Subsonic Airflow

Question 1

Aerofoil

Answer 1

A shape capable of producing lift with relatively high efficiency

Question 2

Chord Line

Answer 2

A straight line joining the centres of curvature of the leading and trailing edges of an aerofoil

Question 3

Chord

Answer 3

The distance between the leading and trailing edges measured along the chord line

Question 4

Angle of Incidence

Answer 4

The angle between the wing root chord line and the longitudinal axis of the aircraft. This angle is fixed for the wing

Question 5

Mean Line or Camber Line

Answer 5

A line joining the leading and trailing edges of an aerofoil, equidistant from the upper and lower surfaces

Question 6

Maximum Camber

Answer 6

The maximum distance of the mean line from the chord line. Max camber is expressed as a % of the chord, with its location as a percentage of the chord aft of the leading
edge.

• camber line lies above the chord line Positive
• camber line is below the chord line Negative
• A symmetrical aerofoil has no camber

Question 7

Thickness/Chord Ratio

Answer 7

The maximum thickness or depth of an aerofoil section expressed as a percentage of the chord.

Thickness / chord line length
determines the shape of a wing and his AERODYNAMAL PROPERTIES

Question 8

Extrados

Answer 8

Upper wing surface

Question 9

Intrados

Answer 9

Lower wing surface

Question 10

Positive Camber

Answer 10

The camber line is located ABOVE the chord line

Question 11

Negative Camber

Answer 11

The camber line is located BELOW the chord line

Question 12

Symmetric

Answer 12

no Camber

Question 13

LEADING EDGE RADIUS

Answer 13

The radius of the front edge

of the wing (the first meets the relative airflow)

Question 14

RELATIVE WIND

Answer 14

Speed with which the air flows over the wing
• V relative wind is = to the V of the airplane BUT OPPOSITE DIRECTIONS!
• Relative wind is the consequence of a wing moving through air, but when studying the wing, it looks as
if the air is moving over the wing

Question 15

Pressure on wind

Answer 15

When a wing is moved through the air, lowered/

reduced static pressure is created ABOVE the wing

Question 16

NEGATIVE AOA Positive Camber

Answer 16

equal decrease in Ps above and below the wing
• The resulting pressure differential is ZERO
• This means that NO AERODYNAMICAL FORCE is
developed

Question 17

AOA ZERO Positive Camber

Answer 17

there is a higher decrease in static pressure above the wing, compared to below the wing
• The resulting pressure differential is ZERO
• This means that there is a SMALL UPWARD AERODYNAMICAL FORCE being developed

Question 18

AOA Positive Camber (from 0 to 12-

16° for most types

Answer 18

there is a significant decrease in static pressure above the wing and an increase in static pressure below the wing
• The resulting pressure differential is POSITIVE (Lift)
• INCREASING UPWARD AERODYNAMICAL FORCE

Question 19

Critical AOA from 12 - 16 + Camber

Answer 19

there is a sudden/significant drop in the decrease in static pressure above the wing
• There is an increase in the Ps below the
wing, but the resulting pressure differential is
NEGATIVE
• sudden/violent reduction in the AERODYNAMICAL FORCE being developed (STALL)

Question 20

Lift generation

Answer 20

Upwing 2/3

downwing 1/3