Aerodynamics

Question 1

How does an airfoil generate lift?

Answer 1

Air flows across a curved upper surface and is accelerated

–> a low pressure region is formed; ⊥ to the relative wind

–> lift is the reaction

Question 2

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

State the lift formula!

Answer 3

FL = CL ● 1/2 ● p ● v² ● S

Question 4

The lift coefficient of an airfoil section:

Answer 4

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

Question 5

What is the magnus effect?

Answer 5

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

Question 6

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

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

The chord line of an airfoil section is the line:

Answer 8

Drawn between the leading edge and the trailing edges.

Question 9

The center of pressure of an airfoil element:

Answer 9

Is the point where total aerodynamic force is acting.

Question 10

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

Explanation:
Means 25 %

Question 11

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

Answer 11

Lift.

Question 12

The Centre of Pressure of an aerofoil section is:

Answer 12

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

Question 13

The chord line of a blade section is:

Answer 13

A straight line from leading to trailing edge.

Question 14

The camber line of a symmetrical airfoil section is:

Answer 14

Common with the chord line.

Question 15

In the case of a symmetrical aerofoil:

Answer 15

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

Question 16

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

Answer 16

Chord.

Question 17

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

Answer 17

The total reaction.

Question 18

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

Answer 18

The separation point.

Question 19

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

The total rotor thrust is:

Answer 20

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

Question 21

State the drag formula!

Answer 21

FD = CD ● 1/2 ● p ● v² ● S

Question 22

CL varies with:

Answer 22

Angle of attack.

Question 23

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

Answer 23

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

Question 24

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

Answer 24

Drag and lift forces.

Question 25

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

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

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 ti the blade element and the air density.

Question 28

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

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

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

Don’t drink water while studying… Why?

Answer 31

Because chemistry says that concentration decreases while adding water.