Question 257-1 : Ground resonance is due to ? [ Explanation maintenance ]

Question 1

Question 257-1 : Ground resonance is due to ? [ Explanation maintenance ]

A coupling between the rotor imbalance frequency and the natural frequency of the undercarriage.

Answer

A condition whereby a rolling motion with wheels in contact with the ground cannot be restrained by cyclic control.

Answer

Is kept approximately constant because movement of the blade about its flapping axis reduces the angle of attack.

Answer

.think back to basic vector diagrams of the main rotor. which way does total rotor thrust act answer = up...ok a tail rotor is exactly the same, just on its side. when we enter auto, we are removing all the torque from the main rotor. in an anti clockwise rotor, with power applied, this normally wants to spin us round to the right viewed inside the cockpit. that is what would happen if the tail rotor failed. remove tq and the fuselage is effectively now going to move in the opposite direction to the main rotor newtons laws equal and opposite blah it is not anywhere near as significant though, as there is no tq to really drive it, it is just trying to follow the main rotor, but there will be an amount of left yaw. the tail assembly design, will assist with directional stability in this instance, but we will still need a little extra help from the tail rotor...aircraft nose wants to go left or anti clockwise viewed from above, and tail wants to go right. we just need to counter this. remember here we have created a moment, and we need to balance it. as i said before, think about your vector diagram, and which direction does the thrust need to act up or in this case, the rotor is on its side, so to the left, in order to pull the tail back and push the nose back to the right...therefore we need a little thrust to the left to do this. the key is the fact that the aircraft wants to follow the main rotor once we have removed all the torque.

Answer

Common with the chord line.

Answer

The chord line and the relative air flow.

Answer

Centre of pressure.

Answer

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

exemple 461 Airflow velocity increasing over upper surface giving decreased pressure and velocity decreasing over lower surface giving increased pressure.

Answer

.transition point the point on the surface of an aerofoil where laminar airflow becomes turbulent. the point moves forward as airspeed increases...the separation point point where airflow leaves the surface of an aerofoil.

Question 2

Question 257-2 : The induced flow component of airflow through the rotor disc ?

Decreases with forward flight so influencing the angle of attack.

Question 3

Question 257-3 : Induced power ?

Is a maximum at the hover in still air.

Question 4

Question 257-4 : The maximum range speed for piston engine helicopters in zero wind conditions is found by ?

Drawing a line tangential to the power required curve from the point of origin of the graph.

Question 5

Question 257-5 : With reference to rotor design, forward speed is limited by ?

Retreating blade stall and relative airspeed.

Question 6

Question 257-6 : A helicopter is most likely to encounter vortex ring under conditions of ?

Low airspeed with power, rate of descent greater than 300 ft/min.

Question 7

Question 257-7 : In autorotation when aft cyclic is applied the effect will be ?

A decrease in airspeed and rate of descent.

Question 8

Question 257-8 : A stable static stability is ?

The tendency of an aircraft to return to its original condition of flight after a disturbance.

Question 9

Question 257-9 : With a tail rotor positioned below the line of the main rotor, a helicopter at the hover will ?

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

Question 10

Question 257-10 : Ground effect is caused by ?

A decreased induced flow velocity.

Question 11

Question 257-11 : In a still air hover induced flow velocity is affected by ?

Disc loading and density.

Question 12

Question 257-12 : What are the conditions necessary for ground resonance in addition to having a helicopter in contact with the ground ?

An out of balance force at the rotor head.

Question 13

Question 257-13 : Dynamic roll over is ?

Question 14

Question 257-14 : The minimum value of the power required curve determines ?

The t.a.s. for maximum rate of climb speed.

Question 15

Question 257-15 : In a level balanced turn ?

Retreating blade stall will occur at a lower i.a.s. than in straight and level flight.

Question 16

Question 257-16 : With forward flight, thrust on the advancing side of a tail rotor system ?

Question 17

Question 257-17 : On a main rotor, if the flapping hinge is offset ?

It improves cyclic control response.

Question 18

Question 257-18 : The centre of pressure is the point on an aerofoil section ?

Through which the resultant aerodynamic force acts.

Question 19

Question 257-19 : In autorotation the tail rotor thrust on a helicopter with anti clockwise main rotor rotation as seen from above is ?

Question 20

Question 257-20 : Induced power ?

Is a maximum at the hover without wind.

Question 21

Question 257-21 : In the flare, the resultant aerodynamic forces on the blades ?

Moves forward, towards the axis of rotation.

Question 22

Question 257-22 : The camber line of a biconvex symmetrical section is ?

Question 23

Question 257-23 : The angle of attack of an aerofoil is the angle between ?

Question 24

Question 257-24 : A reduction in blade section pitch angle towards the tip is termed ?

Washout.

Question 25

Question 257-25 : The force, which acts at right angles to the relative airflow, is ?

Lift.

Question 26

Question 257-26 : The point at which the resultant of lift forces acts is ?

Question 27

Question 257-27 : On a symmetrical blade element with a positive angle of attack lift is produced by ?

Question 28

Question 257-28 : Bernoulli's' theorem indicates that ?

The sum of pressure energy and dynamic energy is constant.

Question 29

Question 257-29 : The point where a laminar boundary layer becomes turbulent is called ?

Question 30

Question 257-30 : The expression, 'in a streamlined flow of fluid, the sum of all energies is a constant,' derives from ?

Bernoulli's theorem.

Question 31

Question 257-31 : Cl varies with ?

Angle of attack.

Question 32

Question 257-32 : Within the normal operating angles of attack the centre of pressure of a biconvex symmetrical aerofoil section ?

Moves very little.

Question 33

Question 257-33 : That point where airflow leaves the surface of an aerofoil is known as ?

The separation point.

Question 34

Question 257-34 : For a rotor which turns in an anti clockwise direction seen from above, with a sideways flight to the left, with zero wind, the pilot will have the advancing blade ?

In front of him

Question 35

Question 257-35 : The power requirement of the tail rotor is greatest during ?

A hover turn oge in the same direction as the main rotor

Question 36

Question 257-36 : 'a line connecting the leading and trailing edge midway between the upper and lower surface of a aerofoil'. this definition is applicable for ?

The camber line.

Question 37

Question 257-37 : What is the effect on induced drag of an increase in aspect ratio ?

Induced drag decreases, because the effect of tip vortices decreases.

Question 38

Question 257-38 : What is the stagnation point ?

The point where the velocity of the relative airflow is reduced to zero.

Question 39

Question 257-39 : When an aerofoil section has accelerated from subsonic to supersonic speeds, its aerodynamic centre will have ?

Shifted from approximately 25% to about 50% of the chord.

Question 40

Question 257-40 : Which boundary layer, when considering its velocity profile perpendicular to the flow, has the greatest change in velocity close to the surface ?

Question 257-1 : Ground resonance is due to ? [ Explanation maintenance ]

A coupling between the rotor imbalance frequency and the natural frequency of the undercarriage.

Question 257-2 : The induced flow component of airflow through the rotor disc ?

Decreases with forward flight so influencing the angle of attack.

Question 257-3 : Induced power ?

Is a maximum at the hover in still air.

Question 257-4 : The maximum range speed for piston engine helicopters in zero wind conditions is found by ?

Drawing a line tangential to the power required curve from the point of origin of the graph.

Question 257-5 : With reference to rotor design, forward speed is limited by ?

Retreating blade stall and relative airspeed.

Question 257-6 : A helicopter is most likely to encounter vortex ring under conditions of ?

Low airspeed with power, rate of descent greater than 300 ft/min.

Question 257-7 : In autorotation when aft cyclic is applied the effect will be ?

A decrease in airspeed and rate of descent.

Question 257-8 : A stable static stability is ?

The tendency of an aircraft to return to its original condition of flight after a disturbance.

Question 257-9 : With a tail rotor positioned below the line of the main rotor, a helicopter at the hover will ?

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

Question 257-10 : Ground effect is caused by ?

A decreased induced flow velocity.

Question 257-11 : In a still air hover induced flow velocity is affected by ?

Disc loading and density.

Question 257-12 : What are the conditions necessary for ground resonance in addition to having a helicopter in contact with the ground ?

An out of balance force at the rotor head.

Question 257-13 : Dynamic roll over is ?

A condition whereby a rolling motion with wheels in contact with the ground cannot be restrained by cyclic control.

Question 257-14 : The minimum value of the power required curve determines ?

The t.a.s. for maximum rate of climb speed.

Question 257-15 : In a level balanced turn ?

Retreating blade stall will occur at a lower i.a.s. than in straight and level flight.

Question 257-16 : With forward flight, thrust on the advancing side of a tail rotor system ?

Is kept approximately constant because movement of the blade about its flapping axis reduces the angle of attack.

Question 257-17 : On a main rotor, if the flapping hinge is offset ?

It improves cyclic control response.

Question 257-18 : The centre of pressure is the point on an aerofoil section ?

Through which the resultant aerodynamic force acts.

Question 257-19 : In autorotation the tail rotor thrust on a helicopter with anti clockwise main rotor rotation as seen from above is ?

To the left.

Question 257-20 : Induced power ?

Is a maximum at the hover without wind.

Question 257-21 : In the flare, the resultant aerodynamic forces on the blades ?

Moves forward, towards the axis of rotation.

Question 257-22 : The camber line of a biconvex symmetrical section is ?

Common with the chord line.

Question 257-23 : The angle of attack of an aerofoil is the angle between ?

The chord line and the relative air flow.

Question 257-24 : A reduction in blade section pitch angle towards the tip is termed ?

Washout.

Question 257-25 : The force, which acts at right angles to the relative airflow, is ?

Lift.

Question 257-26 : The point at which the resultant of lift forces acts is ?

Centre of pressure.

Question 257-27 : On a symmetrical blade element with a positive angle of attack lift is produced by ?

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

Question 257-28 : Bernoulli's' theorem indicates that ?

The sum of pressure energy and dynamic energy is constant.

Question 257-29 : The point where a laminar boundary layer becomes turbulent is called ?

The transition point.

Question 257-30 : The expression, 'in a streamlined flow of fluid, the sum of all energies is a constant,' derives from ?

Bernoulli's theorem.

Question 257-31 : Cl varies with ?

Angle of attack.

Question 257-32 : Within the normal operating angles of attack the centre of pressure of a biconvex symmetrical aerofoil section ?

Moves very little.

Question 257-33 : That point where airflow leaves the surface of an aerofoil is known as ?

The separation point.

Question 257-34 : For a rotor which turns in an anti clockwise direction seen from above, with a sideways flight to the left, with zero wind, the pilot will have the advancing blade ?

In front of him

Question 257-35 : The power requirement of the tail rotor is greatest during ?

A hover turn oge in the same direction as the main rotor

Question 257-36 : 'a line connecting the leading and trailing edge midway between the upper and lower surface of a aerofoil'. this definition is applicable for ?

The camber line.

Question 257-37 : What is the effect on induced drag of an increase in aspect ratio ?

Induced drag decreases, because the effect of tip vortices decreases.

Question 257-38 : What is the stagnation point ?

The point where the velocity of the relative airflow is reduced to zero.

Question 257-39 : When an aerofoil section has accelerated from subsonic to supersonic speeds, its aerodynamic centre will have ?

Shifted from approximately 25% to about 50% of the chord.

Question 257-40 : Which boundary layer, when considering its velocity profile perpendicular to the flow, has the greatest change in velocity close to the surface ?

Turbulent boundary layer.