# What are the differences between a slot and a slat?

If you look at image 5-18 in the PHAK Chapter 5 about leading edge lift devices you see this:

However the paragraph preceding it states

High-lift devices also can be applied to the leading edge of the airfoil. The most common types are fixed slots, movable slats, leading edge flaps, and cuffs.

So is this a typo? Should the image say 'movable slat' instead of 'movable slot'?

This leads into my main question which is, what are the differences between a slat and a slot? If I were to get asked this by an examiner what would a good response be?

I guess it should be movable slat.

A leading edge slot is basically a spanwise opening in the wing. Slats are aerodynamic surfaces in the leading edge, which when deployed, allows the wing to operate at higher angle of attack. When deployed, the slat opens up a slot between itself and the wing.

Image from simhq.com

In some aircraft, the slats are fixed, which opens up a slot between the wing and the slat. In this case, the terms slot and slat are used interchangeably.

"Leading edge slot" by Sanchom - Own work. Licensed under CC BY 3.0 via Commons.

A number of airliners use movable slats, in which case, the system is called slat, rather than slot.

"Voilure A319" by Nicourse - Own work. Licensed under CC BY-SA 3.0 via Commons.

In short, the system is pretty much the same, but is (usually) called slat in case of movable one and slot in case of fixed one.

• Would it be fair to say that a slat is a movable device that creates or closes off a slot in the leading edge of the wing? It seems to me that fixed slot is simply a permanent, spanwise hole in the leading edge of the wing. Dec 29, 2015 at 16:38
• @FreeMan Yes. It would be fair. This was the meaning in which the term slot was originally used. Dec 29, 2015 at 16:48
• Are a leading edge cuff and a droop just two names for the same thing? Dec 29, 2015 at 20:15
• @TomMcW The relationship is kinda similar. The droop is usually a deployable LE device. LE cuff is a fixed LE droop and is used as a general term, which probably got its name from the shape of the sharp cut off point. NASA did a lot of research into this for spin resistance and called it drooped LE, not cuff. Dec 30, 2015 at 1:11