ In neither direction because transverse forces are in balance. ☐ To the right if the tail rotor is on the left of the aircraft and to the left if it is on the right. ☐ To the left.

☐ To the right.

Tail rotor drift is corrected by: ☐ Tilting the main rotor disc in the opposite direction to the drift. ☐ Fitting delta three hinges to the tail rotor. ☐ Fitting the tail rotor as a "tractor type" as opposed to a "pusher type." ☐ Designing the tail rotor to be level with the main rotor.

☐ Tilting the main rotor disc in the opposite direction to the drift.

In hovering, for a single rotor helicopter whose main rotor turns clockwise from above, the thrust of the main rotor will be mainly vertical but with a slight orientation towards the: ☐ Front or back of the helicopter according to longitudinal balance. ☐ Right or the left according to side balance. ☐ Right. ☐ Left.

☐ Right.

With a tail rotor positioned lower than the main rotor, a helicopter at the hover will: ☐ Fly left or right side low depending on which side of the helicopter the tail rotor is positioned. ☐ Fly right side low if main rotor rotates anti-clockwise viewed from above. ☐ Maintain a level attitude. ☐ Fly left side low if main rotor rotates anti-clockwise viewed from above.

☐ Fly left side low if main rotor rotates anti-clockwise viewed from above.

During flight, an increase in main rotor torque will require: ☐ An increase in tail rotor pitch. ☐ A reduction in tail rotor pitch. ☐ A reduction in tail rotor RPM. ☐ No change in tail rotor pitch.

☐ An increase in tail rotor pitch.

An anti-torque rotor is necessary on: ☐ A dual-rotor helicopter. ☐ An autogyro. ☐ A synchrocopter. ☐ A single rotor helicopter.

☐ A single rotor helicopter.

Draw: AR, FWD, ADV, DRIVEN