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The pitch-up stall behaviour of a swept wing aircraft at subsonic speed is due to the centre of pressure moving:
  • A
    Forward when the wing tips stall first, causing the nose to pitch up.
  • B
    Backward when the leading edge of the wing roots stall first, causing the nose to pitch down.
  • C
    Backward when the wing tips stall first causing the nose to pitch down.
  • D

    Forward when the trailing edge of the wing roots stall first, causing the nose to pitch up.

Refer to figure.
A swept wing is fitted to allow a higher maximum speed, but it has an increased tendency to stall first near the tips. Loss of lift at the tips moves the CP forward, giving a nose-up pitching moment.

Effective lift production is concentrated inboard and the maximum downwash now impacts the tail plane, adding to the nose-up pitching moment.

As soon as a swept wing begins to stall, both forward CP movement and increased downwash at the tail plane cause the aircraft nose to rise rapidly, further increasing the angle of attack. This is a very undesirable and unacceptable response at the stall and can result in complete loss of control in pitch from which it may be very difficult, or even impossible, to recover. This phenomenon is known as pitch-up and is a very dangerous characteristic of many high speed, swept wing aircraft.

The tendency of a swept-back wing to tip stall is due to the induced spanwise flow of the boundary layer from root to tip.

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