Aerodynamics COPY Flashcards
1. 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 lilft formula!
FL = cL • ½ • ρ • 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 and the trailing edges.
- The center of pressure of an airfoil element:
is the point where the 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:
25% (0,25)
- 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 al 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 varioations 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 blades, and perpendicular to the plane of rotation.
- State the drag formula!
FD = cD • ½ • ρ • v2 • S
- cL varies with:
angle of attack.
- What is the advantage 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.