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Which of the following are means to reduce induced drag?
  • A
    Increasing the wing thickness, camber, and span.
  • B
    Decreasing the taper ratio, increasing the root chord and sweep angle.
  • C
    Increasing the aspect ratio and wing twist, adding winglets.
  • D
    Decreasing the wingspan, increasing the approach speed and take-off weight.

Whenever a wing produces lift, concentrated vortices form at the wing tips. The vortices are strongest at the wing tips and become progressively weaker toward the centerline of the aircraft.

The vortices induce downwash to the airflow behind the wing, causing the lift vector to tilt rearward. The horizontal component of lift opposes the forward flight of the aircraft and is known as induced drag.

The larger the vortex, the greater the induced downwash, and the greater the induced drag.

It is advantageous to reduce induced drag to a minimum, and this is achieved using the following design features to minimize the formation of wing tip vortices:

Tapering the wing in planform toward the tip reduces the amount of air flowing from the lower surface to the upper surface, thereby reducing the size of the wing tip vortex.

Washout means constructing the wing with a small amount of twist from root to tip, so that the inboard wing section is at a higher angle of incidence, and hence a greater angle of attack, compared to the wing tip. This ensures that the inner part of the wing generates most of the lift, thus minimizing the leakage of airflow around the wing tips. This reduces the size of the wing tip vortex and reduces the total amount of induced drag.

Wing tip modifications reduce the leakage of airflow around the wing tip and limit the size of the vortex. Some of the more typical designs include winglets, wing tip fence and wing tip tank.

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