What flaps do
Extending flaps increases the wing's camber (curvature) and sometimes its area. This raises the lift coefficient — meaning the wing produces more lift at the same airspeed and angle of attack. The result: the aircraft can fly slower without stalling, which is essential for approach and landing.
The cost is significantly increased drag. This drag is actually useful on approach — it allows a steeper descent angle without accelerating — but it becomes a liability if full flaps are used on takeoff, where climb performance matters more.
Quick reference
| Primary effect | Increased lift coefficient; allows slower flight without stalling |
| Secondary effect | Significantly increased drag |
| Location | Inboard trailing edge of each wing (between fuselage and ailerons) |
| Deployed for | Takeoff and landing |
| Retracted for | Cruise — too much drag at cruise speed |
Slats
Slats are the leading-edge equivalent of flaps — they extend forward from the wing's leading edge to increase camber and create a slot. Most large commercial aircraft use both flaps and slats together for maximum low-speed performance on approach.