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At stalling speed, the stall warning vane on the leading edge of small aeroplanes moves:

  • A

    Down due to movement of the stagnation point.

  • B

    Up due to movement of the stagnation point.

  • C

    Down due to movement of the centre of pressure.

  • D

    Up due to movement of the centre of pressure.

Refer to figure.
In aerodynamics, the stagnation point is the point in a flow field where the local velocity of the fluid (in our case the atmosphere) is zero.
This point is located on the leading edge of the wing.
Air above the stagnation point will move upwards and air below it will move downwards if looked at from the side.

If we increase the angle of attack, the stagnation point will move down, causing more air to move upwards over the upper side of the wing.
At a certain angle of attack, this air will move the stall warning upwards, letting off an audible warning horn in the cockpit.

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