Which of these statements about induced drag are correct or incorrect?
I. Induced drag increases as angle of attack decreases.
II. At constant load factor, induced drag increases with decreasing aeroplane mass.
Induced drag is created as a byproduct of lift. The pressure differential between the top and bottom of the wing creates a upwash around the tip of the wing that turns into a downwash behind the wing. This is known as a vortex, which creates a rearward force known as induced drag.
This question is asking for the effect of:
- Angle of attack: The induced drag is proportional to the angle of attack. Therefore, induced drag increases as the angle of attack increases, and, induced drag decreases and the angle of attack decreases.
- Changing mass: Induced drag is proportional to the mass. Therefore, induced drag increases with increasing aeroplane mass, and, induced drag decreases with decreasing aeroplane mass.
This is because, as the aircraft get heavier, the lift that the wings will have to produce increases. To achieve that, the coefficient of lift will have to increase, meaning a higher AoA, which creates stronger vortices. (and vice versa)
Summary:
- Higher AR = Lower induced drag
- Higher AoA = higher induced drag
- Higher weight = higher AoA = higher induced drag
- Higher speed = lower AoA = lower induced drag
- Winglets = lower induced drag.
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