Aerodynamics

Question 1

Lift and drag

How does an airfoil generate lift?

Answer 1

Air flows across a curved upper surface and is accelerated –> a low pressure region is formed perpendicular to the relative wind –> lift is the reaction

Question 2

Lift and drag

The angle of attack of a helicopter rotor blade is defined as the angle between the:

Answer 2

Blade’s chord line and the relative airflow

Question 3

Lift and drag

State the lift formula

Answer 3

FL = CL * 1/2 * p * v^2 * S

Question 4

Lift and drag

The lift coefficient of an airfoil section increases with what?

Answer 4

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

Question 5

Lift and drag

What is the Magnus effect?

Answer 5

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

Question 6

Lift and drag

The blade pitch angle of a rotor blade element is

Answer 6

The angle between the chord line and the tip path plane

Question 7

Lift and drag

Which factors determine the magnitude and direction of the relative airflow in a still air hover?

Answer 7

Induced airflow velocity and rotational velocity of the blade element

Question 8

Lift and drag

The chord line of an airfoil section is the line drawn between:

Answer 8

The leading and the trailing edges

Question 9

Lift and drag

The center of pressure of an airfoil element

Answer 9

Is the point where the total aerodynamic force is acting

Question 10

Lift and drag

The centre of pressure of a symmetrical airfoil section is behind the leading edge approximately at the following % of the section chord?

Answer 10

0,25 = 25%

Question 11

Lift and drag

The force which acts at right angles to the relative airflow is

Answer 11

Lift

Question 12

Lift and drag

The centre of pressure of an airfoil section is

Answer 12

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

Question 13

Lift and drag

The chord line of a blade section is

Answer 13

A straight line from leading to trailing edge

Question 14

Lift and drag

The camber line of a symmetrical airfoil section is

Answer 14

Common with the chord line

Question 15

Lift and drag

In the case of a symmetrical aerofoil

Answer 15

Pitching moment variations due to centre of pressure movement are small

Question 16

Lift and drag

Thickness/chord ratio of an aerofoil section is expressed in percentage of

Answer 16

Chord

Question 17

Lift and drag

The resultant force from pressure envelopes around an aerofoil can be described as

Answer 17

The total reaction

Question 18

Lift and drag

That point where airflow leaves the surface of an aerofoil is known as

Answer 18

The seperation point

Question 19

Lift and drag

A current requirement for the main rotor blade section is that

Answer 19

Changes in angle of attack produce minimum centre of pressure movement

Question 20

Lift and drag

The total rotor thrust is

Answer 20

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

Question 21

Lift and drag

State the drag formula

Answer 21

FD = CD * 1/2 * p * v^2 * S

Question 22

Lift and drag

CL varies with

Answer 22

Angle of attack

Question 23

Lift and drag

What is the advantages a symmetrical aerofoil section as related to helicopter blade design?

Answer 23

The centre of pressure moves little in the normal range of attack range

Question 24

Lift and drag

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

Answer 24

Drag and lift forces

Question 25

Lift and drag

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

Answer 25

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

Question 26

Lift and drag

Rotor blades profile drag is

Answer 26

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

Question 27

Lift and drag

The amount of lift produced by a given helicopter rotor blade element is dependent upon

Answer 27

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

Question 28

Lift and drag

The technical term “geometric twist” can be described as

Answer 28

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

Question 29

Lift and drag

Rotor blade sections are designed so that the center of pressure

Answer 29

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

Question 30

Lift and drag

The term “washout” means

Answer 30

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

Question 31

Lift and drag