Helicopter- Theory of flight

Question 1

Primary aerofoils on a helicopter are collectively called?

Answer 1

the main rotor and they provide the lift and thrust force during flight

Question 2

The span of the blade is?

Answer 2

The distance from the root of the blade to the tip of the blade, measured along the centreline

Question 3

The chord is?

Answer 3

an imaginary line drawn from the leading edge to the trailing edge. This line is called the chord of the blade

Question 4

Aerofoils used for helicopters are usually called?

Answer 4

symmetrical aerofoils as its has the same shape above and below the chord line

Question 5

Curvature of an aerofoil is known has?

Answer 5

Camber

Question 6

The relative wind of the helicopter is

Answer 6

the flow of air with respects to the flight path of the blade

Question 7

Pitch angle is the angle between

Answer 7

the horizontal plane of rotation of the rotor disc and the chord line of the aerofoil.

Question 8

The angle of attack is the angle between the?

Answer 8

chord line of the aerofoil and the relative wind. When pitch angle is increased AOA is increased, when pitch angle is decreased AOA is decreased.

Question 9

Lift is?

Answer 9

The force that overcomes gravity and for an aerofoil it acts perpendicular to the relative wind.

Question 10

Drag is the force?

Answer 10

which tends to resist the aerofoils passage through the air. Its always parallel to the relative wind and perpendicular to lift. Drag varies as the square of velocity.

Question 11

The centre of pressure is?

Answer 11

the point of an aerofoil which all lift is said to act. The CofP will generally move during flight as conditions such as the AOA change

Question 12

Stall is

Answer 12

the undesirable condition which is reached when the rotor blade reaches the parameters of safe operation. It occurs when the aerofoil separates from the wing surface causing turbulent air to develop with an accompany loss of lift.

Question 13

Stall occurs when the?

Answer 13

AOA is too high for the relative airflow.The air does not have sufficient pressure to follow the contour of the aerofoil camber and breaks away causing reverse flow across the blade and an associated loss of lift.

Question 14

In order to avoid a stall condition?

Answer 14

more power must be produced to overcome the increase in drag and thus to maintain the blade velocity within safe parameter.

Question 15

Lift varies with?

Answer 15

density of air, which in turn is affected by localised factors such as humidity, temperature and altitude.E.g. on a relatively hot day the air is less dense and so the rotors will obtain less lift for a given AOA and therefore more AOA and power is required.

Question 16

Blades are somewhat flexible and will?

Answer 16

droop when at rest, due to their weight and span

Question 17

When the rotor is turning, droop is overcome by?

Answer 17

centrifugal force, which will straighten the blade. This centrifugal force is dependent upon blade weight and velocity.

Question 18

When collective pitch is applied to the rotor, an element of?

Answer 18

lift is produced which will result in the blade seeking a new position that will be the resultant of centrifugal force and lift

Question 19

The severity of coning depends on?

Answer 19

the weight of the helicopter. A helicopter with light load will have less coning than a heavily loaded one.

Question 20

The travel path of the blade tips will form the outer perimeter of a circular plane formed by the rotor blades.

Answer 20

This perimeter ring is called the tip path plane

Question 21

The satis relationship of the rotor blades to each other in flight is known as

Answer 21

Track. If relationship is incorrect is known as being out of track. Such a condition will result in vibration to the rotor sys

Question 22

The rotor produces a lift force and the thrust will give?

Answer 22

directional movement

Question 23

If a heli is hovering or vertically ascending lift and thrust are?

Answer 23

given in the same direction. In order to obtain forward, backwards or sideways directional flight, the disc must be tilted in the desired direction of movement.So lift and thrust will be perpendicular to maintain flight and move directionally.

Question 24

Gyroscopic precession occurs when?

Answer 24

you apply a force in the plane of rotation, the external force is transferred to the rotating mass and shifted 90degrees in the direction of the spin.

Question 25

Newtons third law states that?

Answer 25

for every action their is and equal and opposite reaction.