The 4 Types of Flaps Every Pilot Should Know (Plain, Split, Slotted & Fowler)

The four primary types of flaps are plain, split, slotted, and Fowler flaps, and they’re ranked by how much lift they add and how mechanically complex they are. A plain flap simply hinges the trailing edge down; a split flap deflects only the lower surface; a slotted flap opens a gap that re-energizes the airflow; and a Fowler flap slides aft before deflecting to grow the wing’s area. Each one trades simplicity for performance.

Walk down any flight line and you’ll see all four. The 1940s taildragger in the corner might wear plain or split flaps. The Cessna 172 you’re training in uses a slotted Fowler-type design. The airliner taxiing past on the parallel unfolds a multi-element Fowler system in stages as it sets up for takeoff. Same goal — more lift at slower speeds — four different ways of getting there.

Knowing the types of flaps matters more than you’d think. Plenty of pilots can parrot “flaps add lift” and stop there. The ones who understand why their airplane behaves the way it does on final are the ones who fly a smoother approach. So let’s break down all four the way you’d hear it on the ramp, plus the leading-edge devices that round out the high-lift family.

What are the types of flaps?

The four primary types of flaps are the plain, split, slotted, and Fowler flap. All four are trailing-edge high-lift devices — movable panels on the back of the wing that the pilot extends to increase lift and drag at low airspeeds. They appear in exactly that order in the FAA’s Pilot’s Handbook of Aeronautical Knowledge (PHAK, FAA-H-8083-25C, Chapter 5), and the order is meaningful: it runs from least effective and simplest to most effective and most complex.

Every flap does the same fundamental job. By deflecting downward, it increases the wing’s camber — the curvature of the airfoil — so the wing produces more lift at any given airspeed. More lift at a lower speed means a lower stall speed, which is why flaps let you approach and land slower and steeper. The differences between the types are all about how cleverly each one adds that lift and how much drag it brings along for the ride.

A quick mental map before we go one by one: plain and split flaps are the simple, draggy ones you’ll find on older and basic airplanes. Slotted flaps are the efficient middle ground that dominates modern general aviation. Fowler flaps are the heavy hitters that also grow the wing, which is why you’ll find them on everything from your Cessna 172 to a Boeing 737.

How does a plain flap work?

A plain flap is the simplest type: the entire trailing edge of the wing hinges straight down on a pivot, increasing the airfoil’s camber. That added curvature raises the lift the wing produces at a given airspeed — but because the deflected surface also disrupts the smooth airflow behind it, a plain flap produces a comparatively large increase in drag for the lift it buys.

Think of it as the most honest, no-frills high-lift device. There’s almost nothing to break — one hinge line, one panel — which is why you’ll see plain flaps on simpler, older, and many experimental airplanes. (Plenty of basic taildraggers, like the classic Piper J-3 Cub, skip flaps entirely and land just fine with a slip — proof that a plain flap is about the lowest rung on the high-lift ladder.)

The downside is efficiency. Because the airflow over the top of the wing tends to separate as the flap deflects, the plain flap gives up some of its potential lift and runs out of usefulness at large deflection angles. It’s effective, but it’s the baseline the other three types improve on.

How does a split flap work?

A split flap deflects only the lower (bottom) surface of the trailing edge downward while the upper surface stays in line with the wing. This creates a large low-pressure, turbulent wake behind the wing, so the split flap produces a lot of drag — actually more drag than a plain flap at the same angle — while adding a similar amount of lift.

That high-drag personality made split flaps popular on World War II–era and early postwar designs, where a lot of drag was useful for steepening the descent and slowing the airplane down. The Douglas DC-3 is the classic example most pilots picture. The lower-surface-only deflection is also mechanically robust and simple to build.

You won’t see split flaps on many new trainers, but understanding them matters for the knowledge test and for appreciating why the slotted flap that replaced them was such an improvement. The split flap’s weakness is that turbulent wake — it’s draggy without being especially efficient at producing lift, and the separated airflow can affect the tail.

How does a slotted flap work?

A slotted flap is the most widely used flap type in general aviation because it solves the airflow-separation problem. When it deflects, a slot (a gap) opens between the trailing edge of the wing and the leading edge of the flap. High-pressure air from beneath the wing accelerates through that slot and flows over the top of the deflected flap, re-energizing the boundary layer and delaying the airflow separation that limits plain and split flaps.

The payoff is a much better lift-to-drag relationship. A slotted flap produces a significantly larger increase in lift than a plain or split flap, with a more manageable drag penalty — especially at the first stages of deflection. That’s exactly the balance you want in a trainer: strong lift to lower the stall speed, without dragging you out of the sky the moment you select the first notch.

This is why the Cessna single-engine family — the 152, 172, and 182 you’ll likely train in — uses slotted flaps. Some designs use multiple slots (double- and triple-slotted flaps on larger aircraft) to push the effect even further. When you feel that healthy lift gain from the first notch of flaps on a 172, the slot is the reason.

How does a Fowler flap work?

A Fowler flap adds the most lift of the four types because it does something the others don’t: it first slides rearward along a track to increase the wing’s surface area, and only then deflects downward to add camber. More wing area plus more camber means a large lift increase — and well-designed Fowler flaps are also slotted, so they get the airflow-energizing benefit too.

That two-part motion — aft, then down — is the signature of a Fowler. The early deflection is mostly aft travel, which is why the first notch buys you a big jump in lift with relatively little drag. As you extend further, the flap deflects more steeply and drag begins to dominate, giving you that steep, slow final approach. Your Cessna 172 actually uses a slotted Fowler-type flap, which is exactly why that first notch is so effective.

The tradeoff is mechanical complexity. Fowler flaps ride on tracks and carriages, which adds weight and parts to inspect and maintain. But the performance is unmatched, which is why they scale all the way up: airliners use large, multi-element Fowler systems that unfold in stages to transform the wing for takeoff and landing.

What are leading-edge devices?

Leading-edge devices are high-lift devices on the front of the wing — slats, fixed slots, and Krueger flaps — that work alongside trailing-edge flaps to delay the stall to a higher angle of attack. Where trailing-edge flaps mostly add camber and area at the back, leading-edge devices keep the airflow attached at the front of the wing when the nose is high and the angle of attack is steep.

A slat is a small auxiliary airfoil on the leading edge that extends forward to open a slot, channeling high-energy air over the top of the wing — the same boundary-layer trick a slotted flap uses, applied to the front. A fixed slot is a permanent gap built into the leading edge that does the job passively. A Krueger flap extends from the lower leading edge to increase camber, and you’ll find them on the inboard wings of many jets.

You won’t operate leading-edge devices on a typical Cessna or Piper trainer, but the FAA tests them, and they’re worth understanding. Airplanes designed for very short fields, and nearly all jet transports, pair leading-edge devices with Fowler flaps to get the dramatic low-speed performance you see when an airliner crosses the threshold at a remarkably slow speed for its size.

Which type of flap is best?

There’s no single “best” flap — there’s the best flap for a given airplane’s mission and budget. A simple plain or split flap is cheap, light, and rugged for a basic airplane. A slotted flap is the efficiency champion for general aviation. A Fowler flap delivers the most performance when the design can justify the mechanical complexity. The right answer depends on what the airplane is built to do.

Here’s the full comparison so you can hold all four in your head at once:

For the private pilot checkride, the FAA cares far more that you understand the characteristics and functions of each type than that you can identify one by sight — that’s the heart of learning statement PLT266. Know that the order plain → split → slotted → Fowler runs from simplest/least-effective to most-complex/most-effective, and know that all four lower your stall speed by adding lift.

Picture a student pilot on short final into a tight runway, nervous about the trees at the approach end. With the airplane configured for full flaps, that slotted Fowler wing is doing two jobs at once — the steep, slow descent clears the obstacles, and the lower stall speed means a slower, controlled touchdown. The pilot who understands why full flaps give a steeper path and a slower touchdown flies that approach with confidence instead of guessing at the lever. That’s the whole point of knowing your flap type.

If you want every aircraft system taught this way — the why behind the what, with cockpit visuals and checkride-ready procedures — that’s exactly how we build it inside the Private Pilot Ground School. It’s how thousands of students have gone from memorizing facts to actually understanding their airplane.

PLT Study Guide

The FAA writes knowledge-test questions against learning statement codes (PLT codes). For a “types of flaps” topic, these three are the codes whose official FAA wording actually matches the content:

PLT266 — Recall high lift devices: characteristics / functions. This is the core code for this article. Be ready to recognize plain, split, slotted, and Fowler flaps and their general characteristics — that all four increase lift and drag by increasing the wing’s camber (and, for Fowler flaps, its area), and that they run from simplest/least-effective to most-complex/most-effective in that order.

PLT305 — Recall leading edge devices: types / effect / purpose / operation. Know that leading-edge devices — slats, fixed slots, and Krueger flaps — work the front of the wing to keep airflow attached at high angles of attack, delaying the stall. Understand that they complement trailing-edge flaps and are common on jets and short-field designs.

PLT242 — Recall forces acting on aircraft: lift / drag / thrust / weight / stall / limitations. Understand that extending any flap increases both lift and drag, that the balance shifts toward drag as deflection increases, and that flaps lower the stall speed because the flapped wing makes more lift at a given airspeed.

Study these against the real FAA source material — primarily PHAK (FAA-H-8083-25C), Chapter 5 (Aerodynamics of Flight) — rather than memorizing answer letters. If you understand why each flap type behaves the way it does, the written questions answer themselves.

Frequently Asked Questions

FROM CHRIS

Flaps are one of the first systems where understanding the type behind the lever turns guesswork into airmanship. Learn the four — plain, split, slotted, and Fowler — know that all of them lower your stall speed, and you’ll never again wonder why your airplane feels the way it does when you reach for that first notch on final.

Throttle On!

Chris Palmer

Founder & Chief CFI, Angle of Attack — Two-Time Master Aviation Educator and Gold Seal CFI