Standard Book, Technical General
Subsonic Airflow: DGCA Technical General questions
Subsonic airflow questions start from the aerofoil's own terms: chord line, mean camber line, thickness, angle of attack and centre of pressure. Lift and drag questions use these terms throughout.
The 20 questions are mostly definitions and multiple statement items on aerofoil geometry, pressure distribution and pitching moment. Exam sessions have asked 4 of these aerofoil questions.
Angle of attack lies between the chord line and the relative airflow; angle of incidence lies between the chord line and the longitudinal axis. The mean camber line runs midway between the surfaces, while the chord line runs straight from leading edge to trailing edge. On a cambered aerofoil the centre of pressure moves forward as angle of attack increases, up to the stall.
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Question 1 of 5
Which of the following statements about airflow are true? 1 Relative airflow, free stream flow, relative wind and aircraft flight path are parallel. 2 Flight path, relative airflow, relative wind and free stream flow are parallel, but the flight path is opposite in direction. 3 The pressure, temperature and relative velocity of the free stream flow are unaffected by the presence of the aircraft. 4 The relative wind is produced by the aircraft moving through the air. 5 The direction of flight is parallel with and opposite to the relative airflow.
Question 2 of 5
With reference to aerofoil section terminology, which statements are true? 1 The chord line joins the centre of curvature of the leading edge to the centre of the trailing edge, equidistant from both surfaces. 2 The angle of incidence is the angle between the chord line and the horizontal datum of the aircraft. 3 The angle between the chord line and the relative airflow is called the angle of attack. 4 The thickness/chord ratio is the maximum thickness as a percentage of the chord, with max thickness location measured aft of the leading edge.
Question 3 of 5
When considering the effect of angle of attack on the pitching moment, which statements are correct? 1 At normal angles of attack the pitching moment is nose-up. 2 The pitching moment about the aerodynamic centre (AC) is constant at normal angles of attack. 3 The AC is located approximately at the 25% chord point. 4 The moment about the AC is a product of the distance between AC and CP, and the magnitude of lift.
Question 4 of 5
Why does increasing speed also increase lift?
Question 5 of 5
Considering an aerofoil at constant dynamic pressure, which statement is correct?
15 more questions in this chapter
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