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Slat or flap asymmetry occurring after either extension or retraction, may have an effect on controllability since:
  • A
    slat asymmetry causes a yawing moment, whereas flap asymmetry causes a large rolling moment.
  • B
    slat and flap asymmetry both cause a large rolling moment.
  • C
    slat asymmetry causes a large rolling moment, whereas flap asymmetry causes a large yawing moment.
  • D
    slat and flap asymmetry both cause a large yawing moment.

Refer to figure.

Slats are aerodynamic surfaces that extend from the leading edge of the wing during slow flight. Their main purpose us to increase the leading edge camber, which delays separation and in so increases the stall angle and corresponding CLMAX.
Their main contribution is to increase the maximum lift coefficient, but not increase the lift coefficient at a certein AoA. The negative influence of extending slats is a slight increase in drag. Therefore we can say that at a certain AoA, slats will not increase lift, but they will increase drag slightly, therefore the only resultant moment will be a yaw.

Flaps are aerodynamic surfaces that extended from the trailing edge of the wing. Their main purpose is to increase the camber of the wing to increase the coefficient of lift for a certain AoA. This can be seen on the figure. Their main contribution to the wing is extra lift. Whilst drag is also a side effect, lift it more significant.

Therefore the correct answer is: “slat asymmetry causes a yawing moment, whereas flap asymmetry causes a large rolling moment.”

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