What Are Flaps in Aviation? Lift, Drag & When to Use Them

Flaps are hinged panels on the trailing edge of an airplane’s wing that pilots extend to increase both lift and drag at slow speeds. By changing the wing’s camber and area, flaps let you fly slower without stalling, descend at a steeper angle without gaining speed, and touch down on shorter runways. They are the most-used high-lift device in general aviation.

If you train in a Cessna 172, a Piper Cherokee, or almost any trainer on the ramp, you’ll reach for the flap lever or switch on nearly every landing. Understanding why they work — not just when to drop them — is one of the things that separates a pilot who flies the airplane from a pilot the airplane flies.

Let’s break flaps down the way I’d walk you through it on the ramp: what they are, the physics behind them, and how to actually use them on day one of flying solo patterns.

What are flaps in aviation?

Flaps are movable surfaces hinged to the trailing (rear) edge of an airplane’s wing that the pilot extends downward to increase lift and drag at low airspeeds. They are classified as high-lift devices because their job is to let the wing produce enough lift to keep flying at speeds far slower than it could with a clean wing.

When you extend flaps, you change the shape of the wing. The wing gets more curved (more camber), and on most designs the wing area grows too. A more curved, larger wing produces more lift at any given airspeed — so you can slow down before the wing runs out of lift and stalls.

Almost every trainer you’ll fly has flaps. In a Cessna 172, they’re electric, controlled by a switch with detents at 10, 20, and 30 degrees. In a Piper, they’re often a manual handle between the seats, like a parking brake. Same physics, different plumbing.

How do flaps actually work?

Flaps work by increasing the wing’s camber — the curvature of the airfoil — and, on many designs, its surface area. A more cambered wing accelerates air over the top more aggressively, lowering the pressure there and producing more lift at the same airspeed and angle of attack. That’s the core idea straight out of the Pilot’s Handbook of Aeronautical Knowledge (PHAK, FAA-H-8083-25C, Chapter 5).

Because the wing makes more lift at a lower speed with flaps down, the speed at which it finally stalls drops. That’s the whole point: you get to approach and land slower, which means shorter ground roll and more margin over obstacles.

There’s a trade. All that extra curvature and area also disrupts the airflow and creates more drag. The deeper you extend the flaps, the more drag dominates. So flaps give you a dial: a little flap is mostly a lift tool, a lot of flap is mostly a drag tool.

One more thing students miss — extending flaps usually causes a pitch change. Depending on the airplane, the nose may want to pitch up or down as the lift distribution shifts. Your POH and your instructor will show you what your specific airplane does, and you’ll learn to trim it out smoothly.

Do flaps increase lift or drag?

Both — and the balance shifts as you extend them further. The first increment of flaps (say, 10 degrees in a Cessna 172) adds a lot of lift for very little drag, which is why it’s useful for getting airborne sooner off a short or soft field. The final increment (the last notch, 30 degrees in most modern 172s) adds mostly drag, which is what you want on landing to descend steeply without picking up speed.

Here’s a simple way to hold it in your head:

The exact degrees and uses come from your airplane’s POH — these are typical Cessna 172 numbers, not a universal rule. Older 172s extended to 40 degrees; a Piper, a Cirrus, or a 152 will differ again. Always fly the numbers in your book.

This is also why flaps are not a takeoff shortcut. A little flap can shorten your ground roll, but dragging full flaps into a climb just piles on drag and kills your climb performance. Match the setting to the job.

What are the different types of flaps?

The four common flap types you’ll see described in the PHAK are the plain, split, slotted, and Fowler flap. They differ in how much lift and drag they add and how mechanically complex they are. Most general aviation trainers use a slotted flap because it gives an excellent lift-to-drag payoff without a lot of moving parts.

Your Cessna 172 actually uses a slotted Fowler-type flap — it moves rearward as it deflects, which grows the wing area and explains why that first notch is so effective at adding lift. Knowing the type matters less for the checkride than knowing the characteristics, which is exactly what FAA learning statement PLT266 is testing.

When should you use flaps?

You use flaps any time you need to fly slower or descend steeper in a controlled way — most commonly on landing, and selectively on takeoff for short or soft fields. The right setting always comes from your POH for the maneuver you’re flying. Never just guess a notch because it “feels about right.”

On a normal landing, you’ll typically add flaps in stages as you slow down and configure on the approach — a notch on downwind or base, more on final — so the airplane is fully configured and stable before you cross the threshold. Full flaps give you the slowest, steepest, most controlled descent to the numbers.

For takeoffs, it depends on the field. A short-field or soft-field takeoff often calls for a partial flap setting (commonly 10 degrees in a 172) to get the wing flying sooner. A normal takeoff from a long paved runway usually uses no flaps at all. The POH tells you which.

Two habits to build early. First, extend flaps below the white arc — never above VFE. Second, when you go around, the airplane is at full flaps and slow. Add full power, pitch for climb, then milk the flaps up in stages as airspeed builds. Dumping all the flaps at once near the ground can sink you into the runway.

If you want the full configuration flow drilled into you with cockpit visuals and checkride-ready procedures, that’s exactly what we build step by step inside the Private Pilot Ground School — it’s how thousands of students have gone from “what notch do I use?” to flying confident, stabilized approaches.

How do flaps affect stall speed and the white arc?

Extending flaps lowers your airplane’s stall speed because the more cambered, larger wing makes more lift at a given speed — so the wing can keep flying slower before it stalls. That’s why the bottom of the white arc (VS0, the power-off stall speed in the landing configuration) sits below the bottom of the green arc (VS1, the stall speed in a clean configuration). Flaps literally lower the floor.

The white arc on your airspeed indicator is the flap operating range, defined in 14 CFR § 23 airworthiness standards and marked per your airplane’s certification:

The number that gets pilots in trouble is VFE — the top of the white arc, the maximum flap-extended speed. Exceed it with flaps down and you can overstress the flaps and their tracks. So the rule is dead simple: get into the white arc before you select flaps, and don’t let the airspeed climb back above VFE while they’re out. This is FAA learning statement PLT506 territory, and it shows up on the written.

A real lesson: the day flaps saved a short Alaska strip

I do most of my flying out of Alaska, and up here the runways aren’t always the wide paved ribbons you train on in the lower 48. Years back I was taking a student into a short gravel strip hemmed in by spruce on both ends. On the way in, he set up a flat, fast approach — clean wing, plenty of speed, the way a lot of students do when a short runway makes them nervous and they unconsciously want a “safer” buffer.

We were going to float halfway down that strip and run out of gravel. So I had him go around, set up again, and this time we did it by the book: configure early, full flaps, fly the POH approach speed. Same airplane, same strip. With full flaps the airplane came down steep and slow, settled onto the numbers, and we were stopped with room to spare.

That’s the lesson I want you to take. Flaps aren’t just “the thing you drop before landing.” Full flaps gave us a steeper descent path to clear the trees and a slower touchdown speed to stop on short gravel — the exact two things that short strip demanded. The student felt the difference in his hands, and he never flew a flat, fast, flapless approach into a short field again.

Aviation education has been my world since 2006, and I’ve been a CFI since 2017. If there’s one configuration habit I’d burn into every new pilot, it’s this: configure early, fly the numbers, and let the flaps do the job they were built for.

PLT Study Guide

The FAA writes test questions against learning statement codes (PLT codes). For a flaps and high-lift-devices topic, these three are the ones whose official FAA wording actually matches the content:

PLT266 — Recall high lift devices: characteristics / functions. This is the core code for this article. Know that flaps are high-lift devices that increase lift and drag by increasing the wing’s camber and (on Fowler types) its area, letting you fly slower and descend steeper. Be ready to recognize plain, split, slotted, and Fowler flaps and their general characteristics.

PLT506 — Recall V speeds: maneuvering / flap extended / gear extended. Know VFE (maximum flap extended speed) is the top of the white arc, and VS0 (stall speed, landing configuration) is the bottom of the white arc. Understand that the white arc is the flap operating range and you must be at or below VFE before extending flaps.

PLT242 — Recall forces acting on aircraft: lift / drag / thrust / weight / stall / limitations. Understand that extending flaps increases both lift and drag, that the first increments favor lift while the last favor drag, and that flaps lower the stall speed — which is why VS0 is below VS1.

Study these against the real FAA source material — primarily PHAK (FAA-H-8083-25C), Chapter 5 (Aerodynamics) and Chapter 6 (Flight Controls) — rather than memorizing answer letters. If you understand why flaps do what they do, the written questions answer themselves.

Frequently Asked Questions

FROM CHRIS

Flaps are one of the first systems where flying the numbers starts to click — where you feel the airplane respond to a tool you understand instead of one you’re just guessing at. Get comfortable with your white arc, your POH settings, and the simple lift-then-drag mental model, and you’ll fly stabilized approaches that look effortless from the ground.

Throttle On!

Chris Palmer

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