Subsonic Airflow

Question 1

Angle of Incidence

Answer 1

Angle of Incidence: The angle between the wing root chord line and the longitudinal axis of the aircraft. (This angle is fixed for the wing, but may be variable for the tailplane).

Question 2

Mean Line or Camber Line

Answer 2

Mean Line or Camber Line: A line joining the leading and trailing edges of an aerofoil, equidistant from the upper and lower surfaces.

Question 3

Maximum Camber

Answer 3

Maximum Camber: The maximum distance of the mean line from the chord line. Maximum camber is expressed as a percentage of the chord, with its location as a percentages of the chord
aft of the leading edge.

Question 4

A symmetrical aerofoil has ____________ because the _______________________.

Answer 4

A symmetrical aerofoil has no camber because the chord line and camber line are coincidental.

Question 5

Relative Air Flow (Relative Wind or Free Stream Flow): Relative Air Flow has three qualities.
If air flow does not possess all three of these qualities, _______________________.

Answer 5

Relative Air Flow (Relative Wind or Free Stream Flow): Relative Air Flow has three qualities.
- DIRECTION - air parallel to, and in the opposite direction to the flight path of the aircraft, in fact the path of the CG; the direction in which the aircraft is pointing is irrelevant.
- CONDITION - air close to, but unaffected by the presence of the aircraft; its pressure, temperature and velocity are not affected by the passage of the aircraft through it.
- MAGNITUDE - The magnitude of the Relative Air Flow is the TAS.
If air flow does not possess all three of these qualities, it is referred to as EFFECTIVE AIRFLOW.

Question 6

Total Reaction, Centre of Pressure (CP) and Lift

Answer 6

Total Reaction: The resultant of all the aerodynamic forces acting on the aerofoil section.
Centre of Pressure (CP): The point on the chord line, through which Lift is considered to act.
Lift: The aerodynamic force which acts at 90° to the Relative Air Flow.

Question 7

Drag, Angle of Attack , EFFECTIVE ANGLE OF ATTACK.

Answer 7

->Drag: The aerodynamic force which acts parallel to and in the same direction as the Relative Air Flow (or opposite to the aircraft flight path).
- Angle of Attack (α or alpha) (can also be referred to as Aerodynamic Incidence) The angle between the chord line and the Relative Air Flow.
- The angle between the chord line and the effective airflow is referred to as the EFFECTIVE ANGLE OF ATTACK.