Aircraft Flaps Explained: Types, How They Work, and the Right Way to Use Them

Nathan Hodell
Aug 21, 2025
8 min read

Updated: 4 days ago

Flaps are one of the most useful flight controls a pilot has, and also one of the most commonly misused. They're easy to deploy, they make the airplane fly slower and descend steeper, and they're essential for short-field operations — but using them correctly (and in the right sequence) is what separates a professional approach from an awkward one. Using them incorrectly can make a short-field approach impossible, cause a stall, or turn a manageable go-around into an accident.

This post covers the four main flap types you'll encounter across the GA fleet, the aerodynamics behind what they actually do, and the practical techniques for using them correctly on takeoff, landing, and go-around.

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What Flaps Do Aerodynamically

Flaps are trailing-edge devices on the wing that, when extended, change the wing's aerodynamic characteristics in two ways:

Increased lift coefficient: Flaps increase the wing's camber (curvature), which means the wing generates more lift at any given airspeed. This reduces stall speed, allowing the aircraft to fly safely at lower airspeeds — which is exactly what you want on approach and landing.
Increased drag: Flaps also increase drag. Some flap types generate relatively more lift than drag (efficient), while others generate relatively more drag than lift (draggy but useful for steep approaches). The drag increase allows pilots to descend steeper without the airspeed building excessively.

The ratio of lift increase to drag increase varies by flap type. Fowler flaps generate the most lift with relatively moderate drag — efficient. Split flaps generate lots of drag for less lift benefit — better as airbrakes than as lift devices. Plain and slotted flaps sit between these extremes.

One critical point: At high flap settings, most aircraft generate more drag than lift benefit. The first notch of flaps (10° or 15°) produces significant lift with moderate drag. The last notch (30° or 40°) produces relatively little additional lift but substantial additional drag. This is by design — the higher settings are for drag control during approach, not for additional lift.

Plain Flaps

The simplest flap design: a hinged section of the trailing edge that pivots downward when deployed. When the flap deflects, the entire trailing edge of that section moves downward as one unit.

How it increases lift: By increasing wing camber — the curvature of the wing. More camber means more lift at any given angle of attack.

Characteristics: Produces moderate lift gain and relatively high drag increase. Effective for reducing stall speed and providing a steeper descent path, but the lift-to-drag ratio isn't particularly favorable.

Found on: Older and simpler aircraft designs. Many early training aircraft (Piper J-3 Cub, Aeronca Champ, various other classics). Uncommon on modern aircraft.

Split Flaps

The split flap is a piece of the lower wing surface that hinges downward. Unlike a plain flap, the upper surface of the wing stays in place — only the bottom panel deflects.

How it works: Creates significant drag by disrupting the airflow beneath the wing. Provides some lift increase through increased effective camber, but produces much more drag than a plain flap.

Characteristics: High drag, moderate lift. The "airbrake effect" is significant — split flaps produce a dramatic descent capability. This was particularly useful for dive bombers in WWII and carrier aircraft that needed controlled steep approaches.

Found on: Classic aircraft from the 1930s-1950s. The Douglas DC-3/C-47 is the most commonly known example. Rare on modern aircraft because the high drag compromises efficiency.

Slotted Flaps

The most common flap type on modern GA aircraft. When deployed, the flap extends and creates a gap (slot) between the flap and the trailing edge of the wing.

How it works: Air from beneath the wing flows through the slot and re-energizes the airflow over the upper surface of the flap. This delayed airflow separation allows the flap to produce more lift at higher deflection angles before stalling. The slot effectively extends the usable range of the flap.

Single-slotted flaps: One slot, found on most GA aircraft.

Double and triple-slotted flaps: Multiple slots, found on larger transport aircraft. Each additional slot adds efficiency at the cost of complexity.

Characteristics: Good balance of lift and drag. Significantly more effective than plain or split flaps without being much more complex. Can be deployed to higher angles before stalling.

Found on: Cessna 172, Cessna 182, Cessna 152, most modern GA aircraft, nearly all modern airliners (often in slotted-Fowler combinations).

Fowler Flaps

Fowler flaps slide rearward first, then downward as they deploy. This extension-and-deflection combination provides two benefits simultaneously: increased wing area AND increased camber.

How it works: As the flap slides aft, the total wing area increases — a larger wing generates more lift at any given airspeed. As the flap also deflects downward, camber increases, further adding to the lift coefficient. The combined effect is the most dramatic lift increase of any flap type.

Modern implementation: Most modern Fowler flaps also incorporate slots (slotted Fowler flaps), combining the benefits of both designs. The flap slides aft, tilts downward, AND has airflow slots.

Characteristics: The highest lift-to-drag efficiency of any common flap type. Provides the largest reduction in stall speed for a given flap deflection. Enables very slow approach speeds and short-field performance.

Found on: Piper Cherokees (the familiar "johnson bar" manual flap systems), Beechcraft Bonanza, Cessna 206, Cessna 210, nearly all modern airliners (usually in multi-slotted Fowler configurations), and many transport category aircraft.

Leading-Edge Devices (Related But Different)

While technically not trailing-edge flaps, leading-edge devices are worth mentioning because they work together with flaps on many aircraft:

Leading-edge slats: Slide forward and down from the leading edge, creating a slot that improves lift at high angles of attack. Common on airliners and larger aircraft.
Krüger flaps: A type of leading-edge device that deploys forward and downward, increasing camber and preventing leading-edge stall.
Fixed leading-edge slots: Permanent slots in the leading edge that allow air to flow through, delaying stall at high angles of attack. Found on some STOL aircraft like the Maule and Helio Courier.

On airliners, you typically see leading-edge slats working together with multi-slotted Fowler flaps. The slats deploy on takeoff and landing alongside the flaps, providing coordinated high-lift capability.

How to Use Flaps Correctly

Knowing the types of flaps is academic. Knowing how to use them is practical.

On Takeoff:

Most GA aircraft use either no flaps or a small flap setting (10°-15°) for normal takeoffs. The flap setting is specified in the POH. A few principles:

Normal takeoff: Often no flaps or minimal flaps, depending on the aircraft
Short-field takeoff: Usually partial flaps (10°-20°) per the POH — this reduces takeoff roll at the cost of initial climb rate
Soft-field takeoff: Flaps as specified — typically similar to short-field to get off the ground sooner
Full flaps on takeoff: Almost never appropriate for a normal aircraft. The drag penalty exceeds the lift benefit at takeoff speeds. Full flaps on takeoff can prevent the aircraft from climbing after liftoff.

On Landing:

The traditional approach is to deploy flaps progressively as airspeed decreases through the pattern:

Downwind: First flap setting (often 10°) as speed decreases to pattern speed
Base: Second flap setting (often 20°-25°) as speed decreases and descent angle steepens
Final: Full flaps (30°-40° depending on aircraft) as the aircraft is stabilized on final

Each flap extension requires a corresponding adjustment to pitch and power to maintain a stable approach. The specific flap schedule varies by aircraft and by landing type (normal, short-field, soft-field).

Maximum flap speed (VFE):

Every aircraft has a maximum flap extended speed — the white arc on the airspeed indicator. Extending flaps above this speed can damage the flap mechanism or cause structural failure. Reduce airspeed to below VFE before extending flaps.

Each flap notch has its own maximum speed in some aircraft. The first 10° may be approved up to one speed, while full flaps may have a lower limit. Know your aircraft's specific limitations.

The Go-Around Sequence: Where Flap Use Gets Critical

The go-around is where pilots most often handle flaps incorrectly, and it's one of the most important manuvers to have memorized.

The basic go-around sequence (for most GA aircraft):

Full power — push the throttle to the firewall
Pitch up to climb attitude — positive pitch attitude
Reduce flaps to an intermediate setting (typically 20° or the "takeoff" setting) once positive climb is established
Maintain positive climb as airspeed builds
Fully retract flaps when safely clear of obstacles and with adequate airspeed
Clean up — gear if retractable, cowl flaps, etc.

Why not retract all flaps immediately? Going from full flaps to no flaps instantly in most aircraft causes a significant loss of lift at exactly the worst moment — near the runway at slow airspeed. The sudden lift loss can cause the aircraft to sink into the runway or into obstacles. Incremental flap retraction allows the aircraft to accelerate while maintaining sufficient lift throughout the transition.

Common mistake: Pilots instinctively reach for the flap handle and fully retract flaps the moment they decide to go around. This is wrong in most aircraft. Add power first, establish climb, reduce flaps incrementally as airspeed builds.

Pilot-Operated Flap Systems

Different aircraft have different flap systems:

Electric flaps: A switch controls an electric motor that positions the flaps. Most modern GA aircraft use this system. Cessna 172, 182, and most Cirrus aircraft use electric flaps. Usually has a flap position indicator in the panel.
Manual (mechanical) flaps: A johnson bar or lever in the cockpit mechanically extends the flaps. The pilot physically pulls the lever to deploy flaps in notches. Piper Cherokee (PA-28) is the most common example. The mechanical system is simple, reliable, and gives the pilot direct tactile feedback.
Hydraulic flaps: Uncommon on small GA aircraft but found on some older designs (certain Piper Comanches). Hydraulic pressure extends and retracts the flaps.
Each system has different failure modes. Electric flaps can fail from motor problems, switch issues, or electrical faults. Manual flaps rarely fail but can jam mechanically. Hydraulic flaps depend on hydraulic system integrity.

Practical Tips

Know your aircraft's flap speeds. Maximum flap extended speed (VFE) and any incremental limits are in the POH and on the airspeed indicator.

Use the flap schedule that matches your landing type. Short-field uses full flaps for maximum drag and shortest touchdown distance. Soft-field uses partial flaps to protect the nosewheel. Normal uses whatever flap setting matches a stable approach at appropriate airspeeds.

Don't add flaps late in final. Once you're below 100 feet AGL, you should be configured in your final flap setting. Adding flaps very late in final creates significant pitch and airspeed changes at the worst possible time.

Verify flap position before every takeoff. Mis-set flaps for takeoff is a major accident cause. Check the flap indicator and visually verify before each takeoff.

In icing conditions, don't use full flaps. Ice on the tail (tailplane icing) combined with full flap extension can trigger tailplane stall — a dangerous condition that requires counterintuitive recovery (reduce flaps, pull back, maintain power). Avoid full flaps if any tail icing is suspected.

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Author: Nathan Hodell

CFI, CFII, MEI, ATP, Creator and CEO

Nathan is an aviation enthusiast with thousands of hours of flying and dual instruction over the past 15+ years. Through his aviation career he has been able to earn his ATP, fly as an airline pilot, own/operate flight schools, and create and host wifiCFI.