Aerodynamics Flashcards
How does an airfoil generate lift?
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 relative airflow.
State the lift formula!
FL = CL ● 1/2 ● p ● v² ● S
The lift coefficient of an airfoil section:
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.
The blade pitch angle of a rotor blade element is:
The angle between the chord line and the tip path plane.
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.
The chord line of an airfoil section is the line:
Drawn between the leading edge and the trailing edges.
The center of pressure of an airfoil element:
Is the point where 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:
0,25
Explanation:
Means 25 %
The force which acts at right angles to the relative airflow is.
Lift.
The Centre of Pressure of an aerofoil section is:
The point on the chord line through which the resultant of all aerodynamic forces acts.
The chord line of a blade section is:
A straight line from leading to trailing edge.
The camber line of a symmetrical airfoil section is:
Common with the chord line.
In the case of a symmetrical aerofoil:
Pitching moment variations due to centre of pressure movement are small.
Thickness/chord ratio of an aerofoil section is expressed in percentage of:
Chord.
The resultant force from pressure envelopes around an aerofoil can be described as:
The total reaction.
That point where airflow leaves the surface of an aerofoil is known as:
The separation point.
A current requirement for the main rotor blade section is that:
Changes in angle of attack produce minimum centre of pressure movement.
The total rotor thrust is:
A component of total reaction acting at right angles of the aerodynamic forces on the blade, and perpendicular to the plane of rotation.
State the drag formula!
FD = CD ● 1/2 ● p ● v² ● S
CL varies with:
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.
An increase in angle of attack of a rotor blade would cause an increase in:
Drag and lift forces.
