How Do Flaps Work? Understanding Flaps and Their Use During Landing
- Dan George
- Jun 12
- 5 min read
When you’re seated by a window on an airliner during landing, you might notice a part of the wing moving—extending downward more and more as the plane approaches the runway. These moving parts are called flaps. Although not every aircraft is equipped with flaps, many do have them, including smaller general aviation planes like the Piper Arrow. Flaps play an essential role in controlling lift and drag, especially during critical phases of flight such as landing and takeoff. This article dives deep into how flaps work, why they are important, and how pilots use them to safely and efficiently land aircraft.
What Are Flaps and Why Do They Matter?
Flaps are secondary control surfaces located on the trailing edge of an aircraft’s wing. Unlike the primary control surfaces like ailerons, which help with roll control, flaps are designed to change the shape of the wing to increase lift and drag as needed. They can be extended or retracted by the pilot, and their movement significantly affects the wing’s aerodynamic characteristics.
Many smaller aircraft, such as the Piper Arrow, have a simple type of flap called a plain flap. This flap rotates downward on a hinge at the back of the wing. Larger commercial airliners also have flaps but often use more complex multi-element designs for better performance.
The Aerodynamics Behind Flaps: Understanding Wing Shape and Lift
To understand how flaps work, it’s important to first grasp how wings generate lift. When looking at a wing from the side, you’ll notice it has a relatively flat lower surface and a more curved upper surface. This curvature on the top is called the camber.
The wing’s shape can be described using two important lines:
Chord line: A straight line drawn from the leading edge (front) to the trailing edge (back) of the wing.
Mean camber line: A curve that splits the wing equally between the upper and lower surfaces, representing the wing’s camber.
The distance between the chord line and the mean camber line quantifies the wing’s camber. The more curved the upper surface, the greater the camber, which enhances the wing’s ability to produce lift.
Lift is the force that opposes the aircraft’s weight and keeps it aloft. The wing produces lift by deflecting air downward. The more air it deflects, the greater the lift. There are three main ways to increase lift:
Increase airspeed: Flying faster increases the volume of air deflected downward.
Increase angle of attack: Raising the wing’s angle relative to the airflow increases lift up to a point.
Increase camber: A more curved wing surface deflects air more effectively.
Each method has limits. For example, increasing angle of attack too much causes the wing to stall, which means airflow separates from the wing and lift dramatically decreases.
How Flaps Increase Lift by Changing Wing Camber
Instead of swapping wings mid-flight for a curvier version, aircraft use flaps to change the wing’s shape dynamically. When flaps extend downward, they increase both the chord line’s angle and the wing’s camber.
Extending flaps changes the wing’s aerodynamic profile in two key ways:
Increases angle of attack relative to the airflow: By rotating downward, the flap effectively tilts the wing, raising the angle at which air meets the wing.
Increases camber: The flap adds curvature to the wing’s trailing edge, boosting the wing’s lift-producing capability.
These combined effects allow the wing to generate more lift at lower speeds and angles of attack. This is particularly useful when flying slowly during landing approaches, where maintaining lift is critical but airspeed is reduced.
Benefits of Using Flaps During Landing
When preparing to land, pilots want to slow the aircraft down and descend smoothly. Flaps help achieve this by allowing the plane to maintain lift at slower speeds, which offers several advantages:
1. Lower Stall Risk
With flaps extended, the aircraft can fly at a lower angle of attack while still producing enough lift. This means the wing is further from its stall angle, providing a greater safety margin during slow flight.
2. Slower Approach Speeds
Lower speeds during approach make it easier to control the aircraft and improve the pilot’s view out of the cockpit. Flying slower also reduces the landing roll distance, meaning the plane can stop in a shorter runway length.
3. Increased Drag for Better Speed Control
Extending flaps increases drag because the flaps act like “barn doors” sticking into the airflow. This drag helps slow the aircraft during descent without relying solely on pitch changes or brake application after touchdown.
4. Steeper Descent Angles
Because flaps allow the aircraft to descend at slower speeds without gaining excessive speed, pilots can approach the runway on a steeper glide path. This helps clear obstacles and makes for a more controlled landing.
Flaps In Action: Comparing Landings With and Without Flaps
Imagine two identical aircraft both approaching a runway at 80 knots, but one with flaps extended and the other with flaps up. The differences become clear:
The aircraft without flaps needs to approach at a shallower angle to maintain that speed because it has less lift at slow speeds.
The pilot’s view during the approach is not as good without the flaps because the angle of attack must be higher to keep lift.
Without the drag from flaps, the plane doesn’t slow down as quickly, requiring more runway to decelerate and stop.
The aircraft with flaps extended can approach at a steeper angle and slower speed, giving the pilot better visibility and control.
The added drag from flaps allows the plane to bleed off speed more efficiently, reducing the landing roll distance and making it safer to land on shorter runways.
Other Uses of Flaps Beyond Landing
While flaps are most commonly associated with landing, they also play a vital role during takeoff and other phases of flight where increased lift is required without sacrificing airspeed or angle of attack.
During takeoff, extending flaps partially can provide extra lift to help the aircraft get off the ground in a shorter distance. This is especially important on shorter runways or when the aircraft is heavy with fuel and cargo.
In some cases, pilots might also use flaps during slow flight or maneuvering to enhance lift and control responsiveness.
Summary: Why Flaps Are Essential for Safe Flight
Flaps are a simple yet powerful tool that pilots use to control the wing’s shape and aerodynamic properties. By increasing camber and angle of attack, flaps allow aircraft to generate more lift at lower speeds, which is critical for safe landings and takeoffs.
Using flaps effectively means pilots can approach runways more slowly and with better control, reduce stall risk, and land within shorter distances. The extra drag produced by flaps also helps manage airspeed during descent, providing safer and more precise approaches.
Whether you’re flying a small general aviation plane like a Piper Arrow or a large commercial airliner, understanding how flaps work and when to use them is crucial for smooth, safe, and efficient flying.
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