What is the primary effect of deploying flaps and slats on a wing?

What is the primary effect of deploying flaps and slats on a wing?

• A. They increase camber and sometimes wing area, raising max lift and reducing stall speed, but also raise parasitic drag.
• B. They have no effect on lift but reduce drag in cruise.
• C. They only increase wing area without altering camber.
• D. They decrease stall speed but increase wing loading.

Answer: (A)

Deploying flaps and slats mainly changes the wing to produce more lift at lower speeds. By increasing the wing’s camber (and, with some devices, the effective wing area), the lift coefficient at a given angle of attack goes up. That means the wing can generate the same lift at a slower speed, or more lift at the same speed, which lowers stall speed and raises the maximum lift the wing can deliver. At the same time, extending these devices adds surface area and disturbs the airflow, so drag goes up, especially parasitic drag. So the net effect is higher lift capability at lower speeds with a drag penalty. The other statements miss this combination: lift does change (not “no effect on lift”), it’s not only about increasing area, and wing loading isn’t the primary consideration described by how these devices work.

Deploying flaps and slats mainly changes the wing to produce more lift at lower speeds. By increasing the wing’s camber (and, with some devices, the effective wing area), the lift coefficient at a given angle of attack goes up. That means the wing can generate the same lift at a slower speed, or more lift at the same speed, which lowers stall speed and raises the maximum lift the wing can deliver. At the same time, extending these devices adds surface area and disturbs the airflow, so drag goes up, especially parasitic drag. So the net effect is higher lift capability at lower speeds with a drag penalty.

The other statements miss this combination: lift does change (not “no effect on lift”), it’s not only about increasing area, and wing loading isn’t the primary consideration described by how these devices work.