sub sonic Air flow

#15. Which of the following statements is true:

• ARelative airflow, free stream flow, relative wind and aircraft flightpath are parallel.
• BAircraft, flightpath, relative airflow, relative wind and free stream flow are parallel, but the aircraft flightpath is opposite in direction.
• CThe pressure, temperature and relative velocity of the free stream flow are unaffected by the presence of the aircraft.
• DThe relative wind is produced by the aircraft moving through the air.

#20. Ice contamination of the leading portion of the aerofoil has which of the following consequences:

• AThe profile of the leading portion of the surface can be changed, preventing normal acceleration of the airflow and substantially reducing the magnitude of the lift force.
• BForm (pressure) drag will be increased because of the increased frontal area of the aerofoil section.
• CLoss of lift will have a greater effect than an increase in form (pressure) drag.
• DAt 'normal' angles of attack lift can be lost entirely if enough ice accumulates.

#1. With reference to aerofoil section terminology, which of the following statements is true:

• AThe chord line is a line joining the centre of curvature of the leading edge to the centre of the trailing edge, equidistant from the top and bottom surface of the aerofoil.
• BThe angle of incidence is the angle between the chord line and the horizontal datum of the aircraft.
• CThe angle between the chord line and the relative airflow is called the aerodynamic incidence or angle of attack.
• DThe thickness/chord ratio is the maximum thickness of the aerofoil as a percentage of the chord; the location of maximum thickness is measured as a percentage of the chord aft of the leading edge.