Leading Edge Slats
Here’s How Leading Edge Slats Get You Off The Ground
If you’re flying a piston aircraft, chances are, you don’t have slats. Unless, of course, you’re flying a STOL aircraft.
But if you’re flying a swept-wing jet, chances are you do have slats. And you need them, if you want to get off the ground.
Leading edge slats are typically found on the wings of fast aircraft. And when they’re extended, they change the shape of your wing, increasing lift and delaying a stall.
There are two types of movable slats: automatic, and powered. And…drumroll please…here’s how they both work.
AUTOMATIC SLATS: POWERED BY THE WIND
Automatic slats aren’t managed by you. They’re spring-loaded and managed by airflow.
When air approaches the leading edge of the wing, some of it flows over the top of the wing, and some of it flows under the bottom. And the exact spot where the airflow separates is call the “stagnation point.”
When your wing is at a low angle of attack, the stagnation point is on the leading edge, and it pushes the slat closed. This happens when you are flying fast, and at a relatively low angle-of-attack (AOA).
Conversely, when your wing is at a high AOA, the stagnation point is on the bottom surface of the wing, and the spring-loaded slat pushes itself open. And when that happens, higher pressure air flows from the underside of your wing’s leading edge through the slat and into the air moving over the top of the wing, adding energy and lift.
GERMAN ENGINEERING AT WORK: THE BF-109
The Bf-109 was a perfect example of the automatic slat, but it also was problematic. Debris could get between the slat and wing, preventing it from closing. And, they also had problems with slats not opening and closing at the same time. Which, as you could imagine, created some really undesirable flight characteristics.
So while it sounded like a good engineering idea, in reality, it wasn’t quite as practical as they wanted it to be.
POWERED SLATS: THE SLAT FOR THE MODERN AGE
Today’s slats are powered by hydraulics or electrical systems, and you’ll find them on practically every airliner you fly on.
They’re controlled by the pilots, and they’re typically lowered during takeoff, landing, and any other slow-speed operations.
By extending the slat, the wing 1) has more camber, and 2) airflow passing through the slat adds energy to the boundary layer. Both of these increase lift. And without them, most airliners would have a hard time getting off the ground.