Flaps enhance the camber and, in some cases, the area of your wing. When you increase the camber of your wing, it also boosts the amount of lift that your wing can generate. With the flaps down, your wing can produce more lift at slower speeds.
Using flaps offers you three distinct advantages in your plane:
- You can generate more lift, enabling you to have lower takeoff and landing speeds.
- You can produce more drag, allowing for a steeper descent angle without increasing your airspeed during landing.
- You can reduce the length of your takeoff and landing roll.
There are four primary flap designs, and each of them has its own advantages and disadvantages. Here’s how they work.
1) Plain Flaps
The most straightforward flap is the plain flap. Plain flaps hinge to the rear of the wing and pivot down when extended. However, they are fairly limited in the amount of lift they can create. This is because as air flows over the wing, it loses energy and starts to detach from the wing. By extending the flaps, the airflow separation becomes even more pronounced, creating a large wake behind the wing.
But you can utilize this wake to your advantage. The drag caused by the wake allows you to fly a steeper descent to landing without increasing your airspeed.
2) Split Flaps
Next are split flaps, which deflect from the lower surface of the wing. Split flaps generate slightly more lift than plain flaps, but like their plain counterparts, they also generate a significant amount of drag.
Split flaps are not very common these days, but you can find them on the wings of several warbirds at your local airshow.
3) Slotted Flaps
Slotted flaps are the most commonly used flaps today and can be found on both small and large aircraft. What makes them so special? Two things:
- They increase the wing camber, just like other flaps.
- When extended, they open a slot between the wing and the flap.
By opening a slot between the wing and the flap, high-pressure air from the bottom of the wing flows through the slot into the upper surface. This adds energy to the wing’s boundary layer, delays airflow separation, and results in less drag. The outcome? A substantial amount of additional lift without excessive drag.
4) Fowler Flaps
When you require serious lift, you need serious flaps, and Fowlers are here to fulfill that need. Fowler flaps increase the area of your wing by extending out on rails or tracks. Fowler flaps often have a series of slots to add energy to the airflow as well – they are called slotted-Fowler flaps.
In the initial stages of a Fowler flap’s extension, there is a significant increase in lift but only a slight increase in drag, making this setting ideal for takeoff in a large jet. As they continue to extend, the flaps move downward more and more, generating a little more lift but a lot more drag.
Putting It All Together
So there you have it. The next time someone asks you about flaps, not only can you list off the four types, but you can also tell them how each of the flaps actually functions.
