Flaps are movable panels on the trailing edge of the wing that let you fly slower and descend more steeply without gaining speed, which is exactly what you want on landing. Here is how they work and the common types.
Part of our How Airplanes Work guide.
What flaps do
Flaps are high-lift devices. Extending them changes the shape (camber) of the wing, and on some types its area, which lets the wing produce more lift at a given speed. That has two big benefits: it lowers your stall speed, so you can fly approaches more slowly, and it increases drag, so you can descend at a steeper angle without speeding up.
Lift and drag trade-off
The first portion of flap extension adds mostly lift with relatively little drag, useful for shortening a takeoff in some airplanes. Further extension adds a lot of drag, which is why full flaps are typically a landing configuration, not a takeoff one. Your aircraft’s handbook specifies the right settings for each phase.
Common types of flaps
- Plain flap: a simple hinged section of the trailing edge. Increases camber.
- Split flap: the lower surface deflects down while the upper stays put. Lots of drag.
- Slotted flap: a gap lets high-energy air flow over the flap, delaying separation and producing strong lift. The most common type on trainers.
- Fowler flap: slides aft and then down, increasing both wing area and camber. Very effective; common on larger aircraft.
Using flaps
You typically extend flaps in stages on approach as you slow down, giving you a steeper, slower, more controlled path to the runway. On a go-around you retract them in stages as you accelerate and climb. Always follow your aircraft’s published speeds and procedures.
What you'll need
The FAA handbooks that explain how your airplane works, from PilotMall.com.
Frequently asked questions
What do flaps do?
They increase lift and drag, lowering your stall speed and letting you descend more steeply at a slower speed, which is ideal for landing.
Why not use full flaps for takeoff?
Full flaps add a lot of drag. A small flap setting can help some takeoffs, but full flaps are generally a landing configuration.
What is the most common flap type on trainers?
The slotted flap, which uses a gap to keep airflow attached and produce strong lift.