GATE 2026 AE – Question 25

Flight Mechanics & Space Dynamics · Aerodynamic forces and moments, angle of attack and sideslip, high-lift devices, roll, pitch and yaw controls · 1 mark · Multiple select

Shown below are qualitative illustrations of the lift curve for an airfoil when two different control surfaces are in their respective retracted and deployed configurations. Which of the following is/are TRUE?

Two plots of $c_l$ against $\alpha$. In Figure P the deployed curve is the retracted curve shifted up and to the left (lift at zero angle of attack, same slope, higher maximum). In Figure Q the deployed curve follows the retracted curve and then continues to a higher angle of attack and a higher maximum.

Figure P is for a flap
Figure P is for a slat
Figure Q is for a slat
Figure Q is for a flap

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Correct answer: (A) Figure P is for a flap; (C) Figure Q is for a slat

Explanation

A flap increases the camber, so the whole lift curve moves up (more lift at a given angle and a more negative zero-lift angle), as in Figure P. A slat does not change the lift at low angles. It delays stall, so the curve is extended to a higher angle and a higher maximum lift, as in Figure Q.